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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.
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.
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.
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.
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.
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.
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.
Perry's huffin' and puffin' like he's working out. Actually, it was quite a work out, climbing a volcano.
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.
The Lago de Atitlán is a beautiful lake in the highlands of Guatemala; the water level is at 1562 meters (5,125 ft). The lake basin is volcanic in origin, filling an enormous caldera formed by an eruption 84,000 years ago. It is shaped by deep surrounding escarpments and three stratovolcanoes on its southern flank. Lake Atitlán is the deepest lake in Central America with a maximum depth of about 340 meters (1,120 ft). Its surface area is 130 sq km (50 sq mi).
All three volcanos are in view here. To the left are the Volcán Tolimán (right) with an altitude of 3158 meters (10,361 ft) and the Volcán Atitlán (left) with an altitude of 3535 meters (11,598 ft). On the right side is the Volcán San Pedro (a.k.a. Volcán Las Yeguas) with an altitude of 3020 meters (9,908 ft).
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).
On September 29, 2016, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this false-color image (MODIS bands 7-2-1) showing volcanic activity in the South Sandwich Islands. Located in the South Atlantic Ocean, the uninhabited South Sandwich Islands include several active stratovolcanoes. via NASA ift.tt/2dMun9F
Explosive eruption of Mt. Pinatubo on 22 June 1991. (original photo taken by R. Batalon; public domain image provided by the United States Geological Survey)
Mt. Pinatubo’s summer 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 and 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 and Subic Bay).
The photo shows a relatively small explosive eruption on 22 June 1991. The main eruption occurred a week earlier, on 15 June 1991.
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See info. at:
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.
Referred to as the “Ilha Lilás” (the “lilac” or “violet” island), Terceira is an island in the Azores archipelago, in the middle of the North Atlantic Ocean. It is one of the larger islands of the archipelago, with a population of 56,000 inhabitants in an area of approximately 396.75 km². It is the location of the historical capital of the archipelago, the Azores' oldest city and UNESCO Heritage Site (Angra do Heroísmo), the seat of the judicial system (Supreme Court), main base of the Azores Air Zone Command (Commando da Zona Aérea dos Açores) Base Aérea nº 4 and to a United States Air Force detachment.
Historically, there has been uncertainty in the date and the discoverer associated with the islands of the Azores. Nautical charts before the "official" discovery identified islands in the Atlantic Ocean as far back as 1325, when a chart by Angelino Dalorto identified "Bracile" west of Ireland, and later one by Angelino Dulcert which identifies the Canaries, and Madeira, along with mysterious islands denominated as "Capraria" (whom some historians suggest were São Miguel and Santa Maria). Legends also persisted of Atlantis, Sete Cidades (Kingdoms of the Seven Cities), the Terras of São Brandão, the Ilhas Aofortunadas (The Fortuante Islands), the Ilha da Brasil (the Island of Brasil), Antília, the Ilhas Azuis (Blue Islands), the Terra dos Bacalhaus (Land of Codfish), and charts appeared between 1351 and 1439 of several groupings of islands with various names. The first association between the modern island of Terceira and these stories, was that of the island of Brasil; it first appears as Insula de Brasil in the Venetian map of Andrea Bianco (1436), attached to one of the larger islands of a group of islands in the Atlantic.
In 1439 the first official discovery document appeared attributing the discovery of the Formigas islets, to Gonçalo Velho Cabral.[1]. It is unclear when Tereceira was first sighted by Portuguese explorers: the first documents referring to a third island in the Azorean archipelago was a reference to a Ilha de Jesus Cristo (Island of Jesus Christ), and later, Ilha de Jesus Cristo da Terceira. Gaspar Frutuoso, a chronicler and humanist, would later rationalize about the islands first name, noting that:
it was discovered on the first day of January, traditionally the feast day of the name of Jesus;
it was discovered by a captain in the Order of Christ;
it was discovered on a Thursday or Friday, on Corp de Deus (Body of Christ); or
because it was part of the dioceses of Angra, through the invocation of San Salvador (although this implies that an dioceses existed prior to its discovery)
Regardless, it was only a temporary name, as the colloquial Terceira (meaning "third" in Portuguese, as in "the third island" or "third to be discovered") was used more often to describe the island.
