Julie McDermott

Geography 1000, 11:00 a.m.

LAKE BONNEVILLEI 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 drain? What are some characteristics (evidences) of the Lake? What happen to the landscape as a result? What did climate change have to do with the lake filling and draining?

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 there are other claims that the lake may have filled and receded as many as 28 times over the last 800,000 years. Hmmm…hard to know. Let’s just say that the lake was prehistoric, about 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.

Nice writing. Using italic for your quotes is helpful. Consider enlarging the text of your quotes as well.

Good idea to put your sources with quotes and other references. Maybe just make ‘em a bit larger for easy reading.

Photo taken by Julie McDermott at Red Rock Pass, Idaho

Photo taken by Julie McDermott at Red Rock Pass, Idaho

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 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

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 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

Photo taken by Julie McDermott at Red Rock Pass, Idaho

Photo taken by Julie McDermott

Snake River Canyon near Twin Falls, ID...Jim O'Connor photo

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 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.

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

Notice Julie’s use of arrows to point out shoreline beaches.

Photo taken by Tom Foster

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 high-density 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.

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

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

Geology for the RecordMarjorie A. Chan, Donald R. Currey, Andrea N. Dion and Holly S. Godsey

Terrific photos! Now, where did you get ‘em?

This source citation could include a bit more detail. The idea is to make it easy for a reader to find your original source.

Looks like famous Shoshone Falls, just east of Twin Falls, Idaho.

Enlarging the image can help reveal important detail.

Julie posed questions and then answered them. Very good approach to the concept of “scientific methodology”