Gareloi Volcano
Encyclopedia
The Gareloi Volcano is a stratovolcano
in the Aleutian Islands of Alaska
, USA, about 1259 miles (2,026 km) from Anchorage. Gareloi is located on Gareloi Island
, and comprises most of its land mass. The island also has two small glacier
s which protrude to the northwest and southeast.
The volcano is 6 miles (10 km) by 5 miles (8 km) at its base, possessing two summits. The southern crater is largely the greater, 984 feet (300 m) wide with fumarole
s. The size can be attributed to edifice failure in the southern wall. Gareloi's northern crater is enclosed.
had been a prominent sailor in Russia. After successful expeditions in 1725, 1728, and 1730, Bering was sent to explore what is now the Bering Sea
area of the Pacific in 1740. He soon settled on Kamchatka, where he started a settlement and built two additional vessels, dubbed St. Peter and St. Paul. In 1741 Bering and his company started towards North America, but were stalled by a storm. In being delayed, they were forced to take land. During the storm they could not make out the Alaskan coast. The storm proved too powerful so the ships turned around, charting several of the Aleutians, including Gareloi. Since then, it has been barely studied, resulting in a fragmentary knowledge of its eruptions and possibly even unrecorded episodes.
Gareloi Island is uninhabited and is part of the Alaska Maritime National Wildlife Refuge managed by the U.S. Fish and Wildlife Service.
activity. A fissure
, created by Gareloi's 1929 eruption, runs along the southern summit of the volcano. Steep sea cliffs on the southwest side of the island cut into the older caldera
. Three masses offshore of the island were produced by debris flows from the volcano.
Gareloi is of lava flows and pyroclastic origin. Two main episodes contributed to its creation. Lava deposits on the mountain vary from 3 foot (0.9144 m) to 20 feet (6 m) in thickness. Some of them extend from external vents on the volcano, suggesting that activity during the Pleistocene took place.
There are two large lava valleys on the island's southwest side which are shaped like a 'u'. The oldest of these flows are of Pleistocene age. Many of the Pleistocene age deposits are composed of basalt
ic trachyandesite
and basaltic andesite
, while containing amounts of plagioclase
, clinopyroxene, olivine
, and hornblende
.
s and edifice failure (landslide
) debris. The rock, which is comprised by dissected lava flows and pyroclastic masses, has been shaped by glacial retreat. This glacial activity began around 10,000 years past where it fleshed out newly formed rocks. Other landslides have been generated on the north and east flanks of the volcano.
proceeded to map the volcano and its surrounding area in 2003, in addition to implementing seismic monitors in June.
s. Typically they have been characterized by a central vent eruption followed by an explosive eruption, and sometimes a phreatic explosion. All have been of Volcanic Explosivity Index
(VEI) of 1 to 3. Such eruptions have occurred in 1790, 1791, 1792, 1873, 1922, April 1929, 1950, January 17, 1952, August 7, 1980, January 15, 1982, September 4, 1987, and August 17, 1989. Uncertain eruptions occurred in 1760, 1828, 1927, and 1996.
tuff
, volcanic glass
, and scoria
of red tone. Thirteen craters, all located in the fissure, contributed to this episode. All are most likely phreatic
. During the eruption, pyroclastic flow
s convened with tephra
, as suggested by deposits. Lahar
also streamed from the summit.
seismic network. A similar episode took place in 1982 when an ash cloud exceeding 23000 feet (7,010 m) appeared on satellite images on January 15. 1987 marked a milestone in Gareloi's eruptive history, when a flow, likely to be of volcanic origin, was observed by a commercial airplane pilot. The mass extended for 1312 feet (400 m) down the volcano. Steam reportedly emanated from the volcano, but volcanologists were unable to verify an eruption. In 1989 an employee of the US Fish and Wildlife Service spotted another ash plume covering the caldera and climbing 2300 feet (701 m) from the summit on August 17. A minor eruption occurred on September 27, 1996 was reported to the National Weather Service Aviation Weather Unit in nearby Anchorage. The plume, consisting of ash
and steam, rose 5000 feet (1,524 m) from the volcano's summit.
, creates respiratory complexities and irritation of the eye.
Pyroclastic flows would destroy much wildlife about the volcano. Gareloi has a history for pyroclastic flows in its eruptions, which can travel extremely fast. Future flows at Gareloi Volcano could make it off the island into the Pacific Ocean
and, if large enough, could fall into the ocean and generate tsunamis, though unlikely.
Stratovolcano
A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions...
in the Aleutian Islands of Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
, USA, about 1259 miles (2,026 km) from Anchorage. Gareloi is located on Gareloi Island
Gareloi Island
Gareloi is a volcanic island in the Delarof Islands of the Aleutian Islands of Alaska. It is located between the Tanaga Pass and the Amchitka Pass....
, and comprises most of its land mass. The island also has two small glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
s which protrude to the northwest and southeast.
