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Dacite from the Quaternary of California, USA. (public display, Geology Department, Wittenberg University, Springfield, Ohio, 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 (see the example above). 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).
This sample could be 27 ka gray porphyritic dacite, which is common material at & around Lassen Volcano, but specific provenance information is not available. The whitish-colored phenocrysts (click on the photo to zoom in and look around) are feldspar. The black crystals are hornblende amphibole.
Locality: unrecorded/undisclosed site at or near Lassen Peak, Lassen Volcano National Park, northeastern California, USA
This is Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).
Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.
The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).
Locality: Lassen Volcano National Park, northeastern California, USA
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.
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).
In 2008, explorer George Kourounis took a small rubber boat out onto the acid lake to measure its acidity. The pH of the water in the crater was measured to be 0.5 due to sulfuric acid.
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).
(from public signage)
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This is a reconstruction of Brokeoff Volcano in northern California. The remnants of this old volcano are in Lassen Volcanic National Park.
Lassen Volcano and Brokeoff Volcano are 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 has developed in the remnants of 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.
The above reconstruction shows the location of the Brokeoff Caldera and the modern mountain peaks that form the caldera's edge (Brokeoff Mountain, Mt. Diller, and Mt. Conard). 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.
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(Synthesized info. from various public signage):
Using your imagination, you can connect the dots between the surrounding peaks of Brokeoff Mountain, Mount Conard, Mount Diller, and Pilot Pinnacle, recreating the outline of an extinct, Mount Shasta-like composite volcano named Brokeoff Volcano, more commonly known as Mount Tehama. Diamond Peak stands near the ancient volcano's core. It is worth trying to imagine, if only to comprehend its enormous size. The ancient volcano, active 600,000 to 400,000 years ago, measured 11 miles across and towered to 11,500 feet - 1,000 feet taller than Lassen Peak.
When the volcano ceased erupting 400,000 years ago, its slow decay and collapse began. The volcano simply fell apart over time. Hydrothermal features, like those at Sulphur Works and in Little Hot Springs Valley today, circulated hot, corrosive fluids through the volcano, weakening and softening its porous rock. Glaciers and flowing water further altered and eroded the rock. Bit by bit the volcano's structure was whittled and fell away, leaving this valley depression and the resistant skeletal mountain rim you see today.
Sulphur Works rests near the volcano's core. Although the volcano's fire is long extinguished, the hydrothermal system here at Sulphur Works is connected to the same magma system - a network of magma pockets - that fed the extinct volcano.
A composite cone is built of alternating layers of lava flows, volcanic cinders, and ash. The principal lava in composite volcanoes is andesite, a rock commonly found in the Andes Mountains. Andesite contains a little more than fifty-percent silica. Brokeoff Volcano (Mt. Tehama) is an example of a composite volcano.
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Locality: Lassen Volcano National Park, northeastern California, USA
Mount Baker dominates a small harbor in the San Juan Islands.
How do you spell R-E-L-I-E-F (topographic that is)? I spell it Mount Baker ;) You are looking at 10,781 feet (3,286 m) of relief. Mt. Baker is 53 miles away from this photo location and that is Sherman crater near the top.
Mt. Baker is one of the Cascade Stratovolcanoes and is spectacular statistically as well as visually. Baker has set the record for snowfall in a year at 1,140 inches - that is 95 feet or 28.956 meters of snow. All this snow results in the most glacial ice of any of the Cascade volcanoes except Mt. Ranier. In fact, Baker's glaciers contain more ice by volume than all the rest of the Cascade volcanoes combined if you leave out Mt. Ranier.
Volcanic activity is very young here commencing only about 1.5 million years ago. The current crater down to about the edge of the snowline could be as young as 80,000-90,000 years ago or as "old" as 140,000 years ago. That is like yesterday on the geological time scale.
Finally, for all of you oceanographers out there, Mt. Baker was named for Joseph Baker who was 3rd Lieutenant on HMS Discovery (not as famous as HMS Beagle) who first saw and reported on Mt. Baker in 1792 to the captain of the voyage, George Vancouver.
