Wednesday, August 21, 2019

The Hudson Canyon


Depiction of the Hudson Canyon on the continental margin
 off New York and New Jersey at the outlet of the Hudson River.
The color is added. Public Domain via Wikimedia

As a child, I would hear about fisherman going out to "the canyon" to fish for big fish. It was many years later that I actually knew that they were referring to the Hudson Canyon. This submarine canyon begins from the shallow outlet of the estuary at the mouth of the Hudson River. The Hudson Canyon proper is located about 100 miles (160 km) east of the mouth of the Hudson River off the New Jersey coast.

It extends out over 400 mi (640 km) seaward across the continental shelf. The continental shelf is a portion of a continent that is submerged under an area of relatively shallow water known as a shelf sea. Much of the shelves were exposed during glacial periods and interglacial periods. This shelf connects to the deep ocean basin at a depth of 3 to 4 km below sea level.

It all begins as a natural channel that is several kilometers wide. It is a 20–40 m depression southward from Ambrose Light, and silt, sand, and mud are carried down the Hudson River and flow into the canyon and out into the deep sea.

Though it is under a lot of water, this is really a "canyon." The walls rise three-quarters of a mile from the canyon floor. That makes it comparable to the Grand Canyon with cliffs that are over a mile deep and 270 miles (430 km) long. It is the largest known ocean canyon off the East Coast of the United States, and one of the largest submarine canyons in the world.

It was once not under water and exposed as land. The last time it was above water was during the last Ice Age, over 10,000 years ago. Sea level was about 400 feet (120 m) lower and the mouth of the Hudson River was near the edge of the continental shelf. That would put the river's mouth about 100 miles (160 km) east of its present site.

Sediment flowing helped carve the canyon along with underwater avalanches of mud and sand.

Tidal currents move up and down the channel and big storms move cold ocean water up the Hudson Canyon so it continues to be cut by traveling sediments.

Rumor has it that the Hudson Canyon also contains the remnants of pollution and trash from when New York City's sewage and garbage was dumped directly into the river. I have read online that there are plans to use new maps of the canyon to track contaminants from abandoned dumpsites off New York Harbor.

The channel from the Hudson River goes southeast into the ocean and deepens
directly east of most of New Jersey's popular beaches.

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