Ice-capped volcanoes of the Chilean Lake District have shown significant glacier retreat during recent decades, probably in response to tropospheric warming and precipitation decrease. Volcán Mocho-Choshuenco (39°55?S, 72°02W) is one of the main active volcanoes in this part of the country. A mass balance programme was initiated on its southeastern glacier in 2003, in view of its representative conditions as an ice body that is presumably not affected by current volcanic activity. The glaciers of this volcano have been retreating and shrinking in recent decades; by 2003 there had been a reduction of 40% of the original area of 28.4 km² in 1976. A maximum decrease of area was observed in the most recently analysed period, a rate of 0.45 km² year-1 between 1987 and 2003. The glacier average net mass balance of 2003/04 yielded –0.88 m w.e. (water equivalent) per year (±0.18), with an average net accumulation and ablation of 2.59 and –3.47 m w.e. per year, respectively. This is the first direct measurement of glacier mass balance in southern Chile, where very little is known about glacier variations and glacier–volcano interactions.

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