The colonization of the island began by decree of Infante D. Henrique (dated 21 of March, 1450), and placed the island in the administrative-hands of the Flem Jácome de Bruges. This nobleman brought families and settlers from Flanders, as well as animals and provisions, disembarking in the area of Porto Judeu or Pesqueiro dos Meninos, near Ribeira Seca (depending on sources). Gaspar Frutuoso also affirmed that:
"...that ancient settlers of the island of Terceira, that were the first to settle in a band to the north, where they call Quatro Ribeiras, where now the parish of Santa Beatriz is located, and where the first church existed on the island, but were few settlers remained due to difficult access and bad port.''
The first settlement occurred in Quatro Ribeiras, in the locality of Portalegre[2], where a small chapel was raised for the invocation of Santa Ana. Bruges made return trips to Flanders for new settlers to his colony. On one of his trips to Madeira he conscripted Diogo de Teive and assigned him as his Lieutenant and Overseer for the island of Terceira. A few years later, Brugues moved his residence to Praia, began construction on the Matriz Church in 1456, and administered the Captaincy of the island from this location (around 1460), until he disappeared in 1474, on another of his trips between the colony and the continent. Following his disappearance, the Infanta D. Beatriz, in the name of her son the Infante D. Diogo (who inherited the islands of Terceira and Graciosa following the death D. Fernando, the adopted son of the Infante D. Henrique) divided the island of Terceira into two captaincies: Angra (which was given to João Vaz Corte Real) and Praia (which was given to Álvaro Martins Homem[3]). Apart from the Portuguese and Flemish settlers, colonists from Madeira, many slaves from Africa, new Christians and Jews populated the island at this time, developing new commercial ventures including wheat (exported during the 15th Century throughout the empire), sugar-cane, woad (for the dye industry) and woods (principally for the naval construction industries). This development would continue until the end of the 19th century, with the introduction of new products, including tea, tabaco and pineapple.
Battle of Terceira
During the 1580 Dynastic Crisis, the Azores was the only portion of the Portuguese overseas empire to resist the Spanish until the summer of 1583. Philip II of Spain had offered an amnesty if the Azores surrender, but his messenger met with a very hostile reception at Angra do Heroísmo (escaping to São Miguel, which had presented its allegiance to the King of Spain). Following the Battle of Ponta Delgada, where Don Álvaro de Bazán, 1st Marquis of Santa Cruz defeated the Anglo-French supporters of D. António (the pretender to the Portuguese throne) off the coast of São Miguel, the Marquis concentrated his forces at a less defended beach 10 km from Angra do Heroísmo. With a fleet to ninety-six ships and 9,500 men (as well as a garrison of 2,000 on Sao Miguel) the Marquis was able to defeat the forces of D. António after one day's fighting. Although French and English soldiers on the island were allowed to retire unharmed, D. Antonio and a handful of his supporters were lucky to escape with their lives.
With the acclamation of John IV of Portugal, the Azores applauded the restoration of independence from the Iberian Union. This was not lost on the Spanish settlers in Angra do Heroísmo, who had become a privileged class during the Union, and which made it difficult for them to remain after 1642, when Portuguese sovereignty was restored.
In 1766, the reorganization of system of Captaincies was undertaken, resulting in one Captain-General, with his seat in Angra do Heroísmo for the Azores.
It was also on Terceira that in 1829, during the Liberal Wars that a violent battle occurred between Miguelistas (supporters of Miguel I of Portugal and the Liberals (supporters of King John VI of Portugal) at the Battle of Praia da Vitória. In 1832, King Pedro arrived in the Azores to form a government in opposition to the absolutionist regime in Lisbon, presided by the Marques of Palmela, and supported by Azoreans Mouzinho da Silveira and Almeida Garrett that developed many important reforms.
