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

STS056-071-031 Atka Island, Amlia Island, and Aleutian Islands, Alaska, U.S.A. April 1993

The oval, snow-covered northern peninsula of Atka Island, a cluster of severely eroded stratovolcanoes and caldera, is part of the Aleutian chain known as the Central Aleutian Islands. Korovin Volcano, near the northern edge of the island, has the highest elevation on the island [5030 feet (1533 meters)] and the most eruptive activity. Elongated, east-west-oriented Amlia Island to the east rises only 2100 feet (640 meters) at its highest elevation.

AMPATO

Ampato is a dormant 6,288 m (20,630 ft) stratovolcano in the Andes of southern Peru, about 100 km (60 mi) northwest of Arequipa.

It is part of a 20 km (12 mi) north-south chain of three major stratovolcanoes, including the extinct and eroded 6,025 m (19,767 ft) Nevado Hualca Hualca at the northern end and the active 5,976 m (19,606 ft) cone of Volcán Sabancaya in the middle.

In September 1995, the rapidly retreating glacier near the summit of Ampato revealed the frozen mummified body of an Inca girl, killed by a blow to the head about 500 years ago.

The mummy, later called the "Ice Maiden" and nicknamed "Juanita", was recovered by an expedition led by American archaeologist Dr. Johan Reinhard. Subsequent expeditions have led to the recovery of three further mummies above 5,800 m (19,000 ft).

Excerpt from Wikipedia, the free encyclopedia

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).

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; there is also a third volcano named Marapi in Sumatra. The name "Merapi" means "fire" in the Indonesian language.

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. The work is low-paid and very onerous. Workers earn around $5.50-$8.30 (Rp 50,000 - Rp 75,000) per day and once out of the crater, still need to carry their loads of sulfur chunks about three kilometers to the nearby Pultuding valley to get paid.[1]

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 east/west-trending zone across the southern side of the caldera. The active crater at Kawah Ijen has an equivalent radius of 361 metres (1,184 ft), a surface of 0.41 square kilometres (0.16 sq mi). It is 200 metres (660 ft) deep and has a volume of 36 cubic hectometres (29,000 acre·ft).

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.

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

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 Lago de Atitlán is a beautiful lake in the highlands of Guatemala; the water level is at 1562 meters (5,125 ft). The lake basin is volcanic in origin, filling an enormous caldera formed by an eruption 84,000 years ago. It is shaped by deep surrounding escarpments and three stratovolcanoes on its southern flank. Lake Atitlán is the deepest lake in Central America with a maximum depth of about 340 meters (1,120 ft). Its surface area is 130 sq km (50 sq mi).

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.

STS047-081-025 Unimak Island and Aleutian Islands, Alaska, U.S.A. September 1992

Three distinctive, snowcapped stratovolcanoes are easily identified in this near-vertical photograph of Unimak Island, one of many volcanic islands in the Aleutian archipelago. The Aleutian archipelago, formed by the collision of the Pacific Plate with the western extension of the North American Plate, forms a northern part of the Ring of Fire that encircles the Pacific Ocean. Unimak Island, the large island nearest the Alaskan Peninsula, is separated from the peninsula by Bechevin Bay, shown at the bottom of the photograph. Shishaldin Volcano, the westernmost and tallest of the three featured volcanoes, reaches a maximum elevation of 9387 feet (2860 meters) above sea level and has been very active during the last two centuries, especially during the mid-1900s. Isanolski Volcano, the middle volcano, climbs to 8088 feet (2465 meters) above sea level. Each of these volcanoes exhibits a classic erosional drainage pattern that radiates in all directions from the central peak.

ISS014-E-11872 (11 Jan. 2007) --- Pagan Island, Northern Mariana Islands, is featured in this image photographed by an Expedition 14 crewmember on the International Space Station. According to scientists, the Mariana Islands are part a volcanic island arc -- surface volcanoes formed from magma generation as one tectonic plate is overridden (or subducted) beneath another. In the case of the Mariana Islands, the Pacific Plate is being subducted beneath the Philippine Plate along the famously deep Mariana Trench (more than 11 kilometers below sea level). Pagan Island (right) is comprised of two stratovolcanoes (tall, typically cone-shaped structures formed by layers of dense crystallized lava and less-dense ash and pumice) connected by a narrow isthmus of land. Mount Pagan, the larger of the two volcanoes, forms the northeastern portion of the island and has been the most active historically. The most recent major eruption took place in 1981, but since then numerous steam- and ash-producing events have been observed at the volcano -- the latest reported one occurring between Dec. 5-8, 2006. This image records volcanic activity on Jan. 11, 2007 that produced a thin plume (most probably steam, say NASA scientists, possibly with minor ash content) that extended westwards away from Mount Pagan. The island is sparsely populated, and monitored for volcanic activity by the United States Geological Survey and the Commonwealth of the Mariana Islands.

