Unlike most subduction zones worldwide, no oceanic trench is present along the continental margin in Cascadia. Instead, terranes and the accretionary wedge have been lifted up to form a series of coast ranges and exotic mountains. A high rate of sedimentation from the outflow of the three major rivers (Fraser River, Columbia River, and Klamath River) which cross the Cascade Range contributes to further obscuring the presence of a trench. However, in common with most 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 Cascadia earthquake of 1700. Geological evidence indicates that great earthquakes may have occurred at least seven times in the last 3,500 years, suggesting a return time of 400 to 600 years. Also, evidence of accompanying tsunamis with every earthquake is seen, as the prime reason these earthquakes are known is through scars the tsunami left on the coast, and through Japanese records (tsunami waves can travel across the Pacific).