According to seismologists at the University of Liverpool, the majority of the Earth’s water could be buried deep underground.

The Earth is covered by fault lines and experiences frequent earthquakes. Only a few of these quakes ever make the news, because only a few of them are felt by people. Many of them happen in the deep sea, and some of them happen hundreds of kilometers beneath the Earth’s surface.

During these earthquakes, large amounts of water can be driven into the Earth’s mantle. This is especially true during subduction. Subduction occurs when one oceanic tectonic plate is forced between another plate. When this occurs it causes massive earthquakes, and it can force tremendous amounts of water deep underground. Liverpool seismologists estimate that, over the age of the Earth, the Japan subduction zone alone could have moved an amount of water equivalent to 3.5 times all of the world’s oceans into the mantle.

Water in the fault zones, in turn, plays a role in seismic activity. Water percolating through subduction zones interacts with ocean rocks to form serpentinite, a hydrated mineral. As tectonic plates heat up some of the water is released which can cause mantle material to melt and lead to volcanoes.

“It has been known for a long time that subducting plates carry oceanic water to the mantle. This water causes melting in the mantle, which leads to arc releasing some of the water back into the atmosphere. Part of the subducted water however is carried deeper into the mantle and may be stored there,” said Tom Garth, a PhD student in the Earthquake Seismology research group led by Professor Andreas Rietbrock.

“We found that fault zones that form in the deep oceanic trench offshore Northern Japan persist to depths of up to 150 km. These hydrated fault zones can carry large amounts of water, suggesting that subduction zones carry much more water from the ocean down to the mantle than has previously been suggested. This supports the theory that there are large amounts of water stored deep in the Earth.”

Understanding how much water is delivered to the mantle adds to knowledge of how the mantle convects, and how it melts, which helps to understand how plate tectonics started, and how the continental crust was formed.

The new research was published in the journal Geology.

Source: University of Liverpool