Landslide Perturbations in the Nepal Himalaya Induced by the Asia Summer Monsoon, Extreme Rainfall, Earthquake Preconditioning, and Road Construction
Abstract
In mountainous regions, landslide processes dominate landscape evolution and pose serious risk to life and socioeconomic development. Understanding the processes that control the rates of landslide occurrence is thus vital. In the Nepal Himalayas, background rates of landsliding are predominantly controlled by the the Asia Summer Monsoon (ASM). However, this background rate is regularly perturbed by landsliding associated with extreme events such as cloud outburst storms and earthquakes, and by anthropogenic activity such as road construction. Here, we use a 30-year inventory of monsoon-triggered landslides in Nepal to quantify the relative magnitudes and timescales of landsliding caused by the ASM, cloud outburst storms, and earthquake preconditioning. By establishing new empirical relationships between landsliding and ASM strength, we derive an ASM strength-normalised rate of landsliding across the past 30-years. This normalised rate reveals how some years observed landslide rates that were perturbed significantly above that expected from the ASM-strength alone. These perturbations correlate with several extreme events, with perturbations of up to 5 times greater than the rate expected from the ASM strength caused by 5 30-year return period cloud outburst storms and by Gorkha earthquake-induced landscape preconditioning. Finally, we present preliminary results showing that sediment production in Nepal due to road construction is increasing significantly relative to the total landsliding triggered by the ASM, storms and earthquake preconditioning, with road construction-related mass-wasting accounting for ~40% of the total observed mass-wasting in 2018. Overall, our results highlight how extreme events can trigger landslide perturbations that represent significant sediment sources, and that road construction-related mass-wasting is having a growing impact on sediment production.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFMEP42C..02J