Julie McDermott
Geography 1000, 11:00 a.m.
LAKE BONNEVILLE
I can’t remember a time in my adult life when my eyes have not been drawn to the Lake
Bonneville shoreline and not been fascinated by its far reaches and enormity. When we were
given the assignment to explore topics for our eportfolio, I knew exactly what I was interested
in focusing on. Having said that, now that I think about it, I find it quite odd that I haven’t
explored the lake’s history, or evidences for that matter, until now.
Questions that come to mind and that I will explore are the following…What caused the lake
to fill? What area did the lake cover and when did the lake exist? What caused the lake to
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drain? What are some characteristics (evidences) of the Lake?
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as a result? What did climate change have to do with the lake
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and draining?
enlarging the text of your quotes
as well.
What caused the lake to fill: From reading in Wikipedia, I have
learned that Lake Bonneville
was a prehistoric pluvial lake. Pluvial comes from the Latin word pluvia, which means “rain”.
It was the largest of the lakes (I did not know that there were other lakes in the region) that
existed in the great basin area. The formation of such a lake occurs… When warm air from arid
regions meets chilled air from glaciers, it creates cloudy, cool, rainy weather beyond the terminus of the
glacier. This type of humid climate was present during the last glacial period in North America, and causes
more precipitation than evaporation. The increase in rainfall fills the drainage basin and forms a lake. Stanley
Chernicoff 1995, Geology, an Introduction to Physical Geology
During interglacial periods, the climate becomes arid once more and causes these lakes to evaporate and dry
up. Fredrick K. Lutgen, Edward J. Tarbuck 1987, The Earth, An Introduction to physical Geography
What area did the lake cover?: Lake Bonneville was
mostly in Utah covering approximately 1/3 of the state, and
covering the area we currently refer to as The Great Basin,
reaching into present day Nevada and Idaho. Some reports
claim that the lake formed about 32,000 years ago and
existed until about 14,500
years
ago,
but your
theresources
are other
Good
idea
to put
claims that the lake maywith
havequotes
filled and
as many as
and receded
other references.
28 times over the last 800,000 years. Hmmm…hard to
Maybe just make ‘em a bit larger
know. Let’s just say that the lake was prehistoric, about
for easy reading.
the size of Lake Michigan…and much deeper… like about
1,000 feet deep (800 feet deep in the Salt Lake area), and
dried up thousands of years ago.
What caused the lake to drain, and where: Lake Bonneville
was released through The Red Rock Pass in southern Idaho. I
paid a visit to the area in July. If you didn’t know what had
occurred there thousands of years ago, the area would seem
quite insignificant but I found myself wanting to stay and
explore the landscape, including Marsh Creek Valley, where
the catastrophic flood
Photo taken by Julie McDermott at Red Rock
Pass, Idaho
flowed. Too bad I didn’t have the time. Red Rock
Pass is geologically significant as the spillway of the
ancient lake. It’s located along US highway 91.
The pass was cut through resistant Paleozoic shale, limestone,
and dolomite, and forms a narrow gap two miles in length. At
one time the pass was 300 feet higher, where the shoreline of
the lake stood. Idaho for the Curious, by Cort Conley, ©1982 Wikipedia
Photo taken by Julie McDermott at Red Rock Pass, Idaho
You are standing in the outlet of
ancient lake bonneville. A vast
prehistiric inland sea, of which Salt
Lake is a modern remnant.
Covering over 20,000 square miles
when it overflowed here about
14,500 years ago, its winding
shoreline would have stretched from
here to New Orleans if it were
straightened out. This pass was
deepened considerably when Lake Photo taken by Julie McDermott at Red Rock Pass, Idaho
Bonneville began to flow into Snake
River. For a time, a torrent several times larger than the amazon was dischared
here. Finally, with a hotter drier climate that slowly emerged about 8,000 years
ago, Lake Bonneville gradually disappeared.…above plaque
It is believed that during the last ice age, lava flows in the vicinity of Pocatello began to divert the Bear River
through Lake Thatcher and then into Lake Bonneville. This sudden influx caused Bonneville to overflow at Red
Rock about 14,500 years ago. This overflow caused a sudden erosion of unconsolidated material on the
northern shoreline near Red Rock Pass. As the material gave way, Marsh Creek Valley, immediately
downstream, was flooded from wall to wall, and the rapid discharge eroded the pass to its present level. The
flood then flowed into the Snake River Plain, generally following the path of the present-day Snake River to its
outlet in the Pacific Northwest. Univ. of Utah Media – Lake Bonneville – accessed 2009-08-19…Wikipedia
The Bonneville Flood, as it is known, was a catastrophic event. The maximum discharge was about 15 million
cubic feet per second (420,000 m³/s), or about three times the average flow of the Amazon River, the world's
largest river. The speed of flow was approximately 16 mph (7 m/s), and though peak flow lasted only a few
days, voluminous discharges may have continued for at least a year.
http://www.media.utah.edu/UHE/l/LAKEBONNEVILLE.html...Wikepedia
Photo taken by Tom Foster
Evidences and characteristics of the lake and
flood: Evidence of the lakes existence can be
seen in the form of wave eroded shore lines all
along the Wasatch front, areas of Cache Valley,
and elsewhere. In this photo taken in Logan
near Utah State University, you can see at least
3 shore lines. There are no shorelines between
what we
call the
Bonneville
Notice Julie’s use of arrows to
point out shoreline beaches.
Photo taken by Julie McDermott
shoreline,
and the
next major shoreline which we call the Provo shoreline
(about 340 feet lower). This would indicate that the lake
drained quite rapidly and “catastrophically”, scouring the
canyon walls of the Snake River on its route to the Pacific
Ocean.
Snake River Canyon near Twin Falls, ID...Jim O'Connor
photo
The five major shoreline levels of Great Salt
Lake and Lake Bonneville are visible from
this site: the Bonneville, Provo, and
Stansbury levels of Lake Bonneville, and
Gilbert and historic levels of Great Salt
Lake.
Wikipedia
This aerial view shows the Point of the Mountain
spit, which sits at the south end of the Salt Lake
Valley. During the Pleistocene, this was the
shoreline of Lake Bonneville. This shoreline
geoantiquity is a world-class paragliding and hang
gliding area that is being converted into highdensity residential housing (left). To meet urban
growth needs, large amounts of sand and gravel
are being extracted from this Lake Bonneville
landform. Photo supplied courtesy of hang glider
pilot Mark Bennett.
Copyright@ 2011 Official Website of US Magnesium LLC
This photo is obviously quite old as the area is now full of high-density residential housing.
Boulders tumbled by the Lake Bonneville flood found on the Snake River Canyon floor
Photo taken by Tom Foster
The largest of the rocks that
rolled beneath the flood are
rounded boulders of basalt
that look like huge black
watermelons, the melon
gravel. These boulders, most
several feet in diameter, now
litter the surfaces of giant
gravel bars as much as several
hundred feet high; they make hills within the canyon. Look for those gravel bars in the broad reaches of the
canyon floor immediately downstream from the narrow gorges. The Lake Bonneville Flood, By, Vita Taube and Jacqueline
Harvey…Field Nodule Preview
Terrific photos! Now, where did
you get ‘em?
Photo taken by Tom Foster
Geology for the Record
Marjorie A. Chan, Donald R. Currey, Andrea N. Dion and Holly S. Godsey
Looks like famous Shoshone Falls,
just east of Twin Falls, Idaho.
Enlarging the image can help
reveal important detail.
This source citation could include a
bit more detail. The idea is to
make it easy for a reader to find
your original source.
Julie posed questions and then
answered them. Very good
approach to the concept of
“scientific methodology”