Crater Lake and Mount Scott (8,934 feet / 2,723 m) - Oregon

Individual stratovolcanoes and shields that make up Mount Mazama become younger in a west-northwest sense. The oldest Mazama lavas dated are flows near lake level at Phantom Ship and the lavas of Mount Scott (around 400,000 years). The youngest stratovolcano is Hillman Peak (around 70,000 years). Local andesite flows on the north rim are 50-40,000 years old. -- Excerpt from: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press, 354p., p.193-195, Contribution by Charles R. Bacon

This is Brokeoff Mountain in northern California. It is near Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park.

Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen (= well off to the right of this photo) is a large volcanic dome that has developed in the remnants of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today.

In the photo, Brokeoff Mountain forms part of the western edge of the Brokeoff Caldera. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

Eruptions still occur in this area. Mt. Lassen last experienced eruptive activity in the early 1900s.

Locality: view from (probably) Bumpass Hell Trail, just south of Mt. Lassen, Lassen Volcano National Park, northeastern California, USA

This landscape is near Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The rocky rubble in this photo is "Chaos Jumbles", a large landslide deposit (usually mis-referred to as an "avalanche") consisting of porphyritic rhyodacite lava blocks, a rock type between dacite and rhyolite. The landslide occurred in the late 1600s A.D., according to carbon-14 dating of trees killed at the time. The Chaos Jumbles Landslide originated from dome C of Chaos Crags, a nearby cluster of six volcanic domes that formed in the late Holocene on the northern side of Lassen Volcano. Radiometric dating shows that the domes were emplaced sequentially between about 825 A.D. and 1575 A.D.

Only stunted, moderately scattered conifer trees have grown atop the landslide deposit - this is called the "Dwarf Forest".

Locality: Chaos Jumbles, Lassen Volcano National Park, northeastern California, USA

This landscape is near Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The rocky rubble in this photo is "Chaos Jumbles", a large landslide deposit (usually mis-referred to as an "avalanche") consisting of porphyritic rhyodacite lava blocks, a rock type between dacite and rhyolite. The landslide occurred in the late 1600s A.D., according to carbon-14 dating of trees killed at the time. The Chaos Jumbles Landslide originated from dome C of Chaos Crags, a nearby cluster of six volcanic domes that formed in the late Holocene on the northern side of Lassen Volcano. Radiometric dating shows that the domes were emplaced sequentially between about 825 A.D. and 1575 A.D.

Only stunted, moderately scattered conifer trees have grown atop the landslide deposit - this is called the "Dwarf Forest".

Locality: Chaos Jumbles, Lassen Volcano National Park, northeastern California, USA

This is lava from Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The lava boulder shown here is in a volcanic debris flow deposit from 19 and 22 May 1915, when Mt. Lassen last had a significant eruption. The deposit consists of fine sediments, cobbles, and boulders, some of which are quite large. Clasts in the flow deposit include pinkish-reddish porphyritic dacite and gray porphyritic dacite, both of which formed at 27 ka during the Late Pleistocene, early in Mt. Lassen's history. Another clast type in the deposit is black porphyritic dacite that formed in 1915.

This boulder is 27 ka pinkish-reddish porphyritic dacite. The whitish-colored phenocrysts (click on the photo to zoom in and look around) are plagioclase feldspar.

The darker-colored, xenolith-like objects are "quenched blobs". From park signage: "These patches are called quenched blobs, formed during the rock's molten stage. As molten rock, basalt magma mixed with dacite magma. Dacite magma's temperature is much cooler than basalt's. When the hotter basalt injected into the cooler dacite magma, it was like hot wax hitting cold water. The blobs were quenched - cooled suddenly. When the lava oozed from the volcano's vent, the blobs solidified and remained encased in the dacite rock. The mixing of the two magmas likely triggered the May 19 Lassen Peak eruption. When a superheated injection of basalt magma enters a dacite magma, a volatile jolt occurs - sometimes enough to cause a volcano to erupt."

Locality: boulder in Devastated Area, Lassen Volcano National Park, northeastern California, USA

ViewFinders_Overseas_Outing - Surabaya --> Ijen --> Bromo --> Solo --> Jogjakarta

Ijen:

The Ijen volcano complex is a group of stratovolcanoes, in East Java, Indonesia. It is inside a larger caldera Ijen, which is about 20 kilometers wide. The Gunung Merapi stratovolcano (not to be confused with Central Java's Gunung Merapi) is the highest point of that complex.

West of Gunung Merapi is the Ijen volcano, which has a one-kilometer-wide turquoise-colored acid crater lake. The lake is the site of a labor-intensive sulfur mining operation, in which sulfur-laden baskets are carried by hand from the crater floor. Many other post-caldera cones and craters are located within the caldera or along its rim. The largest concentration of post-caldera cones forms an E-W-trending zone across the southern side of the caldera. The active crater at Kawah Ijen has an equivalent radius of 361 meters, a surface of 41 × 106 square meters. It is 200 meters deep and has a volume of 36 × 106 cubic meters.

An active vent at the edge of the lake is a source of elemental sulfur, and supports a mining operation. Escaping volcanic gasses are channeled through a network of ceramic pipes, resulting in condensation of molten sulfur. The sulfur, which is deep red in color when molten, pours slowly from the ends of these pipes and pools on the ground, turning bright yellow as it cools. The cooled material is broken into large pieces and carried out in baskets by the miners. Typical loads range from 70–100 kilograms, and must be carried to the crater rim approximately 200 meters above before being carried several kilometers down the mountain. Most miners make this journey twice a day. The miners are paid by a nearby sugar refinery by the weight of sulfur transported; as of July 2005 the typical daily earnings were equivalent to approximately $5.00 US. The miners often use insufficient protection while working around the volcano and are susceptible to numerous respiratory complaints.

Bromo:

Mount Bromo (Indonesian: Gunung Bromo), is an active volcano and part of the Tengger massif, in East Java, Indonesia. At 2,329 metres (7,641 ft) it is not the highest peak of the massif, but is the most well known. The massif area is one of the most visited tourist attractions in East Java, Indonesia. The volcano belongs to the Bromo Tengger Semeru National Park.

Mount Bromo sits in the middle of a vast plain called the Sand Sea (Indonesian: Lautan Pasir), a protected nature reserve since 1919. The typical way to visit Mount Bromo is from the nearby mountain village of Cemoro Lawang. From there it is possible to walk to the volcano in about 45 minutes, but it is also possible to take an organised jeep tour, which includes a stop at the viewpoint on Mount Penanjakan (2,770 meters) (Indonesian: Gunung Penanjakan). The best views from Mount Bromo to the Sand Sea below and the surrounding volcanoes are at sunrise. The viewpoint on Mount Penanjakan can also be reached on foot in about two hours. From inside the caldera, sulfur is collected by workers.

Solo:

Surakarta is also known by the name "Solo". "Surakarta" is used in formal and official contexts. The city has a similar name with the neighboring district of "Kartasura", where the previous capital of Mataram was located. Variant spelling of Surakarta is found as Soerakarta - and is simply the old spelling prior to the pre 1948's spelling change.

It is approximately 65 km (40 miles) northeast of Yogyakarta, and 100 km (60 miles) southeast of Semarang The eastern part of the town is bordered by Bengawan Solo River, the longest river on Java. The river is the inspiration for the song Bengawan Solo, a 1940s composition by Gesang Martohartono which became famous throughout much of Asia.

Jogjakarta:

Yogyakarta is located in south-central Java. It is surrounded by the province of Central Java (Jawa Tengah) and the Indian Ocean in the south.

