Lava and ice interaction at stratovolcanoes: Use of characteristic features to determine past glacial extents and future volcanic hazards

Abstract

Structures resulting from lava and ice interaction are common at glaciated stratovolcanoes. During summit eruptions at stratovolcanoes, meltwater is produced and travels freely down steep slopes and thin permeable valley glaciers, eroding the ice and enlarging preexisting glacial drainages. As a result, eruptions in this environment have produced few catastrophic floods. Lava flowing into the open channels and voids in the glaciers becomes confined and grows thicker, filling the available space and producing steep‐sided bodies with smooth, bulbous contact surfaces. Quenching of lava against ice or by water forms small‐scale features such as tensional fractures and glass. As the amount of meltwater in contact with the lava increases, the type and abundance of smaller‐scale features become similar to those produced during subglacial eruptions into meltwater lakes. Identification of large‐ and small‐scale lava‐ice contact features in the field can be used to reconstruct paleoglacial extent and, combined with geochronology of lavas, to determine past paleoclimate. An understanding of lava‐ice interaction allows us to better assess the hazards posed by future eruptions at glaciated volcanoes.