Earthquake

Earthquakes can trigger landslides and rock falls many kilometers from their epicenters. Local governments can enact zoning regulations to prevent development in areas susceptible to landslides during earthquakes or heavy rainstorms. In other cases, potentially hazardous slopes can be excavated and regarded into a configuration that is able to resist the destabilizing effects of a large earthquake.

Seismically-triggered landslides can reshape the landscape. In 1959, an earthquake triggered a landslide that dammed the Madison River in Montana and created Hebgen Lake. To prevent this natural dam from washing out and causing catastrophic floods, the U.S. Army Corps of Engineers built an emergency spillway through the landslide material. This enabled them to control the release of the water from the new lake. Prehistoric landslides have dammed the Columbia River and could be the source of a legend of the Northwest Indians. In this legend, tribes walked across the Columbia River on a bridge of land to meet each other.