Icy thermometers: how volcanic heat affects glacier mass balance

<p>&#160; With more than 30 million people living within 10 km of active or dormant volcanoes, eruptions are a natural socio-economic hazard that can have devastating consequences for society. Hence, the timely forecasting of volcanic unrest has real-world, and potentially, life and death implications. A major challenge is the identification and monitoring of precursors to forthcoming volcanic eruptions. The observation and measurement of thermal anomalies is one of the answer to this challenge, with some volcanoes exhibiting signs of thermal unrest over extensive areas of their edifice for several years prior to an eruptive event. Glaciers that sits on volcanoes are likely to respond to the increased heat and could therefore be used as complementary volcano thermometers but a large scale study is missing.&#160;</p> <p>Our study, which covers 600 Andean glaciers and 37 ice-clad volcanoes, demonstrate glacier mass balance sensitivity to volcanic heat. We distinguish between &#8216;volcanic-glaciers&#8217; (located &#8804;1 km from volcanic centres), and &#8216;proximal glaciers&#8217; (1-15 km) and calculate their equilibrium line altitude (ELA). In most instances, proximal glacier ELAs are lower than those of nearby volcanic-glaciers. In some cases, the ELA decrease proportionally with increasing glacier distance from the volcanic edifice, and a&#160;quantitative relationship between &#916;ELA_mean (i.e., the difference in mean ELA between the proximal and volcanic-glaciers) and ASTER-based measurements of volcanic thermal anomalies could be established. These results highlight the impact of volcanic heat on glacier mass balance; emphasise the need to exclude volcanic-glaciers from glacier-climate investigations; and demonstrate the first-order potential of glaciers as &#8216;volcanic thermometers&#8217;, with the &#916;ELA_mean representing a proxy for volcanic heat.</p>