THE DEVELOPMENT OF MOUNT ST. HELENS’ CRATER GLACIER AFTER THE 2004-2008 DOME BUILDING ERUPTION

The crater of Mount St. Helens hosts one of the last advancing glaciers in the world, representing a unique natural laboratory to study volcano-ice interactions. The recent eruption cycles of the volcano have been investigated to some extent, and particularly the effects of the 2004-2008 lava dome formation were closely studied. However, subsequent investigations of the growing glacier are largely lacking. Thus glacial volumes have only been measured at irregular intervals, and only insufficient data exist on rates of ice accumulation, ablation, melt, and movement. We suggest that glacial ice in the crater has a significant impact on the local hydrothermal system, on volcanic rock alteration, and hazards that can be linked to glaciovolcanism. Subglacial processes on Mount St. Helens are observable in its glaciovolcanic caves. Volcano-ice interactions in the crater of Mount St. Helens are concentrated in a semicircular pattern around the 2004-2008 lava dome. Here, the melting of glacial ice by geothermal heat flux is not in equilibrium with ice accumulation and seasonal climate. Repeated surveys from 2014 to 2021 reveal that the extent of glaciovolcanic caves is growing, and they thus represent a dynamic system. Moreover, their recent evolution accompanies the immense growth of the crater glacier in the last decade. Our study of glaciovolcanic caves from Mount St. Helens investigates the transformation of Crater Glacier after the 2004-2008 dome-building eruption and combine cave survey data with petrologic studies performed on tephra samples from the caves. In addition, we evaluated available LiDAR data and aerial photogrammetric results collected in 2021. By combining these approaches, we provide needed insight into the genesis of glaciovolcanic caves on glacier-mantled volcanic edifices. Our analysis reveals a dynamic glaciovolcanic cave system on Mount St. Helens where heat is transferred from steam rising from the lava dome growing caves in glacial and firn ice that rapidly take and change shape. Future studies of the thermodynamics, carbon flux, and hydrology of this unique system will build upon this foundational work.