Final answer:
The 1964 landslide in Turnagain Heights, Alaska, was triggered by an earthquake. This region is prone to seismic activity that can cause landslides, especially when there are steep, weak, or saturated slopes present.
Step-by-step explanation:
The 1964 lateral spread slide in Turnagain Heights, Anchorage, Alaska, was triggered by an earthquake. This area of Alaska is known for its seismic activity due to active plate tectonics, and earthquakes are common occurrences that can lead to various geological hazards, including landslides. In fact, earthquakes of magnitude 4.0 and greater have been known to trigger landslides. The Turnagain Heights slide was one such event, where the shaking caused by an earthquake destabilized the ground, resulting in a massive landslide.
Alaska's geology, especially in areas like Turnagain Heights, is particularly susceptible to landslides due to a combination of factors. These factors include over-steepened slopes created by erosion, saturation of slopes by snowmelt or heavy rains, and the presence of very weak or fractured materials on steep slopes. These conditions, when coupled with an earthquake, can result in catastrophic landslides such as the one that occurred in 1964.