Some geologic hazards, like volcanoes and earthquakes, are present in areas where they have a history of putting communities at risk. Other geologic hazards, such as rock slides and flooding, can happen almost anywhere, making them difficult to predict. In this case, a rock slide across a Tennessee highway was caught on tape, showing how forceful this geologic process can be.
Causes of Rock Slides and Landslides
Landslides are a geologic process that encompasses the downward movement of mass, including rock slides. Rock slides are defined as the downward movement of bedrock. Other types of landslides are a debris slide, which is the downward movement of predominantly coarser material on top of bedrock, and an earth slide, which is the downward movement of predominantly finer material on top of bedrock. In all cases of landslides, there is a weak zone between the unstable material on top and the more stable material on the bottom. Also playing a large role in landslides is gravity, which factors into slope stability and slope failure, or the degree of the slope at which point vertical gravity forces overtake horizontal frictional forces.
Landslides are attributed to volcanic activity, seismic activity and, most commonly, slope saturation by water. Water is a major factor because it adds weight to the top layer of material on a slope, causing slope failure. Human activity such as mining, digging into hillsides, leaking pipes and deforestation can also cause landslides. Often, these activities will weaken slope stability, and then a heavy rainfall will actually cause the landslide.
The Polk County Rock Slide
CNN recently aired a tape provided by Tennessee news station WDEF showing a rock slide in progress. This rock slide occurred in Polk County across U.S. Highway 64 on November 10, 2009. The video shows the sudden movement of bedrock and trees right as slope failure occurs. Noticeable in the foreground is the wet road, which is evidence of a recent rainfall and possibly the cause of the rock slide. The WDEF video crew that captured this rock slide was situated along this portion of the highway to film a story covering a previous rock slide along this highway, which is visible on the background farther up the road.
Landslides can occur anywhere in the world where topography and changes in elevation exist, especially where these changes are more dramatic, such as in mountainous areas and areas with cliffs. In the United States, areas susceptible to landslides are the entire West Coast (known for its scenic ocean-side cliffs), portions of the Rocky Mountains residing in Colorado and the majority of the Appalachian Mountain region. Polk County is situated along the southern extent of the Appalachian Mountains, and therefore in the middle of one of the most landslide susceptible regions in the country. The ancient age of the Appalachian mountains, combined with millions of years of erosion and structural deformation, have caused the entire mountain range to become unstable and prone to landslides.
Sources:
National Atlas: Landslide Types and Processes
 |
 |
