Gareloi+Volcano

= = =Gareloi Volcano =

Summit of the volcano
 * Elevation** 5,161 ft. (1,573 m)


 * Location**
 * Location** Northern Pacific, part of Alaska
 * Range** Aleutian Islands


 * Geology**
 * Type** Stratovolcano
 * Age of rock** Holocene-Pleistocene
 * Volcanic ark/belt** Aleutian Ark
 * Last Eruption** 1996

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 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 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 fumarolic 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 feet (1 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 basaltic trachyandesite and basaltic andersite, while containing amounts of plagioclase, clinopyroxene, olivine, and hornblede.

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 glacires 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.

Process/Steps 1.



Articles

During some explosive eruptions, hot, dense, ground- hugging clouds of gas, ash, and rock flow rapidly from the vent. Called pyroclastic flows, these phenomena kill humans caught in their paths. Pyroclastic surges are fast-moving hot blasts of gas and particles that commonly precede and accompany pyroclastic flows. Flows and surges usually follow topography and travel down gullies and valleys surrounding the volcano. At Gareloi Volcano, deposits from pyroclastic flows and surges that crop out on most flanks of the volcano indicate eruptions have produced flows and surges in the past. Large explosive eruptions could send pyroclastic flows beyond the island’s coastline and as far as 5 km over the sea. These phenomena are primarily a proximal hazard but can commonly produce billowing co-ignimbrite ash clouds above the volcano that can drift tens of kilometers downwind.

An explosive eruption of Gareloi Volcano will inject large quantities of ash and gas into the atmosphere and form an ash cloud or eruption cloud. These clouds may rise to as many as 15,000 meters above sea level, can remain aloft for hours to days, and may drift hundreds to thousands of kilometers beyond the volcano with the prevailing wind. If wind direction varies with altitude, the ash cloud may spread in different directions. Ash clouds from Gareloi will most commonly move eastward, the prevailing wind direction. Eruption clouds are hazardous to aircraft that fly through them, because volcanic ash interferes with engine operation, damages electronics, and abrades exposed surfaces (Casadevall, 1994).

Historically, Gareloi eruptions have produced ash clouds that reached as high as 12,000 m ASL, and similar eruptions can be expected in the future. Satellite observations and ash-cloud trajectory modeling are the most effective tool for monitoring the clouds and mitigating hazard to aircraft and communities downwind. A phreatic eruption is an eruption that occurs when hot, hydrothermally heated ground water transforms to steam, becomes pressurized, and expands explosively at the surface. Phreatic eruptions can produce ash, though typically the ash clouds are smaller in volume and height reached compared to magmatic explosive eruptions. Given the hydrothermal activity and near-vent deposits at Gareloi, small phreatic eruptions may be common there.