The 7 August 2024 Pedersen Lagoon landslide and tsunami

The Landslide Blog is written by Dave Petley, who is widely recognized as a world leader in the study and management of landslides.

At about 5 am local time on 7 August 2024, a large landslide occurred on the rock slopes above Pedersen Lagoon in Alaska, triggering a local tsunami. Whilst this major event is lower profile than one might have expected (I cannot find any news stories about it), the USGS has been quietly putting together a range of fantastic resources about the event. Rather than replicating them, I will simply sign post to them.

First, there is a very good gallery of image about the event, which includes this image by Jeff Pedersen of Alaska Wildland Adventures:-

The exposed rock surface shows a large part of the source area – this is an existing plane of weakness – and there is an element of wedge failure here.

Second, the USGS has put together a very nice page that summarises the dynamics of the landslide. It notes that the estimated initial volume was 2 million m³, occurring in a flysch unit. The tsunami that was generated had an initial height of 17 metres, although this reduced to about a metre along the lagoon. A large area was inundated, but there were no human casualties and little damage in this sparsely populated area.

The seismic data indicates that a seiche occurred.

The National Park Service also has a news item about the landslide.

Planet Labs has captured beautiful imagery of this site. The image below, from 19 August 2024, shows the aftermath of the landslide and the tsunami:-

And below is an image compare with one collected on 19 July, before the event:-

I have placed a marker at the approximate crown of the landslide, situated towards the northwest corner of the image. The initial track is towards the southwest, then curving to the southeast to enter the fjord. Note the extensive erosion of vegetation and soil along the flanks of the lagoon, particularly to the lower lying east end.

Of course this is just the latest in a series of large landslides in Alaska in recent years, underlying the dynamic nature of the landscape in this area. Landslide generally occurring in the spring and summer.

Reference

Planet Team (2024). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/.

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