| Mount Gareloi | |
|---|---|
 Summit of the volcano | |
| Highest point | |
| Elevation | 5,161 ft (1,573 m)[1] |
| Prominence | 5,161 ft (1,573 m)[1] |
| Listing |
|
| Coordinates | 51°47′18″N178°47′39″W / 51.78833°N 178.79417°W /51.78833; -178.79417[1] |
| Geography | |
  Gareloi Alaska | |
| Location | Gareloi Island,Alaska, U.S. |
| Parent range | Aleutian Islands |
| Geology | |
| Formed by | Subduction zonevolcanism |
| Rock age | Holocene-Pleistocene |
| Mountain type | Stratovolcano |
| Volcanic arc | Aleutian Arc |
| Last eruption | August 1989 |
Mount Gareloi, orGareloi Volcano, is astratovolcano in theAleutian Islands ofAlaska, United States, about 1,259 miles (2,026 km) fromAnchorage. Gareloi is located onGareloi Island, and comprises most of its land mass. The island also has two smallglaciers which protrude to the northwest and southeast.[2]
The volcano is 6 miles (10 km) by 5 miles (8 km) at its base, possessing two summits. The southern crater is far greater in size, 984 feet (300 m) wide withfumaroles, which can be attributed to edifice failure in the southern wall, while Gareloi's northern crater is enclosed.
Vitus Bering had been a prominent sailor in Russia. After successful expeditions in 1725, 1728, and 1730, Bering was sent to explore what is now theBering Sea area of the Pacific in 1740. He soon settled onKamchatka, where he started a settlement and built two additional vessels, dubbedSt. Peter andSt. Paul. In 1741 Bering and his company started towards North America, but were stalled by a storm and in being delayed 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, along the way charting several of the Aleutians, including Gareloi.[3] Since then, it has been barely studied, resulting in a fragmentary knowledge of its eruptions and possibly even unrecorded episodes.[4]
Gareloi Island is uninhabited and is part of the Alaska Maritime National Wildlife Refuge managed by the U.S. Fish and Wildlife Service.[5]
Gareloi is the northernmost volcano of theDelarof Group, a subgroup of the Aleutian Islands. It is composed of two craters, the older of which is covered bylava 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,[6] containsfumarolic activity.[7] Afissure created by Gareloi's 1929 eruption runs along the southern summit of the volcano.[8] Steepsea cliffs on the southwest side of the island cut into the oldercaldera. Three masses offshore of the island were produced by debris flows from the volcano.[8]
Gareloi is of lava flows andpyroclastic origin. Two main episodes contributed to its creation. Lava deposits on the mountain vary from 3 feet (1 m) to 20 feet (6 m) in thickness. Some of them extend from externalvents on the volcano, suggesting that activity during thePleistocene took place.[7]
There are two large lava valleys on the island's southwest side which are u-shaped. The oldest of these flows are of Pleistocene age composed ofbasaltictrachyandesite andbasaltic andesite, with smaller amounts ofplagioclase,clinopyroxene,olivine, andhornblende.[6]
The rock that makes up Gareloi Island and its volcano is estimated to be of Pleistocene age.[9] Several factors contribute to this inference, mainly the presence ofglaciers and edifice failure (landslide) debris. The rock, which comprisesdissected lava flows and pyroclastic masses, has been shaped by glacial retreat that began around 10,000 years past and fleshed out newly formed rocks. Other landslides have been generated on the north and east flanks of the volcano.[9]
TheAlaska Volcano Observatory proceeded to map the volcano and its surrounding area in 2003,[10] in addition to implementing seismic monitors in June.[11]
Gareloi has an extensive eruptive history, dating back to at least 1760. At least 12 eruptions have occurred at the summit, accompanied by lava andpyroclastic flows. Typically they have been characterized by a central vent eruption followed by anexplosive eruption, and sometimes aphreatic explosion.[8] All have been ofVolcanic Explosivity Index (VEI) of 1 to 3.[12] 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]
In 1929, Mount Gareloi underwent a majorexplosive eruption where it generated four lava flows,andesitictuff,volcanic glass, andscoria of red tone. Thirteen craters, all located in the fissure, contributed to this episode. All are most likelyphreatic.[7] During the eruption,pyroclastic flows convened withtephra, as suggested by deposits.Lahar also streamed from the summit.
On August 8, 1980 Gareloi erupted for the first time in records since 1929, sending ash plumes over 35,000 feet (10,668 m) into the atmosphere.Precursor earthquakes occurred on August 8 and 9, both west of theAdak seismic network.[13] A similar episode took place in 1982 when an ash cloud exceeding 23,000 feet (7,010 m) appeared onsatellite images on January 15.[13] 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 1,312 feet (400 m) down the volcano. Steam reportedly emanated from the volcano, but volcanologists were unable to verify an eruption.[13] In 1989 an employee of theUS Fish and Wildlife Service spotted another ash plume covering the caldera and climbing 2,300 feet (701 m) from the summit on August 17.[9] A minor eruption occurred on September 27, 1996 was reported to the National Weather Service Aviation Weather Unit in nearby Anchorage. The plume, consisting ofash and steam, rose 5,000 feet (1,524 m) from the volcano's summit.[9]
Proximal volcanic hazards pose a significant threat to human life near Gareloi. If Gareloi were to erupt unexpectedly, ash clouds, falling volcanic ash, pyroclastic flows, and debris avalanches (such as lahars) could easily spawn deadly hazards such as tsunamis. As volcanic ash can induce engine failure, it puts commercial airplanes in particular at high risk.[14] Inhalation of volcanic ash, also known astephra, creates respiratory complexities and irritation of the eye.[15]
Pyroclastic flows from an eruption would destroy much wildlife about the volcano. Gareloi has historically produced several pyroclastic flows, which can travel extremely fast. Future flows at Mount Gareloi could travel off the island into thePacific Ocean and, if large enough, could fall into the ocean and generate tsunamis, though unlikely.[15]
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