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Scientifically valuable information can be learned by listening to the tiny vibrations emanating from a glacier with seismometers. However, this approach has never been employed to better understand glaciers protected from heat by a debris mantle, despite being common in the Himalayas, one of the most glacierized regions in the world. Here we installed a seismic network at a series of challenging high-altitude sites on a glacier in Nepal. Our results show that the diurnal air temperature modulates the glacial seismic noise. The exposed surface of the glacier experiences thermal contraction when the glacier cools, whereas the areas that are insulated with thick debris do not suffer such thermal stress. Thus, the unprotected ice surface bursts with seismicity every night due to cracking, which gradually damages and weathers the ice. This is the first time such processes have been observed at relatively warm temperatures and outside of the polar regions.

Plain Language Summary It has been realized that much scientifically valuable information can be learned by listening to the tiny vibrations emanating from a glacier with sensitive sensors. However, due to their remoteness and the difficulties in accessing glacial environments, this approach has rarely been employed to better understand these important systems. For example, debris-covered glaciers, which are protected from heat by a debris mantle, remain to be studied despite being common in the Himalayas, one of the most glacierized regions in the world. Here we installed a seismic network at a series of challenging high-altitude sites on a glacier in Nepal. Our results show that the diurnal air temperature modulates the glacial seismic activity. A debris mantle dampens the diurnal amplitude of temperature and thus protects the ice from cyclic mechanical damage, whereas debris-free (exposed) ice experiences intensive near-surface fracturing early in the morning. This implies that the unprotected ice surface bursts with seismicity every night due to cracking, which gradually damages and weathers the ice. This is the first time such processes have been observed outside of the polar regions. These findings are in agreement with the personal experiences of climbers who felt and heard loud cracks on high-altitude glaciers at night.