Unlike most subduction zones worldwide , there is no deep oceanic trench present in the bathymetry of the continental margin in Cascadia . This is because the mouth of the Columbia River empties directly into the subduction zone and deposits silt at the bottom of the Pacific Ocean to bury the oceanic trench . Massive floods from prehistoric Glacial Lake Missoula during the Late Pleistocene also deposited massive amounts of sediment into the trench . However , in common with other subduction zones , the outer margin is slowly being compressed , similar to a giant spring . When the stored energy is suddenly released by slippage across the fault at irregular intervals , the Cascadia subduction zone can create very large earthquakes , such as the magnitude 9.0 Cascadia earthquake on January 26 , 1700 . However , earthquakes along the Cascadia subduction zone are fewer than expected and there is evidence of a decline in volcanic activity over the past few million years . The probable explanation lies in the rate of convergence between the Juan de Fuca and North American plates . These two tectonic plates currently converge to per year . This is only about half the rate of convergence of seven million years ago
Cascadia earthquake on January 26 , 1700
1700 Cascadia earthquake
Garibaldi Volcanic Belt