In 1810, a number of journalists and others considered to favor the French, including the industrialist Jácome Ratton, were exiled to the island for a period.
On 24 August 2001, Terceira Island made the news as Air Transat Flight 236 managed to land on Lajes Air Base after running out of fuel in mid-air.
On 16 March 2003, President of the United States George W. Bush, UK Prime Minister Tony Blair, Spanish Prime Minister José María Aznar and Prime Minister of Portugal José Manuel Barroso met on Terceira to discuss the Invasion of Iraq, which began four days later, on 20 March
The island of Terceira consists of four overlapping stratovolcanoes built over a geologic structure called the Terceira Rift: a triple junction between the Eurasian, African and North American tectonic plates. These volcanic structures rise from a depth of over 1,500 metres (5,000 ft) from the floor of the Atlantic Ocean. Radiocarbon dating of eruptive units, in support of geologic mapping, has improved the known chronology of Middle to Late Pleistocene and Holocene volcanic activity on the island of Terceira, Azores, defining the east-to-west progression in stratovolcano growth. These have commonly resulted in a classification of the eruptive events into the following structures:
Cinco Picos Volcanic Complex - the oldest on Terceira (defined by the Serra do Cume), which completed its main sub-aerial activity by about 370–380,000 years ago. Collapse of the upper part of the stratovolcanic edifice formed an enormous 7 × 9 km caldera about 370,000 years ago. Post-caldera eruptions of basalt from cinder cones on and near the caldera floor and trachytic pyroclastic flow and pumice fall deposits from younger volcanoes west of Cinco Picos have refilled much of the caldera producing an almost-uninterrupted fertile plain.
Guilherme Moniz Volcanic Complex - the southern portion , in the central part of the island, began erupting about 100,000 years later (about 270,000 ka) and produced trachyte domes (approximately 808 m/2651 ft in altitude), flows, and minor pyroclastic deposits for another 100,000 years (until at least 111 ka). The highest point along the caldera rim reaches 623 metres (2,044 ft). The northern portion of the Caldera is less well exposed, but reflects a similar age range. The northwest portion of the caldera was formed sometime after 44 ka. Several well-studied ignimbrites that blanket much of the island likely erupted from Guilherme Moniz Volcano.
Pico Alto Volcanic Complex - Center, a tightly spaced cluster of trachyte domes and short flows, is a younger part of Guilherme Moniz Volcano. Stratigraphic studies and radiocarbon analysis suggest that most of the Pico Alto eruptions occurred during the period from about 9000 to 1000 years BP.
Santa Barbara Volcanic Complex - the youngest stratovolcano on Terceira, began erupting prior to 29,000 years ago, and has been active historically, comprises the western end of the island and at its highest point is 1,023 m (3,356 ft). This stratovolcano is surrounded by several domes and coulee trachyte formations that occupy the volcano's caldera and along various alignments of the volcano's flanks.
Fissural Zone - Connecting the eastern portion of Santa Bárbara, the western frontier of Pico Alto and Guilherme Moniz exist a grouping of fissural volcanoes and basaltic cones (Hawaiian and Strombolian), the youngest of which formed about 15,000 years ago. The only historical eruptions occurred in 1761, along a fissure on the eastern face of Santa Bárbara, and in 1867 and between 1998–2000 from submarine vents off the western coast (Serreta (Azores)). The groupings of volcanic structures on the island are aligned along a northwest-southwest and west-northwest-east-southeast orientation that extends to the submarine vents/volcanoes towards the eastern basin of Graciosa, including geomorphological alignments of smaller volcanic structures (including both basaltic and trachytic cones).
Island tectonics are highlighted by two great faults in the northeast corner (the Lajes and the Fontinhas faults), the Lajes Graben has been responsible for severe seismic events. Historically, both faults have produced earthquakes that are relatively shallow, strong and responsible for the destruction of property in the northeastern corner (specifically in 1614 and 1841). During the 1614 event, whose epicenter was located along the Lajes fault eight kilometers offshore, recorded magnitudes for the earthquake were between 5.8 and 6.3 on the Richeter scale (Wells and Coppersmith,1994). Both the Lajes and Fontinhas faults are separated by three kilometers). A second, less-developed, graben is located on the southeast of the Santa Bárbara stratovolcano. This feature is marked by trachyte domes and crosses from the coast at Ponta do Queimado (from the historical basin of Serreta (Azores)) to the cliffs, faults, basaltic lava and fissural eruptions near the center of the island.
