Ukinrek Maars
The ukinrek Maare
Eruption of the eastern ukinrek - maar in 1977
The ukinrek - maars are a pair of maars in Becharof National Wildlife Refuge, Alaska, Aleutian Island chain on the Alaska Peninsula. They were formed by phreatomagmatic explosions.
Description
The maars are at a low, less than a hundred meters high and 4 km long ridge that rises over the Bering Sea to the adjacent lowlands. The maars are located approximately 1.5 km south of the Becharof Lake and 12 km north-west of Mount Peulik volcano.
Both maars are filled with water. The western, older Maar ( Maar West ) was formed at the northwest end of the country back. It has an elliptical outline and is 105 × 170 m tall at a depth of 35 m. The younger Maar ( Maar East ) is located 600 m to the east and slightly deeper. It is round in shape, 300 meters tall and about 70 m deep. In its center a lava dome has formed, the approximately 49 m high rises of the lake floor.
Formation
The maars were formed during a ten- day-long eruption period in 1977. The resulted Tuff subjects ( base surges ) have been ejected mainly to the northwest. The extracted material had a volume of about 2.6 × 107 m3, it was of olivine basaltic composition.
The eruption began on 30 March 1977. Apparently rising magma met on ground water, which was contained in a lying between impermeable glacial deposits Tuffschicht. The western Maar was formed as the first under the explosive discharge of steam and volcanic ash that rose up to 6500 m altitude. After a few days the activity of the Eastern Maar moved into a new crater. For a few days violent explosions generated an ash cloud up to 4000 m altitude, it came to Base Surges and the ejection of boulders that flew up to 600 m wide. The ejected ash was observed to the north still 160 km away as a light rain of ash. Towards the end of the eruption lava fountains were visible in the East Maar and a lava dome formed. On April 10, 1977 witnessed only by the lava dome rising steam from the eruption, while the Maarkessel filled with water.
Surroundings
The volcanic activity in 2500 km long Aleutenbogen goes back to the subduction of the Pacific plate under the North American plate at about 7000 m deep Aleutengraben. The western part up to 165 ° W width is a classic island arc, while the eastern part is influenced by the continental margin of the North American plate. Since 1700 more than 40 volcanoes were active in this area.
The location of the ukinrek Maare is probably bound to the intersection between a local disturbance ( Bruin Bay Fault) and other regional structures. Before the eruption, no volcanic structures in this area were known. The next volcanic field are the lava domes of gas Rocks on the shore of Lake Becharof about three kilometers north of the ukinrek Maare, the dazitischer about 2900 years before rock composition promoted.