Earthquake, tsunami and liquefaction: how a third disaster swallowed up whole villages in Indonesia

As the death toll rises along the tsunami-battered coastline of Sulawesi, it may have been the devastating earthquake, rather than the huge waves, that caused many of the casualties. 

Balaroa and Petobo were two villages that escaped the wall of water that engulfed much of Palu and Donggala. But the sheer force of the magnitude 7.5 earthquake turned the earth temporarily to mush, causing whole neighbourhoods to be sucked into the ground.  

Both were turned into mass graves by the terrifying phenomenon called liquefaction, where saturated sand and silt take on the characteristics of a liquid during the intense shaking of an earthquake.

It takes place when a quake has increased water pressure in…