Mount St. Helens: One Tunnel Between a Lake and 50,000 People

When the north side of Mount St. Helens collapsed on May 18, 1980, the largest landslide in recorded history slammed into Spirit Lake, raised its surface by about 200 feet and buried its outlet. The lake was left with no way out. The dam that holds it back today is the avalanche itself, and since May 6, 1985, the lake has drained through a single tunnel bored through Harry's Ridge. This is the story of that lake: the 1982 state of emergency and the pumps on a barge, the Mole and the soft clay zones nicknamed Julie and Kathy L., the winter of 1997 when the gauge reached the maximum safe level of 3,460 feet, what the U.S. Geological Survey's 1983 model says a breakout would do to Castle Rock, Kelso and Longview, and the second tunnel in the Forest Service's 2026 draft decision that still needs money from Congress. Chapters: 0:00 The line 1:06 Strange facts 2:05 A closed basin 3:35 The water budget 4:41 A date for the crest 6:16 Pumps, then the Mole 9:22 Closed for repairs 12:33 If it goes 15:41 Built in a hurry 18:07 The lake today Main sources: Swift & Kresch, Mudflow hazards along the Toutle and Cowlitz Rivers from a hypothetical failure of Spirit Lake blockage (USGS 1983), Kresch & Laenen (USGS 1984), Meyer & Carpenter, Filling of Spirit Lake (USGS 1983), Grant, Major & Lewis (USDA Forest Service PNW Research Station and USGS 2017), National Academies of Sciences, Engineering, and Medicine, A Decision Framework for Managing the Spirit Lake and Toutle River System (2018), George & Cannon (USGS 2025), U.S. Army Corps of Engineers Portland District archives, USDA Forest Service, Spirit Lake Outflow Safety Improvement Project (2024 to 2026), USGS gauge 14240304 (NWIS). Image credits (Wikimedia Commons unless noted; some images cropped): CC BY 4.0 (https://creativecommons.org/licenses/... Larry D. Moore CC BY-SA 3.0 (https://creativecommons.org/licenses/... Grossbildjaeger, TedQuackenbush, Dirtsc, Stephan Schulz CC BY-SA 4.0 (https://creativecommons.org/licenses/... Tequask, Dirtsc Data and diagrams: Wikipedia: Toutle River (coordinates) (https://en.wikipedia.org/wiki/Toutle_...) Wikipedia: Cowlitz River (coordinates) (https://en.wikipedia.org/wiki/Cowlitz...) Wikipedia: Columbia River (coordinates) (https://en.wikipedia.org/wiki/Columbi...) Wikipedia: Mount St. Helens, Washington (coordinates) (https://en.wikipedia.org/wiki/Mount_S...) Relief: own hillshade from Mapzen Terrain Tiles on AWS Open Data. ArcticDEM terrain data DEM(s) were created from DigitalGlobe, Inc., imagery and funded under National Science Foundation awards 1043681, 1559691, and 1542736; Australia terrain data © Commonwealth of Australia (Geoscience Australia) 2017 (CC BY); Austria terrain data © offene Daten Österreichs – Digitales Geländemodell (DGM) Österreich (CC BY); Canada terrain data contains information licensed under the Open Government Licence – Canada; Europe terrain data produced using Copernicus data and information funded by the European Union - EU-DEM layers; Global ETOPO1 terrain data U.S. National Oceanic and Atmospheric Administration; Mexico terrain data source: INEGI, Continental relief, 2016; New Zealand terrain data Copyright 2011 Crown copyright (c) Land Information New Zealand and the New Zealand Government (CC BY); Norway terrain data © Kartverket (CC BY); United Kingdom terrain data © Environment Agency copyright and/or database right 2015 (Open Government Licence v3); United States 3DEP (formerly NED) and global GMTED2010 and SRTM terrain data courtesy of the U.S. Geological Survey (https://github.com/tilezen/joerd/blob...) #MountStHelens #SpiritLake #History