Rainwater can penetrate below the Earth's fractured upper crust, according to a new study.
It had been thought that surface water could not penetrate the ductile crust, where temperatures of more than 300°C and high pressures cause rocks to flex and flow rather than fracture, but researchers have now found fluids derived from rainwater at these levels.
Fluids in the Earth's crust can weaken rocks and may help to initiate earthquakes along locked fault lines. They also concentrate valuable metals such as gold. The new findings suggest that rainwater may be responsible for controlling these important processes, even deep in the Earth.