MG_0888
ISS018-E-035716 (24 Feb. 2009) --- Minchinmávida and Chaitén Volcanoes in Chile are featured in this image photographed by an Expedition 18 crewmember on the International Space Station. The Andes mountain chain along the western coastline of South America includes numerous active stratovolcanoes. The majority of these volcanoes are formed, and fed, by magma generated as the oceanic Nazca tectonic plate moves northeastward and plunges beneath the less dense South American continental tectonic plate (a process known as subduction). The line of Andean volcanoes marks the approximate location of the subduction zone. This astronaut photograph highlights two volcanoes located near the southern boundary of the Nazca -- South America subduction zone in southern Chile. Dominating the scene is the massive Minchinmávida stratovolcano at center. An eruption of this glaciated volcano was observed by Charles Darwin during his Galapagos Island voyage in 1834; the last recorded eruption took place the following year. The white, snow covered summit of Minchinmávida is blanketed by gray ash erupted from its much smaller but now active neighbor to the west, Volcan (volcano) Chaitén. The historically inactive Chaitén volcano, characterized by a large lava dome within a caldera (an emptied and collapsed magma chamber beneath a volcano) roared back to life unexpectedly on May 2, 2008, generating dense ash plumes and forcing the evacuation of the nearby town of Chaitén. Volcanic activity continues at Chaitén, including partial collapse of a new lava dome and generation of a pyroclastic flow several days before this photograph was taken. A steam and ash plume is visible extending to the northeast from the eruptive center of the volcano.
Another from the digital archives. A scene typical of central parts of New Zealand's North Island in early spring, looking across Lake Taupo to the active stratovolcanoes of the central volcanic plateau (L to R: Ruapehu, Ngauruhoe, and Tongariro). New Zealand's largest volcano is in the middle distance (Lake Taupo).
This mountain is near Lassen Peak (Mt. Lassen), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).
Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.
The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).
Shown here is Chaos Crags, a cluster of six volcanic domes that formed in the late Holocene on the northern side of Lassen Volcano. All six domes are composed of porphyritic rhyodacite, a lava type between dacite and rhyolite. Published analyses indicate that the Chaos Crags rhyodacite domes are 68% to 70% silica. Radiometric dating shows that the domes were emplaced sequentially between about 825 A.D. and 1575 A.D.
Dome F is seen in the photo. Dome F rocks are composed of 68% silica porphyritic rhyodacite. Phenocrysts in the rocks are principally plagioclase feldspar, hornblende amphibole, biotite mica, and quartz.
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; 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.
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).
In 2008, explorer George Kourounis took a small rubber boat out onto the acid lake to measure its acidity. The pH of the water in the crater was measured to be 0.5 due to sulfuric acid.
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.
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).
In 2008, explorer George Kourounis took a small rubber boat out onto the acid lake to measure its acidity. The pH of the water in the crater was measured to be 0.5 due to sulfuric acid.
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).
Mt. Lassen is in the far background on the right side of this photo. The large, gray feature in the center background is Chaos Crags, a cluster of six volcanic domes that formed in the late Holocene on the northern side of Lassen Volcano. All six domes are composed of porphyritic rhyodacite, a lava type between dacite and rhyolite. Published analyses indicate that the Chaos Crags rhyodacite domes are 68% to 70% silica. Radiometric dating shows that the domes were emplaced sequentially between about 825 A.D. and 1575 A.D.
The rubble in the bottom foreground of the photo is "Chaos Jumbles", a large landslide deposit (usually mis-referred to as an "avalanche") consisting of porphyritic rhyodacite lava blocks. 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. Dome C is the central front face of Chaos Crags, as seen in this picture. Dome C rocks and Chaos Jumbles Landslides rocks are composed of 68% silica porphyritic rhyodacite with ~10 volume% mafic inclusions. Phenocrysts in the rocks are principally plagioclase feldspar, hornblende amphibole, biotite mica, and quartz.
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
Sabancaya is a 6000m high active stratovolcano in the Andes in southern Peru, located about 100km northwest of Arequipa (2,335m).
It is the most active volcano in Peru and part of a 20 km long north-south chain of 3 large stratovolcanoes.
Nevado Hualca Hualca 6025m, the always most active Sabancaya 6000m, Ampato 6300m.
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.
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).
In 2008, explorer George Kourounis took a small rubber boat out onto the acid lake to measure its acidity. The pH of the water in the crater was measured to be 0.5 due to sulfuric acid.
The watershed of the Amazon basin begins in the high Andes. In Ecuador, the continental divide is adorned by a string of massive, glacier-capped stratovolcanoes. One of the most impressive of these giants is Cotopaxi, which at 5,897 m (19,347 ft) is Earth’s highest active volcano. Steeped in lore and considered a sacred mountain by local Andean peoples, Cotopaxi has erupted more than 50 times since 1738. There has not been a major eruption since 1904, but minor eruptions have occurred as recently as January 2016. A major eruption in the future a concern for Quito, Ecuador’s capital city, due to its close proximity to the volcano. Past major eruptions have produced pyroclastic flows, melting the icecap and forming massive lahars - or volcanic mudflows - that destroyed local towns and traveled more than 100km to both the Pacific Ocean and Amazon basin.
