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

Andesite comes out of volcanoes. Sometimes it cools in columns, like basalt does, but in less orderly joints. John McPhee calls andesite "the Butterscotch topping" that covers the bathylith of plutonic granite that one associates with the Sierras - Half Dome, for example, is a jumbo scoop of that granite, exposed by glaciers that scraped the andesite off.

The Sierras of today are very young, only a few million years old; the youngest mountain range in North America. But long before the Sierras rose, great stratovolcanoes on the Nevadaplano, the old edge of North America that was about where Nevada borders California now, poured out ash and lava. This is a picture of what's left of that ancient volcanism.

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.

Porphyritic dacite from the Cenozoic of California, USA. (public display, Geology Department, Wittenberg University, Springfield, Ohio, USA)

Porphyritic rocks are crystalline-textured igneous rocks having a mix of large crystals (phenocrysts; = the light-colored, angular masses seen here) and small crystals (groundmass; = the medium to dark gray-colored material). This particular rock is a porphyritic dacite. Dacites are extrusive igneous rocks - they are a type of volcanic lava. Dacite is the extrusive equivalent of quartz diorite & tonalite, all three of which have a mix of quartz and plagioclase feldspar, with little to no potassium feldspar. In general, dacite is a type of lava between andesite and rhyolite. Dacite is a common lava type erupted from subduction zone stratovolcanoes. Examples of such volcanoes include Mt. St. Helens, Mt. Rainier (both are in Washington State), and Mt. Pinatubo (Philippines).

Locality: unrecorded/undisclosed site at or near Clear Creek [is that a town or a stream?], Shasta County, northern California, USA

Dacite pumice and dacite ash from the 15 June 1991 eruption of Mt. Pinatubo. Collected on the grounds of the U.S. Subic Bay Naval Base.

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Mt. Pinatubo’s 1991 eruption was the largest on Earth since 1912. Pinatubo's big eruption is also famous for having been successfully predicted by American volcanologists. The prediction & subsequent evacuation saved thousands of lives.

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

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

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

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

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

Xenolith in 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).

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

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...

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.

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

ISS030-E-122047 (6 March 2012) --- Pagan Island, Northern Marianas is featured in this image photographed by an Expedition 30 crew member on the International Space Station. A steam plume flows south from the peak of Pagan Island’s northernmost volcano in this photograph. Pagan is part of the Commonwealth of the Northern Marianas, an island chain of volcanoes that form the margin between the Pacific Ocean (to the east) and the Philippine Sea (to the west). Pagan is made up of two stratovolcanoes separated by an isthmus, and is one of the more volcanically active islands. The last eruption was in 2010, but the island was completely evacuated in 1981 when a large eruption forced the small Micronesian community to flee. According to NASA scientists, the islands themselves mark the tectonic boundary where the old, cold Pacific plate is subducted beneath the younger, less dense Philippine Sea crust at the Marianas Trench. The subduction results in substantial volcanic activity on the upper plate, forming the island arc of the Marianas. Considered to be one of the type examples for an oceanic subduction zone, the Marianas Trench includes the deepest spot in Earth’s oceans (more than 10,000 meters). The foreshortened appearance of the island is due to the viewing angle and distance from the space station, which was located over the Pacific Ocean approximately 480 kilometers to the southeast of Pagan Island when the image was taken.

Dacite pumice (air-fall tephra) from the Holocene of the Philippines. (3.5 centimeters across at its widest)

