Indonesia earthquake: Torrents of 'liquid soil' washed away buildings

Rivers of soil swept away entire neighborhoods in Indonesia following a ...

Posted: Oct 5, 2018 11:49 AM
Updated: Oct 5, 2018 11:49 AM

Rivers of soil swept away entire neighborhoods in Indonesia following a powerful earthquake last week that also generated a tsunami in a disaster that has killed at least 1,407 people.

Experts say the destruction is due to soil liquefaction, a process occurring when soil becomes saturated with water causing it to erupt into tumultuous torrents, as it did on Friday, shifting and tumbling buildings.

Accidents, disasters and safety

Asia

Continents and regions

Earthquakes

Indonesia

Natural disasters

Southeast Asia

Environment and natural resources

Landforms and ecosystems

Volcanoes

Tsunamis

Footage has emerged from the stricken city of Palu showing people running to find solid ground as structures were swept away and destroyed by waves of undulating earth. Images show a section of the city being erased by surging soil.

In Petobo town the ground under the length of an entire main road was torn up, with the tide of soil leaving broken stretches of tarmac-topped debris in wave-shaped mounds and troughs.

"Liquefaction occurs when loose sandy soils with shallow groundwater are subjected to sudden loading such as shaking from an earthquake," said Jonathan Stewart, a professor in the Civil and Environmental Engineering Department at the University of California, Los Angeles.

Many experts liken the process to waves lapping on a sandy beach. When the waves come in, the sand softens, but when the waves withdraw, the sand stiffens.

"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."

Soil running downhill, known as "flow failure," is one of the most severe effects of liquefaction, and prone to occur in areas with a particular soil structure.

"The soils in the slide area are likely geologically young, loose, sandy materials with shallow groundwater," said Stewart.

'I though it was doomsday'

Residents of Petrobo spoke with horror about the nightmare that unfolded when the ground beneath their feet suddenly began to run following the earthquake and tsunami on Friday.

"I saw asphalt rolling and the road folded ... I saw houses rolling, and the ground breaking open," Muryatim Galanu, a 42-year-old public service officer living in the town, told CNN.

"A lot of people fall inside. It's thanks to God I am alive now, with my children ... I thought it was doomsday."

Not everyone in her family was as lucky. Galanu said she believed her parents and one of her cousins were killed in the disaster. She watched their house collapse as she ran away from the mud.

She even nearly lost her own granddaughter. "The mud rose up to her neck. I pulled her out, as if I was delivering a baby. I thought she was dead," she told CNN.

Galanu said she had no intention of returning to her town following the disaster. "I don't want to go back home again. I can't ... Better to find another place," she said.

Geotechnical engineering

Though such a chain of events is rare and therefore difficult to mitigate, scientists say that engineering techniques do exist to lessen the impact of soil liquefaction.

"As with most problems, the first step in mitigation is recognizing that a problem exists," said Stewart. "We have engineering procedure for this. Had they been applied, there is a good chance the hazard would have been recognized."

Several techniques are used to stop flow slides. The easiest is the construction of a strengthened zone in the soil near the lower end of the slope, said Stewart.

Approaches to this in geotechnical engineering include densification of the soil by the injection of materials, or the compaction of sediments and soils using weights or vibration that mimic earthquake processes, said Adam Switzer, principal investigator at the Earth Observatory of Singapore.

Another method, he added, is the use of "earthquake drains'" that aim to mitigate liquefaction by releasing pressure before it reaches critical levels.

Costas Synolakis, director of the University of Southern California Tsunami Research Center, said that other ways to treat liquefaction are to avoid building multi-story structures and regulate to require deep foundations.

But in poorer countries these techniques might be too costly for government and individual budgets.

"Many of the mitigation techniques are likely to be well beyond the means of the average homeowner in southeast Asia," Switzer told CNN.

In absolute terms careful choice of construction sites or relocation is the best defense against soil liquefaction, scientists said.

"The only way to completely mitigate the problem would be to... move developments off the liquefied soils," said Stewart.

The process is thought to have played a key role in previous disasters, such as the Japan earthquake in 2011, where the extent of the liquefaction over hundreds of miles was daunting to experienced engineers.

A study found that liquefaction wrought more devastation than shaking in the Christchurch, New Zealand, earthquake in 2011.