The population of DIY in 2003 was approximately 3,000,000. The province of Yogyakarta has a total area of 3,185.80 km2. Yogyakarta is the second-smallest area of the provinces in Indonesia, after the Jakarta Capital Region. However it has, along with adjacent areas in Central Java, some of the highest population densities of Java.

it was my first time up a real volcano, with all of the fumes and deadly sulfuric surroundings. An eerie place, yet mesmerizing and beautiful at the same time. For a split second it crossed my mind that Japan just had an tsunami due to tectonic activity. This also could trigger volcanoes to erupt. But my fear only lasted a second, and was completely wiped away the minute we got a glimpse of the caldera's volcanic lake. Turqoise, pacific blues, surrounded by volcanic ashes and wrinkled hill sides, a volcanic (toxic-ish) fume coming from an opening next to the lake. The Gods of Wind were in our favor, enabling us to see what was going on. Men carrying sulfur on their shoulders, toursist getting photos, quiet, yet it was not. Strange, yet it felt like coming home. Views uncomparable to all I have seen till now. In one word: wow. Thanks Aris, for keeping up the spirit, for showing us this magnificent landscape. For pushing our limits and go up that extra mile. For sharing your culture. Your land.

The Ijen volcano complex is a group of stratovolcanoes, in East Java, Indonesia. It is inside a larger caldera Ijen, which is about 20 kilometers wide. The Gunung Merapi stratovolcano is the highest point of that complex. The name of this volcano resembles that of a different volcano, Mount Merapi in central Java, also known as Gunung Merapi. The name "Merapi" means "fire" in the Indonesian language. From: wiki.

Java is the world's most densely populated island (population: 136 million). It is home to 60% of Indonesia's population. Much of Indonesian history took place on Java; it was the centre of powerful Hindu-Buddhist empires, Islamic sultanates, the core of the colonial Dutch East Indies, and was at the centre of Indonesia's campaign for independence. The island dominates Indonesian social, political and economic life. More information on wikipedia.

ViewFinders_Overseas_Outing - Surabaya --> Ijen --> Bromo --> Solo --> Jogjakarta

Ijen:

The Ijen volcano complex is a group of stratovolcanoes, in East Java, Indonesia. It is inside a larger caldera Ijen, which is about 20 kilometers wide. The Gunung Merapi stratovolcano (not to be confused with Central Java's Gunung Merapi) is the highest point of that complex.

West of Gunung Merapi is the Ijen volcano, which has a one-kilometer-wide turquoise-colored acid crater lake. The lake is the site of a labor-intensive sulfur mining operation, in which sulfur-laden baskets are carried by hand from the crater floor. Many other post-caldera cones and craters are located within the caldera or along its rim. The largest concentration of post-caldera cones forms an E-W-trending zone across the southern side of the caldera. The active crater at Kawah Ijen has an equivalent radius of 361 meters, a surface of 41 × 106 square meters. It is 200 meters deep and has a volume of 36 × 106 cubic meters.

An active vent at the edge of the lake is a source of elemental sulfur, and supports a mining operation. Escaping volcanic gasses are channeled through a network of ceramic pipes, resulting in condensation of molten sulfur. The sulfur, which is deep red in color when molten, pours slowly from the ends of these pipes and pools on the ground, turning bright yellow as it cools. The cooled material is broken into large pieces and carried out in baskets by the miners. Typical loads range from 70–100 kilograms, and must be carried to the crater rim approximately 200 meters above before being carried several kilometers down the mountain. Most miners make this journey twice a day. The miners are paid by a nearby sugar refinery by the weight of sulfur transported; as of July 2005 the typical daily earnings were equivalent to approximately $5.00 US. The miners often use insufficient protection while working around the volcano and are susceptible to numerous respiratory complaints.

Bromo:

Mount Bromo (Indonesian: Gunung Bromo), is an active volcano and part of the Tengger massif, in East Java, Indonesia. At 2,329 metres (7,641 ft) it is not the highest peak of the massif, but is the most well known. The massif area is one of the most visited tourist attractions in East Java, Indonesia. The volcano belongs to the Bromo Tengger Semeru National Park.

Mount Bromo sits in the middle of a vast plain called the Sand Sea (Indonesian: Lautan Pasir), a protected nature reserve since 1919. The typical way to visit Mount Bromo is from the nearby mountain village of Cemoro Lawang. From there it is possible to walk to the volcano in about 45 minutes, but it is also possible to take an organised jeep tour, which includes a stop at the viewpoint on Mount Penanjakan (2,770 meters) (Indonesian: Gunung Penanjakan). The best views from Mount Bromo to the Sand Sea below and the surrounding volcanoes are at sunrise. The viewpoint on Mount Penanjakan can also be reached on foot in about two hours. From inside the caldera, sulfur is collected by workers.

Solo:

Surakarta is also known by the name "Solo". "Surakarta" is used in formal and official contexts. The city has a similar name with the neighboring district of "Kartasura", where the previous capital of Mataram was located. Variant spelling of Surakarta is found as Soerakarta - and is simply the old spelling prior to the pre 1948's spelling change.

It is approximately 65 km (40 miles) northeast of Yogyakarta, and 100 km (60 miles) southeast of Semarang The eastern part of the town is bordered by Bengawan Solo River, the longest river on Java. The river is the inspiration for the song Bengawan Solo, a 1940s composition by Gesang Martohartono which became famous throughout much of Asia.

Jogjakarta:

Yogyakarta is located in south-central Java. It is surrounded by the province of Central Java (Jawa Tengah) and the Indian Ocean in the south.

The population of DIY in 2003 was approximately 3,000,000. The province of Yogyakarta has a total area of 3,185.80 km2. Yogyakarta is the second-smallest area of the provinces in Indonesia, after the Jakarta Capital Region. However it has, along with adjacent areas in Central Java, some of the highest population densities of Java.

The Ijen volcano complex is a group of stratovolcanoes, in East Java, Indonesia. It is inside a larger caldera Ijen, which is about 20 kilometers wide.

References : Wikipedia

(photos & photo stitch by Mary Ellen St. John)

--------------------

This is the landscape south of Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in northern California's Lassen Volcanic National Park.

Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen (= well off to the right of this photo) is a large volcanic dome that has developed in the remnants of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today.

In the photo, the mountain peak in the left background is Brokeoff Mountain. The peak near the center is Mt. Diller. The peak to the right of that is Pilot Pinnacle. Brokeoff-Diller-Pilot form the western edge of the Brokeoff Caldera. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

Eruptions still occur in this area. Mt. Lassen last experienced eruptive activity in the early 1900s.

The conspicuous rock at left is a glacial erratic, a large boulder left behind by melting glaciers. Glacial erratics have a somewhat rounded shape due to glacial and post-glacial meltwater abrasion.

Locality: Bumpass Hell Trailhead, just south of Mt. Lassen, Lassen Volcano National Park, northeastern California, USA

The Ijen volcano complex is a group of stratovolcanoes inside a larger caldera Ijen, which is about 20 kilometers wide. The Gunung Merapi stratovolcano is the highest point of that complex. West of Gunung Merapi is the Ijen volcano, which has a one-kilometer-wide turquoise-colored acid crater lake. The lake is the site of a labor-intensive sulfur mining operation, in which sulfur-laden baskets are carried by hand from the crater floor (http://en.wikipedia.org/wiki/Ijen).

