Background
Used with permission of MBARI
The seafloor of Monterey Bay, California is characterized by the network of large canyons and trenches. This area of the seafloor is constantly active as sediment is eroded from one area of the canyons, then carried and deposited onto other areas of the seafloor geology. This constant morphing of the seafloor causes many situations where canyon side slopes can no longer support their structure, due to an abundance of sediment deposition (gravitational failure) or the conditions under which the sediment slopes are being subjected to, such as wave, current, or seismic behavior. Events such as those that have taken place in Indonesia and the Grand Banks, where an earthquake is the trigger for a slope failure leading to the formation of a tsunami, have led geologists and engineers to consider the possibility and magnitude of such an event in the Monterey Bay seafloor.
Used with permission of MBARI
USGS expeditions have completed general sampling of the entire Monterey Bay region and have found the seafloor sediment to be comprised of three primary layers; an upper region of recently deposited sand, a mid layer of fine grained sediment, lying on top of another layer of sandy sediment (Edwards et al. 2005). The area's topography as well as its composition makes it prone to sediment flow or slope failure events regularly. One gravity flow in particular has been calculated to have included as much as 2,200,000 m3 and is believed to on a cycle that has it occurring once every five years (Ussler et al. 2002). Due to the nature of the seafloor in Monterey Bay and its proximity to seismic areas, the greatest concern is that an earthquake may trigger large volume of sediment and trigger a tsunami that could devastate the bordering costal regions.
The last major tsunami to hit the coast in this area occurred in 1964; the waves reached as tall as 21 feet, devastating costal communities and being responsible for 11 deaths (Masters 2005). The problem is thought to be one of low occurrence but high consequence, meaning that the likely hood of a large scale hitting the Monterey area is low, however the community is so little prepared that if an event were to occur the effects would be disastrous. It is for this reason that the seafloor conditions and possible tsunami triggering mechanisms must be studied further and protocols put into place to minimize the potential for a major natural disaster.