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 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.

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

Yosemite Valley in California's Sierra Nevada Mountains is a spectacularly scenic area. The rocks in the Yosemite Valley area are principally Cretaceous-aged, felsic to intermediate, intrusive igneous rocks. Many discrete intrusions are present, ranging in composition from granite to granodiorite to diorite to quartz monzonite. Most of these intrusive rocks have a strongly porphyritic texture (= a mix of large and small crystals). The rocks in this area are part of the Sierra Nevada Batholith, a series of old, cooled magma chambers that were originally beneath a chain of stratovolcanoes developed along an ancient subduction zone.

Features: Half Dome is the rounded mountain top above the geologist's head.

Locality: Yosemite Valley (view from Glacier Point), Yosemite National Park, Sierra Nevada Mountains, eastern California, USA

ISS019-E-005286 (8 April 2009) --- Mount Fuji, Japan is featured in this image photographed by an Expedition 19 crew member on the International Space Station. The 3,776 meters high Mount Fuji volcano, located on the island of Honshu in Japan, is one of the world's classic examples of a stratovolcano. The volcano's steep, conical profile is the result of numerous interlayered lava flows and explosive eruption products -- such as ash, cinders, and volcanic bombs -- building up the volcano over time. The steep profile is possible because of the relatively high viscosity of the volcanic rocks typically associated with stratovolcanoes. This leads to thick sequences of lava flows near the eruptive vent that build the cone structure, rather than low viscosity flows that spread out over the landscape and build lower-profile shield volcanoes. According to scientists, Mount Fuji, or Fuji-san in Japan, is actually comprised of several overlapping volcanoes that began erupting in the Pleistocene Epoch (1.8 million to approximately 10,000 years ago). Scientists believe that the currently active volcano, known as Younger Fuji, began forming approximately 11,000 to 8,000 years ago. The most recent explosive activity occurred in 1707, creating Hoei Crater on the southeastern flank of the volcano (center). This eruption deposited ash on Edo (present-day Tokyo) located 95 kilometers to the northeast. While there have been no further eruptions of Mount Fuji, steam was observed at the summit during 1780--1820, and the volcano is considered active. This oblique photograph illustrates the snow-covered southeastern flank of the volcano; the northeastern flank can be seen here. A representation of the topography of Mt. Fuji and its surroundings can be viewed here.

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

Panorama of oblique images showing many volcanoes on Russia's Kamchatka Peninsula.

The Lago de Atitlán is a beautiful lake in the highlands of Guatemala; the water level is at 1562 meters (5,125 ft). The lake basin is volcanic in origin, filling an enormous caldera formed by an eruption 84,000 years ago. It is shaped by deep surrounding escarpments and three stratovolcanoes on its southern flank. Lake Atitlán is the deepest lake in Central America with a maximum depth of about 340 meters (1,120 ft). Its surface area is 130 sq km (50 sq mi).

In view are the Volcán Tolimán (right) with an altitude of 3158 meters (10,361 ft) and the Volcán Atitlán (left) with an altitude of 3535 meters (11,598 ft).

These boats serve as public transportation for communities along the lake. They have powerful motors and go pretty fast.

The Lago de Atitlán is a beautiful lake in the highlands of Guatemala; the water level is at 1562 meters (5,125 ft). The lake basin is volcanic in origin, filling an enormous caldera formed by an eruption 84,000 years ago. It is shaped by deep surrounding escarpments and three stratovolcanoes on its southern flank. Lake Atitlán is the deepest lake in Central America with a maximum depth of about 340 meters (1,120 ft). Its surface area is 130 sq km (50 sq mi).

All three volcanos are in view here. To the left are the Volcán Tolimán (right) with an altitude of 3158 meters (10,361 ft) and the Volcán Atitlán (left) with an altitude of 3535 meters (11,598 ft). On the right side is the Volcán San Pedro (a.k.a. Volcán Las Yeguas) with an altitude of 3020 meters (9,908 ft).