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

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

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

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

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

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

ISS023-E-022411 (31 March 2010) --- Volcanoes near Usulutan, El Salvador are featured in this image photographed by an Expedition 23 crew member on the International Space Station. The Pacific coastline of much of Central America is marked by a line of active and quiescent volcanoes known to geologists as the Central American Volcanic Arc, or CAVA. The volcanoes result from the upward movement of magma generated along the subduction zone between the Cocos and Caribbean tectonic plates; frequent earthquakes also occur along the plate boundary. This photograph includes four stratovolcanoes -- a type of volcano associated with active subduction zones -- located near the midpoint of the CAVA in El Salvador. Scientists believe while all of the volcanoes shown here have been active during the Holocene Epoch (approximately 10,000 years ago to present), only the 2,130-meter-high San Miguel (also known as Chaparrastique) has been active during historical times. The most recent activity of San Miguel was a minor gas and ash emission in 2002. The steep conical profile and well-developed summit crater are evident at left, along with dark lava flows produced by San Miguel. Immediately to the northwest the truncated summit of Chinameca volcano (also known as El Pacayal) is marked by a two-kilometer-wide caldera, formed when the volcano's magma chamber was emptied by a powerful eruption followed by collapse of the chamber's roof. Like its neighbor San Miguel, Chinameca's slopes host coffee plantations. Moving to the southwest the eroded cone of El Tigre volcano is visible. According to scientists, El Tigre volcano formed during the Pleistocene Epoch (1.8 million to approximately 10,000 years ago) and is likely the oldest of the stratovolcanoes depicted in the image. Usulutan volcano is located directed to the southwest of El Tigre. While the flanks of Usulutan have been dissected by stream flow it still retains a summit crater that is breached on the eastern side. Several urban areas - recognizable as light gray to white regions contrasting with green vegetation and tan fallow agricultural fields - are located in the vicinity of these volcanoes, including Usulutan (upper right) and Santiago de Mara (lower right).

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

ISS033-E-018010 (3 Nov. 2012) --- Volcanoes in central Kamchatka are featured in this image photographed by an Expedition 33 crew member on the International Space Station. The snow-covered peaks of several volcanoes of the central Kamchatka Peninsula are visible standing above a fairly uniform cloud deck that obscures the surrounding lowlands. In addition to the rippled cloud patterns caused by interactions of air currents and the volcanoes, a steam and ash plume is visible at center extending north-northeast from the relatively low summit (2,882 meters above sea level) of Bezymianny volcano. Volcanic activity in this part of Russia is relatively frequent, and well monitored by Russia's Kamchatka Volcanic Eruption Response Team (KVERT). The KVERT website provides updated information about the activity levels on the peninsula, including aviation alerts and webcams. Directly to the north and northeast of Bezymianny, the much larger and taller stratovolcanoes Kamen (4,585 meters above sea level) and Kliuchevskoi (4,835 meters above sea level) are visible. Kliuchevskoi, Kamchatka's most active volcano, last erupted in 2011 whereas neighboring Kamen has not erupted during the recorded history of the region. An explosive eruption from the summit of the large volcanic massif of Ushkovsky (3,943 meters above sea level; left) northwest of Bezymianny occurred in 1890; this is the most recent activity at this volcano. To the south of Bezymianny, the peaks of Zimina (3,081 meters above sea level) and Udina (2,923 meters above sea level) volcanoes are just visible above the cloud deck; no historical eruptions are known from either volcanic center. While the large Tobalchik volcano to the southwest (bottom center) is largely formed from a basaltic shield volcano, its highest peak (3,682 meters above sea level) is formed from an older stratovolcano. Tobalchik last erupted in 1976. While this image may look like it was taken from the normal altitude of a passenger jet, the space station was located approximately 417 kilometers above the southeastern Sea of Okhotsk; projected downwards to Earth's surface, the space station was located over 700 kilometers to the southwest of the volcanoes in the image. The combination of low viewing angle from the orbital outpost, shadows, and height and distance from the volcanoes contributes to the appearance of topographic relief visible in the image.

Saying goodbye to Cascadia for a couple of weeks

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.

Scoria cones, also known as cinder cones, are the most common type of volcano. They are also the smallest type, with heights generally less than 300 meters. They can occur as discrete volcanoes on basaltic lava fields, or as parasitic cones generated by flank eruptions on shield volcanoes and stratovolcanoes. Scoria cones are composed almost wholly of ejected basaltic tephra. The tephra is most commonly of lapilli size, although bomb-size fragments and lava spatter may also be present. The tephra fragments typically contain abundant gas bubbles (vesicles), giving the lapilli and bombs a cindery (or scoriaceous) appearance. The tephra accumulates as scoria-fall deposits which build up around the vent to form the volcanic edifice. The edifice has very steep slopes, up to 35 degrees. Unlike the other two main volcano types, scoria cones have straight sides and very large summit craters, with respect to their relatively small edifices. They are often symmetric, although many are asymmetric due to (1) the build up of tephra on the downwind flank of the edifice, (2) elongation of the volcano above an eruptive fissure, or (3) partial rafting of an outer wall of the volcano due to basalt lava oozing outward from beneath the volcano edifice. Where scoria cones have been breached, they typically reveal red-oxidized interiors.