This is lava from Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The lava boulder shown here is in a volcanic debris flow deposit from 19 and 22 May 1915, when Mt. Lassen last had a significant eruption. The deposit consists of fine sediments, cobbles, and boulders, some of which are quite large. Clasts in the flow deposit include pinkish-reddish porphyritic dacite and gray porphyritic dacite, both of which formed at 27 ka during the Late Pleistocene, early in Mt. Lassen's history. Another clast type in the deposit is black porphyritic dacite that formed in 1915.

This boulder is 27 ka pinkish-reddish porphyritic dacite. The whitish-colored phenocrysts (click on the photo to zoom in and look around) are plagioclase feldspar.

The darker-colored, xenolith-like object is a "quenched blob". From park signage: "These patches are called quenched blobs, formed during the rock's molten stage. As molten rock, basalt magma mixed with dacite magma. Dacite magma's temperature is much cooler than basalt's. When the hotter basalt injected into the cooler dacite magma, it was like hot wax hitting cold water. The blobs were quenched - cooled suddenly. When the lava oozed from the volcano's vent, the blobs solidified and remained encased in the dacite rock. The mixing of the two magmas likely triggered the May 19 Lassen Peak eruption. When a superheated injection of basalt magma enters a dacite magma, a volatile jolt occurs - sometimes enough to cause a volcano to erupt."

Locality: boulder in Devastated Area, Lassen Volcano National Park, northeastern California, USA

ViewFinders_Overseas_Outing - Surabaya --> Ijen --> Bromo --> Solo --> Jogjakarta

Ijen:

The Ijen volcano complex is a group of stratovolcanoes, in East Java, Indonesia. It is inside a larger caldera Ijen, which is about 20 kilometers wide. The Gunung Merapi stratovolcano (not to be confused with Central Java's Gunung Merapi) is the highest point of that complex.

West of Gunung Merapi is the Ijen volcano, which has a one-kilometer-wide turquoise-colored acid crater lake. The lake is the site of a labor-intensive sulfur mining operation, in which sulfur-laden baskets are carried by hand from the crater floor. Many other post-caldera cones and craters are located within the caldera or along its rim. The largest concentration of post-caldera cones forms an E-W-trending zone across the southern side of the caldera. The active crater at Kawah Ijen has an equivalent radius of 361 meters, a surface of 41 × 106 square meters. It is 200 meters deep and has a volume of 36 × 106 cubic meters.

An active vent at the edge of the lake is a source of elemental sulfur, and supports a mining operation. Escaping volcanic gasses are channeled through a network of ceramic pipes, resulting in condensation of molten sulfur. The sulfur, which is deep red in color when molten, pours slowly from the ends of these pipes and pools on the ground, turning bright yellow as it cools. The cooled material is broken into large pieces and carried out in baskets by the miners. Typical loads range from 70–100 kilograms, and must be carried to the crater rim approximately 200 meters above before being carried several kilometers down the mountain. Most miners make this journey twice a day. The miners are paid by a nearby sugar refinery by the weight of sulfur transported; as of July 2005 the typical daily earnings were equivalent to approximately $5.00 US. The miners often use insufficient protection while working around the volcano and are susceptible to numerous respiratory complaints.

Bromo:

Mount Bromo (Indonesian: Gunung Bromo), is an active volcano and part of the Tengger massif, in East Java, Indonesia. At 2,329 metres (7,641 ft) it is not the highest peak of the massif, but is the most well known. The massif area is one of the most visited tourist attractions in East Java, Indonesia. The volcano belongs to the Bromo Tengger Semeru National Park.

Mount Bromo sits in the middle of a vast plain called the Sand Sea (Indonesian: Lautan Pasir), a protected nature reserve since 1919. The typical way to visit Mount Bromo is from the nearby mountain village of Cemoro Lawang. From there it is possible to walk to the volcano in about 45 minutes, but it is also possible to take an organised jeep tour, which includes a stop at the viewpoint on Mount Penanjakan (2,770 meters) (Indonesian: Gunung Penanjakan). The best views from Mount Bromo to the Sand Sea below and the surrounding volcanoes are at sunrise. The viewpoint on Mount Penanjakan can also be reached on foot in about two hours. From inside the caldera, sulfur is collected by workers.

Solo:

Surakarta is also known by the name "Solo". "Surakarta" is used in formal and official contexts. The city has a similar name with the neighboring district of "Kartasura", where the previous capital of Mataram was located. Variant spelling of Surakarta is found as Soerakarta - and is simply the old spelling prior to the pre 1948's spelling change.

It is approximately 65 km (40 miles) northeast of Yogyakarta, and 100 km (60 miles) southeast of Semarang The eastern part of the town is bordered by Bengawan Solo River, the longest river on Java. The river is the inspiration for the song Bengawan Solo, a 1940s composition by Gesang Martohartono which became famous throughout much of Asia.

Jogjakarta:

Yogyakarta is located in south-central Java. It is surrounded by the province of Central Java (Jawa Tengah) and the Indian Ocean in the south.

The population of DIY in 2003 was approximately 3,000,000. The province of Yogyakarta has a total area of 3,185.80 km2. Yogyakarta is the second-smallest area of the provinces in Indonesia, after the Jakarta Capital Region. However it has, along with adjacent areas in Central Java, some of the highest population densities of Java.

This is lava from Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The lava boulder shown here is in a volcanic debris flow deposit from 19 and 22 May 1915, when Mt. Lassen last had a significant eruption. The deposit consists of fine sediments, cobbles, and boulders, some of which are quite large. Clasts in the flow deposit include pinkish-reddish porphyritic dacite and gray porphyritic dacite, both of which formed at 27 ka during the Late Pleistocene, early in Mt. Lassen's history. Another clast type in the deposit is black porphyritic dacite, shown here, that formed on 14 May 1915. The whitish-colored phenocrysts (click on the photo to zoom in and look around) are plagioclase feldspar.

The darker-colored, xenolith-like object is a "quenched blob". From park signage: "These patches are called quenched blobs, formed during the rock's molten stage. As molten rock, basalt magma mixed with dacite magma. Dacite magma's temperature is much cooler than basalt's. When the hotter basalt injected into the cooler dacite magma, it was like hot wax hitting cold water. The blobs were quenched - cooled suddenly. When the lava oozed from the volcano's vent, the blobs solidified and remained encased in the dacite rock. The mixing of the two magmas likely triggered the May 19 Lassen Peak eruption. When a superheated injection of basalt magma enters a dacite magma, a volatile jolt occurs - sometimes enough to cause a volcano to erupt."

Quenched blobs in May 1915 black dacite may be composed of andesite.

Locality: boulder in Devastated Area, Lassen Volcano National Park, northeastern California, USA

Gorely is an active volcano and consists of 5 overlapping stratovolcanoes. The last major eruption was in 1986.

Yosemite Valley in California's Sierra Nevada Mountains is a spectacularly scenic area. The bedrock is all Cretaceous granite and granite-like rocks of the Sierra Nevada Batholith (Cretaceous), representing cooled magma chambers that originally sat well underneath a chain of ancient subduction zone stratovolcanoes. The broad U-shaped valley shape is the result of glacial erosion during the Pleistocene (= the last Ice Age). The actual bedrock valley floor is well below the present surface. The valley has partially filled with glacial and fluvial sediments.

Features: Bridalveil Falls is at right-center; El Capitan is the ~vertical cliff on the left; Half-Dome is the rounded mountain top in the far-distance at center.

