High‐Frequency Harmonic Tremor Associated With a Water‐Filled Crevasse at Tête Rousse Glacier, Mont‐Blanc Massif

Abstract Tête Rousse glacier is a small polythermal glacier in the Mont‐Blanc massif (French Alps) that released a large outburst flood in 1892 when a water‐filled intraglacial cavity suddenly drained. A new water‐filled cavity was detected again in the central part of the glacier by a geophysical campaign in 2007. It has been pumped three times since to avoid another catastrophic flood. The volume of water in this central reservoir has decreased recently but recent geophysical surveys suggested that significant volumes of water could be stored in the upper part of the glacier. Here, we describe a seismic tremor signal detected in May 2022 probably generated by a water‐filled reservoir within the glacier. The tremor started on 15 May a few days after temperature first increased above 0°C. Tremor amplitude was stronger in the evening and is correlated with water level measured in a crevasse about 230 m downglacier. The time delay between temperature and tremor or water level is consistent with the time needed for water to infiltrate within the snow and into the glacier. We used different methods to locate this signal both from amplitude decay and from P and S waves arrival times. Both methods provide a similar location near the northern boundary of the glacier. Ground penetrating radar surveys performed in May 2024 have since detected a water‐filled reservoir near this location. These results validate our interpretation of this seismic tremor being produced by changes in water‐level in this reservoir.