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umerous areas of Central Sulawesi have been affected by a geological phenomenon called soil liquefaction, following a 7.4-magnitude earthquake and tsunami that struck the province on Friday, with more potentially coming.

Soil liquefaction is a natural process that occurs when the ground loses its firmness as heavy soil and rock sink while light soil and sand rise to the surface, often as a result of powerful tremors and particularly in coastal areas.

“This is a common phenomenon to occur after a powerful earthquake. It occurred in Aceh [during the 2004 earthquake and tsunami] as well as in Lombok [in August], although [the Lombok one] was not as big as the one in Palu,” National Disaster Mitigation Agency (BNPB) spokesman Sutopo Purwo Nugroho said during a press briefing on Monday.

According to the agency, several areas in the provincial capital of Palu have been affected by the phenomenon, such as Petobo subdistrict in South Palu, located around 10 kilometers from the coast. A subdistrict in West Palu was flattened by the same phenomenon as entire houses sank into the ground.

Soil liquefaction also struck several districts in Sigi regency, located around 57 km from Palu, such as Biromaru and Sidera.

Sri Hidayati, the head of earthquake mitigation with the Center for Volcanology and Geological Hazard Mitigation (PVMBG), told The Jakarta Post that the phenomenon might also have happened in Donggala, an area rescue teams have yet to reach.

“We estimate that lots of people have drowned in what looks like a mudflow; [we estimate] the mud was 3 meters high,” Sutopo said.

It is feared that about 2,000 people were killed in Petopo, which is located only about 1 km from the Palu-Koro fault line. More than 744 houses in a residential complex in the subdistrict have been dragged away by the mud. Meanwhile, thousands more are feared to be dead in West Palu.

Yusuf Hasmin, 45, said residents had tried to escape the mudflow, which they had described as waves rolling in. He and his family had survived, but he had not heard from other relatives.

Search and rescue teams were on the scene Sunday afternoon with heavy equipment to dig and clear away debris.

Amateur footage of the soil liquefaction was circulating online on Sunday, showing buildings sinking into the ground. The broadcast text suggested that the incident occurred in Jono Oge village in Sigi regency on Saturday afternoon.

The person recording the event could be heard saying, “Oh Jesus Christ!” while the houses before him were moving.

Another video posted on Twitter depicts people running and houses collapsing in an unidentified location in Palu.

While rescuers and residents are overwhelmed with efforts to save people, they must also stay alert amid the risk of similar incident incidents occurring. A scientific report indicates that several areas of Palu city are susceptible to soil liquefaction should another powerful earthquake strike the area.

A report released by the Energy and Mineral Resources Ministry’s Indonesian Geological Agency in 2012 stipulated that Palu, one of many regions of high seismic activity in Indonesia, has a high risk of soil liquefaction because of its geological conditions characterized by saturated or partly saturated sediments and shallow groundwater.

“It can reoccur if there’s another large earthquake, with a magnitude [of 6.5 or more] in the area,” said Taufiq Wira Buana, a researcher with the geological agency.

As soil liquefaction could not be prevented given the geological characteristics, Taufiq added, the extent of destruction and number of casualties might be reduced by designing buildings accordingly.