Locality: Yosemite Valley (view from Wawona Tunnel overlook), Yosemite National Park, Sierra Nevada Mountains, eastern California, USA

This is Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

Locality: view from road near Mt. Lassen, Lassen Volcano National Park, northeastern California, USA

This map (provided by the United States Geological Survey) shows about 1300 small earthquakes at & just offshore from Tanaga Island in Alaska's Aleutian Islands from 1 November 2022 to 26 February 2023. Most occurred under Takawangha Volcano. Magnitudes ranged from -0.2 to +4.1. Clusters of earthquakes without a main shock are called "swarms". The Alaska Volcano Observatory considers this swarm as possibly due to magma movement.

Takawangha Volcano is located on Tanaga Island, which has four stratovolcanoes. The other three are Tanaga Volcano, East Tanaga Volcano, and Sajaka Volcano. The Aleutian Islands are a long volcanic arc formed by subduction of the Pacific Plate beneath the Bering Plate. Active and potentially active volcanoes are common in the Aleutians, as are earthquakes of tectonic and volcanic origin.

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Info. at:

en.wikipedia.org/wiki/Tanaga_Island

Dacite pumice (air-fall tephra) from the Holocene of the Philippines.

Mt. Pinatubo is one of several subduction zone stratovolcanoes in the Luzon Volcanic Arc of the Philippines. Published information indicates that Pinatubo is 35,000+ years old and is composed principally of dacitic and andesitic rocks.

Mt. Pinatubo had a significant explosive ash eruption in 1991 that was the largest anywhere on Earth since 1912. Pinatubo's eruption is also famous for having been successfully predicted by American volcanologists. The prediction and subsequent evacuation saved thousands of lives.

The mid-June 1991 eruptions from Pinatubo blanketed ash, pumiceous lapilli, and pumice over the surrounding countryside, including two American military bases (Clark and Subic Bay). The sample seen here is dacite pumice from the 15 June 1991 eruption - it was collected at the U.S. Subic Bay Naval Base, ~20 miles south of Mt. Pinatubo.

Location of volcano: Mt. Pinatubo, Luzon Volcanic Arc, western Luzon Island, northern Philippines

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For additional geologic information on the 1991 Pinatubo eruption, see:

Newhall & Punongbayan (1996) - Fire and Mud, Eruptions and Lahars of Mount Pinatubo, Philippines. Quezon City & Seattle & London. Philippine Institute of Volcanology and Seismology & University of Washington Press. 1126 pp.

STS047-075-082 Atlasova Island, Kuril Islands, Russia September 1992

This low-oblique, southwest-looking photograph of Atlasova Island shows the classic radial drainage pattern seen in most stratovolcanoes. Atlasova Island is located at the northern end of the Kuril Islands arc about 60 miles (95 kilometers) west of the southern tip of Kamchatka Peninsula, Russia. This island’s summit reaches 7675 feet (2340 meters) above sea level, making it the highest point in the Kuril chain. The other land visible in this photograph is the northern end of Paramushir Island, another volcanic island in the Kuril archipelago. The Kuril Islands are a continuation of the volcanic mountains of Kamchatka Peninsula to the north and the Japanese islands to the south. (Refer to STS-068-231-054 for a view of other Kuril Islands, including Onekotan Island.)

Dacitic volcanic dust from the Holocene of Washington State, USA. (field of view ~~5.5 centimeters across)

The 1980 Mt. St. Helens eruption was the largest in recent American history. The volcano was intermittently active until 1986. Minor activity occurred from 1989 to 1991 and from 2004 to 2006.

Mt. St. Helens is the most active volcano in the Cascade Range, a series of subduction zone stratovolcanoes in a ~north-south line from northern California to Oregon to Washington State to southwestern British Columbia. St. Helens is a 40,000 to 50,000 year old, andesitic-dacitic-basaltic volcano that typically has explosive ash eruptions (as do all subduction zone stratovolcanoes).

The initial 1980 eruption was a northward-directed lateral blast that followed an enormous landslide of the northern face of the volcano. The landslide was triggered by a moderate earthquake at 8:32 AM, Sunday, 18 May 1980. Snow and ice on the mountain melted during the eruption, mixed with ash and other debris, and rushed down nearby river valleys as lahars (volcanic mud flows).

The ash, lapilli, and pumice erupted from Mt. St. Helens in May 1980 was dacite, an intermediate extrusive igneous rock. Most of the air-fall dacite ash fell in Washington State, Oregon, and Idaho, but a minor amount accumulated as far east as Minnesota and Oklahoma. Light dustings of ash were also observed in Ohio. The sample seen here is distal air-fall volcanic dust from Deary, Idaho - it was collected on 20 May 1980.

Location of volcano: Mt. St. Helens, northwestern Skamania County, Cascade Range, southwestern Washington State, USA (46˚ 12’ 04” North latitude, 122˚ 11” 18” West longitude)

Sample collection site: town of Deary, east-central Latah County, northern Idaho, USA

The Pico de Orizaba, or Citlaltépetl, is a stratovolcano, the highest mountain in Mexico and the third highest in North America.

A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers (strata) of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions. The lava that flows from stratovolcanoes typically cools and hardens before spreading far due to high viscosity. The magma forming this lava is often felsic, having high-to-intermediate levels of silica (as in rhyolite, dacite, or andesite), with lesser amounts of less-viscous mafic magma. Extensive felsic lava flows are uncommon, but have travelled as far as 15 km.

More photos Mexico - One the Road (B&W) HERE

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ViewFinders_Overseas_Outing - Surabaya --> Ijen --> Bromo --> Solo --> Jogjakarta

Ijen:

The Ijen volcano complex is a group of stratovolcanoes, in East Java, Indonesia. It is inside a larger caldera Ijen, which is about 20 kilometers wide. The Gunung Merapi stratovolcano (not to be confused with Central Java's Gunung Merapi) is the highest point of that complex.

West of Gunung Merapi is the Ijen volcano, which has a one-kilometer-wide turquoise-colored acid crater lake. The lake is the site of a labor-intensive sulfur mining operation, in which sulfur-laden baskets are carried by hand from the crater floor. Many other post-caldera cones and craters are located within the caldera or along its rim. The largest concentration of post-caldera cones forms an E-W-trending zone across the southern side of the caldera. The active crater at Kawah Ijen has an equivalent radius of 361 meters, a surface of 41 × 106 square meters. It is 200 meters deep and has a volume of 36 × 106 cubic meters.

An active vent at the edge of the lake is a source of elemental sulfur, and supports a mining operation. Escaping volcanic gasses are channeled through a network of ceramic pipes, resulting in condensation of molten sulfur. The sulfur, which is deep red in color when molten, pours slowly from the ends of these pipes and pools on the ground, turning bright yellow as it cools. The cooled material is broken into large pieces and carried out in baskets by the miners. Typical loads range from 70–100 kilograms, and must be carried to the crater rim approximately 200 meters above before being carried several kilometers down the mountain. Most miners make this journey twice a day. The miners are paid by a nearby sugar refinery by the weight of sulfur transported; as of July 2005 the typical daily earnings were equivalent to approximately $5.00 US. The miners often use insufficient protection while working around the volcano and are susceptible to numerous respiratory complaints.

Bromo:

Mount Bromo (Indonesian: Gunung Bromo), is an active volcano and part of the Tengger massif, in East Java, Indonesia. At 2,329 metres (7,641 ft) it is not the highest peak of the massif, but is the most well known. The massif area is one of the most visited tourist attractions in East Java, Indonesia. The volcano belongs to the Bromo Tengger Semeru National Park.

