Landslide

Description

A landslide is defined as the movement of a mass of rock, debris, or earth down a slope. The term "landslide" encompasses five modes of slope movement: falls, topples, slides, spreads, and flows. These are further subdivided by the type of geologic material (bedrock, debris, or earth). Debris flows (commonly referred to as mudflows or mudslides) and rock falls are examples of common landslide types. In Virginia, heavy rainfall is the major cause of landslides, but they can also be triggered by rapid snow melt or oversteepening of slopes by stream incision. Certain man-made changes to the land, such as slope modification or drainage alteration, can greatly increase the likelihood of landslides.

Location and Extent

Landslides are a major geologic hazard and occur most frequently in the mountainous terrain of Virginia because of the presence of steep slopes and highly fractured bedrock that exists over shallow soils. The lower-relief areas of the Piedmont region also have landslides, but they are often smaller and generated by human disturbance, such as making an over-steepened road cut. The most disastrous landslide events have been associated with heavy rainfall along the steep slopes of the Blue Ridge Mountains and the Appalachians.

LiDAR, which stands for Light Detection and Ranging, is an active remote sensing method that uses light in the form of a pulsed laser to measure distances to Earth. LiDAR technology has been increasingly used as a way to detect and analyze the phenomenon of natural disasters such as landslides. Very-high resolution digital terrain models (DTM) obtained from airborne LiDAR data, and derivative products (such as contour maps, slope maps, shaded relief images, curvature, and measures of surface roughness) help geologists to map, monitor, and even predict landslides. With advances in computational capabilities and LiDAR acquisition projects in Virginia, the utility of LiDAR provides an efficient yet economic way in visual analysis of the topographic surface, and semi-automatic recognition of morphometric landslide features. The high-resolution LiDAR dataset, once available for the CVPDC, will be valuable to help with landslide preparedness and mitigation planning for the area.

History

There are very few documented landslides events for the CVPDC area. Historically, major rainfall events have caused the greatest numbers of documented landslides in the Virginia mountains. Hurricane Camille in 1969 stalled over the Blue Ridge Mountains, dropping more than 30 inches of rain in less than eight hours. Flooding and numerous landslides and debris flows occurring in the north of the CVPDC area (Nelson, Amherst, and Rockbridge counties), led to the deaths of more than 150 people, 100 injuries, destruction of more than 100 bridges, and more than $150 million in property damage. This event resulted in the most recorded deaths by a natural hazard in the Commonwealth.

There are two minor landslide events occurring recently recorded in the U.S. Landslide inventory by USGS. On September 19, 2010, mudslide caused by downpour knocked out the boiler in Central Virginia Training Center, Madison Heights, Amherst county. On May 18, 2018, heavy rain triggered a mudslide on US route 460 near Route 122 interchange and the exit for the National D-Day Memorial. It caused traffic jams and at least one lane in Bedford County was shut down.

Plan Chapter

CVPDC HMP 2020