Friday, May 11, 2012

Alaska's Mt Iliamna Flexes But Doesn't Blow

Alaska's Mount Iliamna, which I earlier reported to be experiencing dike intrusion, has begun to subside in terms of its heightened seismicity. According to AVO, "Seismic activity at Iliamna Volcano remains slightly above background, and the rate of seismic activity has declined over recent weeks. Nothing unusual was observed in web camera and cloudy satellite images over the past 24 hours.The current activity at Iliamna does not indicate an imminent or certain eruption. A similar seismic swarm at Iliamna in 1996-1997 was not followed by eruptive activity. Prior to an eruption, AVO would expect to see a further increase in earthquake activity."

Iliamna has not erupted since monitoring began, but is suspected to have erupted in the Holocene. Due to active glaciation in the region, some volcanoes and mountains in the area display morphologies that make them look far older than they actually are. Iliamna has active fumeroles on the SE face near the summit that have been shown to be much more active after the previous swarm of earthquakes a few months back.

The diminishing seismicity can mean several things, but in this case it most likely means that the dike intrusion has slowed or ceased, and most likely has begun the slow process of cooling.

It seems, much like the 1996-1997 dike intrusion, this will most likely not result in an eruption. Due to the depth of the magma intrusion (from under a kilometer, to over 7km in depth) and the massive amounts of ice on the volcano, the magma will most likely degas and cool. This does not mean activity can't resume at any time however, as the area could easily experience another injection of magma at any time.

It is my guess that the above statement from AVO means they will probably lower the alert level for the volcano in the next couple of weeks, but continue to keep an eye on the simmering mountain. If new magma intrusion occurs now, it could trigger uplift and possible slope failure, compounded by a possible eruption. There are no GPS monitoring devices on Iliamna, however there is a network of seismic sensors all around it. Uplift is only measured by the occasional satellite job.

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