Terre Haute
Overcast
30° wxIcon
Hi: 37° Lo: 24°
Feels Like: 19°
Robinson
Overcast
30° wxIcon
Hi: 35° Lo: 22°
Feels Like: 19°
Indianapolis
Overcast
29° wxIcon
Hi: 32° Lo: 26°
Feels Like: 16°
Rockville
Overcast
28° wxIcon
Hi: 35° Lo: 23°
Feels Like: 17°
Casey
Overcast
29° wxIcon
Hi: 33° Lo: 22°
Feels Like: 18°
Brazil
Overcast
30° wxIcon
Hi: 35° Lo: 23°
Feels Like: 19°
Marshall
Overcast
30° wxIcon
Hi: 36° Lo: 23°
Feels Like: 19°
WTHI Planner
WTHI Temps
WTHI Radar

WTHI Events

 

Illinois Coronavirus Cases

(Widget updates once daily at 7 p.m. CT)

Cases: 720114

Reported Deaths: 12882
CountyCasesDeaths
Cook3042206595
DuPage45087788
Will38684563
Lake37299631
Kane31767467
Winnebago18948262
Madison14379255
McHenry14269156
St. Clair13410259
Champaign1079858
Sangamon1015799
Peoria9147133
Kankakee8636103
Rock Island8612135
McLean848954
Tazewell6835104
Macon6517132
Kendall626947
LaSalle6108134
DeKalb499047
Adams473548
Vermilion391551
Boone390733
Whiteside3743115
Williamson361083
Clinton330861
Coles329859
Ogle285037
Knox280766
Grundy277618
Effingham277021
Henry270015
Jackson268536
Marion248551
Stephenson246635
Randolph226826
Livingston224527
Macoupin223218
Morgan220936
Bureau211643
Monroe207545
Franklin204825
Lee201034
Christian189443
Jefferson187859
Woodford175827
Fayette170931
Logan170113
Iroquois169326
McDonough158241
Fulton146012
Shelby137426
Douglas135416
Jersey127224
Union118228
Montgomery115519
Crawford112213
Saline111625
Perry110223
Warren109020
Jo Daviess107617
Carroll107024
Lawrence107011
Bond104810
Pike101427
Cass96423
Hancock95612
Wayne90833
Moultrie89810
Clay84020
Greene82831
Edgar80815
Clark79820
Piatt7835
Richland78019
Ford75222
Mercer74510
Mason72120
Johnson7136
Washington7002
Jasper64411
Cumberland61416
White6148
De Witt61317
Massac5993
Wabash5708
Menard4661
Pulaski4132
Marshall4066
Hamilton3873
Brown3224
Henderson2891
Schuyler2711
Stark2683
Alexander2562
Calhoun2470
Putnam2430
Scott2310
Edwards2263
Gallatin1913
Unassigned1850
Hardin1551
Pope1011
Out of IL100

Indiana Coronavirus Cases

(Widget updates once daily at 8 p.m. ET)

Cases: 333312

Reported Deaths: 5685
CountyCasesDeaths
Marion45371865
Lake28722469
Allen19325304
Elkhart17945235
St. Joseph17599237
Hamilton14061171
Vanderburgh10280127
Tippecanoe920230
Porter873389
Johnson6973170
Hendricks6674158
Vigo637392
Monroe560850
Madison5410122
Clark540478
Delaware5184103
LaPorte492897
Kosciusko480741
Howard379478
Bartholomew347365
Warrick343073
Wayne340985
Floyd334978
Marshall317946
Cass307931
Grant295450
Hancock286957
Noble269347
Henry262837
Boone261955
Dubois249632
Dearborn238231
Jackson235534
Morgan228743
Gibson201229
Shelby199859
Knox196621
DeKalb190234
Clinton189222
Lawrence187949
Wabash181122
Miami176817
Adams176223
Daviess165845
Fayette157634
Steuben156415
Jasper155913
Montgomery154629
Harrison154124
Ripley151521
LaGrange150631
Whitley146815
Huntington140210
Decatur137144
Putnam134828
White134823
Wells134630
Clay132724
Randolph132622
Jefferson131316
Posey127718
Scott118921
Greene109053
Sullivan105016
Jay104414
Jennings97814
Starke96624
Spencer9078
Fulton88619
Perry86421
Fountain8608
Washington8387
Franklin75727
Carroll73713
Orange71828
Vermillion6867
Owen6598
Tipton62727
Parke6226
Rush5918
Newton58812
Blackford57312
Pike54020
Pulaski44215
Benton3843
Martin3826
Brown3705
Crawford3221
Union2862
Switzerland2725
Warren2653
Ohio2437
Unassigned0267