About 74,000 years ago, Indonesia experienced one of the largest volcanic eruptions in recent Earth's history, emitting about 2,800 cubic kilometers of volcanic material into the atmosphere. Scientists have long wondered where this massive amount of magma came from, able to create such a mega-eruption, and now they may have finally found the answer.

The tremendous amount of lava that spews out of super volcanoes such as the one that occurred in the Toba caldera in Indonesia actually builds up over millions of years in the Earth's crust, before unleashing its fiery wrath. These below-ground reservoirs consist of magma positioned in numerous horizontally oriented sheets resting on top of each other, just like a pile of pancakes.

"With a new seismological method we were able to investigate the internal structure of the magma reservoir beneath the Toba-caldera. We found that the middle crust below the Toba supervolcano is horizontally layered," study co-author Christoph Sens-Schönfelder, from the German Research Centre for Geosciences (GFZ), said in a statement.

Over a six-month period, the researchers recorded the ambient seismic noise - the natural vibrations that usually are regarded as disturbing signals - in the Toba area. They found that in the middle crust, located seven kilometers below the surface, the structure of these horizontal magma pancakes allows room for the lava to grow before getting released during a supervolcano.

While the findings may make one nervous that this buildup of magma would mean supervolcanoes are likely to occur pretty often, in reality that actually happen only every couple of hundred thousand years or so. But when they do erupt, it's not pretty. Besides the one that Indonesia experienced, other known supervolcanoes include the area of the Yellow-Stone-Park, volcanoes in the Andes, and the caldera of Lake-Taupo in New Zealand.

This new research can help scientists better understand the processes that lead to such gigantic events.

The findings were published in the journal Science.