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No high-altitude ash from latest Bogoslof eruption, scientists say

  • Author: Chris Klint
  • Updated: December 2, 2017
  • Published February 13, 2017

The Alaska Volcano Observatory has reduced warning levels for Bogoslof volcano in the Aleutian Islands, after an eruption early Monday failed to produce an anticipated high-level ash cloud.

The volcano, about 60 miles west of Unalaska, erupted at 7:24 a.m., according to seismic data tracked by the observatory. It was raised first to an aviation color code of orange and a warning level of watch, then to red and warning – AVO's highest levels of eruptive status – shortly before 8 a.m.

Features and deposits on Bogoslof Island after the eruptive events of January 30-31, 2017. Shallow groundwater flow through the new volcanic deposits from the sea toward the center depression has resulted in the formation of concentric headscarps and channels. This process, called sapping, is common in areas of concentrated groundwater discharge where it undermines slopes and leads to headward erosion and the formation of arcuate headscarps. Rubbly appearing rock debris scattered over parts of the island was likely generated by near surface explosions of a still submarine lava plug, showering the island with blocks and bombs of rock debris. Some of these rock fragments are up to 2.5 m in length. The mound of tephra on the southern part of the island is a tuff cone, and the level area making up the northern half of the island is a tuff ring. These are characteristic landforms of shallow submarine eruptions. The Bogoslof Island landscape is susceptible to rapid erosion, primarily by ocean waves, and erosion of the surficial volcanic deposits will be ongoing and changes in the configuration of the island are likely. ©2017 Digital Globe NextView License. (Chris Waythomas via U.S. Geological Survey / Alaska Volcano Observatory)

In a 10 a.m. update lowering alert levels back to orange and watch, the observatory said no volcanic cloud was visible above clouds at an altitude of 10,000 feet in the region.

Since mid-December, eruptions at Bogoslof have sporadically disrupted aviation across much of Southwest Alaska. Most ashfall from those blasts has been blown over water, but eastward winds pushed ash over Unalaska following an eruption in late January.

Cheryl Searcy, a geologist at the observatory, said any ashfall in Unalaska from Bogoslof's eruption Monday was "unlikely," although the cloud layer prevented AVO from directly observing Bogoslof in satellite imagery.

"The seismicity has currently returned to background, but how long it will stay there is unknown," Searcy said. "We did have a nice break there – for almost a week it was relatively quiet – but until we get a better look at it, we're not sure what is going on."

A marine weather statement had been issued for the area as a precautionary step, Searcy said.