-0.711533, -78.445567
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.
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).
In 2008, explorer George Kourounis took a small rubber boat out onto the acid lake to measure its acidity. The pH of the water in the crater was measured to be 0.5 due to sulfuric acid.
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 volcanoes 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).
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
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).
A wide angle view after making a turn during a flight out of Portland. With the runway in the immediate foreground, I wanted to capture a sweeping view as one looked up to see Mount Rainier, St. Helens and Adams along with the Washington countryside.
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
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).
Pumice from the Holocene of Washington State, USA. (~5.4 centimeters across at its widest)
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.
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: unknown/unrecorded
Summit of Moro Rock exfoliation dome
Moro Rock is a large exfoliation dome in the Sierra Nevada Mountains of eastern California, USA. It is accessible by road and hiking trail in the western part of Sequoia National Park, a little east of Generals Highway (Rt. 198).
Exfoliation domes are common in the Sierra Nevada Mountains. They form by large-scale spheroidal weathering of granites and granitoids of the Sierra Nevada Batholith. The batholith represents a Late Jurassic to Late Cretaceous-aged mass of cooled magma chambers originally beneath a chain of subduction zone stratovolcanoes.
Pressure release from erosional unroofing of the batholith resulted in the rocks having curved sheeting joints. Spheroidal weathering followed, akin to peeling the layers from an onion (“exfoliation”). The end result is a rounded mountain top - an exfoliation dome.
Moro Rock is the type locality of the Cretaceous-aged Giant Forest Granodiorite, one of numerous specific igneous intrusions in the Sierra Nevada Batholith. Granodiorite is dominated by quartz and sodic plagioclase feldspar and some potassium feldspar. The Giant Forest Pluton is also rich in hornblende amphibole (= black crystals) and relatively rich in small, ~honey-colored crystals of titanite (a.k.a. sphene - CaTiSiO5).
Geologic unit & age: Giant Forest Granodiorite, Sequoia Intrusive Suite, late Albian Stage to early Cenomanian Stage, mid-Cretaceous, 97-102 Ma
This is lava from Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).
Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.
The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).
The lava boulder shown here is in a volcanic debris flow deposit from 19 and 22 May 1915, when Mt. Lassen last had a significant eruption. The deposit consists of fine sediments, cobbles, and boulders, some of which are quite large. Clasts in the flow deposit include pinkish-reddish porphyritic dacite and gray porphyritic dacite, both of which formed at 27 ka during the Late Pleistocene, early in Mt. Lassen's history. Another clast type in the deposit is black porphyritic dacite, shown here, that formed on 14 May 1915. The whitish-colored phenocrysts (click on the photo to zoom in and look around) are plagioclase feldspar.
The darker-colored, xenolith-like objects are "quenched blobs". From park signage: "These patches are called quenched blobs, formed during the rock's molten stage. As molten rock, basalt magma mixed with dacite magma. Dacite magma's temperature is much cooler than basalt's. When the hotter basalt injected into the cooler dacite magma, it was like hot wax hitting cold water. The blobs were quenched - cooled suddenly. When the lava oozed from the volcano's vent, the blobs solidified and remained encased in the dacite rock. The mixing of the two magmas likely triggered the May 19 Lassen Peak eruption. When a superheated injection of basalt magma enters a dacite magma, a volatile jolt occurs - sometimes enough to cause a volcano to erupt."
Quenched blobs in May 1915 black dacite may be composed of andesite.
Locality: boulder in Devastated Area, Lassen Volcano National Park, northeastern California, USA
This is a view of the eroded remains of the Late Eocene-aged Guffey Volcanic Center, which consisted of coalesced stratovolcanoes. The volcanic rocks are mostly alkaline, including the scarce lava type shoshonite. The rocks date to about 36 million years ago.
The prominent peak at right is McIntyre Mountain. The hills and mountains in this immediate area have lava flows and lahars (volcanic mudflows) that were originally on the flanks of the Guffey Volcanic Center's stratovolcano complex.
