Columbia River Basin:
The Columbia River pours more
water into the Pacific Ocean than any
other river in North or South America. In
its 1,270 mile course to the Pacific Ocean,
the Columbia flows through four mountain
ranges -- the Rockies, Selkirks, Cascades,
and coastal mountains -- and drains
258,000 square miles.
The mainstem of the
Columbia rises in Columbia Lake on the west slope of the
Rocky Mountain Range in Canada.
Its largest tributary,
the Snake, travels 1,038 miles from its
source in Yellowstone National Park in
Wyoming before joining the Columbia.
When Lewis and Clark explored the
region in the early 19th century, huge
numbers of fish (salmon) returned to spawn every
year. "The multitudes of this fish are
almost inconceivable," Clark wrote in the
autumn of 1805. At that time, the
Columbia and its tributaries provided
12,935 miles of pristine river habitat.
Columbia River Flood Basalts:
During late Miocene and early Pliocene times
(between 17 and 6 million years ago),
one of the largest basaltic lava floods ever to
appear on the earths surface engulfed about
63,000 square miles of the Pacific Northwest.
Over a period of perhaps 10 to 15 million
years lava flow after lava flow poured out,
eventually accumulating to a thickness of
more than 6,000 feet.
Over 300 high-volume individual lava
flows have been identified, along with
countless smaller flows.
Numerous linear
vents, some over 90 miles long, show
where lava erupted near the eastern edge of
the Columbia River Basalts. Older vents
were probably buried by younger flows.
As the molten rock came to
the surface, the earths crust gradually
sank into the space left by the rising lava. The
subsidence of the crust produced a large,
slightly depressed lava plain now known as the
Columbia Basin (Plateau). The ancient
Columbia River was forced into its present course by
the northwesterly advancing lava.
Columbia River Gorge National Scenic Area:
The Columbia River Gorge is a spectacular river
canyon cutting the only sea-level route through the
Cascade Mountain Range.
The Gorge is 80 miles long and up
to 4,000 feet deep, with the north canyon walls in
Washington State and the
south canyon walls in Oregon State.
The Columbia River Gorge National Scenic Area is located
east of Portland along both sides of the
Columbia River.
Missoula Floods:
With the beginning of the Pleistocene
time, about one million years ago, cooling
temperatures provided conditions favorable
for the creation of great sheets of moving ice.
Thus began the Ice Age.
At the end of the last Ice Age, a finger
of the Cordilleran ice sheet crept southward into the
Idaho panhandle, forming a large ice dam
that blocked the mouth of the Clark Fork River,
creating a massive lake 2,000 feet deep
and containing more than 500 cubic miles of water.
Glacial Lake Missoula stretched eastward
for some 200 miles and contained more water
than Lake Erie and Lake Ontario combined.
When the highest of these ice dams failed, lake
water burst through, shooting out at a rate
10 times the combined flow of all
the rivers of the world.
This towering mass of water and ice
literally shook the ground as it thundered toward the
Pacific Ocean, stripping away hundreds
of feet of soil and cutting deep canyons -- "coulees"
-- into the underlying bedrock. With
flood speeds approaching 65 miles per hour,
the lake would have drained in as little as 48 hours.
Over time the Cordilleran ice sheet
continued moving south and blocked the Clark Fork
River again and again, recreating Glacial
Lake Missoula. Over approximately 2,500 years,
the lake, ice dam and flooding sequence
was repeated dozens of times, leaving a lasting
mark on the landscape.
Wallula Gap:
Glacial-outburst waters that crossed
the Channeled Scablands during the
Spokane floods (Missoula Floods) were channeled
through Wallula Gap. For several
weeks, as much as 200 cubic miles
of water per day were delivered to a
gap that could discharge less than
40 cubic miles per day. Ponded
water filled the Pasco Basin and the
Yakima and Touchet valleys to form
temporary Lake Lewis.
Geologic Maps of Washington:
- Geologic Map of Washington State with Select Stratigraphic
Units. (Click to enlarge). From: King and Beikman, USGS, 1974.
- Geologic Map of Washington State with Select Stratigraphic Units. (Click to enlarge).
From: Schuster, Washington DNR, 1992.
-- Excerpts from:
U.S. Army Corps of Engineers Website, 2002,
USGS/NPS Geology in the Parks Website, 2002,
U.S. National Park Service, Lake Roosevelt National Recreation Area Website, 2002,
U.S. National Park Service, Ice Age Floods Website, 2002,
U.S. National Park Service, National Natural Landmarks Program Website,
2002,
and
U.S. Forest Service, Columbia Gorge National Scenic Area Website, 2002
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