The Ocean Floor

Etched into the continental shelf off the mainland, and before reaching deep sea waters, are a series of dramatic changes in topography. The deep sea channels - unusual for a shelf so close to shore - are the reason the stretch of water between the mainland of Santa Barbara and Ventura and the northern Channel Islands is called the Santa Barbara Channel. Likewise, between Los Angeles and the southern Channel Islands the deep sea channel is the reason the waters are called the San Pedro Channel. These channels are deep broad open expanses cut far below the surrounding seabed level.

Other features in the underwater geography - oceanography - of the Channel are sea mounts, sea basins, and sea canyons.

A sea mount is an underwater mountain that once, like the island mountain tops we can see today, was pushed up above the seabed by volcanic and sometimes seismic activity. These sea mounts are of great danger to mariners, who must follow their charts closely s they navigate the Channel waters.

Sea basins are the shallower under water plains between the sea mounts, and that are not the deep sea channels. Much like the Oxnard plains and the Los Angeles basin, these underwater basins are fairly level surfaces. There are six sea basins in the inner and outer Channel. Those between the islands and the mainland are usually not more than 1500 feet in depth. These inner Channel basins are called the Santa Barbara Basin ( 1500 feet depth ) to the north, and the Santa Monica and San Pedro Basins heading south ( 2250 in depth ).

The outer Channel basins lie to the west of the Islands and are on the last stretch of the continental shelf before truly deep sea waters begin. The Catalina Basin is deeper yet at 3750 feet, while the San Nicolas and Santa Cruz Basins drop over 5,280 feet ( a mile in depth ).

Sea canyons are much like their mainland counterparts - narrow V channels cut into the sea bed. Scientists believe that some of these canyons were cut by water run off when areas of the sea floor were exposed to air, wind, and rain during the ice ages. But even when submerged as the sea levels rose, the currents themselves erode away at the canyons each year.

We are learning more and more about the underwater Channel topography by using sonar to bounce back the forms of the sea floor to advanced computers, and thanks to technological innovations that are enabling scientists to work in mobile submerged units that dive down to the sea floor and examine first hand the amazing variations in features of the sea floor beneath the California Channel. Channel Island National Marine Sanctuary staff have had the opportunity to make use of these submersibles - and have even beamed back radio transmissions of their expedition over the Internet ! In fact the National Geographic Society is funding a nationwide submersible expedition program that will be visiting and studying all of the National Sanctuaries. Keep an eye on Camp Internet for news from these exciting expeditions.