Locality: Thirtynine Mile Volcanic Field overlook at Cripple Creek Granite outcrop, northern side of Guffey Road (= Rt. 102), about 2.7 road-miles west of the Guffey Road-Rt. 11 intersection, southeastern Park County, central Colorado, USA (looking from ~38º 46’ 09.64” North latitude, ~105º 20’ 12.31” West longitude)
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Most info. from:
Meyer et al. (2004) - Field guide to the paleontology and volcanic setting of the Florissant fossil beds, Colorado. Geological Society of America Field Guide 5: 151-166.
Granodiorite in the Cretaceous of California, USA.
Moro Rock is a large exfoliation dome in the Sierra Nevada Mountains of eastern California, USA. It is accessible by road and hiking trail in the western part of Sequoia National Park, a little east of Generals Highway (Rt. 198).
Exfoliation domes are common in the Sierra Nevada Mountains. They form by large-scale spheroidal weathering of granites and granitoids of the Sierra Nevada Batholith. The batholith represents a Late Jurassic to Late Cretaceous-aged mass of cooled magma chambers originally beneath a chain of subduction zone stratovolcanoes.
Pressure release from erosional unroofing of the batholith resulted in the rocks having curved sheeting joints. Spheroidal weathering followed, akin to peeling the layers from an onion (“exfoliation”). The end result is a rounded mountain top - an exfoliation dome.
Moro Rock is the type locality of the Cretaceous-aged Giant Forest Granodiorite, one of numerous specific igneous intrusions in the Sierra Nevada Batholith. Granodiorite is dominated by quartz and sodic plagioclase feldspar and some potassium feldspar. The Giant Forest Pluton is also rich in hornblende amphibole (= black crystals) and relatively rich in small, ~honey-colored crystals of titanite (a.k.a. sphene - CaTiSiO5).
Geologic unit & age: Giant Forest Granodiorite, Sequoia Intrusive Suite, late Albian Stage to early Cenomanian Stage, mid-Cretaceous, 97-102 Ma
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.
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).
In 2008, explorer George Kourounis took a small rubber boat out onto the acid lake to measure its acidity. The pH of the water in the crater was measured to be 0.5 due to sulfuric acid.
Arequipa - Mirador de vólcanes
Sabancaya is an active 5,976-metre (19,606 ft) stratovolcano in the Andes of southern Peru. It is the most active volcano in Peru and is part of a 20-kilometre (12 mi) north-south chain of three major stratovolcanoes
Puedes conocer más sobre Perú entrando a mi álbum Peruvian Marvels
Central Java, Indonesia.
[en-route JOG-KUL. Almost dusk. View of Mount Sindoro- Mount Sumbing volcanic complex. Both are active stratovolcanoes.]
The picture was taken from the plane window seat in Central Java ca. 9K m (ca. 30K ft) asl en-route JOG-KUL flight path. The twin Mount Sumbing and Mount Sindoro (a distance further) are two adjacent mountain, as well as having the shape and height are nearly equal. Mount Sumbing height of about 3340 m asl, slightly higher than the Sindoro (3155 m asl). Located in the east side of the city of Winosobo.
Ref.
Google Earth
en.wikipedia.org/wiki/Mount_Sumbing
fotosintesa.com/index.php/landscapes/210-mount-sindoro-an...
Xenolith in grandiorite in the Cretaceous of California, USA.
Moro Rock is a large exfoliation dome in the Sierra Nevada Mountains of eastern California, USA. It is accessible by road and hiking trail in the western part of Sequoia National Park, a little east of Generals Highway (Rt. 198).
Exfoliation domes are common in the Sierra Nevada Mountains. They form by large-scale spheroidal weathering of granites and granitoids of the Sierra Nevada Batholith. The batholith represents a Late Jurassic to Late Cretaceous-aged mass of cooled magma chambers originally beneath a chain of subduction zone stratovolcanoes.
Pressure release from erosional unroofing of the batholith resulted in the rocks having curved sheeting joints. Spheroidal weathering followed, akin to peeling the layers from an onion (“exfoliation”). The end result is a rounded mountain top - an exfoliation dome.
Moro Rock is the type locality of the Cretaceous-aged Giant Forest Granodiorite, one of numerous specific igneous intrusions in the Sierra Nevada Batholith. Granodiorite is dominated by quartz and sodic plagioclase feldspar and some potassium feldspar. The Giant Forest Pluton is also rich in hornblende amphibole (= black crystals) and relatively rich in small, ~honey-colored crystals of titanite (a.k.a. sphene - CaTiSiO5).
The dark-colored mass in the above photo is a xenolith ("xeno" = foreign; "lith" = rock). Xenoliths are pieces of rock that have fallen from the walls or roof of a cooling magma chamber. This particular xenolith is rich in mafic minerals, resulting in a dark color. Mafic xenoliths, or "inclusions", are fairly common in the Giant Forest Granodiorite at Moro Rock.