Scoria cones are generated by strombolian or hawaiian eruptions. Many scoria cones are monogenetic in that they only erupt once.

This photo, taken in april 2001, shws a parasitic cone (called Château Fort) on the Flank of Piton de la Fournaise

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.

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.

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

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

ISS024-E-012425 (22 Aug. 2010) --- This photograph, featuring a landscape in the central Andes mountains near the Chile/Argentina border dominated by numerous volcanoes and associated landforms, was photographed by an Expedition 24 crew member on the International Space Station. Layers of older sedimentary rocks are visible to the southeast (upper right). Many of the volcanic cones show grooves eroded by water to form gullies. Such erosion has occurred since the host volcano was built up, indicating that most volcanoes in this view have been inactive for centuries or millennia. A few volcanoes exhibit much less erosion, and even show tongues of recent, dark lava flows (top left). According to scientists, two of these volcanoes, Cerro el Condor and Peinado have likely erupted within approximately the last 12,000 years (the Holocene Epoch). Also visible in the image is the world's highest active volcano, Nevado Ojos del Salado, with a summit at 6,887 meters above sea level. The most recent confirmed eruption of this volcano has been dated to 700 (approximately 300 years), but minor eruptive activity may have occurred as recently as 1993. Stratovolcanoes such as Cerro el Condor, Peinado, and Nevado Ojos del Salado are formed partly by buildup of lava flows and partly by buildup of explosively vented material dropping back down onto the surface. One type of material associated with explosive eruptions is welded tuff, which is formed by molten and fragmented rock that accumulates on the ground and later solidifies. A large tuff sheet is visible at top left. Formed very rapidly, these sheets have been termed "instant landscapes." So active has the Andean volcanic system been that the origin of many of the tuffs in the Andes cannot be pinpointed since source vents have been overprinted by subsequent volcanic events. The volcanic landscape also shows that the erosive work of rivers—and glaciers repeatedly in the recent past—is slower than the opposite processes of the upward building of the volcanoes. The bright blue, nearly 7-kilometer-long lake near the center of the image is known as Laguna Verde. This and other less obvious lakes indicate that water (snowmelt or direct precipitation) is unable to reach the sea, but is rather impounded in the depressions between the volcanic edifices.

Pumice from the Holocene of California, USA. (pale-colored pumice at upper right is 2.7 centimeters long)

Medicine Lake Volcano is a shield volcano in far-northern California, USA. It is associated with the Cascade Range of stratovolcanoes. The Cascade Range stretches from northern California to Oregon to Washington State, and into southwestern British Columbia. It formed by subduction of the Juan de Fuca Plate underneath the North American Plate. Medicine Lake Volcano has erupted a variety of materials that include basalt, andesite, rhyolite, dacite, obsidian, and pumice.

The rocks shown here are airfall pumice pieces from a ~1065 A.D. eruption at the Glass Mountain eruptive center, on the eastern side of Medicine Lake Volcano.

