Moses Coulee Flood Bar Earthcache EarthCache
Moses Coulee Flood Bar Earthcache
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At this intersection between Washington State Highway 2 and Moses
Coulee Road you find yourself deep inside the Moses Coulee which
was formed by flood waters, but you are also up on a flood bar
formed during those same floods. Grand in scale, it takes a moment
to find the land features that form the flood bar.
Moses Coulee cuts into the Waterville Plateau, which lies in the
northwest corner of the Columbia River Plateau. Lava flows from the
Columbia River Basalt Group (laid in the late Miocene and early
Pliocene time which covers over 63,000 square miles) have been
extensively exposed by the erosion resulting from the Great Ice Age
Floods, which laid bare many layers of the basalt flows on the
edges of the plateau along the course of Moses Coulee.
Two million years ago the Pliestocene epoch began and Ice Age
glaciers invaded the area. They scoured the Columbia River Plateau,
reaching as far south as the middle of the Waterville Plateau
highlands above the Grand Coulee and south to the head of Moses
Coulee. In some areas north of the Grand Coulee they were as much
as 3km thick. Grooves in the exposed granite bedrock are still
visible in the area from the movement of glaciers and numerous
glacial erratics in the elevated regions to the Northwest of the
coulee. The south terminus of the Okanogan lobe is clearly marked
by an abrupt south limit of lumpy, rocky moraines which can be seen
while driving thorough the area or from satellite photography. The
ice-dammed Columbia River backed up to form Glacial Lake Columbia
and Lake Spokane, larger than Lake Roosevelt, which is currently
backed up in the same location behind the Grand Coulee Dam. The
overflow of these glacial lakes created Moses Coulee.
A coulee is: applied rather loosely to different landforms, all of
which refer to a kind of valley or drainage zone, usually a deep
gully formed by rain or melting snow and usually dry in the
summer.
A bar is: An underwater ridge, usually of sand and/or gravel, that
forms from the deposition and reworking of sediments by currents
and/or waves. Bars occur in rivers, river mouths and in offshore
waters.
Along the western side of the coulee is a flood bar with deposits
from the erosion created during the Great Ice Age Floods. From here
you can see the floor of Moses Coulee. Just north of you is a cut
in the western coulee wall, creating a shield to the rushing waters
and allowing the flood bar to form.
To get credit for this Earthcache send an email to the owner with
answers to the following:
1. Estimate the dimensions of the flood bar. How tall, long, and
wide.
2. Looking at the eastern wall of Moses Coulee, can you see
evidence of the different lava flows? How many do you see?
3. What does the ground look like? Are the rocks smooth or
angular?
You may post a picture, but please do not place answers in your
log.
Thanks for visiting.
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