Flash Floods and Storm-Triggered Debris Avalanches in the Appalachians and Possible Trends in a Future Warming Climate

Abstract:

This study analyzes storm-triggered landslides in the US Appalachians, in the current geological setting. Concave valleys that favor the convergence of surface runoff are the primary locales for landslides. If the slopes are weathered to the same degree and have the same vegetation coverage, slope orientation (azimuthal) is not critical for slope stability. However, it is found that for the region south of the Black Mountains (North Carolina), north-facing slopes are more prone to slide, because the northern slopes usually are grass slopes for the regions not limited by annual precipitation (water availability). For the slopes of the Blue Ridge Mountains, south facing slopes are more prone to slide. Deforestation and topsoil erosion are critical contributors to the massive sizes of the debris flows. Gravity measurements over the past decade reveal that geological conditions, the chute system and underground cracks over the region are stable, and sliding material is plentiful. Future changes in storm-triggered landslide frequency are primarily controlled by changes in extreme precipitation. Thus, a series of ensemble climate model experiments is carried out of possible changes in future extreme precipitation events, using the WRF model forced by temperature perturbations. The focus is the impact on storm-triggered landslides, and over 50 locations are identified as prone to future landslides. In a future warmer climate, more severe extreme precipitation events are projected because of increased vapor content and more frequent passage of tropical cyclone remnants. There also is a likely shift of tropical cyclone tracks and associated extreme precipitation, and the Appalachians scarps cluster center is expected to move westward. The remote sensing way of detecting unstable regions are applicable to other regions of interest. We further examine the following regions (except the Fuji Mount) recently (since 1900) experienced volcanic eruption: Pelee, Agung, Elchichon, Pinatubo, St. Helens, and Fuji mountains. The state of the surface chute system and underground chanelling system are estimated and for the region of accelerating underground water gains, possible future unstable regions are projected.