Dacitic lapilli metatuff (dacitic meta-lapillistone) from the Precambrian of Minnesota, USA (cut surface). (public display, Soudan Underground Mine State Park visitor center, Soudan, Minnesota, USA)

This is a metamorphosed volcanic tuff. Volcanic tuff is a clastic-textured, extrusive igneous rock that forms by explosive volcanic eruptions. The fragments generated by an eruption are deposited by ash fall or ash flow (pyroclastic flow), then buried and lithified. Lapilli are fragments between 2 and 64 mm in size (= granule- and pebble-sized in sediment classification). Fragments smaller than 2 mm are referred to as volcanic ash and volcanic dust (= sand-sized & silt-sized & clay-sized grains in sediment classification). The rock shown above has abundant lapilli-sized fragments, and is thus a lapilli tuff. The composition of the lapilli is dacitic. Dacite is an extrusive igneous rock that is common at subduction zone stratovolcanoes. It is a high-silica intermediate rock or a low-silica felsic rock, depending on which definition of the felsic-intermediate boundary one uses. This rock has been metamorphosed, as has much of Minnesota's Precambrian rock record, so a full lithologic name is dacitic lapilli metatuff. The nature and size of the lapilli are still readily apparent in the rock, despite metamorphic alteration.

The lapilli metatuff succession from which this rock derives is closely associated with the famous Soudan Iron-Formation (see: www.flickr.com/photos/jsjgeology/albums/72157652553006284). A description of the lapilli tuff succession is given by Vallowe et al. (2010): "Dirty white to light grey and in areas, sulfide stained, poorly bedded to massive. Fragments locallly consist of light to dark chert and at times small egg shaped concretions. North and east of the Soudan Mine in Section 27, the unit consists of 1 x 3 cm domains of cherty tuff (± sericite) in, and separated by, a coarse anastamosing sericite-chlorite foliation with pyrite clots common. May have local massive beds nor oriented parallel to foliation. Immediately north of the historic workings of the Soudan Mine, the unit is virtually a sericite-quartz schist with foliation wrapping around 2 to 5 m angular to subrounded cherty tuff clasts."

Stratigraphy: "upper sequence" of Vallowe et al. (2010), above the Soudan Iron-Formation & below the Lake Vermilion Formation, Neoarchean, ~2.7 to 2.72 Ga

Locality: undisclosed locality near the Soudan Mine, Soudan Underground Mine State Park, Soudan, northeastern Minnesota, USA

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Site-specific geologic info. synthesized from:

Vallowe et al. (2010) - Surface and subsurface geologic maps of the Soudan Underground Mine State Park, St. Louis County, northeastern Minnesota. Precambrian Research Center Map Series Map-2010-01.

(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

(still image from the Brown Peak 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. Thirteen episodes of subsequent explosive ash eruptions took place 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, 3 October, and 2-3 November 2023. Seen here is Shishaldin with a small steam plume on 12 November 2023. The Alaska Volcano Observatory reported volcanic tremor, small earthquakes, minor steam emissions, and elevated summit area surface temperatures for that day and the previous night.

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. Shishaldin's erupted materials in 2023 have been mafic (basaltic).

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

Info. at:

en.wikipedia.org/wiki/Mount_Shishaldin

and

en.wikipedia.org/wiki/Aleutian_Arc

This slide, and the next several in this series were taken on the hazy summer day a shipmate and I drove up to the Vesuvius parking lot and then climbed the trail the rest of the way to the summit.

After a lot of noodling around on Google Earth Street View, I'm convinced that this photo documents our approach to Vesuvius from the south-southeast. We were probably on the main access road to the summit (Via Cifelli), or somewhere else nearby. Consequently, we're facing north-northwest.

Mount Vesuvius is one of a chorus-line of volcanoes, stretching from Tuscany to Sicily, that is sometimes called the Campanian Volcanic Arc. It marks a major plate boundary involving the subducting African Plate and the overriding Eurasian Plate.

This famous fire-mountain, which in AD 79 pyroclastically buried such Imperial Roman communities as Pompeii and Herculaneum, is a classic stratovolcano in that it's composed of alternating layers of lava and ash. Stratovolcanoes are characteristically steep-sided and especially dangerous due to their propensity for erupting explosively and violently.

And they're usually made of felsic or intermediate igneous rock types—rhyolite, andesite, and so forth. But in this respect Vesuvius is somewhat weird, in that its prevailing rock varieties are basaltic tephrite and intermediate phonolite, and intergradations of the two (tephritic phonolite and phonolitic tephrite, believe it or not.) This unusual geochemistry may be the result of there being a slab window—a gap due to breakage in the descending African Plate—that permits mantle-derived magma to rise to the surface.

