Sink Hole: Anchorage, Alaska
Anchorage residents, take note: If your home is equipped with a solid roof, strong windows, and sturdy concrete-and-steel walls, it may withstand initial seismic activity from a Castle Mountain fault-line quake. But all bets are off if the city experiences a quake like the one that rocked the coastline in 1964.
That earthquake lasted nearly 5 minutes and measured 9.2 on the Richter scale. It was the most powerful quake recorded in North America and caused $311 million in damages, most of which came from ground liquefaction. Anchorage sits atop Alaska's "quick clay"—also known as Bootlegger Cove Clay—and any drastic movement in the earth can turn the clay from a solid, underground gel to a liquid pool. Should that happen again, large portions of the city could be swallowed by the earth.