Mont Blanc Mountain (France & Italy)

Deep, persistent groundwater system in fractured crystalline rock, supplied by high-altitude recharge, detectable through thermal anomalies, and capable of influencing seismic activity through changes in fluid pressure

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Location: Alps mountains, France-Italy

Elevation: 1000 - 4800 masl

Geology: Crystalline rock (crystalline schist, granite)

Aquifer type: fractured crystalline-rock aquifer

Scientific question: "How does groundwater flow at great depth in mountains?"

Location map

Key findings

Major deep groundwater flow: a major fracture zone in the crystalline massif carries exceptionally large and persistent groundwater flows, from about 1,000 L/s during tunnel excavation to ~200 L/s decades later.
High-altitude recharge: deep groundwater is ultimately supplied by infiltration of alpine surface water, with modelling indicating very slow thermal adjustment since the last glacial period.
Temperature as a groundwater tracer: rock-temperature anomalies can be used to identify and quantify deep groundwater circulation and potentially predict major water inflows in fractured crystalline massifs.
Groundwater–seismicity coupling: recent work shows that meltwater reaching deep faults can increase pore pressure and trigger seasonal seismicity, while a subsequent migratory seismic component involves additional tectonic/aseismic processes.