February 14th, 2010 Category: Mountains, Volcanoes

USA - February 4th, 2010

This orthorectified image shows the wide, circular Okmok Caldera, which truncates the top of a large shield volcano. The highest point on the caldera rim is  called Mount Okmok. Both are located in the northeastern part of Umnak Island in the eastern Aleutian Islands of Alaska, USA.

Although the last major eruptions of Okmok—with an estimated VEI strength of 6—occurred 8,300 and 2,400 years ago, on Saturday, July 12, 2008, Okmok Caldera exploded without warning, sending a plume of ash over 33,000 feet (10,000 m) into the air. No lava flow was reported, though the volcano has issued flows in the past.

Before then, the volcano had last erupteded in 1997 and produced a lava flow, once again erupting with no initial warnings. Residents of Fort Glenn, a nearby ranch, fled from falling ash and volcanic rock.

Tags: Alaska Aleutian Islands Mount Okmok Okmok Caldera Umnak Island USA Volcanoes | Comments |

July 18th, 2009 Category: Volcanoes

Alaska, USA - July 9th, 2009

Mount Okmok is the highest point on the rim of Okmok Caldera on the northeastern part of Umnak Island, in the eastern Aleutian Islands of Alaska, USA. Two other volcanoes, Mount Recheshnoi  and Mount Vsevido, are visible on the southwestern part of the island in this orthorectified image.

Mount Okmok’s 5.8 mile (9.3 km) wide circular caldera truncates the top of a large shield volcano. A crater lake once filled much of the caldera to a depth of over 500 ft, but the lake ultimately drained through a notch eroded in the northeast rim. Only a small remnant lake about 1000 ft across exists in a depression in the western area of the largely flat caldera floor.

The last major eruptions of Okmok—with an estimated VEI strength of 6—occurred 8,300 and 2,400 years Before Present. The volcano is currently rated by the Alaska Volcano Observatory as Aviation Alert Level Yellow and Volcanic-alert Level Advisory.

Tags: Alaska Aleutian Islands Mount Okmok Mount Recheshnoi Mount Vsevido Orthorectification Umnak Island USA | Comments |

December 9th, 2009 Category: Volcanoes

Alaska, USA - November 10th, 2009

Volcanoes with distinctive shapes can be observed on Umnak Island, one of the Aleutian Islands that are part of the state of Alaska, USA, in this orthorectified image. The northern end of the island is mostly occupied by the circular volcanic caldera of Mount Okmok.

The southern end of the island is home to the steep symmetrical cone of Mount Vsevidof  and the heavily eroded Mount Recheshnoi (right of the former).

Both Mount Vsevidof and Mount Recheshnoi are stratovolcanoes, while Mount Okmok is a shield volcano. The summit of Mount Vsevidof is the highest point on Umnak Island at 7051 ft (2149 m), while its neighbor Mount Recheshnoi is lower, due in part to erosion, with a maximum elevation of 6,509 feet (1984 m). Returning to the north end of the island, Mount Okmok itself, near the caldera rim, is much lower than its southern-end counterparts, with a height of 3,520 feet (1073 m).

Tags: Alaska Aleutian Islands ASAR Mount Okmok Mount Recheshnoi Mount Vsevidof Orthorectification Umnak Island USA | Comments |

November 3rd, 2009 Category: Volcanoes

Alaska, USA - October 22nd, 2009

The circular caldera of Mount Okmok occupies much of Umnak Island, one of Alaska’s Aleutian Islands in the USA.  The caldera is 5.8 mile (9.3 km) wide, cutting across the top of a large shield volcano.

The caldera rim can be observed in detail in this orthorectified image. Of particular interest are an eroded section through which the lake that once filled the caldera drained, visible around the 12 o’clock position, and Mount Okmok itself, the highest point of the volcano at over 3400 feet, visible around 10 o’clock.

Tags: Alaska Aleutian Islands ASAR Caldera Mount Okmok Orthorectification Umnak Island USA Volcanoes | Comments |