Mount Bromo sits in the middle of a vast plain called the Sand Sea (Indonesian: Lautan Pasir), a protected nature reserve since 1919. The typical way to visit Mount Bromo is from the nearby mountain village of Cemoro Lawang. From there it is possible to walk to the volcano in about 45 minutes, but it is also possible to take an organised jeep tour, which includes a stop at the viewpoint on Mount Penanjakan (2,770 meters) (Indonesian: Gunung Penanjakan). The best views from Mount Bromo to the Sand Sea below and the surrounding volcanoes are at sunrise. The viewpoint on Mount Penanjakan can also be reached on foot in about two hours. From inside the caldera, sulfur is collected by workers.

Solo:

Surakarta is also known by the name "Solo". "Surakarta" is used in formal and official contexts. The city has a similar name with the neighboring district of "Kartasura", where the previous capital of Mataram was located. Variant spelling of Surakarta is found as Soerakarta - and is simply the old spelling prior to the pre 1948's spelling change.

It is approximately 65 km (40 miles) northeast of Yogyakarta, and 100 km (60 miles) southeast of Semarang The eastern part of the town is bordered by Bengawan Solo River, the longest river on Java. The river is the inspiration for the song Bengawan Solo, a 1940s composition by Gesang Martohartono which became famous throughout much of Asia.

Jogjakarta:

Yogyakarta is located in south-central Java. It is surrounded by the province of Central Java (Jawa Tengah) and the Indian Ocean in the south.

The population of DIY in 2003 was approximately 3,000,000. The province of Yogyakarta has a total area of 3,185.80 km2. Yogyakarta is the second-smallest area of the provinces in Indonesia, after the Jakarta Capital Region. However it has, along with adjacent areas in Central Java, some of the highest population densities of Java.

This is lava from Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The lava boulder shown here is in a volcanic debris flow deposit from 19 and 22 May 1915, when Mt. Lassen last had a significant eruption. The deposit consists of fine sediments, cobbles, and boulders, some of which are quite large. Clasts in the flow deposit include pinkish-reddish porphyritic dacite and gray porphyritic dacite, both of which formed at 27 ka during the Late Pleistocene, early in Mt. Lassen's history. Another clast type in the deposit is black porphyritic dacite, which formed on 14 May 1915. The clast type shown above is lava that formed on 22 May 1915. It consists of banded dacite pumice mixed with andesite. The light-colored streaks are pumice, a frothy-textured, light-weight, extrusive igneous rock. The dark-colored areas are andesite. The rock formed by mixing of two magma types, which resulted in an eruption.

Locality: boulder in Devastated Area, Lassen Volcano National Park, northeastern California, USA

This is Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

Locality: Lassen Volcano National Park, northeastern California, USA

This is lava from Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The lava boulder shown here is in a volcanic debris flow deposit from 19 and 22 May 1915, when Mt. Lassen last had a significant eruption. The deposit consists of fine sediments, cobbles, and boulders, some of which are quite large. Clasts in the flow deposit include pinkish-reddish porphyritic dacite and gray porphyritic dacite, both of which formed at 27 ka during the Late Pleistocene, early in Mt. Lassen's history. Another clast type in the deposit is black porphyritic dacite, shown here, that formed on 14 May 1915. The whitish-colored phenocrysts (click on the photo to zoom in and look around) are plagioclase feldspar.

The darker-colored, xenolith-like objects are "quenched blobs". From park signage: "These patches are called quenched blobs, formed during the rock's molten stage. As molten rock, basalt magma mixed with dacite magma. Dacite magma's temperature is much cooler than basalt's. When the hotter basalt injected into the cooler dacite magma, it was like hot wax hitting cold water. The blobs were quenched - cooled suddenly. When the lava oozed from the volcano's vent, the blobs solidified and remained encased in the dacite rock. The mixing of the two magmas likely triggered the May 19 Lassen Peak eruption. When a superheated injection of basalt magma enters a dacite magma, a volatile jolt occurs - sometimes enough to cause a volcano to erupt."

Quenched blobs in May 1915 black dacite may be composed of andesite.

Locality: boulder in Devastated Area, Lassen Volcano National Park, northeastern California, USA

This is Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

Locality: Lassen Volcano National Park, northeastern California, USA

This is lava from Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The lava boulder shown here is in a volcanic debris flow deposit from 19 and 22 May 1915, when Mt. Lassen last had a significant eruption. The deposit consists of fine sediments, cobbles, and boulders, some of which are quite large. Clasts in the flow deposit include pinkish-reddish porphyritic dacite and gray porphyritic dacite, both of which formed at 27 ka during the Late Pleistocene, early in Mt. Lassen's history. Another clast type in the deposit is black porphyritic dacite, shown here, that formed on 14 May 1915. The whitish-colored phenocrysts (click on the photo to zoom in and look around) are plagioclase feldspar.

The darker-colored, xenolith-like object is a "quenched blob". From park signage: "These patches are called quenched blobs, formed during the rock's molten stage. As molten rock, basalt magma mixed with dacite magma. Dacite magma's temperature is much cooler than basalt's. When the hotter basalt injected into the cooler dacite magma, it was like hot wax hitting cold water. The blobs were quenched - cooled suddenly. When the lava oozed from the volcano's vent, the blobs solidified and remained encased in the dacite rock. The mixing of the two magmas likely triggered the May 19 Lassen Peak eruption. When a superheated injection of basalt magma enters a dacite magma, a volatile jolt occurs - sometimes enough to cause a volcano to erupt."

Quenched blobs in May 1915 black dacite may be composed of andesite.

Locality: boulder in Devastated Area, Lassen Volcano National Park, northeastern California, USA

Flying over North Iraq on our way to India Mumbai then Delhi, I recognized well the distant Turkish Mt Ararat (about 5,165 meters high) volcano which is said to have received on its summit the Noah's Arch and all the animals of the Creation during the downpour; Behind on right at 11 km we can see its son called 'Little Ararat' 3,896 meters high.

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Ijen volcano in East Java contains the world's largest acidic volcanic crater lake, called Kawah Ijen, famous for its turquoise color. The active crater measuring 950x600 m is known for its rich sulphur deposits which are being quarried.

The volcano is one of several active stratovolcanoes constructed over the 20 km wide Ijen caldera, the largest caldera in Java.

Eruptions from Ijen are very hazardous because of the risk of the lake draining to form catastrophic lahars. Sulphur mine inside the crater of Ijen near the shore of Kawah Ijen

Background:

The Ijen volcano complex at the eastern end of Java consists of a group of small stratovolcanoes constructed within the large 20-km-wide Ijen (Kendeng) caldera. The north caldera wall forms a prominent arcuate ridge, but elsewhere the caldera rim is buried by post-caldera volcanoes, including Gunung Merapi stratovolcano, which forms the 2799 m high point of the Ijen complex. Immediately west of Gunung Merapi is the renowned historically active Kawah Ijen volcano, which contains a nearly 1-km-wide, turquoise-colored, acid crater lake. Picturesque Kawah Ijen is the world's largest highly acidic lake and is the site of a labor-intensive sulfur mining operation in which sulfur-laden baskets are hand-carried from the crater floor. Many other post-caldera cones and craters are located within the caldera or along its rim. The largest concentration of post-caldera cones forms an E-W-trending zone across the southern side of the caldera. Coffee plantations cover much of the Ijen caldera floor, and tourists are drawn to its waterfalls, hot springs, and dramatic volcanic scenery.

One of the most active volcanoes in Southern Kamchatka. It is formed from four (predominantly basaltic) coalescing stratovolcanoes. The crater contains a powerful geothermal field with numerous fumaroles, boiling mud pools/springs. Care is required when visiting this site (should keep away from the direction of the toxic fumes emanating from the fumaroles and any unstable areas).

