Ongoing genesis of a novel glaciovolcanic cave system in the crater of Mount St. Helens, Washington, USA

Linda Sobolewski, Christian Stenner, Charlotte HĂĽser, Tobias Berghaus, Eduardo Cartaya, and Andreas Pflitsch


Mount St. Helens, one of the highest-risk volcanoes in the Cascade Volcanic Arc, hosts a novel system of glaciovolcanic caves that has formed around the 2004?2008 lava dome. From 2014 to 2021 a multidisciplinary research team systematically explored and mapped these new caves to ascertain their characteristics. Air and fumarole temperatures, volume flow rates, and wind regimes were also monitored. More than 3.0 km of cave passages have formed in a semicircular pattern in the volcanic crater and provide an opportunity to (1) observe cave development over time, (2) identify low temperature fumaroles as the main driving force for cave formation, (3) verify the impact of seasonal snow accumulation on cave climate, and (4) assess heat distribution in subglacial and subaerial portions of the new lava dome. Glaciovolcanic cave systems on Mount St. Helens are comparatively young (<10 years) and the most dynamic in the Pacific Northwest. Observed cave expansion during the study suggests ongoing genesis and future formation of interconnected systems. However, further expansion may also be limited by increasing fumarole temperatures towards the upper parts of the lava dome, cave instability due to snow overload, or variable subglacial volcanic heat output. New glaciovolcanic cave system development provides a unique barometer of volcanic activity on glacier-mantled volcanoes and to study the subglacial environment. We present the results of eight years of initial study within this dynamic cave system, and discuss a pathway towards future longitudinal analyses.


Mount St. Helens, a volcano known for its high risk of eruption, has a unique system of caves formed by the interaction of lava and ice around the lava dome that was created between 2004 and 2008. A team of researchers from different fields explored and mapped these caves from 2014 to 2021 to learn more about them. They measured things like air and fumarole (gas vent) temperatures, how fast the air was moving, and wind patterns. They discovered more than 3.0 kilometers (almost 2 miles) of cave passages that have formed in a half-circle pattern in the volcanic crater. Studying these caves gives the scientists the chance to watch how caves develop over time, figure out that low temperature fumaroles are the main cause of these cave formations, see how seasonal snow buildup affects the cave's climate, and understand how heat is spread in the parts of the new lava dome under the glacier and in the open air. The cave systems on Mount St. Helens are quite young (less than 10 years old) and are the most changeable in the Pacific Northwest. The team observed the caves expanding during the study, suggesting that they will keep growing and forming connections. But, the growth could also be limited by increasing fumarole temperatures towards the top of the lava dome, instability caused by heavy snow, or changes in volcanic heat under the glacier. The development of these new cave systems gives us a unique way to measure volcanic activity on volcanoes covered by glaciers and study the environment under the glacier. The researchers share the results of their initial eight-year study and discuss plans for future in-depth analyses.