As the death toll from the 7.5 magnitude earthquake and tsunami continues to mount in Indonesia, footage that shows the ground turning into liquid has amazed and horrified.
“The ground rose up like a spine and suddenly fell. Many people were trapped and buried under collapsed houses. I could do nothing to help,” one survivor told The Associated Press of the phenomenon, known as liquefaction.
Soil liquefaction has been blamed for countless building collapses in Indonesia, The Guardian reported.
Much of the damage done during the quake was due to liquefaction. One neighborhood in Palu saw 1,700 houses destroyed by the rolling, muddy soil, according to Indonesia’s national rescue agency, as Time reported.
“When the quake hit, the layers below the surface of the earth became muddy and loose,” Sutopo Purwo Nugroho, the spokesperson for Indonesia’s national rescue agency, was quoted by Time magazine as saying.
A Red Cross official said that 34 children died when their church collapsed due to liquefaction, according to the report.
Approximately 2,000 people are feared to have been killed in Petobo, located south of Palu. A mudslide washed away homes, the report said.
“The mud rose up to her neck. I pulled her out, as if I was delivering a baby. I thought she was dead,” one woman told CNN in describing the incident. She was referring to her granddaughter.
Some experts told CNN that rivers of liquid soil swept away entire neighborhoods.
“Liquefaction occurs when loose sandy soils with shallow groundwater are subjected to sudden loading such as shaking from an earthquake,” Jonathan Stewart, a professor in the Civil and Environmental Engineering Department at the University of California, Los Angeles, told the network.
“During the earthquake, water pressure is generated in the soil, which causes a dramatic loss of strength,” said Stewart. “The strength loss can be so great that the soil behaves almost like a liquid.”
Liquefaction has been seen during other major earthquakes, such as the 1989 earthquake that hit Northern California or during the 1948 Fukui earthquake in Japan. Liquefaction was also observed during the 2011 Christchurch earthquake in New Zealand.
Some Areas at a Higher Risk
One expert told the Guardian that some areas are at a higher risk of liquefaction.
“Reclaimed land and river banks which typically consist of loose deposits are prime locations for liquefaction in case of strong shaking,” Stavroula Kontoe of Imperial College London, told the outlet. Galasso said the earthquake, rather than the tsunami, was responsible for the liquefaction.
Kontoe added: “There are several mitigation techniques which can limit or even eliminate [soil liquefaction’s] consequences. These techniques usually involve strengthening the soil deposits in areas where liquefaction has been identified as a major hazard and/or adopting drainage measures to prevent the increase of the water pressure during the strong shaking.”
There are more ways to reduce the risk of earthquake-triggered liquefaction.
“Building codes and standards in many countries require engineers to consider the effects of soil liquefaction in the design of new buildings and infrastructure such as bridges, embankment dams and retaining structures,” she said.