Identifying Landslides with LiDAR
Landslides are defined as gravitational movements of earth materials (rock, soil, etc.) down a slope. They are considered a geologic hazard because they can cause considerable damage to infrastructure (roads, buildings, utilities, etc.) and pose a hazard to public safety. There are many different types of landslides. Each is categorized by the type of material that moved downslope (rock, earth, etc) and the mechanism of the movement (fall, slide, flow). All of these types of landslides, when present and of sufficient size, are clearly visable on LiDAR DEMs.Debris Flows
1-meter resolution LIDAR slopeshade of the Davis Creek area of Nelson County, Virginia
The image above shows a 1-meter resolution LIDAR slopeshade of the Davis Creek area of Nelson County. Numerous debris flows, were produced in the area outlined in purple during Hurricane Camille in 1969. Debris flows are a swift-moving type of landslide that can be hundreds of feet-to-miles long, narrow in width, and have a pronounced headscarp. Many thousands of debris flows occurred in Nelson, Albemarle, and Amherst Counties in 1969 due to heavy rainfall from Hurricane Camille. New LIDAR data is helping DGMR geologists identify many more debris flows from Hurricane Camille than were previously known. This information helps geologists slope thresholds that are most prone to generating landslides and if geology plays a role in where landslides are occurring.
Debris flows near Myndus in Nelson County, Virginia
This image shows a series of converging debris flows near Myndus in Nelson County, generated during Hurricane Camille. Letters on the images compare the headscarp locations of debris flows on the LIDAR data to locations in a photograph taken by Tom Gathright, a DGMR geologist, in 1969.
Download a sample of LiDAR data for the Myndus debris flows here. You will need Google Earth loaded on your computer to view the data.Debris and Rock Slides
Landslides can travel downslope in different ways. Sometimes they flow, like the examples above, and sometimes they slide, either as an entire block of material or disaggregating into smaller pieces. They look very different on LIDAR data, compared to the debris flows above.
Big Walker Mountain near Long Spur, in Bland County, Virginia
Large rock slide on Big Walker Mountain near Long Spur, in Bland County. Notice how this landslide has detached from the hillside and traveled down slope as a single block of material.
Debris slide near Schuyler in Nelson County, Virginia
This is a small debris slide near Schuyler in Nelson County. There is a prominent break in the slope at the top of the slide and the transported material has broken up into pieces. This landslide is probably associated with Hurricane Camille in 1969.
Landslides can be move very swiftly (up to 30 miles per hour) or can travel slowly and gradually, only a few inches in a year. These slower moving landslides tear hillsides apart and can cause ongoing maintenance problems for roads and property owners.
A slow-moving landslide along U.S. 460 near the town of Narrows in Giles County, Virginia
This slow-moving debris slide (red arrow) has been a problem along U.S. 460 near the town of Narrows in Giles County since the early 1900’s. Excavation along the base of the slide has caused it to continuously move downslope, causing maintenance issues for the road and railroad. You can read more about this landslide here.
A creeping boulder field Tazewell County, Virginia
This image shows a boulder field, composed of rock from the cliff line above, which is slowly creeping down the south slope of Beartown Mountain, in Tazewell County.
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