Dacite pumice (air-fall tephra) from the Holocene of the Philippines.

Mt. Pinatubo is one of several subduction zone stratovolcanoes in the Luzon Volcanic Arc of the Philippines. Published information indicates that Pinatubo is 35,000+ years old and is composed principally of dacitic and andesitic rocks.

Mt. Pinatubo had a significant explosive ash eruption in 1991 that was the largest anywhere on Earth since 1912. Pinatubo's eruption is also famous for having been successfully predicted by American volcanologists. The prediction and subsequent evacuation saved thousands of lives.

The mid-June 1991 eruptions from Pinatubo blanketed ash, pumiceous lapilli, and pumice over the surrounding countryside, including two American military bases (Clark and Subic Bay). The sample seen here is dacite pumice from the 15 June 1991 eruption - it was collected at the U.S. Subic Bay Naval Base, ~20 miles south of Mt. Pinatubo.

Location of volcano: Mt. Pinatubo, Luzon Volcanic Arc, western Luzon Island, northern Philippines

-------------------

For additional geologic information on the 1991 Pinatubo eruption, see:

Newhall & Punongbayan (1996) - Fire and Mud, Eruptions and Lahars of Mount Pinatubo, Philippines. Quezon City & Seattle & London. Philippine Institute of Volcanology and Seismology & University of Washington Press. 1126 pp.

Pumice from the Holocene of Washington State, USA.

The 1980 Mt. St. Helens eruption was the largest in recent American history. The volcano was intermittently active until 1986. Minor activity occurred from 1989 to 1991 and from 2004 to 2006.

Mt. St. Helens is the most active volcano in the Cascade Range, a series of subduction zone stratovolcanoes in a ~north-south line from northern California to Oregon to Washington State to southwestern British Columbia. St. Helens is a 40,000 to 50,000 year old, andesitic-dacitic-basaltic volcano that typically has explosive ash eruptions (as do all subduction zone stratovolcanoes).

The 1980 eruption was a northward-directed lateral blast that followed an enormous landslide of the northern face of the volcano. The landslide was triggered by a moderate earthquake at 8:32 AM, Sunday, 18 May 1980. Snow and ice on the mountain melted during the eruption, mixed with ash and other debris, and rushed down nearby river valleys as lahars (volcanic mud flows).

The ash, lapilli, and pumice erupted from Mt. St. Helens in May 1980 was dacite, an intermediate extrusive igneous rock. Most of the air-fall dacite ash fell in Washington State, Oregon, and Idaho, but a minor amount accumulated as far east as Minnesota and Oklahoma. Light dustings of ash were also observed in Ohio.

Seen here is pumice, a felsic to intermediate to alkaline, frothy-textured, extrusive igneous rock. Pumice ranges from white to light gray to light tan in color. It is lightweight and often floats in water. This is likely from the 1980 eruption, so is probably dacite pumice.

Location of volcano: Mt. St. Helens, northwestern Skamania County, Cascade Range, southwestern Washington State, USA (46˚ 12’ 04” North, 122˚ 11” 18” West)

Sample collection site: Johnston Ridge, ~north of Mt. St. Helens

This is lava from Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The lava boulders shown here are in a volcanic debris flow deposit from 19 and 22 May 1915, when Mt. Lassen last had a significant eruption. The deposit consists of fine sediments, cobbles, and boulders, some of which are quite large. Clasts in the flow deposit include pinkish-reddish porphyritic dacite and gray porphyritic dacite, both of which formed at 27 ka during the Late Pleistocene, early in Mt. Lassen's history. Another clast type in the deposit is black porphyritic dacite, shown here, that formed on 14 May 1915. The whitish-colored phenocrysts (click on the photo to zoom in and look around) are plagioclase feldspar.

From park signage:

"After the May 19 avalanche carried hot lava rocks here, the surrounding air temperature rapidly cooled them. As they cooled - from the outside in - some of the rocks fractured inwardly and radially like this one, breaking into pyramid-like shapes. Like a jigsaw puzzle, many of the rock pieces you see here today could easily be reconfigured - solving a hot puzzle of the past."

Locality: boulder in Devastated Area, Lassen Volcano National Park, northeastern California, USA

El odio y la ira son como el fuego... sólo quema al que lo sostiene.

Escuintla, Guatemala by Zaigowitch 2008

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Dacite pumice (air-fall tephra) from the Holocene of the Philippines.

Mt. Pinatubo is one of several subduction zone stratovolcanoes in the Luzon Volcanic Arc of the Philippines. Published information indicates that Pinatubo is 35,000+ years old and is composed principally of dacitic and andesitic rocks.

Mt. Pinatubo had a significant explosive ash eruption in 1991 that was the largest anywhere on Earth since 1912. Pinatubo's eruption is also famous for having been successfully predicted by American volcanologists. The prediction and subsequent evacuation saved thousands of lives.

The mid-June 1991 eruptions from Pinatubo blanketed ash, pumiceous lapilli, and pumice over the surrounding countryside, including two American military bases (Clark and Subic Bay). The sample seen here is dacite pumice from the 15 June 1991 eruption - it was collected at the U.S. Subic Bay Naval Base, ~20 miles south of Mt. Pinatubo.

Location of volcano: Mt. Pinatubo, Luzon Volcanic Arc, western Luzon Island, northern Philippines

-------------------

For additional geologic information on the 1991 Pinatubo eruption, see:

Newhall & Punongbayan (1996) - Fire and Mud, Eruptions and Lahars of Mount Pinatubo, Philippines. Quezon City & Seattle & London. Philippine Institute of Volcanology and Seismology & University of Washington Press. 1126 pp.

This is Pilot Pinnacle in northern California. It is near Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park.

Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen (= well off to the right of this photo) is a large volcanic dome that has developed in the remnants of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today.

In the photo, Pilot Pinnacle forms part of the western edge of the Brokeoff Caldera. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

Eruptions still occur in this area. Mt. Lassen last experienced eruptive activity in the early 1900s.

Locality: view from Bumpass Hell Trailhead, just south of Mt. Lassen, Lassen Volcano National Park, northeastern California, USA

This is a volcanic deposit near Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The boulders shown here are in a volcanic debris flow deposit from 19 and 22 May 1915, when Mt. Lassen last had a significant eruption. The deposit consists of fine sediments, cobbles, and boulders, some of which are quite large. Clasts in the flow deposit include pinkish-reddish porphyritic dacite and gray porphyritic dacite, both of which formed at 27 ka during the Late Pleistocene, early in Mt. Lassen's history. Another clast type in the deposit is black porphyritic dacite, which formed on 14 May 1915. Other clast types present include dacite pumice and banded andesite-dacite pumice, both of which formed on 22 May 1915.

Locality: Devastated Area, Lassen Volcano National Park, northeastern California, USA

This is lava from Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The lava boulder shown here is in a volcanic debris flow deposit from 19 and 22 May 1915, when Mt. Lassen last had a significant eruption. The deposit consists of fine sediments, cobbles, and boulders, some of which are quite large. Clasts in the flow deposit include pinkish-reddish porphyritic dacite and gray porphyritic dacite, both of which formed at 27 ka during the Late Pleistocene, early in Mt. Lassen's history. Another clast type in the deposit is black porphyritic dacite, shown here, that formed on 14 May 1915. The whitish-colored phenocrysts (click on the photo to zoom in and look around) are plagioclase feldspar.

