Natural disasters are always troubling because they are so often unpredictable. Even when they are forecast in advance, they often defy the prediction in size and scope of devastation. The best people can do is reduce the impact of such events with human ingenuity. Beaches, for example, can be protected from hurricane erosion with sea walls and sand dunes. Many skyscrapers on the U.S. west coast and on the Pacific Rim are engineered with foundational springs and interior weights (called mass dampeners) to absorb seismic shock from earthquakes. Harder to foresee and to prepare for, however, are landslides. Their damage can be minor or can be massive.

Facts about Landslides

  • A landslide is defined as dirt, rock and debris that becomes dislodged at a higher altitude and falls to a lower altitude.
  • A number of factors can cause landslides, including earthquakes, too much rainfall, and human activity.
  • Certain factors make some areas more prone to landslides, such as rock type, high amounts of rainfall in an area, and steep slopes.
  • Parts of the west coast of North America are particularly prone to landslides. These include parts of California, Oregon, Washington and British Columbia.
  • There are a number of types of landslides, including spread, slide and flow types.

What exactly is a landslide?

A landslide occurs when dirt, rocks and assorted rubble are dislodged and pulled by gravity down a slope. This phenomenon is sometimes called slope failure because the underlying earth holding the debris in place fails to maintain that hold. The speed and intensity of the landslide can depend on the materials moving downward and on the steepness of the incline. Yet even the slowest landslides, moving at only a few inches a year, can cause serious property damage, especially when the mass of movement is large. Those that move swiftly, on the other hand, provide little warning and powerful impact.

What causes a landslide?

The reasons for landslide activity are many, both natural and human induced. The use of dynamite or other technologies causing substantial percussion (or vibrations) can set off a landslide, as can mining activity; roads and railways where drainage is poor; leaking subterranean pipes; and quarrying in unstable areas. Some of these factors point to the problems of too much moisture that weakens the earth’s grip on the topsoil. Natural conditions can cause this, as well. When there is an overabundance of rainfall; when rivers erode their banks and cut into cliffs; or when earthquakes move the underlying tiers of the earth, landslides become more likely, if not inevitable.

What kinds of damage can landslides create?

Landslides can destroy roads and train tracks, bury farms and crops, collapse buildings and cause many deaths. Furthermore, landslides can dam rivers and streams that serve as essential water supply resources for communities. Because they can disrupt transportation infrastructure, they can delay shipments of food, medicine and other necessities. In addition to the economic losses and the toll on human lives, landslides exact a heavy toll on the environment: taking down trees, burying fish stocks and disabling sewage systems. In fact, landslides have been known to do all these things, and more.

When and where were the worst landslides?

The magnitude of landslides can be measured in a couple of ways: the first method is to determine how much earth actually moved in any given landslide. In this case, the worst in United States recorded history occurred in 2013 at Bingham Canyon outside of Salt Lake City, Utah, where an estimated 55 million cubic meters slid downward. Fortunately, there were no commercial or residential settlements in the vicinity so damage was not severe. On the other hand, if damage is the indicator of how powerful a landslide is, another Utah slide—just outside of the town of Thistle—practically destroyed the entire community, resulting in up to 400 million dollars in economic losses. In terms of lives lost, a 2014 slide at Oso, Washington took nearly 25 lives in its wake.

What are the types of landslides?

  • A spread is probably the tamest of landslides as it occurs on very shallow inclines, and even on nearly flat landscapes. The sediment is usually loose ahead of any movement.
  • A slide, or slump, happens when the very edge of a slope gets undercut. Movement is moderate and the masses move largely intact without getting broken.
  • A flow is named such because water makes up a good portion of the sliding mass. This adds power and acceleration to the landslide, making it most unpredictable and dangerous.
  • A topple results from a fissure in the rock pattern, causing quick descent characterized by bounces, rolls and drops.
  • A fall could aptly be named a freefall since debris descends very rapidly, usually instigated by erosion or earthquake.