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The importance of snowmelt as a source of moisture for the crustose lichen Buellia frigida in the early austral summer was investigated at Cape Geology, Granite Harbour, southern Victoria Land (77 degrees 01’s, 162 degrees 32’E). Surface and air temperatures and irradiance were recorded on the surface of a slightly inclined granite boulder for 5 weeks. Observations were made of lichen thallus hydration during a 5-day period. The results confirmed the strong warming effect of high irradiance; the rock surface and hydrated lichen were up to 19K above air temperature and, overall, the rock surface averaged 5.5K warmer. Therefore water condensation on the rock surface (dew or hoarfrost) was not possible during that period. Thalli were moistened by meltwater from both a small area of snow pack and from occasional snowfalls. The distribution of lichen thalli on the rock surface can be explained by the frequency and duration of meltwater moistening. Despite the very high irradiance whilst moist, the lichens seem well adapted to the combination of hydration, low temperatures and strong light.