Geologic unit & age: Giant Forest Granodiorite, Sequoia Intrusive Suite, late Albian Stage to early Cenomanian Stage, mid-Cretaceous, 97-102 Ma
STS056-098-078 Lake Taupo Area, New Zealand April 1993
Lake Taupo, the largest lake in New Zealand, is captured in this low-oblique, northwest-looking photograph. The lake, 25 miles (40 kilometers) long and covering 234 square miles (606 square kilometers), is similar to Yellowstone Lake in northwestern Wyoming in that it sits in the middle of a hot springs region, which extends from the lake northward to near Lake Rotorua. With an abundance of rainbow trout, numerous geysers, hot springs, and other geothermal phenomena, the region is a famous resort area in New Zealand. Visible south of Lake Taupo are two of New Zealand’s four active volcanoes, Mount Ngauruhoe and the larger Mount Ruapehu, two stratovolcanoes that have a history of recent eruptions. Mount Ngauruhoe, with a near-perfect cone, has erupted more than 50 times since 1839, the last eruption occurring in July 1977. Snowcapped Mount Ruapehu has a large hot-crater lake, where more than 30 eruptions have occurred since 1861. Mud flows from the erupting volcano and crater lake occasionally flood adjacent valleys causing property damage and loss of life, as happened in 1953. In June 1996, Mount Ruapehu erupted, and many communities around the volcano were evacuated; minor eruptions continue. The volcanoes, like many of the volcanic mountains in the Cascade Range of the U.S. Pacific Northwest, are tourist attractions with many ski resorts. East of Lake Taupo, the world’s largest expanse of timber plantations appears as agricultural field patterns in the photograph. Several species of Northern Hemisphere conifers have been introduced, but Monterey pine trees cover the largest acreage.
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 large, gray feature in the center background is Chaos Crags, a cluster of six volcanic domes that formed in the late Holocene on the northern side of Lassen Volcano. All six domes are composed of porphyritic rhyodacite, a lava type between dacite and rhyolite. Published analyses indicate that the Chaos Crags rhyodacite domes are 68% to 70% silica. Radiometric dating shows that the domes were emplaced sequentially between about 825 A.D. and 1575 A.D.
The rubble in the bottom foreground of the photo is "Chaos Jumbles", a large landslide deposit (usually mis-referred to as an "avalanche") consisting of porphyritic rhyodacite lava blocks. 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. Dome C is the central front face of Chaos Crags, as seen in this picture. Dome C rocks and Chaos Jumbles Landslides rocks are composed of 68% silica porphyritic rhyodacite with ~10 volume% mafic inclusions. Phenocrysts in the rocks are principally plagioclase feldspar, hornblende amphibole, biotite mica, and quartz.
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
The Ijen volcano complex is a group of stratovolcanoes inside a larger caldera Ijen, which is about 20 kilometers wide. The Gunung Merapi stratovolcano is the highest point of that complex. West of Gunung Merapi is the Ijen volcano, which has a one-kilometer-wide turquoise-colored acid crater lake. The lake is the site of a labor-intensive sulfur mining operation, in which sulfur-laden baskets are carried by hand from the crater floor (http://en.wikipedia.org/wiki/Ijen).
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).
Moro Rock is a large exfoliation dome in the Sierra Nevada Mountains of eastern California, USA. It is accessible by road and hiking trail in the western part of Sequoia National Park, a little east of Generals Highway (Rt. 198).
Exfoliation domes are common in the Sierra Nevada Mountains. They form by large-scale spheroidal weathering of granites and granitoids of the Sierra Nevada Batholith. The batholith represents a Late Jurassic to Late Cretaceous-aged mass of cooled magma chambers originally beneath a chain of subduction zone stratovolcanoes.
Pressure release from erosional unroofing of the batholith resulted in the rocks having curved sheeting joints. Spheroidal weathering followed, akin to peeling the layers from an onion (“exfoliation”). The end result is a rounded mountain top - an exfoliation dome.
Moro Rock is the type locality of the Cretaceous-aged Giant Forest Granodiorite, one of numerous specific igneous intrusions in the Sierra Nevada Batholith. Granodiorite is dominated by quartz and sodic plagioclase feldspar and some potassium feldspar. The Giant Forest Pluton is also rich in hornblende amphibole (= black crystals) and relatively rich in small, ~honey-colored crystals of titanite (a.k.a. sphene - CaTiSiO5).
