MESSAGE
| DATE | 2017-02-14 |
| FROM | Rick Moen
|
| SUBJECT | Re: [Hangout-NYLXS] Geological floods
|
Quoting Ruben Safir (ruben-at-mrbrklyn.com):
> https://www.youtube.com/watch?v=Qgo4vZqRa48
Moral of the story: If you live downstream from a glacial ice-dam
impounding as much water as two of the Great Lakes, it's time to move.
I mentioned over the telephone that the bursting through of a glacial-fed
lake (a larger version of San Francisco Bay), through a narrow neck of
land during the last Ice Age, created the Golden Gate (the strait
connecting San Francisco Bay and the Sacramento & San Joaquin Rivers
that feed it with the Pacific Ocean). The same water-scouring effect,
at its greatest intensity about 18,000 years ago when the last Ice Ace
ended, created the undersea Hudson Canyon just outside the outlet of the
Hudson River.
Am guessing our conversation prompted you to make a search that found
that super-interesting Nova episode.
Of course, when the Golden Gate got carved out as a deep canyon, it
wasn't at the shoreline. Because ocean levels were far lower (about 300
feet lower), the Pacific Coast was about 30 miles west, just past the
present-day Farallon Islands.
Still, it might have been spectacular to be there when the lake
broke through, about 18k years before present. It
might have happened all at once.
On the telephone, I had that confused with another event 560,000 years
before present. At that time, the entire middle of California, what is
now the 800 mile long Central Valley betweent the Coast Range and the
Sierra Nevada, was filled with a colossal fresh-water lake that
geologists call Lake Corcoran. During the Late Pleistocene, lake levels
rose until the lake forced an outlet via Carquinez Strait, the
present-day outlet of the Sacramento-San Joaquin River Delta to San
Francisco Bay (and starting the carving out of the Golden Gate, further
west). That breakthough might also have been spectacular.
Similar breakthough events also occurred with other places like the
Mediterranean (the 'Zanclean flood' breakthrough near Gibraltar), Black
Sea (near Constantinople), and of course the Missoula Floods discussed
in the Nova episode.
https://en.wikipedia.org/wiki/Outburst_flood
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