Tuesday, June 3, 2008

The Moraine

At the West end of the Valley is the Glacial Moraine...just about where Bridal Veil Falls is...at one time...well.... before it was blown up...the Moraine blocked the Merced enough that it caused water to fill the Meadows...making much of the Valley a kinda swamp...at Spring High Water...I imagine most of it!...and I was thinking on the value of Wetlands today over in Two Top Pine Meadow...the Ponds over there are beginning to recede...but this evening I saw more and different birds in one place thant I have anywhere in the Valley....lots of still water...lots of mud...and grasses and bugs...and if not for the Moraine's sorta dam being gone...there would be a lot more of this!...dont know but something like this is going on at Mirror Lake....

now!...here's a curio!...Galen Clark writes up a lament about the Valley in 1907...


It may be interesting to the Public to know the cause of there being in recent years so much more activity in the river currents cutting away the river banks than during the earlier known history of Yosemite. When the El Capitan Iron Bridge was built in 1879 it was located across the narrow channel of the river between the two points of what remains of an old glacial terminal moraine. The river channel at this place was filled with large boulders which greatly obstructed the free outflow of the flood waters in the spring, causing extensive overflows of the low meadowland above, greatly interfering with travel, especially to Yosemite Falls and Mirror Lake. In order to remedy this matter the large boulders in the river channel at the Bridge were blasted and the fragments leveled down so as to give a free outflow of the flood waters. This increased the force of the river currents which now commenced its greater eroding work on the river banks and as the winding turns become more abrupt the destructive force annually increases. Some thorough system of protection should be promptly used to save the river banks from further damage.



and here...the culprit that dynamited the Moraine!...


The road crosses the El Capitan recessional moraine. This Tioga till impounded the waters of the latest Lake Yosemite (Matthes, 1930). Early visitors to Yosemite Valley were treated to mosquito-ridden swamps because the recessional moraines impeded the flow of the Merced River. In 1879, Galen Clark had a deeper channel blasted through the moraine (Schaffer, 1997). The resulting lower water table may have allowed conifers to encroach the meadows at the lower part of the valley, and the river has entrenched several feet into the valley floor. The action did ease the mosquito problem, though.



In the lament, Clark too mentions the encroachment of the conifers...basically the Valley floor was allowed to dry out...it doesn't seem likely in any conceivable scenario that it can be returned to being a wetland....

And this...

Two Top Pine meadow was control burned last Fall...and the Ponds there have black mud shorelines...in fact...the whole Meadow is kinda sticky slushy...over in Cook's there's no open black mud...the Hummocks are thriving...the Ponds sorta being taken over by the Grasses... Two Top may be the only meadow that is even remotely like what it was before the Tourists(no, I've learned Two Top was once plowed and pasture, while, from an overheard conversation, Cook's has never been plowed, which suggests it looks like a preTouirst Meadow...oh, but this something to determine! 8/3/10)...as I imagine the Indians in their Fall control burns kept the Meadows in an optimal wetland condition for the critters.

The Merced of course is now rip rapped in many places which prevented further wild erosion...the Creek from Wee Bridge to Lower Falls...in spite of protests that the paths and walk bridges would damage its hydrology...has pretty wild erosion...in fact I wonder if in twenty years or less it will begin to erode right up to the Bridge...right now it bends just at the last minute...from Wee Bridge to the Merced the Creek is rip rapped and banked...with some erosion...

What Clark recalls is the 'oxbows'...when the Creek and Merced were wild...they made loops through the Valley...the Floor being that flat...and the Moraine just enough of a dam to back things up all the way to Mirror Lake. The old loops are still visible in the Meadows...what I've been calling Ponds.


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