Clatsop County residents and guests are at risk of being impacted by tsunamis, a series of waves usually caused by an undersea earthquake. 

As these waves enter shallow water near land, they increase in height and can cause great loss of life and property damage. 

The first wave is often not the largest. Additional waves may be spaced many minutes apart and can continue arriving for several hours.

Tsunamis may be caused by an earthquake near shore, such as one generated at the Cascadia fault line, or they may be created by a quake hundreds or thousands of miles away.