The western part of Terceira Island is more heavily forested than the eastern part, due to the prevailing westerly winds bringing increased precipitation to that side, resulting in forests of Cryptomeria (Cryptomeria japonica). Other geomorphological points of interest include the plains of Achada, the mounts near Santa Bárbara, the small lakes of Lagoa das Patas and Lagoa da Falca. The nothern coast is an area marked by evidance of volcanic activity with several "mistérios" (lava fields), the swimming pools of Biscoitos, while the centre of the island is highlighted by the Algar do Carvão and Furnas do Enxofre (dormant and active volcanic forms) that are popular with tourists and geologists. Most of the island is ringed by coastal cliffs about 20 m (60 ft) high, except on the south coast near Angra do Heroísmo. Here, an eruption of basaltic lava in shallow water formed the tuff cone of Monte Brasil, which protects and shelters the harbor of the island's capital. The cone is about 1 km (0.6 mi) in diameter and rises 205 m (673 ft) above the western side of the harbor
The Portuguese bullfight is popular on the island, coming in two variations: the traditional equestrian bullfight (in the ring) and the popular “touradas à corda” that occur in the streets.
Popular since the 16th Century, the “touradas à corda” (literally “bullfights by rope”) are held by local Terceiran villagers from April/May to late September. In these events, similar to the “Running of the Bulls”, a bull is let loose from the town’s square (or other open space) with a very long rope around its neck. Courageous people then attempt to provoke the animal and get as close to it while avoiding being gored (resulting in many examples of humorous provokations, fearless attempts and the occasional injury or mayhem). Some “touradas à corda” also do away with the rope entirely or become semi-aquatic (when the bulls chase the participants off a dock). Following these “games” the animal is eventually retrieved and a festival will begin.
In some towns, a Portuguese equestrian bullfight will take place involving a grande procession and participation of men dressed in 16th-Century costume: the pantalones (the horsemen), the bandarilheiros (the horsemen's assistants), the matadores and the widely popular forcados (eight men who challenge the bull). A horsemen will ride a Lusitanian breed of horse and will wearout the bull (while lancing a dart on the bull's back), then the forcados will challenge the bull to charge where they will subdue the animal on mass
STS053-096-083 Volcanoes, Kamchatka Peninsula, Russia December 1992
No volcanoes appear to be active at the time this photograph was taken of the southern tip of snow-covered Kamchatka Peninsula. The snow-covered terrain actually increases the clarity of the volcanic landscape for the viewer. Except for the plains along the west coast of Kamchatka, a variety of volcanic landforms (stratovolcanoes, shield volcanoes, complex volcanoes, cinder cones, and calderas) covers almost the entire Kamchatka Peninsula. Three prominent volcanic features appear in the photograph—the massive but severely eroded volcano along the northwest side of the photograph, approximately 30 miles (50 kilometers) in diameter at its base; the lake near the southern end of Kamchatka (Kurile Lake), which is actually a water-filled caldera from an older volcano (Pauzhetka Volcano); and a large caldera (Ksudach Volcano) northeast of Lake Kurile that reveals just a small area of open water. The peaks of several of the taller stratovolcanoes in this photograph exceed 6000 feet (1800 meters) above sea level. The Kamchatka Peninsula is bounded by the Bering Sea on the east and the Sea of Okhotsk on the west.
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
(looking ~east; photo by Miranda Manross)
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In the foreground is Mt. St. Helens, the most active volcano in the Cascade Range, which is a series of subduction zone stratovolcanoes in a ~north-south line from northern California to Oregon to Washington State to southwestern British Columbia. St. Helens is a 40,000 to 50,000 year old, andesitic-dacitic-basaltic volcano that typically has explosive ash eruptions (as do all subduction zone stratovolcanoes).
