Back in 2018, massive landslides were triggered after a Mw 7,5 earthquake struck the city of Palu, Indonesia. According to a new study, published in Nature Journal, rice irrigation may have exacerbated their impact.
Three shallow, flow-type landslides resulted in critical infrastructure damage and over 4300 fatalities making the seismic shock the deadliest in 2018.
The powerful tremblor provoked soil liquefaction which is associated with rice irrigation, according to the new findings. In particular, the scientific team showed the landslides were affected by widespread liquefaction that occurred in highly irrigation regions due to rice cultivation.
The researchers came to that conclusion by comparing satellite images (before and after the seismic shock) to derive the total damage to the affected areas. They found out that irrigated fields were highly affected. On the contrary, forest areas were far more stable. The team proposes altering the crops in each field by inserting more plants and trees to avoid extensive landsliding in a similar incident.
“Hazards that are created by humans can often be more readily moderated than other natural hazards. Based on the relative resiliency of areas planted with mixed tree crops and irrigated fields, we propose that more intermixed planting could decrease the hazard of large landslides in the future,” Dr. Kyle Bradley, lead author of the study and principal investigator at Nanyang Technological University, Earth Observatory of Singapore (EOS), stated.
Water level table had almost reached the ground level as farmers used an old aqueduct to water the rice fields. Water level elevation enables soil liquefaction when it is subjected to a dynamic load such as an earthquake load. During liquefaction, soil loses its strength and stiffness and tends to behave like a liquid. "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," the paper emphasizes.
Dr. Bradley stated that this incident is a "wake-up call" regarding earthquake-prone regions where rice irrigation thrives. “We need to improve the awareness and understanding of liquefaction-related landslides and pay closer attention to places where irrigation has artificially raised the water table," Dr. Bradley, added. The researchers suggest that officials should consider taking action in similar areas which may pose a significant threat.
Source: Nanyang Technological University
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