Mount Gareloi
Vorlage:Infobox Mountain The Gareloi Volcano is a stratovolcano in the Aleutian Islands of Alaska, USA, and about Vorlage:Convert from Anchorage. Gareloi is located on Gareloi Island and composes the majority of its mass. It is also populated by two small glaciers which protrude to the northwest and southeast.
The volcano is Vorlage:Convert by Vorlage:Convert at its base, possessing two summits. The southern crater is largely the greater, Vorlage:Convert wide with fumaroles. The size can be attributed to edifice failure in the southern wall. Gareloi's northern crater is enclosed.
Discovery
Vitus Bering had been a prominent sailor in Russia. After successful observation 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 make out the Alaskan coast. The storm proved too powerful so the ships turned around, charting several of the Aleutians, including Gareloi. Vorlage:Citation</ref> Since then, it has been barely studied, leading to a lackluster knowledge of its eruptions and possibly even unrecorded episodes.[1]
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[2] contains fumarolic activity.[3] A fissure, created by Gareloi's 1929 eruption, runs along the southern summit of the volcano.[4] Steep sea cliffs can be found on the southwest side of the island cutting into the older caldera. Offshore of the island are three masses produced from three debris flows on the volcano.[4]
Gareloi is of lava flows and pyroclastic origin. Two main episodes contributed to its creation. Lava deposits on the mountain vary from Vorlage:Convert to Vorlage:Convert in thickness. Some of them extend from external vents on the volcano, suggesting that activity during the Pleistocene took place.[3]
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 basaltic trachyandesite and basaltic andesite, while containing amounts of plagioclase, clinopyroxene, olivine, and hornblende.[2]
Rock
The rock that makes up Gareloi Island and its volcano is estimated to be of Pleistocene age.[5] Several factors contribute to this inference, mainly the presence of glaciers 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.[5]
Mapping
The Alaska Volcano Observatory proceeded to map the volcano and its surrounding area in 2003,[6] in addition to implementing seismic monitors in June.[7]
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 flows. Typically they have been characterized by a central vent eruption followed by an explosive eruption, and sometimes a phreatic explosion.[8] All have been of Volcanic Explosivity Index (VEI) of 1 to 3.[9] 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.[8]
1929
In 1929 Gareloi Volcano underwent a major explosive eruption where it generated four lava flows, andesitic tuff, volcanic glass, and scoria of red tone. Thirteen craters, all located in the fissure, contributed to this episode. All are most likely phreatic.[3] During the eruption, pyroclastic flows convened with tephra, as suggested by deposits. Lahar also streamed from the summit.
1980s-1990s activity
In August 8, 1980 Gareloi erupted for the first time in records since 1929, sending ash plumes over Vorlage:Convert into the atmosphere. Precursor earthquakes occurred on August 8 and 9, both west of the Adak seismic network.[10] A similar episode took place in 1982 when an ash cloud exceeding Vorlage:Convert appeared on satellite images on January 15.[10] 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 Vorlage:Convert down the volcano. Steam reportedly emanated from the volcano, but volcanologists were unable to verify an eruption.[10] In 1989 an employee of the US Fish and Wildlife Service spotted another ash plume covering the caldera and climbing Vorlage:Convert from the summit on August 17.[5] 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 Vorlage:Convert from the volcano's summit.[5]
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.[11] Inhalation of volcanic ash, scientifically known as tephra, creates respiratory complexities and irritation of the eye.[12]
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.[12]
References
Notes
Sources
- ↑ Coombs, McGimsey and Browne, page 1.
- ↑ a b Brandon Browne, Coombs, Michelle L. and Larsen, J: Preliminary Geology of Gareloi Volcano, Western Aleutian Islands (Alaska). United States Geological Survey, abgerufen am 3. Mai 2009.
- ↑ a b c Gareloi description and statistics. Alaska Volcano Observatory, abgerufen am 15. April 2009.
- ↑ a b Gareloi. Global Volcanism Program, abgerufen am 13. April 2009.
- ↑ a b c d Coombs, McGimsey and Browne, page 9.
- ↑ Gareloi geologic, topographic, and location maps, as well as references that are classified as maps or that contain maps. Alaska Volcano Observatory, abgerufen am 3. Mai 2009.
- ↑ Neal, McGimsey, Dixon and Melnikov, page 1.
- ↑ a b Gareloi: Eruptive History. Global Volcanism Program, abgerufen am 13. April 2009.
- ↑ Gareloi, Aleutian Islands, Alaska. Volcano World, abgerufen am 5. Mai 2009.
- ↑ a b c Coombs, McGimsey and Browne, page 8.
- ↑ Coombs, McGimsey and Browne, page 14.
- ↑ a b Coombs, McGimsey and Browne, page 15.