Vesuvius is in fact a younger stratovolcano nestled within the shattered remnants of an older, known as Mount Somma. From this perspective, the relationship between the two is not apparent, but I'll next post some views of both the Somma caldera rim and Vesuvius' Gran Cono (Large Cone, which is also nicely visible here).

And botanically speaking: in the foreground, and marching up the lava-flow slope, is a forest of Stone Pines (Pinus pinea). The magnificent umbrella crown of the freestanding specimen at left is typical of the species. No other tree has done more to define the Italian landscape.

I also really like the Stone Pine's taxonomic name, which translates to something like "Piney Pine" or "Really Pinelike Pine," with the implication that it is the one member of its genus to which all other members must be compared. However, I'm also partial to the much loftier Eastern White Pine (P. strobus) of my own native land, which has been recorded to grow to over 200 ft (61 m) tall. Earlier today I was sitting across from one growing in a neighboring yard, and I contemplated its architectural majesty and sheer pineyness. But of course I diverge, in my lateral-minded way.

The other photos and descriptions of this series can be found in my Integrative Natural History of Mount Vesuvius & the Gulf of Naples album.

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.

(public domain image by Chris Barnes & 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, 25 September, and 3 October 2023. Seen here is Shishaldin with a dark-colored ash eruption cloud and whitish steam plume.

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.

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

Info. at:

en.wikipedia.org/wiki/Mount_Shishaldin

and

en.wikipedia.org/wiki/Aleutian_Arc

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.

Pumice from the Holocene of Washington State, USA. (~6.1 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

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.

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.

Andesite from the Pleistocene of Oregon, USA. (~11.9 centimeters across at its widest)

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 than 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)

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.

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.

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

Lake Toba (Indonesian: Danau Toba) is a large natural lake in North Sumatra, Indonesia, occupying the caldera of a supervolcano. The lake is located in the middle of the northern part of the island of Sumatra, with a surface elevation of about 900 metres, the lake stretches from 2.88°N 98.52°E to 2.35°N 99.1°E. The lake is about 100 kilometres long, 30 kilometres wide, and up to 505 metres deep. It is the largest lake in Indonesia and the largest volcanic lake in the world. Lake Toba Caldera is one of the twenty Geoparks in Indonesia, which is recognised in July 2020 as one of the UNESCO Global Geopark.

Lake Toba is the site of a supervolcanic eruption estimated at VEI 8 that occurred 69,000 to 77,000 years ago, representing a climate-changing event. Recent advances in dating methods suggest a more accurate identification of 74,000 years ago as the date. It is the largest-known explosive eruption on Earth in the last 25 million years. According to the Toba catastrophe theory, it had global consequences for human populations; it killed most humans living at that time and is believed to have created a population bottleneck in central east Africa and India, which affects the genetic make-up of the human worldwide population to the present. More recent studies have cast doubt on this theory and found no evidence of substantial changes in population.

It has been accepted that the eruption of Toba led to a volcanic winter with a worldwide decrease in temperature between 3 to 5 °C, and up to 15 °C in higher latitudes. Additional studies in Lake Malawi in East Africa show significant amounts of ash being deposited from the Toba eruptions, even at that great distance, but little indication of a significant climatic effect in East Africa.

GEOLOGY

The Toba caldera complex in North Sumatra comprises four overlapping volcanic craters that adjoin the Sumatran "volcanic front". At 100 by 30 kilometres it is the world's largest Quaternary caldera, and the fourth and youngest caldera. It intersects the three older calderas. An estimated 2,800 km3 of dense-rock equivalent pyroclastic material, known as the youngest Toba tuff, was released during one of the largest explosive volcanic eruptions in recent geological history. Following this eruption, a resurgent dome formed within the new caldera, joining two half-domes separated by a longitudinal graben.

At least four cones, four stratovolcanoes, and three craters are visible in the lake. The Tandukbenua cone on the northwestern edge of the caldera has only sparse vegetation, suggesting a young age of several hundred years. Also, the Pusubukit (Hill Center) volcano (1,971 m above sea level) on the south edge of the caldera is solfatarically active.

