The study, published in the Journal of Geophysical Research: Solid Earth, discovered that the scorching magma from the Arjuno-Welirang volcano has essentially been "baking" the organic rich sediments underneath Lusi.
This process builds pressure by generating gas that becomes trapped below the surface. In Lusi's case, the pressure grew until an earthquake triggered it to erupt.
"We clearly show the evidence that the two systems are connected at depth," said Adriano Mazzini, a geoscientist at the Centre for Earth Evolution and Dynamics, University of Oslo in Norway. "What our new study shows is that the whole system was already existing there - everything was charged and ready to be triggered," Mazzini said.
The Lusi eruption began on May 29, 2006 and by September 2006 enough mud gushed on the surface to fill 72 Olympic-sized swimming pools daily.
Indonesians frantically built levees to contain the mud and save the surrounding settlements and rice fields from being covered.
The eruption is still ongoing and has become the most destructive ongoing mud eruption in history.
The relentless sea of mud has buried some villages 40 metres deep and forced nearly 60,000 people from their homes.
It is now oozing around 80,000 cubic metres of mud each day - enough to fill 32 Olympic-sized pools. To determine the source of the eruption, researchers applied a technique geophysicists use to map Earth's interior to image the area beneath Lusi.
The images show the conduit supplying mud to Lusi is connected to the magma chambers of the nearby Arjuno-Welirang volcanic complex through a system of faults six kilometres below the surface.
Researchers suspect a magnitude 6.3 earthquake that struck Java two days before the mud started flowing was what triggered the Lusi eruption, by reactivating the fault system that connects it to Arjuno-Welirang.
While mud volcanoes are fairly common on Java, Lusi is a hybrid between a mud volcano and a hydrothermal vent, and its connection to the nearby volcano will keep sediments cooking for years to come, researchers said.
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