What goes down must come up — maybe in the form of molten lava.

As tectonic plates shift, they pull our oceans deep into the Earth’s crust, and that water triggers earthquakes, magma production and volcanic eruptions.

All business as usual, geologically speaking.

But it turns out the planet is sucking in a lot more ocean water than we previously thought — triple the amount — and that’s making scientists nervous.

Using seismic sensors placed around the Mariana Trench — the deepest point on the planet, where the Philippine Sea meets the Pacific Ocean — a team of researchers from Washington University in St. Louis tracked rumblings miles beneath the surface.

The slower the quakes move, the more water is presumed to be buffering its wake, and the team observed these “slowdowns” almost 18 miles into the Earth’s crust.

While also factoring in temperatures and pressures down below, the researchers concluded that 3 billion teragrams — or a billion kilograms — are being pulled down every million years.

While these enormous numbers may not offer much context, it helps to know that water that travels into the Earth will eventually come up — through volcanic eruptions — and this, according to scientists, is three times more hydration than the Earth seems to be emitting currently.

The fact that these numbers do not correlate means scientists understand a lot less about the planet’s interior than they thought.

“Many more studies need to be focused on this aspect,” lead researcher Chen Cai tells Live Science.

As it is, the new study results indicate “major ramifications,” says Donna Shillington, a researcher at the Lamont-Doherty Earth Observatory at Columbia University, who wrote an op-ed to accompany the study.

“If extrapolated globally . . . the authors’ result implies that the amount of water entering Earth’s interior greatly exceeds current estimates of the amount being emitted by volcanoes, and thus requires a rethink of the global water budget,” she writes.

Shillington’s bottom line: Water beneath the surface of the Earth contributes to the development of magma and can lubricate faults, making earthquakes more likely.