25 May 2023
The 14 May 2023 debris flow at Johnston Ridge Observatory Access Road, Mount Saint Helens
Guest post by loyal reader Funkenbeachin
On the evening of 14 May 2023, rapid snowmelt in response to unusually warm weather contributed to the occurrence of a large debris slide [46.2807, -122.1906] and debris flow that damaged the access road, State Route 504 [46.2822, -122.1952], to the Johnston Ridge Observatory at Mount Saint Helens in Washington, USA. Twelve people and a dog were evacuated by helicopter the following day.
King 5 Seattle television provided helicopter views of the debris slide and damage in the channel of South Coldwater Creek, tributary to the Toutle River: https://www.youtube.com/watch?v=aSX1Z1KBN54
The author has put together a video of the topography of the site using Lidar and aerial imagery, which also includes meteorological data at the end: https://youtu.be/uRPwXvy-uOI
The debris-slide overlies the Spirit Lake Outlet Tunnel, designed to control overflow of Spirit Lake. The 12 meter diameter tunnel was drilled from the SR-504 bridge crossing [46.2822, -122.1952] to a 12 meter deep shaft on the shore of the lake [46.276447, -122.162624].
There is a gallery of images of the landslide, which includes the source area, on the WSDOT Flickr page:-
Whilst this image shows the damage to the road:
Grant, G., Major, J., Lewis, S., 2017, The Geologic, Geomorphic, and Hydrologic Context Underlying Options for Long-Term Management of the Spirit Lake Outlet Near Mount St. Helens, Washington. Pacific Northwest Research Station General Technical Report, PNW-GTR-954. https://www.fs.usda.gov/pnw/pubs/pnw_gtr954.pdf
Watts, A., 2019, The Spirit Lake dilemma: Engineering a solution for a lake with a problematic outlet. Science Findings, Issue 218, Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station.
Many thanks to Ken for pulling this together at a very busy time for me, and to others for contacting me about it.