The darker-colored, xenolith-like object is a "quenched blob". From park signage: "These patches are called quenched blobs, formed during the rock's molten stage. As molten rock, basalt magma mixed with dacite magma. Dacite magma's temperature is much cooler than basalt's. When the hotter basalt injected into the cooler dacite magma, it was like hot wax hitting cold water. The blobs were quenched - cooled suddenly. When the lava oozed from the volcano's vent, the blobs solidified and remained encased in the dacite rock. The mixing of the two magmas likely triggered the May 19 Lassen Peak eruption. When a superheated injection of basalt magma enters a dacite magma, a volatile jolt occurs - sometimes enough to cause a volcano to erupt."

Quenched blobs in May 1915 black dacite may be composed of andesite.

Locality: boulder in Devastated Area, Lassen Volcano National Park, northeastern California, USA

ViewFinders_Overseas_Outing - Surabaya --> Ijen --> Bromo --> Solo --> Jogjakarta

Ijen:

The Ijen volcano complex is a group of stratovolcanoes, in East Java, Indonesia. It is inside a larger caldera Ijen, which is about 20 kilometers wide. The Gunung Merapi stratovolcano (not to be confused with Central Java's Gunung Merapi) is the highest point of that complex.

West of Gunung Merapi is the Ijen volcano, which has a one-kilometer-wide turquoise-colored acid crater lake. The lake is the site of a labor-intensive sulfur mining operation, in which sulfur-laden baskets are carried by hand from the crater floor. Many other post-caldera cones and craters are located within the caldera or along its rim. The largest concentration of post-caldera cones forms an E-W-trending zone across the southern side of the caldera. The active crater at Kawah Ijen has an equivalent radius of 361 meters, a surface of 41 × 106 square meters. It is 200 meters deep and has a volume of 36 × 106 cubic meters.

An active vent at the edge of the lake is a source of elemental sulfur, and supports a mining operation. Escaping volcanic gasses are channeled through a network of ceramic pipes, resulting in condensation of molten sulfur. The sulfur, which is deep red in color when molten, pours slowly from the ends of these pipes and pools on the ground, turning bright yellow as it cools. The cooled material is broken into large pieces and carried out in baskets by the miners. Typical loads range from 70–100 kilograms, and must be carried to the crater rim approximately 200 meters above before being carried several kilometers down the mountain. Most miners make this journey twice a day. The miners are paid by a nearby sugar refinery by the weight of sulfur transported; as of July 2005 the typical daily earnings were equivalent to approximately $5.00 US. The miners often use insufficient protection while working around the volcano and are susceptible to numerous respiratory complaints.

Bromo:

Mount Bromo (Indonesian: Gunung Bromo), is an active volcano and part of the Tengger massif, in East Java, Indonesia. At 2,329 metres (7,641 ft) it is not the highest peak of the massif, but is the most well known. The massif area is one of the most visited tourist attractions in East Java, Indonesia. The volcano belongs to the Bromo Tengger Semeru National Park.

Mount Bromo sits in the middle of a vast plain called the Sand Sea (Indonesian: Lautan Pasir), a protected nature reserve since 1919. The typical way to visit Mount Bromo is from the nearby mountain village of Cemoro Lawang. From there it is possible to walk to the volcano in about 45 minutes, but it is also possible to take an organised jeep tour, which includes a stop at the viewpoint on Mount Penanjakan (2,770 meters) (Indonesian: Gunung Penanjakan). The best views from Mount Bromo to the Sand Sea below and the surrounding volcanoes are at sunrise. The viewpoint on Mount Penanjakan can also be reached on foot in about two hours. From inside the caldera, sulfur is collected by workers.

Solo:

Surakarta is also known by the name "Solo". "Surakarta" is used in formal and official contexts. The city has a similar name with the neighboring district of "Kartasura", where the previous capital of Mataram was located. Variant spelling of Surakarta is found as Soerakarta - and is simply the old spelling prior to the pre 1948's spelling change.

It is approximately 65 km (40 miles) northeast of Yogyakarta, and 100 km (60 miles) southeast of Semarang The eastern part of the town is bordered by Bengawan Solo River, the longest river on Java. The river is the inspiration for the song Bengawan Solo, a 1940s composition by Gesang Martohartono which became famous throughout much of Asia.

Jogjakarta:

Yogyakarta is located in south-central Java. It is surrounded by the province of Central Java (Jawa Tengah) and the Indian Ocean in the south.

The population of DIY in 2003 was approximately 3,000,000. The province of Yogyakarta has a total area of 3,185.80 km2. Yogyakarta is the second-smallest area of the provinces in Indonesia, after the Jakarta Capital Region. However it has, along with adjacent areas in Central Java, some of the highest population densities of Java.

(looking ~east; photo by Miranda Manross)

-------------------------------------

In the foreground is Mt. St. Helens, the most active volcano in the Cascade Range, which is a series of subduction zone stratovolcanoes in a ~north-south line from northern California to Oregon to Washington State to southwestern British Columbia. St. Helens is a 40,000 to 50,000 year old, andesitic-dacitic-basaltic volcano that typically has explosive ash eruptions (as do all subduction zone stratovolcanoes).

The 1980 eruption of Mt. St. Helens was a northward-directed lateral blast that immediately followed an enormous landslide event on the northern face of the volcano. The landslide was triggered by a moderate earthquake at 8:32 AM, Sunday, 18 May 1980. Snow and ice on the mountain melted during the eruption, mixed with ash and other debris, and rushed down nearby river valleys as lahars (volcanic mud flows).

The ash, lapilli, and pumice erupted from Mt. St. Helens in May 1980 was dacite, an intermediate extrusive igneous rock. Most of the air-fall dacite ash fell in Washington State, Oregon, and Idaho, but a minor amount accumulated as far east as Minnesota and Oklahoma. Light dustings of ash were also observed in Ohio.

The 1980 eruption was the largest in recent American history. The volcano was intermittently active until 1986. Minor activity occurred from 1989 to 1991 and from 2004 to 2006.

The area is now a park ("national volcanic monument") and is accessible to tourists. The top third of the mountain was blown away during the 1980 eruption. Much of the surrounding landscape is still nonvegetated and covered with gray volcanic tephra.

In the background is Mt. Adams, another subduction zone stratovolcano. Adams is a Pleistocene-Holocene dacitic-andesitic-basaltic volcano composed of lava flows (mostly) and tephra deposits (some). Its last eruption was in prehistoric times, about 1,000 years ago.

Location: Mt. St. Helens (northwestern Skamania County) & Mt. Adams (southwestern Yakima County), Cascade Range, southwestern Washington State, USA

-------------------------------------

See info. at:

en.wikipedia.org/wiki/Mount_St._Helens

and

en.wikipedia.org/wiki/Mount_Adams_(Washington)

Pumice from the Holocene of Washington State, USA.

The 1980 Mt. St. Helens eruption was the largest in recent American history. The volcano was intermittently active until 1986. Minor activity occurred from 1989 to 1991 and from 2004 to 2006.

Mt. St. Helens is the most active volcano in the Cascade Range, a series of subduction zone stratovolcanoes in a ~north-south line from northern California to Oregon to Washington State to southwestern British Columbia. St. Helens is a 40,000 to 50,000 year old, andesitic-dacitic-basaltic volcano that typically has explosive ash eruptions (as do all subduction zone stratovolcanoes).

The 1980 eruption was a northward-directed lateral blast that followed an enormous landslide of the northern face of the volcano. The landslide was triggered by a moderate earthquake at 8:32 AM, Sunday, 18 May 1980. Snow and ice on the mountain melted during the eruption, mixed with ash and other debris, and rushed down nearby river valleys as lahars (volcanic mud flows).

