jeudi, janv. 01, 1970
L'AVO a élevé le niveau de danger pour le code couleur jaune, en raison de la sismicité accrue. Une éruption dans un proche avenir est possible. [details]
jeudi, août 21, 2008
AVO reported that on 13 August low-level steam-and-ash plumes from Okmok were visible on satellite imagery drifting SE at altitudes of 3-4.6 km (10,000-15,000 ft) a.s.l. During 14-17 August satellite observations were hindered due to cloud cover; seismic levels fluctuated possibly indicating that steam-and-ash emissions continued. During 18-19 August, ash plumes were seen on satellite imagery at altitudes of 3-4.6 km (5,000-15,000 ft) a.s.l. The Volcano Alert Level remained at Watch and the Aviation Color Code at Orange. [details]
Okmok volcanOkmok is one of the most active volcanoes in the Aleutian island chain (Alaska). It consists of a complex of shields truncated by a caldera and several active vents inside the caldera, which have built small cones and lava flows.
Introduction:Okmok's caldera was formed by at least two collapses following catastrophic pyroclastic eruptions, at around 8200 y B.P. and 2400 y. B.P.
Within the caldera, the oldest volcanic deposits are brecciated pillow lavas and pyroclastic rocks once deposited in a caldera lake. The lake attained a maximum depth of about 150 m and the upper surface reached an elevation of about 475 m, at which point it overtopped the low point of the caldera rim. A small shallow lake near the outlet of the caldera is all that remains today. Three dissected tuff cones may have been produced by eruptions beneath the former caldera lake. Other cinder cones occur atop pillow lavas; such cones apparently breached the surface of the former lake. Cinder cones and associated lava flows that are younger than the caldera lake are identified by structures and textures characteristic of subaerial eruption. The documented eruption of 1945 occurred at a cinder cone near the southwest caldera wall; this cone may have been the site of all historical activity of Okmok volcano. Hot springs and fumaroles occur both within Okmok caldera and at Hot Springs cove, 20 km to the southwest.
Source: abbreviated from AVO (http://www.avo.alaska.edu/volcanoes/volcinfo.php?volcname=Okmok)
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