Geologic unit & age: Giant Forest Granodiorite, Sequoia Intrusive Suite, late Albian Stage to early Cenomanian Stage, mid-Cretaceous, 97-102 Ma
Andesite from the Pleistocene of Oregon, USA. (field of view ~9.0 cm across)
Andesite is an aphanitic, intermediate, extrusive igneous rock. It is a common type of lava at subduction zone volcanoes. The andesite seen here is a low-silica andesite from the Larch Mountain Shield Volcano in Oregon's Boring Volcanic Field.
The Boring Volcanic Field is named after the Boring Hills and the town of Boring, southeast of the city of Portland, Oregon. The Boring Hills are volcanic centers or piles of fluvial gravels. The volcanic field is pretty well defined based on surface outcrops, but there are also some buried vents and subsurface intrusions. The Boring Volcanic Field has scattered, isolated vents and vent clusters - most are monogenetic, but there are some polygenetic vents such as Mt. Scott and Highland Butte. These vents had longer-lived eruptions that typical Boring Volcanic Field eruptions. All edifices tapped the same magma source. The field dates from the Late Pliocene onward. The youngest vent in the field is 57 ka (= a cinder cone that was washed away by Missoula floods, leaving a volcanic plug - Beacon Rock). Accurately dating Boring Volcanic Field samples has been problematic due to fine-grained groundmass and excess argon.
There is a diversity of lithologies in the field - a tremendous compositional variety. Some Boring Volcanic Field basalts are arc-like and some are not arc-like, based on different barium/niobium ratios (Ba/Nb). Mid-ocean ridge-like basalts are present in the field - low-potassium tholeiites. They look like mid-ocean ridge basalts at slow-spreading ridges. There are some calc-alkaline lavas in the Boring Volcanic Field as well - some are very enriched in potassium (arc-related lavas - high-K calc-alkaline basalts).
The Boring Volcanic Field occurs west of the axis of the Cascade Range (= north-south trending chain of active and potentially active subduction zone stratovolcanoes in northern California, Oregon, Washington State, and British Columbia). Something anomalous brought magma here, but the volcanic compositions are generally the same as in the Cascade Range proper, so the field is still subduction-related. There might be a discontinuity or a tear in the subducting slab that may account for the field's location. Small vent/edifice sizes in the field imply that magma rose upward quickly. Magma may have moved upward along extensional fractures, formed as a result of Juan de Fuca Plate subduction not being orthogonal with the North American Plate. This has produced transpressional and transtensional features. Subduction has been occurring in this area for ~40 million years.
Age: lower Lower Pleistocene, 1.43 Ma
Locality: roadcut along the southern side of Larch Mountain Road, western flanks of the Larch Mountain Shield Volcano, Boring Volcanic Field, Multnomah County, northwestern Oregon, USA (~45° 32' 15.43" North latitude, ~112° 06' 50.6" West longitude)
(still image from the Isanotski-Lazaref River web camera on Unimak Island, Alaska)
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Shishaldin Volcano is a subduction zone stratovolcano on Unimak Island in the Aleutian Islands of Alaska. Minor lava eruptions in the summit crater started on 12 July 2023. Twelve episodes of explosive ash eruptions have occurred since then, on 14 July, 15 July, 18 July, 22-23 July, 25-26 July, 4 August, 14-15 August, 25 August, 5 September, 15 September, 25 September, and 3 October 2023. Seen here is Shishaldin with a prominent white steam plume. It is likely the result of snow, ice, and meltwater vaporizing upon contact with hot volcanic rocks and fresh lava in the summit area.
The Aleutian Arc is a subduction zone formed as the Pacific Plate dives underneath the North American Plate (this area is sometimes called the Bering Plate). The diving plate in subduction zones releases water at depth, which causes partial melting of overlying mantle rocks. The low-density melt rises and eventually reaches the surface, forming volcanoes. All subduction zones have volcanoes and frequent seismicity. Volcanoes in such settings tend to have explosive ash eruptions. Rocks and tephra deposits at subduction zone volcanoes are usually intermediate in composition - typically andesitic to dacitic.
