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

Structures resulting from lava and ice interaction are common at glaciated stratovolcanoes. During summit eruptions at stratovolcanoes, meltwater is p roduced and travels freely down steep slopes and thin permeable valley glac iers, eroding the ice and enlarging preexisting glacial drainages. As a res ult, eruptions in this environment have produced few catastrophic floods. L ava flowing into the open channels and voids in the glaciers becomes confin ed and grows thicker, filling the available space and producing steep-sided bodies with smooth, bulbous contact surfaces. Quenching of lava against ic e or by water forms small-scale features such as tensional fractures and gl ass. As the amount of meltwater in contact with the lava increases, the typ e 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 recon struct paleoglacial extent and, combined with geochronology of lavas, to de termine past paleoclimate. An understanding of lava-ice interaction allows us to better assess the hazards posed by future eruptions at glaciated volc anoes.