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 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 south-southwest of Mt. Lassen, 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 (= foreground valley in the photo). 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 south-southwest of Mt. Lassen, Lassen Volcano National Park, northeastern California, USA

Yosemite Valley in California's Sierra Nevada Mountains is a spectacularly scenic area. The rocks in the Yosemite Valley area are principally Cretaceous-aged, felsic to intermediate, intrusive igneous rocks. Many discrete intrusions are present, ranging in composition from granite to granodiorite to diorite to quartz monzonite. Most of these intrusive rocks have a strongly porphyritic texture (= a mix of large and small crystals). The rocks in this area are part of the Sierra Nevada Batholith, a series of old, cooled magma chambers that were originally beneath a chain of stratovolcanoes developed along an ancient subduction zone.

Features: Half Dome is the rounded mountain top above the geologist's head.

Locality: Yosemite Valley (view from Glacier Point), Yosemite National Park, Sierra Nevada Mountains, eastern California, USA

AMPATO

Ampato is a dormant 6,288 m (20,630 ft) stratovolcano in the Andes of southern Peru, about 100 km (60 mi) northwest of Arequipa. It is part of a 20 km (12 mi) north-south chain of three major stratovolcanoes, including the extinct and eroded 6,025 m (19,767 ft) Nevado Hualca Hualca at the northern end and the active 5,976 m (19,606 ft) cone of Volcán Sabancaya in the middle.

In September 1995, the rapidly retreating glacier near the summit of Ampato revealed the frozen mummified body of an Inca girl, killed by a blow to the head about 500 years ago. The mummy, later called the "Ice Maiden" and nicknamed "Juanita", was recovered by an expedition led by American archaeologist Dr. Johan Reinhard. In October 1995 and December 1997, Reinhard and Peruvian archaeologist Jose Antonio Chavez directed expeditions that led to the recovery of three further mummies above 5,800 m (19,000 ft).

From Wikipedia, the free encyclopedia

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

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.

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

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 and cobbles 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 Mt. Diller 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, Mt. Diller 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 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.

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

ISS021-E-005555 (11 Oct. 2009) --- This picture of the active Soufriere Hills volcano on Montserrat Island was photographed on Oct. 11, 2009 by the Expedition 21 crew members onboard the International Space Station. Meteorologists and other scientists note that this area is nearly always cloudy so it is considered rare when astronauts get good images of the plumes or volcanic activity. Soufriere Hills is identified as a "stratovolcano" by geologists because it is built of layers (the "strato" part of the name) of both lavas and pyroclastic flows from older eruptions. Another name for this kind of volcano is a "composite volcano" referring to the fact that when it erupts it produces both lava and fragmented deposits during explosive eruptions. Scientists point out that the magma feeding the Soufriere Hills volcano is created by the subduction of local tectonic plates -- stratovolcanoes are commonly associated with this type of geologic environment. Photo credit: NASA

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 and cobbles 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

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.

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 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

This mosaic of two astronaut photographs illustrates the closeness of Arequipa, Peru to the 5,822-meter-high El Misti Volcano. The symmetric conical shape of El Misti is typical of a stratovolcano, a type of volcano characterized by alternating layers of lava and debris from explosive eruptions, such as ash and pyroclastic flows. The magma feeding the stratovolcanoes of the Andes Mountains, including El Misti, is associated with ongoing subduction of the Nazca Plate beneath the South American Plate. ASU-IPF-3032

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

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 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

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.

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, 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 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.

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

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

Altitude: 3 426m. Age: 500 000 ans; USA Oregon State Mt Hood loop tour and wilderness.

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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

The Hakkōda Mountains (八甲田山系 Hakkōda-sankei) is a volcanic complex that lies to the south of Aomori in Aomori Prefecture, Japan. The range consists of more than a dozen stratovolcanoes and lava domes arranged into two volcanic groups.[1] The Northern Hakkōda Volcanic Group emerges from the rim of an 8-km wide caldera that dates back to the Pleistocene.[1] The Southern Hakkōda Volcanic Group predates the caldera.[2]

The highest peak in the range is Mount Ōdake, which can be climbed from Sukayu Onsen in about four hours. Heavy snowfall makes Hakkoda a prime destination for backcountry and mountain skiers, and there are two mountain huts for overnight trips. The lower slopes of the mountains are forested interspersed with moorland. Above 1300 meters,[3] the Alpine climate zone starts.

The Hakkōda Mountains, along with Lake Towada and the Oirase Valley make up the Towada-Hachimantai National Park.[3]

en.wikipedia.org/wiki/Hakkōda_Mountains

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