Picture the Grand Canyon under water. Then you’ll have the right scale in your mind when thinking about the Monterey Canyon in California. It is truly a huge underwater feature! It is the largest submarine canyon along the coast of North America.
Just Another River?
Initially scientists thought submarine canyons were carved like river canyons on land. They thought the process just happened at low stands in sea level during a glacial period, and that the canyon was later submerged during an inter-glacial period, when the sea level rose. The problem with this theory is that through all known glacial periods, sea level never dropped the required thousands of feet to expose the land so a river could carve the deep canyon.
Turbidity Currents to the Rescue
Today it has become clear that submarine canyons may indeed start forming during a low stand in sea level, like a normal river, but once sea level rises again, the main canyon cutting happens underwater by turbidity currents.
Turbidity currents are plumes of sediment (dense gravel, sand and mud) that rush downslope after being triggered by an earthquake or even large storms. In the picture above, red arrows indicate the general direction of sediment transport along the edges of the bay down into the canyon. The top-left arrow is from the San Lorenzo River, the center arrow is the Pajaro River and the right one is the Salinas River.
A Very Old Canyon
The Monterey Canyon is simply too deep and large to have been created by the sediments coming out from the current rivers. It was actually carved millions of years ago from a much larger load of sediment coming from California’s Central Valley. The canyon has moved away from its original drainage system as it moves northward along the San Andreas Fault at a rate of about 1.5 inches per year. Twenty five million years ago the canyon was 250 miles to the south and the local geography was very different! Deep sediments from cores within the canyon confirm that the sediment source used to be very far south of here.
Research in the Canyon
Much of the understanding of the Monterey Canyon comes from research done by the Monterey Bay Aquarium Research Institute (MBARI). MBARI specializes in combining scientific research with engineering design. This combination has allowed them to see and measure what no other scientists have seen and measured before — both within the Monterey Canyon, and all over the world.
Within the submarine canyon, MBARI uses underwater robots called remotely operated vehicles (ROVs) to explore and perform research experiments in the deep waters. The photo above shows a launch of the ROV Ventana on board the research vessel Point Lobos. Launching and recovering a 2-ton, 10-foot long ROV is a tricky business in the open waters of Monterey Bay.
A Home for Diversity
Submarine canyons extend from shallow to very deep waters, and thus contain a wide range of habitats and a very diverse array of organisms. Each habitat is home to its own set of fishes and invertebrates.
One example of an interesting creature is Vampyroteuthis infernalis, which means “vampire squid from hell.” It spends most of its time lurking in the always dark, low-oxygen waters about half a mile below the surface. It has a dark red body, huge blue eyes, and a cloak-like web that stretches between eight arms. If threatened, it will turn itself inside out, flaunting rows of evil-looking “cirri.”
Protecting the Canyon
Controlling pollution entering the Monterey Bay is very important to the health of the canyon ecosystem because it is the gravitational low point and is where trash and pollutants accumulate. Comparisons between surface and deep fish in the Monterey Canyon find deep fish to have much higher concentrations of persistent organic compounds such as PCBs and DDT.
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