MAJOR ERUPTION

The Toba eruption (the Toba event) occurred at what is now Lake Toba about 73,700±300 years ago. It was the last in a series of at least four caldera-forming eruptions at this location, with the earlier known caldera having formed around 1.2 million years ago. This last eruption had an estimated VEI=8, making it the largest-known explosive volcanic eruption in the Quaternary.

Bill Rose and Craig Chesner of Michigan Technological University have estimated that the total amount of material released in the eruption was at least 2,800 km3 about 2,000 km3 of ignimbrite that flowed over the ground, and approximately 800 km3 that fell as ash mostly to the west. However, as more outcrops become available, Toba possibly erupted 3,200 km3 of ignimbrite and co-ignimbrite. The pyroclastic flows of the eruption destroyed an area of least 20,000 km2, with ash deposits as thick as 600 m by the main vent. The eruption was large enough to have deposited an ash layer approximately 15 cm thick over all of South Asia; at one site in central India, the Toba ash layer today is up to 6 m thick and parts of Malaysia were covered with 9 m of ash fall.

The subsequent collapse formed a caldera that filled with water, creating Lake Toba. The island in the center of the lake is formed by a resurgent dome.

The exact year of the eruption is unknown, but the pattern of ash deposits suggests that it occurred during the northern summer because only the summer monsoon could have deposited Toba ashfall in the South China Sea. The eruption lasted perhaps two weeks, and the ensuing volcanic winter resulted in a decrease in average global temperatures by 3.0 to 3.5 °C for several years. Ice cores from Greenland record a pulse of starkly reduced levels of organic carbon sequestration. Very few plants or animals in southeast Asia would have survived, and it is possible that the eruption caused a planet-wide die-off. However, the global cooling has been discussed by Rampino and Self. Their conclusion is that the cooling had already started before Toba's eruption. This conclusion was supported by Lane and Zielinski who studied the lake-core from Africa and GISP2. They concluded that there was no volcanic winter after Toba eruption and that high H2SO4 deposits do not cause long-term effects. Furthermore, due to the low solubility of sulfur in the magma, the emission of volatiles and climate impacts are likely limited.

Evidence from studies of mitochondrial DNA suggests that humans may have passed through a genetic bottleneck around this time that reduced genetic diversity below what would be expected given the age of the species. According to the Toba catastrophe theory, proposed by Stanley H. Ambrose of the University of Illinois at Urbana–Champaign in 1998, the effects of the Toba eruption may have decreased the size of human populations to only a few tens of thousands of individuals. However, this hypothesis is not widely accepted because similar effects on other animal species have not been observed, and paleoanthropology suggests there was no population bottleneck. The genetic bottleneck is now recognized to be the Out-of-Africa founder effect, rather than an actual reduction in population.

MORE RECENT ACTIVITY

Since the major eruption ~70,000 years ago, eruptions of smaller magnitude have also occurred at Toba. The small cone of Pusukbukit formed on the southwestern margin of the caldera and lava domes. The most recent eruption may have been at Tandukbenua on the northwestern caldera edge, suggested by a lack of vegetation that could be due to an eruption within the last few hundred years.

Some parts of the caldera have shown uplift due to partial refilling of the magma chamber, for example, pushing Samosir Island and the Uluan Peninsula above the surface of the lake. The lake sediments on Samosir Island show that it has risen by at least 450 m since the cataclysmic eruption. Such uplifts are common in very large calderas, apparently due to the upward pressure of below-ground magma. Toba is probably the largest resurgent caldera on Earth. Large earthquakes have recently occurred in the vicinity of the volcano, notably in 1987 along the southern shore of the lake at a depth of 11 km Such earthquakes have also been recorded in 1892, 1916, and 1920–1922.

In 2016, a study revealed that the Toba Supervolcano has a magma chamber containing 50,000 cubic kilometres of eruptible magma, about 30–50 kilometres underground. This makes the supervolcano's magma chamber more than four times larger than the volume of Lake Superior in North America, and also larger than the magma chamber underneath Yellowstone.

