LONG VALLEY: The Supervolcano With a Ski Resort Built Inside Its Crater

At the top of the gondola the view is a postcard: a white bowl twenty miles wide, a town glittering on the floor of it, a sunset burning along the far ridge. That ridge is the wall of a crater. The town is standing on the floor that fell into it. And in 1980, that floor started rising again. Long Valley erupted once with a force that dropped a slab of California more than a mile and carried ash as far as present-day Nebraska. The textbooks called it ancient, and ancient meant finished. Then the ground lifted more than two and a half feet. Four magnitude-six earthquakes hit in forty-eight hours under a ski town. A forest died standing in soil that was ninety percent carbon dioxide. A hole melted itself under the snowpack beside Lift 3, and killed three ski patrollers who went to fix a fence. So what is under the snow? Why was an evacuation road renamed before it opened? Why did a two-mile hole drilled into the rising dome find no magma where the instruments said it had to be? And how old are the black glass cones running north out of the crater? This is the story of a working supervolcano with a ski resort inside it, and of what it cost to learn that the resort is not built next to the hazard. It is the instrument that measures it. Timestamps: 00:00 The Crater Beneath the Snow 00:38 The Supereruption That Built Long Valley 02:31 A Town Inside the Caldera 05:21 The 1980 Earthquake Swarm 07:03 Skiing on a Collapsed Volcano 09:58 Hot Springs and Geothermal Power 11:37 Black Glass Cones and Recent Eruptions 12:30 The Ground Begins to Rise 15:29 The Hazard Notice and the Town's Backlash 17:40 The Evacuation Road With a Scenic Name 20:07 Earthquakes Move Under the Ski Mountain 21:18 Dead Trees and Carbon Dioxide Gas 24:31 The Lift 3 Tragedy 27:48 Eruptions Only Centuries Ago 30:40 Hot Creek Turns Into a Vent 32:30 Drilling Into the Resurgent Dome 36:21 Imaging the Magma Reservoir 40:22 The Resort as a Volcano Observatory 43:27 One of America's Highest-Risk Volcanoes 45:19 No Clock in the Ground Principal sources: Bailey, R.A., Dalrymple, G.B., Lanphere, M.A. Volcanism, Structure, and Geochronology of Long Valley Caldera. Journal of Geophysical Research, 1976 — the caldera, its collapse structure and the age of the eruption. Hildreth, W. Volcanological Perspectives on Long Valley, Mammoth Mountain, and Mono Craters. Journal of Volcanology and Geothermal Research, 2004 — erupted volumes, and the case that these are contiguous but separate systems. Hill, D.P. Unrest in Long Valley Caldera, California, 1978-2004. Geological Society, London, Special Publications, 2006 — uplift of the resurgent dome, the swarms, and the hazard response. Farrar, C.D., Sorey, M.L., Evans, W.C., et al. Forest-Killing Diffuse CO2 Emission at Mammoth Mountain. Nature, 1995 — the tree kill, the soil gas measurements and the magmatic origin of the gas. Cantrell, L., Young, M. Fatal Fall Into a Volcanic Fumarole. Wilderness and Environmental Medicine, 2009 — the account of the April 2006 deaths in the snow-covered vent. Sieh, K., Bursik, M. Most Recent Eruption of the Mono Craters. Journal of Geophysical Research, 1986 — dating that places the last Mono eruption in the fourteenth century. Farrar, C.D., Evans, W.C., Venezky, D.Y., et al. Boiling Water at Hot Creek. USGS Fact Sheet 2007-3045 — the 2006 temperature surge, the geysering and the closure. Finger, J.T., Jacobson, R.D. Long Valley Exploratory Well: Summary. Sandia National Laboratories, 1999 — the drilling record and the temperature log that found no shallow magma. Biondi, E., Zhu, W., Li, J., et al. An Upper-Crust Lid Over the Long Valley Magma Chamber. Science Advances, 2023 — fiber-optic imaging of the reservoir depth and its crystalline lid. Ewert, J.W., Diefenbach, A.K., Ramsey, D.W. 2018 Update to the National Volcanic Threat Assessment. USGS Scientific Investigations Report 2018-5140 — the ranking that places Long Valley in the very high threat category.