The 1980 eruption of Mt. St. Helens was a northward-directed lateral blast that immediately followed an enormous landslide event on the northern face of the volcano. The landslide was triggered by a moderate earthquake at 8:32 AM, Sunday, 18 May 1980. Snow and ice on the mountain melted during the eruption, mixed with ash and other debris, and rushed down nearby river valleys as lahars (volcanic mud flows).
The ash, lapilli, and pumice erupted from Mt. St. Helens in May 1980 was dacite, an intermediate extrusive igneous rock. Most of the air-fall dacite ash fell in Washington State, Oregon, and Idaho, but a minor amount accumulated as far east as Minnesota and Oklahoma. Light dustings of ash were also observed in Ohio.
The 1980 eruption was the largest in recent American history. The volcano was intermittently active until 1986. Minor activity occurred from 1989 to 1991 and from 2004 to 2006.
The area is now a park ("national volcanic monument") and is accessible to tourists. The top third of the mountain was blown away during the 1980 eruption. Much of the surrounding landscape is still nonvegetated and covered with gray volcanic tephra.
In the background is Mt. Adams, another subduction zone stratovolcano. Adams is a Pleistocene-Holocene dacitic-andesitic-basaltic volcano composed of lava flows (mostly) and tephra deposits (some). Its last eruption was in prehistoric times, about 1,000 years ago.
Location: Mt. St. Helens (northwestern Skamania County) & Mt. Adams (southwestern Yakima County), Cascade Range, southwestern Washington State, USA
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See info. at:
en.wikipedia.org/wiki/Mount_St._Helens
and
The Lago de Atitlán is a beautiful lake in the highlands of Guatemala; the water level is at 1562 meters (5,125 ft). The lake basin is volcanic in origin, filling an enormous caldera formed by an eruption 84,000 years ago. It is shaped by deep surrounding escarpments and three stratovolcanoes on its southern flank. Lake Atitlán is the deepest lake in Central America with a maximum depth of about 340 meters (1,120 ft). Its surface area is 130 sq km (50 sq mi).
In view are the Volcán Tolimán (right) with an altitude of 3158 meters (10,361 ft) and the Volcán Atitlán (left) with an altitude of 3535 meters (11,598 ft).
(photo by Mary Ellen St. John)
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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 near the center is McIntyre Mountain. The peak to the right of that 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.
(photo by Kathy Stott)
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The Andes Mountains are a long, mostly north-south trending orogenic belt along South America's western coast. They principally formed by subduction - one tectonic plate diving beneath another. Compressional mountain building in the Andes occurred during the Cretaceous and Tertiary.
Some Andean mountains are active & potentially active volcanoes, such as Lonquimay Volcano shown here. Subduction zone volcanoes are typically large, steep-sided cones with alternating layers of ash beds and lava flows, and are called stratovolcanoes (also known as composite volcanoes). Stratovolcanoes usually erupt extrusive igneous materials having an intermediate composition (for example, andesite and dacite). Major activity tends to be explosive ash eruptions, but lava flow eruptions also occur.
The last significant activity at Lonquimay Volcano was a lava flow eruption from late 1988 to early 1990. Andesite was erupted from the Navidad Cone, a vent on the eastern flank of the volcano. Lava flowed about 10 kilometers to the northeast and partially filled up the Lolco River Valley (= left side of the photo).
Locality: Lonquimay Volcano (looking east), Andes Mountains, northeastern Araucanía Region, central Chile, South America (38° 22' 45.24" South latitude, 71° 35' 25.10" West longitude)
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Some info. from:
Kerr & Lyman (2007) - Importance of surface crust strength during the flow of the 1988-1990 andesite lava of Lonquimay Volcano, Chile. Journal of Geophysical Research 112(B03209). 8 pp.
