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Tonight Nova explained the Scablands of eastern Washington state - the result of a massive flood created when Lake Missoula (a glacial lake 15,000 years ago in western Montana and Idaho about half the size of Lake Michigan) burst threw a glacial damn taking about a week to scar the lands to the west.
But later in the show they claimed this flooding occured many times, which makes sense. If a glacier was blocking off a river, the glacier didnt go away when the damn broke, it just kept growing until a new damn was formed. So big and smaller floods carved out the Scablands during the last ice advance (why not even earlier ice advances?) over the period of maybe 20.000 years between 35 and 15 K bp with floods occuring maybe 1,000 years apart.
To bolster this theory Nova showed a rock face with about 15 clearly defined layers each representing different floods. At (or near) the bottom was a white layer of ash from an eruption of St Helens ~15, 000 years ago. I didn't see any layers below the ash fall, just the layers above.
The diagram below shows this structure
-------last layer from glacial flood 15 K bp----------------
-------layer from flood before that-------------------------
-------layer from flood before that-------------------------
-------layer from flood before that-------------------------
-------layer from flood before that-------------------------
-------layer from flood before that-------------------------
-------layer from flood before that-------------------------
-------layer from flood before that-------------------------
-------layer from flood before that-------------------------
-------layer from flood before that-------------------------
-------layer from flood before that-------------------------
-------layer from flood before that-------------------------
-------layer from flood before that-------------------------
-------St Helens ash layer 15 K bp-------------------------
See a problem with this theory? I mean, the general theory is sound - the notion that a glacier repeatedly blocked off a river while the ice sheets were advancing or stabilising resulting in repeated floods over 20,000 years as the damns kept breaking is logical. But it is not logical to say these 15 or so floods occured between the last flood 15 K bp and an ash layer from an eruption 15 K bp.
Anyone familiar with the subject matter? It seems to me the eruption/ash layer was mis-dated or the layers dont represent separate floods. Nova didn't provide dates for all the layers, but if the ash layer is accurate, the flooding occured more recently. But the flooding ended shortly after the ice began receding, and that supposedly began 13-14 K bp, so the only way the ash layer could have been deposited 15 K bp is if the 15 floods occured between 13-15 K bp with evidence of earlier floods obscured even more by the floods since the eruption. Thats about 15 floods over 2,000 years or maybe 1 every century. Nova wasn't clear about how long it took for the process of damn formation and flooding, but the 2 layers at the top and bottom could not have been dated to ~15 K...
Very interesting show nonetheless, reminded me of a documentary on Orca where a Tlingit elder said the great flood happened 13,000 years ago. I wonder if his ancestors had crossed over the Bering land bridge or had to paddle, but "the Deluge" almost enters the realm of reality given what we are finding out about the ice age (we're still in,
to global warming).
Or does global warming trigger an ice advance?
We're screwed, the Earth will do what it wants and we'll just try to hang on for the ride.
But later in the show they claimed this flooding occured many times, which makes sense. If a glacier was blocking off a river, the glacier didnt go away when the damn broke, it just kept growing until a new damn was formed. So big and smaller floods carved out the Scablands during the last ice advance (why not even earlier ice advances?) over the period of maybe 20.000 years between 35 and 15 K bp with floods occuring maybe 1,000 years apart.
To bolster this theory Nova showed a rock face with about 15 clearly defined layers each representing different floods. At (or near) the bottom was a white layer of ash from an eruption of St Helens ~15, 000 years ago. I didn't see any layers below the ash fall, just the layers above.
The diagram below shows this structure
-------last layer from glacial flood 15 K bp----------------
-------layer from flood before that-------------------------
-------layer from flood before that-------------------------
-------layer from flood before that-------------------------
-------layer from flood before that-------------------------
-------layer from flood before that-------------------------
-------layer from flood before that-------------------------
-------layer from flood before that-------------------------
-------layer from flood before that-------------------------
-------layer from flood before that-------------------------
-------layer from flood before that-------------------------
-------layer from flood before that-------------------------
-------layer from flood before that-------------------------
-------St Helens ash layer 15 K bp-------------------------
See a problem with this theory? I mean, the general theory is sound - the notion that a glacier repeatedly blocked off a river while the ice sheets were advancing or stabilising resulting in repeated floods over 20,000 years as the damns kept breaking is logical. But it is not logical to say these 15 or so floods occured between the last flood 15 K bp and an ash layer from an eruption 15 K bp.
Anyone familiar with the subject matter? It seems to me the eruption/ash layer was mis-dated or the layers dont represent separate floods. Nova didn't provide dates for all the layers, but if the ash layer is accurate, the flooding occured more recently. But the flooding ended shortly after the ice began receding, and that supposedly began 13-14 K bp, so the only way the ash layer could have been deposited 15 K bp is if the 15 floods occured between 13-15 K bp with evidence of earlier floods obscured even more by the floods since the eruption. Thats about 15 floods over 2,000 years or maybe 1 every century. Nova wasn't clear about how long it took for the process of damn formation and flooding, but the 2 layers at the top and bottom could not have been dated to ~15 K...
Very interesting show nonetheless, reminded me of a documentary on Orca where a Tlingit elder said the great flood happened 13,000 years ago. I wonder if his ancestors had crossed over the Bering land bridge or had to paddle, but "the Deluge" almost enters the realm of reality given what we are finding out about the ice age (we're still in,
to global warming).Or does global warming trigger an ice advance?
We're screwed, the Earth will do what it wants and we'll just try to hang on for the ride.
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