Earthquake-triggered 2018 Palu Valley landslides enabled by wet rice cultivation

• Published in: Nature geoscience Vol. 12; no. 11; pp. 935 - 939
• Main Authors: Bradley, Kyle, Mallick, Rishav, Andikagumi, Harisma, Hubbard, Judith, Meilianda, Ella, Switzer, Adam, Du, Nairong, Brocard, Gilles, Alfian, Dedy, Benazir, Benazir, Feng, Guangcai, Yun, Sang-Ho, Majewski, Jedrzej, Wei, Shengji, Hill, Emma M.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.11.2019; Nature Publishing Group
• Subjects: 704/2151/215; 704/2151/3930; 704/2151/508; 704/242; 706/134; Alluvial soils; Anthropogenic factors; Cultivation; Debris flow; Earth and Environmental Science; Earth Sciences; Earth System Sciences; Earthquake damage; Earthquakes; Economic impact; Economics; Fatalities; Geochemistry; Geology; Geophysics/Geodesy; Grain cultivation; Ground level; Groundwater table; Human influences; Impact analysis; Irrigation; Landslides; Landslides & mudslides; Lateral displacement; Liquefaction; Plains; Sandy soils; Seismic activity; Shaking; Slope; Slopes; Soil; Valleys; Water table
• ISSN: 1752-0894; 1752-0908
• DOI: 10.1038/s41561-019-0444-1

The death toll and economic impact of an earthquake can be greatly exacerbated if seismic ground shaking triggers landslides. Earthquake-triggered landslides typically occur in two different contexts: localized failure of steep slopes and resulting landslides that pose a major threat to life in areas below; and lateral spreading of nearly flat sediment plains due to shaking-induced liquefaction, which can damage large areas of critical infrastructure. Unexpected catastrophic landsliding triggered by the 28 September 2018 earthquake at Palu, Indonesia did not occur in either typical context, but produced both destructive outcomes. Here, we show that alluvial ground failure in the Palu Valley was a direct consequence of irrigation creating a new liquefaction hazard. Aqueduct-supported cultivation, primarily of wet rice, raised the water table to near ground level, saturating sandy alluvial soils that liquefied in response to strong ground shaking. Large-displacement lateral spreads occurred on slopes of 1°. Slopes steeper than 1.5° sourced long-runout landslides and debris flows that swept through villages occupying the gentler slopes below. The resulting damage and loss of life would probably not have occurred in the absence of a raised water table. Earthquake-triggered landsliding of gentle, irrigated alluvial slopes is an under-recognized, but avoidable, anthropogenic hazard. Aqueduct-supported cultivation of rice resulted in liquefaction of the alluvial soils that led to the landslides triggered by the Palu 2018 earthquake, according to satellite analyses.