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See info. at:
en.wikipedia.org/wiki/Lonquimay_(volcano)
and
The Lago de Atitlán is a beautiful lake in the highlands of Guatemala; the water level is at 1562 meters (5,125 ft). The lake basin is volcanic in origin, filling an enormous caldera formed by an eruption 84,000 years ago. It is shaped by deep surrounding escarpments and three stratovolcanoes on its southern flank. Lake Atitlán is the deepest lake in Central America with a maximum depth of about 340 meters (1,120 ft). Its surface area is 130 sq km (50 sq mi).
In view are the Volcán Tolimán (front, right) with an altitude of 3158 meters (10,361 ft) and the Volcán Atitlán (back, left) with an altitude of 3535 meters (11,598 ft).
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 forest-covered hill at left and center-left is Witcher 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.
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).
These boats serve as public transportation for communities along the lake. They have powerful motors and go pretty fast.
The Ijen volcano complex is a group of stratovolcanoes in the Banyuwangi Regency of East Java, Indonesia. It is inside a larger caldera Ijen, which is about 20 kilometers wide. 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 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.
The active crater at Kawah Ijen has a diameter of 722 metres (2,369 ft) and a surface area 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).
The lake is recognised as the largest highly acidic crater lake in the world.
Zhupanovsky (Russian: Жупановский) is a volcanic massif located in the southeastern part of Kamchatka Peninsula, Russia. It consists of four overlapping stratovolcanoes. After 54 years of inactivity, the volcano began erupting on October 23, 2013 and again in 2014, continuing into 2015.
LAT 53°35′18″N
LONG 159°08′54″W
N - 88°
Pagan Island, Commonwealth of the Northern Mariana Islands.
Pagan is a currently uninhabited island in the Northern Marianas island chain. Formed by two active stratovolcanoes and a small land strip between the two, the island has historically hosted a small population and has been governed by the Spanish, Germans, Japanese and Americans.
During World War Two, Japanese forces built an airstrip on the island which was subsequently subject to near-daily American attacks from June to November 1944. On September 2, 1945 USS Rhind DD-404 arrived at the island with Commodore Vernon F. Grant who accepted the surrender of the Japanese garrison on Pagan.
In 1980 the island's Northern volcano erupted and lava flows destroyed much of the small village on the island, forcing the inhabitants to evacuate. Further eruptions in 2006 caused more lava flows to cover much of the airfield and the island remains uninhabited.
Kawah Ijen, carrying sulphur down the mountain
The Ijen volcano complex is a group of stratovolcanoes in East Java, Indonesia. The Ijen volcano 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 paid well considering the cost of living in the area, but is very onerous. Workers earn around Rp 50,000 - 75,000 ($5.50-$8.30) 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 run east-west across the southern side of the caldera. The active crater at Kawah Ijen has a diameter of 722 metres and a surface area of 0.41 square kilometres. It is 200 metres deep and has a volume of 36 cubic hectometres.
The lake is recognised as the largest highly acidic crater lake in the world. In 2008, the pH of the water in the crater was measured to be 0.5 due to sulfuric acid.
(source: en.wikipedia.org/wiki/Ijen)
Kawah Ijen
The Ijen volcano complex is a group of stratovolcanoes in East Java, Indonesia. The Ijen volcano has a one-kilometer-wide turquoise-colored acid crater lake. The lake is the site of a labor-intensive sulfur mining operation, in which sulfur-laden baskets are carried by hand from the crater floor.
Many other post-caldera cones and craters are located within the caldera or along its rim. The largest concentration of post-caldera cones run east-west across the southern side of the caldera. The active crater at Kawah Ijen has a diameter of 722 metres and a surface area of 0.41 square kilometres. It is 200 metres deep and has a volume of 36 cubic hectometres.
The lake is recognised as the largest highly acidic crater lake in the world. In 2008, the pH of the water in the crater was measured to be 0.5 due to sulfuric acid.
(source: en.wikipedia.org/wiki/Ijen)
Mount Thielsen is an extinct shield volcano in the Oregon High Cascades, near Mount Bailey and Diamond Lake. Because eruptive activity ceased 250,000 years ago, glaciers have heavily eroded the volcano's structure, creating precipitous slopes and a horn-like peak. The spire-like shape of Thielsen attracts lightning strikes and creates fulgurite.