Lake Toba lies near the Great Sumatran fault, which runs along the centre of Sumatra in the Sumatra Fracture Zone. The volcanoes of Sumatra and Java are part of the Sunda Arc, a result of the northeasterly movement of the Indo-Australian Plate, which is sliding under the eastward-moving Eurasian Plate. The subduction zone in this area is very active: the seabed near the west coast of Sumatra has had several major earthquakes since 1995, including the 9.1 2004 Indian Ocean earthquake and the 8.7 2005 Nias–Simeulue earthquake, the epicenters of which were around 300 km from Toba.

PEOPLE

Most of the people who live around Lake Toba are ethnically Bataks. Traditional Batak houses are noted for their distinctive roofs (which curve upwards at each end, as a boat's hull does) and their colorful decor.

FLORA AND FAUNA

The flora of the lake includes various types of phytoplankton, emerged macrophytes, floating macrophytes, and submerged macrophytes, while the surrounding countryside is rainforest including areas of Sumatran tropical pine forests on the higher mountainsides.

The fauna includes several species of zooplankton and benthic animals. Since the lake is oligotrophic (nutrient-poor), the native fish fauna is relatively scarce, and the only endemics are Rasbora tobana (strictly speaking near-endemic, since also found in some tributary rivers that run into the lake) and Neolissochilus thienemanni, locally known as the Batak fish. The latter species is threatened by deforestation (causing siltation), pollution, changes in water level and the numerous fish species that have been introduced to the lake. Other native fishes include species such as Aplocheilus panchax, Nemacheilus pfeifferae, Homaloptera gymnogaster, Channa gachua, Channa striata, Clarias batrachus, Barbonymus gonionotus, Barbonymus schwanenfeldii, Danio albolineatus, Osteochilus vittatus, Puntius binotatus, Rasbora jacobsoni, Tor tambra, Betta imbellis, Betta taeniata and Monopterus albus.

Among the many introduced species are Anabas testudineus, Oreochromis mossambicus, Oreochromis niloticus, Ctenopharyngodon idella, Cyprinus carpio, Osphronemus goramy, Trichogaster pectoralis, Trichopodus trichopterus, Poecilia reticulata and Xiphophorus hellerii.

SINKING OF MV SINAR BANGUN

On 18 June 2018, Lake Toba was the scene of a ferry disaster, in which over 190 people drowned. MV Sinar Bangun was an irregular operating vessel on the lake which capsized with many passengers on board. The incident caused the death of 190 people and injuries to a number of others. Preliminary reports found the vessel was in operation with irregularities. Ignoring overloading on the vessel and operating in rough weather conditions were concluded as the main reasons leading to the disaster. Around 50 cars and 100 motorbikes, which were aboard, also sank into the lake on that day.

WIKIPEDIA

Volcanic bomb from the Pleistocene of Arizona, USA. (bottom view; ~32.5 centimeters across at its widest)

Volcanic bombs are tephra fragments larger than 64 millimeters. They represent blobs of lava erupted into the air during an eruption. While airborne, they often acquire an aerodynamic shape. The bomb shown above has a fusiform shape, formed by spinning around its long axis.

Volcanic bombs are often mafic in composition - this one is composed of basaltic andesite. It formed 71,000 years ago during an eruption from SP Crater, a cinder cone volcano in Arizona. Cinder cones are relatively small, steep-sided volcanoes composed of loose igneous debris, usually vesicular basalt and scoria. They have few eruptions before going extinct - this accounts for their relatively small size. Large volcanoes, such as shields and stratovolcanoes, are long-lived and have numerous eruptions.

Age: Late Pleistocene, 71 ka

Locality: SP Crater (Shit Pot Crater), west of Rt. 89, northern San Francisco Volcanic Field, Coconino County, north-central Arizona, USA

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

For more info., see:

en.wikipedia.org/wiki/Volcanic_bomb

and

en.wikipedia.org/wiki/S_P_Crater

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.

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

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

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

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).