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Info. at:
en.wikipedia.org/wiki/Mount_Shishaldin
and
ISS030-E-030265 (31 Dec. 2011) --- The Payun Matru Volcanic Field in Argentina is featured in this image photographed by an Expedition 30 crew member on the International Space Station. The Payun Matru (3,680 meters above sea level) and Payun Liso (3,715 meters above sea level) stratovolcanoes are the highest points of the Payun Matru Volcanic Field located in west-central Argentina, approximately 140 kilometers to the east of the Andes mountain chain. This photograph illustrates some of the striking geological features of the field visible from space. The summit of Payun Matru is dominated by a roughly 15 kilometer-in-diameter caldera (center), formed by an explosive eruption sometime after approximately 168,000 years ago. Several dark lava flows, erupted from smaller vents and fissures, are visible in the northwestern part of the volcanic field. One distinct flow, erupted from Volcan Santa Maria located to the northwest of Payun Matru, is approximately 15 kilometers long. A number of small cinder cones, appearing as brown dots due to the short lens used, are built on older lava flows (grey) to the northeast of Payun Matru. While there is no recorded historical observation of the most recent volcanic activity in the field, oral histories suggest that activity was witnessed by indigenous peoples. Most Andean volcanoes—and earthquakes—follow the trend of the greater Andes chain of mountains, and are aligned roughly N-S above the tectonic boundary between the subducting (descending) Nazca Plate and the overriding South American Plate as is predicted from plate tectonic theory. Other major volcanic centers located some distance away from the major trend typically result from more complex geological processes associated with the subduction zone, and can provide additional insight into the subduction process.
This is lava from Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).
Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.
The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).
The lava boulder shown here is in a volcanic debris flow deposit from 19 and 22 May 1915, when Mt. Lassen last had a significant eruption. The deposit consists of fine sediments, cobbles, and boulders, some of which are quite large. Clasts in the flow deposit include pinkish-reddish porphyritic dacite and gray porphyritic dacite, both of which formed at 27 ka during the Late Pleistocene, early in Mt. Lassen's history. Another clast type in the deposit is black porphyritic dacite, shown here, that formed on 14 May 1915. The whitish-colored phenocrysts (click on the photo to zoom in and look around) are plagioclase feldspar.
The darker-colored, xenolith-like objects are "quenched blobs". From park signage: "These patches are called quenched blobs, formed during the rock's molten stage. As molten rock, basalt magma mixed with dacite magma. Dacite magma's temperature is much cooler than basalt's. When the hotter basalt injected into the cooler dacite magma, it was like hot wax hitting cold water. The blobs were quenched - cooled suddenly. When the lava oozed from the volcano's vent, the blobs solidified and remained encased in the dacite rock. The mixing of the two magmas likely triggered the May 19 Lassen Peak eruption. When a superheated injection of basalt magma enters a dacite magma, a volatile jolt occurs - sometimes enough to cause a volcano to erupt."
Quenched blobs in May 1915 black dacite may be composed of andesite.
Locality: boulder in Devastated Area, Lassen Volcano National Park, northeastern California, USA
This is 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
(video taken by Robbie Armijo & provided by the Alaska Volcano Observatory)
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Shishaldin Volcano is a subduction zone stratovolcano on Unimak Island in the Aleutian Islands of Alaska. Minor lava eruptions in the summit crater started on 12 July 2023. Twelve episodes of explosive ash eruptions have occurred since then, on 14 July, 15 July, 18 July, 22-23 July, 25-26 July, 4 August, 14-15 August, 25 August, 5 September, 15 September, 24 to 25 September, and 3 October 2023. This video shows fresh, dark-colored ash and lahar deposits at Shishaldin on 14 July 2023, which contrasts with the bright white surface snow a couple days earlier.
The Aleutian Arc is a subduction zone formed as the Pacific Plate dives underneath the North American Plate (this area is sometimes called the Bering Plate). The diving plate in subduction zones releases water at depth, which causes partial melting of overlying mantle rocks. The low-density melt rises and eventually reaches the surface, forming volcanoes. All subduction zones have volcanoes and frequent seismicity. Volcanoes in such settings tend to have explosive ash eruptions. Rocks and tephra deposits at subduction zone volcanoes are usually intermediate in composition - typically andesitic to dacitic.
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Info. at:
en.wikipedia.org/wiki/Mount_Shishaldin
and
This is a view of the eroded remains of the Late Eocene-aged Guffey Volcanic Center, which consisted of coalesced stratovolcanoes. The volcanic rocks are mostly alkaline, including the scarce lava type shoshonite. The rocks date to about 36 million years ago.
The prominent peak at far-left is McIntyre Mountain. The peak at ~center is Castle Mountain. The somewhat flat-topped mountain at the far-right is Thirtynine Mile Mountain. The double-humped mountain just in front of that is Saddle Mountain. These mountains have lava flows and lahars (volcanic mudflows) that were originally on the flanks of the Guffey Volcanic Center's stratovolcano complex.
