One fifth of Earth's volcanoes are covered by snow or ice and many have active geothermal systems that interact with the overlying ice. These glaciovolcanic interactions can melt voids into glaciers, and are subject to controls exerted by ice dynamics and geothermal heat output. Glaciovolcanic voids have been observed to form prior to volcanic eruptions, which raised concerns when such features were discovered within Job Glacier on Qw̓elqw̓elústen (Mount Meager Volcanic Complex), British Columbia, Canada. In this study we model the formation, evolution, and steady-state morphology of glaciovolcanic voids using analytical and numerical models. Analytical steady-state void geometries show cave height limited to one quarter of the ice thickness, while numerical model results suggest the void height h scales with ice thickness H and geothermal heat flux $\dot {Q}$ as $h/H = a H^b \dot {Q}^c$, with exponents b = −n/2 and c = 1/2 where n is the creep exponent. Applying this scaling to the glaciovolcanic voids within Job Glacier suggests the potential for total geothermal heat flux in excess of 10 MW. Our results show that relative changes in ice thickness are more influential in glaciovolcanic void formation and evolution than relative changes in geothermal heat flux.

Accurate quantification of rates of glacier mass loss is critical for managing water resources and for assessing hazards at ice-clad volcanoes, especially in arid regions like southern Peru. In these regions, glacier and snow melt are crucial dry season water resources. In order to verify previously reported rates of ice area decline at Nevado Coropuna in Peru, which are anomalously rapid for tropical glaciers, we measured changes in ice cap area using 259 Landsat images acquired from 1980 to 2014. We find that Coropuna Ice Cap is presently the most extensive ice mass in the tropics, with an area of 44.1 km2, and has been shrinking at an average area loss rate of 0.409 km2 a−1 (~0.71% a−1) since 1980. Our estimated rate of change is considerably lower than previous studies (1.4 km2 a−1 or ~2.43% a−1), but is consistent with other tropical regions, such as the Cordillera Blanca located ~850 km to the NW (~0.68% a−1). Thus, if glacier recession continues at its present rate, our results suggest that Coropuna Ice Cap will likely continue to contribute to water supply for agricultural and domestic uses until ~2120, which is nearly 100 years longer than previously predicted.

Supraglacial deposits are known for their influence on glacier ablation. The magnitude of this influence depends on the thickness and the type of the deposited material. The effects of thin layers of atmospheric black carbon and of thick moraine debris have been intensively studied. Studies related to regional-scale deposits of volcanic tephra with thicknesses varying between millimetres and metres and thus over several orders of magnitude are scarce. We present results of a field experiment in which we investigated the influence of supraglacial deposits of tephra from Grímsvötn volcano on bare-ice ablation at Svínafelsjökull, Iceland. We observed that the effective thickness at which ablation is maximized ranges from 1.0 to 2.0 mm. At ~10 mm a critical thickness is reached where sub-tephra ablation equals bare-ice ablation. We calibrated two empirical ablation models and a semi-physics-based ablation model that all account for varying tephra-layer thicknesses. A comparison of the three models indicates that for tephra deposits in the lower-millimetre scale the temperature/radiation-index model performs best, but that a semi-physics-based approach could be expected to yield superior results for tephra deposits of the order of decimetres.