A Day in the Teton Mountains

You haven't seen mountains until you have been to the Teton mountains in Wyoming. Reaching elevations of close to 14,000 feet, these mountains touch the clouds! Today, MCC's field studies Geology group took a nice ten minute boat ride across Jenny Lake. Jenny Lake is a lake that was specifically formed from the melting of Teton's most recent glaciation, the Pinedale, which was dated to be around 70-13 thousand years ago. During the mile long hike, the group saw a specific type of metamorphic rock called gneiss which had pegmatite veins of quartz pegmatite.  And of course, granite was also found on the trail. Although the weather was rainy, cold, and cloudy, the group was determined to make it to Inspiration Point, which had the best view of Jenny Lake and the ancient moraines that hold the lake in place and the outwash plane that formed thousands of years ago. 

But the question remains about how these massive mountains formed. The Tetons are on a fault which is a specific place where there is crustal motion. The name of this fault is the Teton fault and long ago the land was pulled apart due to tensional stress. As the land eroded away, the less erosive metamorphic rock stayed creating these spectacular mountains. 

 Next to the Teton Mountains there is an end moraine which is composed of unsorted sediments. These sediments were deposited during the receding of the Pinedale glaciation. This also help form many of the lakes at the base of the Tetons. You can tell that it's a moraine due to the fact that there are pine trees growing along the moraine due to its low permeability. Beyond the moraines are stream terraces, flat region steps adjacent to the base of the mountain, that are formed by the Snake River. The river down cuts when the base level drops, also this is the river's response to the uplift of the region. 

On a couple of the mountains you can see some features such as arêtes which are basically a narrow, sharp edged ridge, as well as U-shaped valleys. Both of these features are due to valley glaciers. The Tetons have three glaciers the Teton, Teepee, and Middle-Teton glaciers. During the last 40 years these glaciers have lost 25 percent of their total surface area.