The volcano is 6 miles (10 km) by 5 miles (8 km) at its base, possessing two summits. The southern crater is largely the greater, 984 feet (300 m) wide with fumarole
Fumarole
A fumarole is an opening in a planet's crust, often in the neighborhood of volcanoes, which emits steam and gases such as carbon dioxide, sulfur dioxide, hydrochloric acid, and hydrogen sulfide. The steam is created when superheated water turns to steam as its pressure drops when it emerges from...
s. The size can be attributed to edifice failure in the southern wall. Gareloi's northern crater is enclosed.
Discovery and accessibility
Vitus BeringVitus Bering
Vitus Jonassen Bering Vitus Jonassen Bering Vitus Jonassen Bering (also, less correNavy]], a captain-komandor known among the Russian sailors as Ivan Ivanovich. He is noted for being the first European to discover Alaska and its Aleutian Islands...
had been a prominent sailor in Russia. After successful expeditions in 1725, 1728, and 1730, Bering was sent to explore what is now the Bering Sea
Bering Sea
The Bering Sea is a marginal sea of the Pacific Ocean. It comprises a deep water basin, which then rises through a narrow slope into the shallower water above the continental shelves....
area of the Pacific in 1740. He soon settled on Kamchatka, where he started a settlement and built two additional vessels, dubbed St. Peter and St. Paul. In 1741 Bering and his company started towards North America, but were stalled by a storm. In being delayed, they were forced to take land. During the storm they could not make out the Alaskan coast. The storm proved too powerful so the ships turned around, charting several of the Aleutians, including Gareloi. Since then, it has been barely studied, resulting in a fragmentary knowledge of its eruptions and possibly even unrecorded episodes.
Gareloi Island is uninhabited and is part of the Alaska Maritime National Wildlife Refuge managed by the U.S. Fish and Wildlife Service.
Geography and geology
Gareloi is the northernmost volcano of the Delarof Group, a subgroup of the Aleutian Islands. It is composed of two craters, the older of which is covered by lava flows running to the northwest and southern coasts. The northern crater is small, with a feature suggesting dome collapse in its northwest flank. The southern flank, higher up and considerably larger, contains fumarolicFumarole
A fumarole is an opening in a planet's crust, often in the neighborhood of volcanoes, which emits steam and gases such as carbon dioxide, sulfur dioxide, hydrochloric acid, and hydrogen sulfide. The steam is created when superheated water turns to steam as its pressure drops when it emerges from...
activity. A fissure
Fissure vent
A fissure vent, also known as a volcanic fissure or simply fissure, is a linear volcanic vent through which lava erupts, usually without any explosive activity. The vent is usually a few meters wide and may be many kilometers long. Fissure vents can cause large flood basalts and lava channels...
, created by Gareloi's 1929 eruption, runs along the southern summit of the volcano. Steep sea cliffs on the southwest side of the island cut into the older caldera
Caldera
A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption, such as the one at Yellowstone National Park in the US. They are sometimes confused with volcanic craters...
. Three masses offshore of the island were produced by debris flows from the volcano.
Gareloi is of lava flows and pyroclastic origin. Two main episodes contributed to its creation. Lava deposits on the mountain vary from 3 foot (0.9144 m) to 20 feet (6 m) in thickness. Some of them extend from external vents on the volcano, suggesting that activity during the Pleistocene took place.
There are two large lava valleys on the island's southwest side which are shaped like a 'u'. The oldest of these flows are of Pleistocene age. Many of the Pleistocene age deposits are composed of basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
ic trachyandesite
Trachyandesite
Trachyandesite is an extrusive igneous rock. It has little or no free quartz, but is dominated by alkali feldspar and sodic plagioclase along with one or more of the following mafic minerals: amphibole, biotite or pyroxene...
and basaltic andesite
Basaltic andesite
Basaltic andesite is a black volcanic rock containing about 55% silica. Minerals in basaltic andesite include olivine, augite and plagioclase. Basaltic andesite can be found in volcanoes around the world, including in Central America and the Andes of South America. Basaltic andesite is common in...
, while containing amounts of plagioclase
Plagioclase
Plagioclase is an important series of tectosilicate minerals within the feldspar family. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a solid solution series, more properly known as the plagioclase feldspar series...
, clinopyroxene, olivine
Olivine
The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....
, and hornblende
Hornblende
Hornblende is a complex inosilicate series of minerals .It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole....
.
Rock
The rock that makes up Gareloi Island and its volcano is estimated to be of Pleistocene age. Several factors contribute to this inference, mainly the presence of glacierGlacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
s and edifice failure (landslide
Landslide
A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...
) debris. The rock, which is comprised by dissected lava flows and pyroclastic masses, has been shaped by glacial retreat. This glacial activity began around 10,000 years past where it fleshed out newly formed rocks. Other landslides have been generated on the north and east flanks of the volcano.
Mapping
The Alaska Volcano ObservatoryAlaska Volcano Observatory
The Alaska Volcano Observatory is a joint program of the United States Geological Survey, the Geophysical Institute of the University of Alaska Fairbanks, and the State of Alaska Division of Geological and Geophysical Surveys...
proceeded to map the volcano and its surrounding area in 2003, in addition to implementing seismic monitors in June.