In 1884 a United States Geological Survey team headed by J. S. Diller began studying the mountains of the Cascade Range. Their intended destinations included Thielsen, which was climbed and sampled for its fulgurite variant. Thielsen's spire-like top is hit by lightning so frequently that some rocks on the summit have melted into a rare mineraloid known as lechatelierite, a variety of fulgurite. The mountain has earned the nickname "the lightning rod of the Cascades".
Diamond Lake, formed by one of Thielsen's eruptions, lies to the west of Mount Thielsen and beyond lies Mount Bailey, a much less eroded and younger stratovolcano. Thielsen's sharp peak is a prominent feature of the skyline visible from Crater Lake National Park. All three volcanoes are part of the Oregon High Cascades, a range that sections off the stratovolcanoes of Oregon that are younger than 3.5 million years.
The view is from the Diamond Lake overlook off Oregon highway 138 on June 22, 2021.
Dacite pumice (air-fall tephra) from the Holocene of the Philippines.
Mt. Pinatubo is one of several subduction zone stratovolcanoes in the Luzon Volcanic Arc of the Philippines. Published information indicates that Pinatubo is 35,000+ years old and is composed principally of dacitic and andesitic rocks.
Mt. Pinatubo had a significant explosive ash eruption in 1991 that was the largest anywhere on Earth since 1912. Pinatubo's eruption is also famous for having been successfully predicted by American volcanologists. The prediction and subsequent evacuation saved thousands of lives.
The mid-June 1991 eruptions from Pinatubo blanketed ash, pumiceous lapilli, and pumice over the surrounding countryside, including two American military bases (Clark and Subic Bay). The sample seen here is dacite pumice from the 15 June 1991 eruption - it was collected at the U.S. Subic Bay Naval Base, ~20 miles south of Mt. Pinatubo.
Location of volcano: Mt. Pinatubo, Luzon Volcanic Arc, western Luzon Island, northern Philippines
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For additional geologic information on the 1991 Pinatubo eruption, see:
Newhall & Punongbayan (1996) - Fire and Mud, Eruptions and Lahars of Mount Pinatubo, Philippines. Quezon City & Seattle & London. Philippine Institute of Volcanology and Seismology & University of Washington Press. 1126 pp.
Dacitic volcanic ash from the Holocene of Washington State, USA. (field of view ~5.1 cm 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 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.
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: Yakima, northern Yakima County, southern Washington State, USA
Entering the spectacular fjiords of Tufi. The volcano Trafalgar is in the foreground with Mount Nelson to the left.
"Mt Trafalgar volcano is located north east of Victory Volcano in Papua New Guinea. The volcano is deeply eroded. Mt Trafalgar is a major andesite volcano which is located in an area without a Benioff-Wadati zone. The magmas erupted from the volcano have unusually high levels of Nickel and Chromium.
Mount Trafalgar is one of four large Quaternary stratovolcanoes on the north coast of southeastern New Guinea. The other three are Hydrographers Range, Mount Lamington, and Mount Victory."
Source: Victory.http://volcanolive.com/trafalgar.html
The sides of Mount Trafalgar eroded and created a series of deep "V" shaped valleys. These valleys were flooded to form the fjiords of today
"Over geologic time sea level has fluctuated by more than 300 metres, possibly more than 400 metres. The main reasons for sea level fluctuations in the last 15 million years are the Antarctic ice sheet and Antarctic post-glacial rebound during warm periods.
The current sea level is about 130 metres higher than the historical minimum. Historically low levels were reached during the Last Glacial Maximum (LGM), about 20,000 years ago. The last time the sea level was higher than today was during the Eemian, about 130,000 years ago." en.wikipedia.org/wiki/Past_sea_level
Image: PONANT
(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 steam plume in the morning of 18 November 2023.
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).
