Unlike most subduction zones worldwide , there is no deep oceanic trench present along the continental margin in Cascadia . The mouth of the Columbia River empties directly into the subduction zone and deposits silt at the bottom of the Pacific Ocean , burying this large depression , or area of sunken land . Massive floods from prehistoric Glacial Lake Missoula during the also deposited large amounts of sediment into the trench . However , as with other subduction zones the outer margin is slowly being compressed like a giant spring . When the stored energy is suddenly released by slippage across the fault at irregular intervals , the Cascadia subduction zone can create enormous earthquakes such as the magnitude 9.0 Cascadia earthquake on January 26 , 1700 . However earthquakes along the Cascadia subduction zone are uncommon , and there is evidence of a decline in volcanic activity over the last few million years . The probable explanation lies in the rate of convergence between the Juan de Fuca and North American plates , which converge at to per year , about half the rate of convergence from seven million years ago
Cascadia earthquake on January 26 , 1700
1700 Cascadia earthquake
Mount Meager massif