MASS FLOWS ASSOCIATED WITH VOLCANO-ICE INTERACTION: PRODUCTION AND DEPOSIT IDENTIFICATION

Studies of recent eruptions at glaciated volcanoes have highlighted that there are a large variety of possible volcano-ice interactions. These interactions produce different types of mass flows including: 1) volcanic mixed avalanches and 2) ice diamicts that are both unique to volcano-ice interaction; 3) debris flows and 4) floods that can be produced by both volcanic and non-volcanic processes. Properly identifying and/or determining the formation mechanisms for these mass flow types, where no observations are available, can be challenging and after long periods of time, impossible. As a result, it is difficult to determine the past frequency of specific types of volcano-ice interactions.

I propose to distinguish these different types of mass flows associated with volcano-ice interaction using a triangular plot of the ratios of rock, snow/ice and water. The ratios of these end members allow us to evaluate flow mechanisms and to track transitions between mass flow types. Variations in mass flow type may result from high versus low rock temperatures. Hot (high temperature) rocks can cause further melting of snow/ice, generating more water and causing transitions to more water-rich flow types. Cold rock and/or snow/ice can either be incorporated into flows through near vent explosions or through scouring of the glacial surface. Melt water is produced by in situ melting of snow/ice associated with high heat flow near vent or during the flow by interaction with hot rock.

Deposits from these mass flows preserve limited evidence of volcano-ice interaction, including the presence of ice blocks, snow clumps or clasts of frozen sediments. As the ice and snow melt, depressions are left behind, such as kettles associated with jokulhlaups. Other types of evidence include mounds of rocks that melt out of frozen blocks and extend above the surrounding deposits. It is also sometimes possible to infer volcano-ice interaction by mapping gradations from clearly volcanic deposits (i.e., pyroclastic flow deposits) into mass flow deposits when the relationships between the deposits have not been modified by subsequent flows. Due to the ephemeral nature of evidence of volcano-ice interaction in mass flow deposits, it is critical to conduct studies as soon after an eruption as safe and practical.