Locality: Thirtynine Mile Volcanic Field overlook at Cripple Creek Granite outcrop, northern side of Guffey Road (= Rt. 102), about 2.7 road-miles west of the Guffey Road-Rt. 11 intersection, southeastern Park County, central Colorado, USA (looking from ~38º 46’ 09.64” North latitude, ~105º 20’ 12.31” West longitude)
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Most info. from:
Meyer et al. (2004) - Field guide to the paleontology and volcanic setting of the Florissant fossil beds, Colorado. Geological Society of America Field Guide 5: 151-166.
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
(photo stitch by Mary Ellen St. John)
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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
Mt Teide Volcano, from Hotel Parador.
The large triangular island of Tenerife is composed of a complex of overlapping Miocene-to-Quaternary stratovolcanoes that have remained active into historical time.
Background:
The NE-trending Cordillera Dorsal volcanic massif joins the Las Cañadas volcano on the SW side of Tenerife with older volcanoes, creating the largest volcanic complex of the Canary Islands. Controversy surrounds the formation of the dramatic 10 x 17 km Las Cañadas caldera, which is partially filled by 3715-m-high Teide stratovolcano, the highest peak in the Atlantic Ocean. The origin of the caldera has been considered to be due entirely or in part to either a massive landslide (in a manner similar to the earlier formation of the massive La Orotava and Guimar valleys in the Cordillera Dorsal) or due to major explosive eruptions. The most recent stage of activity beginning in the late Pleistocene included the construction of the Pico Viejo and Teide edifices. Tenerife was perhaps observed in eruption by Christopher Columbus, and several flank vents on the Canary Island's most active volcano have been active during historical time.
Source: Smithsonian GVP
Dacitic volcanic dust from the Holocene of Washington State, USA. (field of view ~~5 centimeters across)
The 1980 Mt. St. Helens eruption was the largest in recent American history. The volcano was intermittently active until 1986. Minor activity occurred from 1989 to 1991 and from 2004 to 2006.
Mt. St. Helens is the most active volcano in the Cascade Range, a series of subduction zone stratovolcanoes in a ~north-south line from northern California to Oregon to Washington State to southwestern British Columbia. St. Helens is a 40,000 to 50,000 year old, andesitic-dacitic-basaltic volcano that typically has explosive ash eruptions (as do all subduction zone stratovolcanoes).
The initial 1980 eruption was a northward-directed lateral blast that followed an enormous landslide of the northern face of the volcano. The landslide was triggered by a moderate earthquake at 8:32 AM, Sunday, 18 May 1980. Snow and ice on the mountain melted during the eruption, mixed with ash and other debris, and rushed down nearby river valleys as lahars (volcanic mud flows).
The ash, lapilli, and pumice erupted from Mt. St. Helens in May 1980 was dacite, an intermediate extrusive igneous rock. Most of the air-fall dacite ash fell in Washington State, Oregon, and Idaho, but a minor amount accumulated as far east as Minnesota and Oklahoma. Light dustings of ash were also observed in Ohio. The sample seen here is distal air-fall volcanic dust from Deary, Idaho - it was collected on 20 May 1980.
Location of volcano: Mt. St. Helens, northwestern Skamania County, Cascade Range, southwestern Washington State, USA (46˚ 12’ 04” North latitude, 122˚ 11” 18” West longitude)
Sample collection site: town of Deary, east-central Latah County, northern Idaho, USA
STS052-073-014 Tousside, Tibesti Mountains, Chad October 1992
The Tibesti Mountains in northwestern Chad consist of rugged volcanic peaks, many impressive craters, and hot springs. Near the center of the photograph is Tousside Peak, which rises more than 10 710 feet (3265 meters) above sea level, the westernmost volcano of this high mountain range. The peak is almost centered within the black shape that has tentacle-shaped lava flows extending down the western flank. The volcano’s base measures approximately 55 miles (90 kilometers) in diameter. The light brownish area surrounding the peak shows a distinctive radial drainage pattern that is quite common for stratovolcanoes as the terrain falls away from the main peak. The depression southeast of the volcano measures approximately 5 miles (8 kilometers) in diameter and 3300 feet (1000 meters) in depth. The white base is caused by an accumulation of carbonate salts, creating this soda lake of Tibesti. With the exception of small vents that emit gasses and a few hot springs that continue to deposit minerals at the surface of the crater floor, little volcanic activity presently occurs in this region.