Controls on andesitic glaciovolcanism at ice-capped volcanoes from field and experimental studies

Glaciovolcanic deposits at Tongariro and Ruapehu volcanoes, New Zealand, represent diverse styles of interaction between wet-based glaciers and andesitic lava. There are iceconfined lavas, and also hydroclastic breccia and subaqueous pyroclastic deposits that formed during effusive and explosive eruptions into meltwater beneath the glacier; they are rare among globally reported products of andesitic glaciovolcanism. The apparent lack of hydrovolcanically fragmented andesite at ice-capped volcanoes has been attributed to a lack of meltwater at the interaction sites because either the thermal characteristics of andesite limit meltwater production or meltwater drains out through leaky glaciers and down steep volcano slopes. We used published field evidence and novel, dynamic andesite-ice experiments to show that, in some cases, meltwater accumulates under glaciers on andesitic volcanoes and that meltwater production rates increase as andesite pushes against an ice wall. We concur with models for eruptions beneath ice sheets showing that the glacial conditions and preeruption edifice morphology are more important controls on the style of glaciovolcanism and its products than magma composition and the thermal properties of magmas. Glaciovolcanic products can be useful proxies for paleoenvironment, and the range of andesitic products and the hydrological environments in which andesite erupts are greater than hitherto appreciated.

Automated summary

Research shows that meltwater can accumulate under glaciers on andesitic volcanoes, leading to an increase in meltwater production rates as andesite pushes against an ice wall. The study also suggests that glacial conditions and preeruption edifice morphology are more influential in controlling the style of glaciovolcanism than magma composition and thermal properties. Glaciovolcanic products can serve as useful proxies for paleoenvironment, with a greater range of andesitic products and hydrological environments in which andesite erupts than previously appreciated.