Mount Okmok

Aerial view of the caldera Okmok

The Mount Okmok is the highest point of the rim of the Caldera Okmok on the northeastern part of Umnak in the eastern Aleutian Islands in Alaska.

The circular caldera with a diameter of 9.5 kilometers, is located on a large shield volcano with a diameter of 35 kilometers. A large, 150 meter deep crater filled once a 12,000 -year-old caldera, but was discharged by an eroded in the northeastern edge notch. Today there are only a small lake left behind with 300 meters in diameter, in the western part of the flat caldera floor. In the caldera there are hot springs and fumaroles. Numerous secondary cones and lava domes, one of which is the 1253 meter high Mount Tulik, located on the flanks of the mountain down to the coast.

The formation of the volcano began in late Tertiary or early Quaternary. Huge pyroclastic eruptions led to two overlapping calderas. The older was formed about 8200 years ago, the younger about 2400 years ago.

Between 1805 and 1988, 14 outbreaks were held. At the outbreak of 1817, the Aleutian village was destroyed by the Cape Tanak. On 12 July 2008, an explosive eruption that lasted about five weeks began. An eruption column reached 15 km altitude. A danger message was issued by the Alaska Volcano Observatory.