Peter Cervelli, a geophysicist for the U.S. Geological Survey and the observatory, said it is hard to predict if or when an eruption will occur but "nothing is imminent."
According to the observatory's Web page, an explosive eruption could occur in the coming days to weeks. Volcanic activity could be ash plumes exceeding 33,000 feet above sea level, with lava flows, or it could be nothing.
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Even a small eruption can cause floods, debris and mud flows, so the area on remote Cape Douglas is considered hazardous, according to the observatory.
Fourpeaked Mountain is about 80 miles northwest of Kodiak and 220 miles southwest of Anchorage across Cook Inlet.
The observatory is installing seismometers around the mountain, a Web camera and instruments that measure how the ground is moving, Cervelli said. The mountain had not been monitored by instruments.
Observatory staff who flew over Fourpeaked over the weekend reported linear vents running north from the summit. Many were emitting steam and vapors.
Near the vents, a glacier was slumping and pieces had sloughed into the vents, Cervelli said.
Staff members detected sulfur dioxide, hydrogen sulfide and carbon dioxide coming from the vents. Volcanic gases could be smelled far away from the summit.
Ash emission Sept. 17, the abundant volcanic gases, the presence of new vents at the summit and the disruption and floods occurring at and below glaciers suggest new magma at shallow levels beneath the volcano, according to the observatory.
Fourpeaked Volcano is not known to have erupted in the last 10,000 years. However, geological investigations have been limited and ice covers much of the area, the observatory said.
The Alaska Volcano Observatory is a consortium that includes USGS, the University of Alaska Fairbanks Geophysical Institute and the state Division of Geological and Geophysical Surveys.