The evolving volcano-ice interactions of Crater Glacier, Mount St. Helens, Washington (USA)

Interactions between volcanoes and glaciers provide insight to the evolution of a volcanic edifice and may be an indicator for renewed volcanic activity. At Mount St. Helens, Crater Glacier, which has formed in the volcanic crater after the eruption in 1980, is one of the world’s last expanding glaciers and provides a unique opportunity to characterize the evolution of a glacier expanding onto an area of significant thermal flux. We combine photographic documentation and glaciovolcanic cave surveys with remote sensing data from Google Earth, UAS, and LiDAR to analyze the present state of Crater Glacier and reconstruct its development since the emplacement of the 2004–2008 lava dome. Our results show that snow accumulation has caused Crater Glacier to grow from 2009 to 2019 by approximately 13.8 × 10 6 m 3 , during which time the glacier toe advanced by several hundred meters. The glacier-dome interface shift toward higher elevations against the 2004–2008 lava dome and subsequent encroachment onto thermally active areas led to glacier modification via extensive subglacial cave system formation. Analysis of subglacial tephra layers revealed the existence of juvenile material from the 2004–2008 eruption cycle, providing insights about glacier subsidence of ~ 40 m since 2004/2005 in spite of net growth. Although the lava dome is cooling, the glacier-dome interface seems to have become increasingly stable in the past few years. Our results suggest that glacier development in the accumulation area adjacent to the dome is now being affected by the thermal characteristics of the lava dome itself, making monitoring internal glacier development via tracking glaciovolcanic cave expansion a potentially important volcano monitoring tool.