Eruptive history
Gareloi has an extensive eruptive history, dating back to at least 1760. At least 12 eruptions have occurred at the summit, accompanied by lava and pyroclastic flowPyroclastic flow
A pyroclastic flow is a fast-moving current of superheated gas and rock , which reaches speeds moving away from a volcano of up to 700 km/h . The flows normally hug the ground and travel downhill, or spread laterally under gravity...
s. Typically they have been characterized by a central vent eruption followed by an explosive eruption, and sometimes a phreatic explosion. All have been of Volcanic Explosivity Index
Volcanic Explosivity Index
The Volcanic Explosivity Index was devised by Chris Newhall of the U.S. Geological Survey and Stephen Self at the University of Hawaii in 1982 to provide a relative measure of the explosiveness of volcanic eruptions....
(VEI) of 1 to 3. Such eruptions have occurred in 1790, 1791, 1792, 1873, 1922, April 1929, 1950, January 17, 1952, August 7, 1980, January 15, 1982, September 4, 1987, and August 17, 1989. Uncertain eruptions occurred in 1760, 1828, 1927, and 1996.
1929
In 1929 Gareloi Volcano underwent a major explosive eruption where it generated four lava flows, andesiticAndesite
Andesite is an extrusive igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. In a general sense, it is the intermediate type between basalt and dacite. The mineral assemblage is typically dominated by plagioclase plus pyroxene and/or hornblende. Magnetite,...
tuff
Tuff
Tuff is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. Tuff is sometimes called tufa, particularly when used as construction material, although tufa also refers to a quite different rock. Rock that contains greater than 50% tuff is considered...
, volcanic glass
Volcanic glass
Volcanic glass is the amorphous product of rapidly cooling magma. Like all types of glass, it is a state of matter intermediate between the close-packed, highly ordered array of a crystal and the highly disordered array of gas...
, and scoria
Scoria
Scoria is a volcanic rock containing many holes or vesicles. It is most generally dark in color , and basaltic or andesitic in composition. Scoria is relatively low in mass as a result of its numerous macroscopic ellipsoidal vesicles, but in contrast to pumice, all scoria has a specific gravity...
of red tone. Thirteen craters, all located in the fissure, contributed to this episode. All are most likely phreatic
Phreatic eruption
A phreatic eruption, also called a phreatic explosion or ultravulcanian eruption, occurs when rising magma makes contact with ground or surface water. The extreme temperature of the magma causes near-instantaneous evaporation to steam, resulting in an explosion of steam, water, ash, rock, and...
. During the eruption, pyroclastic flow
Pyroclastic flow
A pyroclastic flow is a fast-moving current of superheated gas and rock , which reaches speeds moving away from a volcano of up to 700 km/h . The flows normally hug the ground and travel downhill, or spread laterally under gravity...
s convened with tephra
Volcanic ash
Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact...
, as suggested by deposits. Lahar
Lahar
A lahar is a type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water. The material flows down from a volcano, typically along a river valley. The term is a shortened version of "berlahar" which originated in the Javanese language of...
also streamed from the summit.
1980s–1990s activity
On August 8, 1980 Gareloi erupted for the first time in records since 1929, sending ash plumes over 35000 feet (10,668 m) into the atmosphere. Precursor earthquakes occurred on August 8 and 9, both west of the AdakAdak Island
Adak Island is an island near the western extent of the Andreanof Islands group of the Aleutian Islands in Alaska. Alaska's southernmost town, Adak, is located on the island...
seismic network. A similar episode took place in 1982 when an ash cloud exceeding 23000 feet (7,010 m) appeared on satellite images on January 15. 1987 marked a milestone in Gareloi's eruptive history, when a flow, likely to be of volcanic origin, was observed by a commercial airplane pilot. The mass extended for 1312 feet (400 m) down the volcano. Steam reportedly emanated from the volcano, but volcanologists were unable to verify an eruption. In 1989 an employee of the US Fish and Wildlife Service spotted another ash plume covering the caldera and climbing 2300 feet (701 m) from the summit on August 17. A minor eruption occurred on September 27, 1996 was reported to the National Weather Service Aviation Weather Unit in nearby Anchorage. The plume, consisting of ash
Volcanic ash
Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact...
and steam, rose 5000 feet (1,524 m) from the volcano's summit.
Threat
Proximal volcanic hazards pose a significant threat to the life near Gareloi. If Gareloi were to erupt unexpectedly, ash clouds, falling volcanic ash, pyroclastic flows and debris avalanches (such as lahars) could easily span deadly hazards such as tsunamis. Commercial airplanes in particular are at risk from the masses of ash emanating from the volcano-volcanic ash induces engine failure. Inhalation of volcanic ash, scientifically known as tephraTephra
200px|thumb|right|Tephra horizons in south-central [[Iceland]]. The thick and light coloured layer at center of the photo is [[rhyolitic]] tephra from [[Hekla]]....
, creates respiratory complexities and irritation of the eye.
Pyroclastic flows would destroy much wildlife about the volcano. Gareloi has a history for pyroclastic flows in its eruptions, which can travel extremely fast. Future flows at Gareloi Volcano could make it off the island into the Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
and, if large enough, could fall into the ocean and generate tsunamis, though unlikely.