Slabs of Earth's crust that are plunging deep into the planet could be carrying much larger amounts of water into the planet's mantle than previously thought.

In the northwest Pacific Ocean, where the Pacific plate sinks beneath Japan, Tom Garth and Andreas Rietbrock of the University of Liverpool, UK, studied earthquakes originating from within the diving slab. Modelling indicated that the quakes occur along water-rich faults that form as the plate bends before diving below.

Over Earth's lifetime, the Pacific plate could have taken the equivalent of 3.5 oceans into the mantle. Some of that water is released and rises upward, fuelling volcanoes; the rest plunges deeper into the planet.

Geology http://doi.org/q7p (2014)