As one of the geologically calmest subduction zones in the world, the Cascadia subduction zone has long been at the center of a debate among geologist. Many geologist have attempted to explain why this subduction zone is so quiet. One theory postulated that Juan de Fuca plate had gradually rotated due to its larger neighbors. Another theorized that one of the plate's downward angles did not produce enough friction. It wasn't until March 1986 that Brian Atwater was able to find evidence of historical geological activity related to the subduction zone. An analysis of the sediment and ancient plant life there had revealed that there was sudden drop in elevation. This showed that a large tsunami or wave had come and sealed the arrowgrass from decay.