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Info. at:
en.wikipedia.org/wiki/Mount_Shishaldin
and
A view of Cleveland Avenue at sunset with a towering Mount Garibaldi (elevation 8,786 feet) in the background. Like other stratovolcanoes in the Pacific Northwest, it has a very long and explosive history. Were Garibaldi to erupt today, it could easily cause massive problems (ashfall, lahars, pyroclastic flows).
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 masses in the above photo are xenoliths ("xeno" = foreign; "lith" = rock). Xenoliths are pieces of rock that have fallen from the walls or roof of a cooling magma chamber. These xenoliths are 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
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.
Rhyolite ash (ash fall deposit), erupted early May 2008 from Chaitén Volcano, southern Chile. Collected between 3 May & 16 May 2008 from a farm in the town of Esquel, northwestern Chubut Province, southern Argentina.
(field of view ~3.4 centimeters across)
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Here's an unusual volcanic ash sample. This is rhyolite ash from a subduction zone stratovolcano in southern Chile. The Chaitén Volcano erupted in May 2008 and its wind-blown ash got deposited in Chile and Argentina. The color of the ash is very pale yellow to cream - it's one of two volcanic ash samples I have that are this light-colored (a Lava Creek B ash-fall sample from Oklahoma that was erupted 640,000 years ago from the Yellowstone Hotspot is just a bit paler yellow than this Chaitén sample).
What makes this pale yellow rhyolite ash sample from Chile so unusual? Well, subduction zone stratovolcanoes typically have andesite or dacite ash eruptions. Andesite and dacite are intermediate extrusive igneous rocks, having total silica contents between 52% and 65%. Rhyolite ash has a total silica content over 65%. The Chaitén 2008 erupted material has a 73% to 76% silica content - very high for a subduction zone.
Published research on the May 2008 Chaité Volcano indicates that the rhyolite magma ascended very rapidly for a felsic magma, at about 1 meter/second, before having an explosive ash eruption. This is the quickest ascent of rhyolitic magma ever recorded - four hours elapsed for the magma ascent, starting from an estimated >5 km depth, and reaching the near-surface. Rhyolitic melt is famous for typically having a high viscosity. Some rhyolitic lava outcrops have the appearance of toothpaste oozing from a vent. Chaitén Volcano's rhyolite melt broke the rules (see Castro & Dingwell, 2009 for details).
Location of Chaitén Volcano: ~10 km northeast of the town of Chaitén, southern Andes Mountains, southern Chile (42º 50' 18" S, 72º 39' 01" W).
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Some info. from:
Castro, J.M. & D.B. Dingwell. 2009. Rapid ascent of rhyolitic magma at Chaitén Volcano, Chile. Nature 461: 780-784.
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 moderately large, darker-colored, xenolith-like object is a "quenched blob". From park signage: "These patches are called quenched blobs, formed during the rock's molten stage. As molten rock, basalt magma mixed with dacite magma. Dacite magma's temperature is much cooler than basalt's. When the hotter basalt injected into the cooler dacite magma, it was like hot wax hitting cold water. The blobs were quenched - cooled suddenly. When the lava oozed from the volcano's vent, the blobs solidified and remained encased in the dacite rock. The mixing of the two magmas likely triggered the May 19 Lassen Peak eruption. When a superheated injection of basalt magma enters a dacite magma, a volatile jolt occurs - sometimes enough to cause a volcano to erupt."
Quenched blobs in May 1915 black dacite may be composed of andesite.
Locality: boulder in Devastated Area, Lassen Volcano National Park, northeastern California, USA
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
Cerro Toco is a stratovolcano located in the eastern part of the Atacama desert in Chile's II Region (Antofagasta), approximately 6 km (4 mi) south of the border between Bolivia and Chile and 12 km (7 mi) SE of the Juriques and Licancabur volcanoes. It conforms the north eastern extreme of the Purico Complex, a pyroclastic shield made up by several stratovolcanoes, lava domes and a maar.
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.
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
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
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 pumice (air-fall tephra) from the Holocene of the Philippines. (the long axis of the pumice piece at center is 1.9 centimeters)
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 samples seen here are dacite pumice from the 15 June 1991 eruption - they were 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.
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