Mount Iliamna: a large landslide in Alaska on 20th June 2019

A very large landslide occurred on the flanks of Mount Iliamna, a volcano located in Alaska, on 20th June 2019.  The landslide has been described by the Alaska Volcano Observatory, who have posted a number of images of the aftermath.  The best of these was taken by Loren Prosser on the day after the landslide:-

The large landslide on the flanks of Mount Iliamna on 21st June 2019. Image by Loren Prosser, posted by the Alaska Volcano Observatory.

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The caption for the image is as follows:

Photo of Red Glacier avalanche that occurred on 6/21 ~00:05 UTC (6/20 ~4:05 pm AK). Description from the photographer: “attached pics from a fly by this past Friday evening. The slide appeared a few days old at that point, and seemed to originate near the summit. The slide & debris are visible from across the inlet now as well. Debris field approx 2+ miles wide & the toe. Pretty impressive slide altogether!”

The landslide has been captured by a Sentinel 2 satellite image that is available via the Sentinel Hub:-

A Sentinel 2 image, collected on 25th June 2019, showing the Mount Iliamna landslide. Image via Sentinel Hub Playground.

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The landslide appears to be in the order of about 6 km in length, and over 2 km wide at the toe.  This image, also via the Alaska Volcano Observatory, and taken by Dennis Anderson on 22nd June 2019, gives a better impression of the scale of the event:-

The Mount Iliamna landslide. Image collected by Dennis Anderson and posted online by the Alaska Volcano Observatory.

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The caption for this image states:

Rockslide on Iliamna volcano on 6/21/2019. This image was taken around 11:00 am on 6/22/2019 by Dennis Anderson from Diamond Ridge NW of Homer using a tablet at the eyepiece of some 11×80 binoculars with a 4.5 degree field of view. This might have occurred sometime in the past 12-48 hours as Illiamna was obscured by clouds most of yesterday.

The trigger of this landslide is not clear, but Alaska has experienced a series of very large landslides (often in the early part of the summer) in recent years, including Juneau, Icy Bay / Tyndall Glacier, Glacier Bay / Lamplugh, and Sitka.  There is good evidence that this is associated with climate change.