The ash, lapilli, and pumice erupted from Mt. St. Helens in May 1980 was dacite, an intermediate extrusive igneous rock. Most of the air-fall dacite ash fell in Washington State, Oregon, and Idaho, but a minor amount accumulated as far east as Minnesota and Oklahoma. Light dustings of ash were also observed in Ohio.

Seen here is pumice, a felsic to intermediate to alkaline, frothy-textured, extrusive igneous rock. Pumice ranges from white to light gray to light tan in color. It is lightweight and often floats in water. This is likely from the 1980 eruption, so is probably dacite pumice.

Location of volcano: Mt. St. Helens, northwestern Skamania County, Cascade Range, southwestern Washington State, USA (46˚ 12’ 04” North, 122˚ 11” 18” West)

Sample collection site: Johnston Ridge, ~north of Mt. St. Helens

This is Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

Locality: Lassen Volcano National Park, northeastern California, USA

Montage of MODIS Terra images (250m/pixel) of Russia's Kamchatka Peninsula. Look for the shadows of the stratovolcanoes - they look like dark triangles on the snow.

ViewFinders_Overseas_Outing - Surabaya --> Ijen --> Bromo --> Solo --> Jogjakarta

Ijen:

The Ijen volcano complex is a group of stratovolcanoes, in East Java, Indonesia. It is inside a larger caldera Ijen, which is about 20 kilometers wide. The Gunung Merapi stratovolcano (not to be confused with Central Java's Gunung Merapi) is the highest point of that complex.

West of Gunung Merapi is the Ijen volcano, which has a one-kilometer-wide turquoise-colored acid crater lake. The lake is the site of a labor-intensive sulfur mining operation, in which sulfur-laden baskets are carried by hand from the crater floor. Many other post-caldera cones and craters are located within the caldera or along its rim. The largest concentration of post-caldera cones forms an E-W-trending zone across the southern side of the caldera. The active crater at Kawah Ijen has an equivalent radius of 361 meters, a surface of 41 × 106 square meters. It is 200 meters deep and has a volume of 36 × 106 cubic meters.

An active vent at the edge of the lake is a source of elemental sulfur, and supports a mining operation. Escaping volcanic gasses are channeled through a network of ceramic pipes, resulting in condensation of molten sulfur. The sulfur, which is deep red in color when molten, pours slowly from the ends of these pipes and pools on the ground, turning bright yellow as it cools. The cooled material is broken into large pieces and carried out in baskets by the miners. Typical loads range from 70–100 kilograms, and must be carried to the crater rim approximately 200 meters above before being carried several kilometers down the mountain. Most miners make this journey twice a day. The miners are paid by a nearby sugar refinery by the weight of sulfur transported; as of July 2005 the typical daily earnings were equivalent to approximately $5.00 US. The miners often use insufficient protection while working around the volcano and are susceptible to numerous respiratory complaints.

Bromo:

Mount Bromo (Indonesian: Gunung Bromo), is an active volcano and part of the Tengger massif, in East Java, Indonesia. At 2,329 metres (7,641 ft) it is not the highest peak of the massif, but is the most well known. The massif area is one of the most visited tourist attractions in East Java, Indonesia. The volcano belongs to the Bromo Tengger Semeru National Park.

Mount Bromo sits in the middle of a vast plain called the Sand Sea (Indonesian: Lautan Pasir), a protected nature reserve since 1919. The typical way to visit Mount Bromo is from the nearby mountain village of Cemoro Lawang. From there it is possible to walk to the volcano in about 45 minutes, but it is also possible to take an organised jeep tour, which includes a stop at the viewpoint on Mount Penanjakan (2,770 meters) (Indonesian: Gunung Penanjakan). The best views from Mount Bromo to the Sand Sea below and the surrounding volcanoes are at sunrise. The viewpoint on Mount Penanjakan can also be reached on foot in about two hours. From inside the caldera, sulfur is collected by workers.

Solo:

Surakarta is also known by the name "Solo". "Surakarta" is used in formal and official contexts. The city has a similar name with the neighboring district of "Kartasura", where the previous capital of Mataram was located. Variant spelling of Surakarta is found as Soerakarta - and is simply the old spelling prior to the pre 1948's spelling change.

It is approximately 65 km (40 miles) northeast of Yogyakarta, and 100 km (60 miles) southeast of Semarang The eastern part of the town is bordered by Bengawan Solo River, the longest river on Java. The river is the inspiration for the song Bengawan Solo, a 1940s composition by Gesang Martohartono which became famous throughout much of Asia.

Jogjakarta:

Yogyakarta is located in south-central Java. It is surrounded by the province of Central Java (Jawa Tengah) and the Indian Ocean in the south.

The population of DIY in 2003 was approximately 3,000,000. The province of Yogyakarta has a total area of 3,185.80 km2. Yogyakarta is the second-smallest area of the provinces in Indonesia, after the Jakarta Capital Region. However it has, along with adjacent areas in Central Java, some of the highest population densities of Java.

The Ijen volcano complex is a group of stratovolcanoes inside a larger caldera Ijen, which is about 20 kilometers wide. The Gunung Merapi stratovolcano is the highest point of that complex. West of Gunung Merapi is the Ijen volcano, which has a one-kilometer-wide turquoise-colored acid crater lake. The lake is the site of a labor-intensive sulfur mining operation, in which sulfur-laden baskets are carried by hand from the crater floor (http://en.wikipedia.org/wiki/Ijen).

This mountain is near Lassen Peak (Mt. Lassen), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

Shown here is Chaos Crags, a cluster of six volcanic domes that formed in the late Holocene on the northern side of Lassen Volcano. All six domes are composed of porphyritic rhyodacite, a lava type between dacite and rhyolite. Published analyses indicate that the Chaos Crags rhyodacite domes are 68% to 70% silica. Radiometric dating shows that the domes were emplaced sequentially between about 825 A.D. and 1575 A.D.

Two of the six domes are seen in the photo. Dome C is the large front face at center and right. Dome C rocks are composed of 68% silica porphyritic rhyodacite with ~10 volume% mafic inclusions. Phenocrysts in the rocks are principally plagioclase feldspar, hornblende amphibole, biotite mica, and quartz. Dome E is at the top and left. It is also composed of 68% silica porphyritic rhyodacite with plagioclase, hornblende, biotite, and quartz phenocrysts. Part of dome D is visible at the far upper right of the photo.

Dome C had a major collapse event in the late 1600s A.D. This resulted in a large landslide - the deposit is called "Chaos Jumbles" (see nearby pictures in this photostream).

Locality: Lassen Volcano National Park, northeastern California, USA

The Ijen volcano complex is a group of stratovolcanoes, in East Java, Indonesia. It is inside a larger caldera Ijen, which is about 20 kilometers wide. The Gunung Merapi stratovolcano is the highest point of that complex. The name of this volcano resembles that of a different volcano, Mount Merapi in central Java, also known as Gunung Merapi. The name "Merapi" means "fire" in the Indonesian language. From: wiki.

Java is the world's most densely populated island (population: 136 million). It is home to 60% of Indonesia's population. Much of Indonesian history took place on Java; it was the centre of powerful Hindu-Buddhist empires, Islamic sultanates, the core of the colonial Dutch East Indies, and was at the centre of Indonesia's campaign for independence. The island dominates Indonesian social, political and economic life. More information on wikipedia.