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Re: Ocean Depth

On Wed, 16 Oct 1996 01:56:33 -0600 Jim Green said:

What is the range of the depth of the oceans??? Is 3-5km reasonable?

It depends on which ocean and where you are in the ocean. The Atlantic and
Pacific are very different because the shores of the Atlantic are tectonically
passive while much of the Pacific is bounded by active plate margins and most
of these are subduction zones. The Atlantic shelves are roughly 100-200m
deep and extend 50-100 km from shore. In the next 100-200 km the ocean drops
off from the shelf to the abyssal plains at a depth of 4-6 km. The abyssal
plains account for the largest area of the ocean, but are split in the mid
Atlantic by a volcanic ridge roughly a km wide and rising to depth of about
2 km. Of course there are volcanic sea mounts all over the place and some
(Bermuda) actually break the surface. While the Atlantic is more or less
symetric about the mid Atlantic ridge, which makes sense since this is where
it came from, the Pacific is much more complicated. Starting from S. America
the shelf is only about 1/2 the width of an Atlantic shelf and drops into
an 8 km trench. It then rises from the trench to roughly 4km then up to 2 km
for the E. Pacific Rise (another spreading center like the mid Atlantic) then
gradually back to 4 km until it approaches the Tonga Trench (11 km), then back
to around 3 or 4 km until it rises to meet the Australian shelf. If we went
to Japan instead of Australia we'd get a similar result, trench, then Japan,
but the trench is not as deep as the Tonga, and very close to Japan. More
like the S. American side.