The Jackson Lake Overlook in Wyoming provides a stunning view of Jackson Lake and the Teton Range, located in Grand Teton National Park. The area's geology and geological history are a combination of tectonic activity, glaciation, and sedimentation, making it a geologically rich and diverse landscape.
Geological History
Jackson Lake in Wyoming was formed through a series of geological events beginning with the uplift of the Teton Range due to tectonic forces, particularly along the Teton Fault, which occurred approximately 10 million years ago. This uplift created the dramatic topography of steep mountain peaks. During the Pleistocene Epoch, around 2.6 million to 11,700 years ago, massive glaciers advanced across the region, flowing down the valleys and sculpting the landscape into U-shaped valleys. As these glaciers moved, they eroded the earth, deepening and widening the existing valleys, including the area that would become Jackson Lake. At the end of the last Ice Age, the glaciers began to melt, and the resulting meltwater flowed into the newly formed basin, filling it with water and creating Jackson Lake. Additionally, as the glaciers melted, they brought sediments from the surrounding landscape, further shaping the lake. Today, Jackson Lake is continuously fed by rivers, including the Snake River, which drains the surrounding Teton Range, influencing the lake's water levels and ecological balance.
Geological Features
There are four primary geological features that can be seen from this overlook.
1. Teton Range Formation
The Teton Range, which rises dramatically to the west of Jackson Lake, is relatively young in geological terms, having formed over the past 9 million years. The Tetons are an example of a fault-block mountain range, created by movement along the Teton Fault. The range was uplifted when the Earth's crust stretched and broke, with the Teton Fault acting as the boundary where the land was thrust upward to form the mountains. The eastern side of the Teton Range (facing Jackson Lake) was pushed up, while the land on the western side dropped, creating a sharp contrast between the high peaks and the flat valley floor of Jackson Hole.
This uplift exposed ancient Precambrian rocks that are over 2.5 billion years old, some of the oldest rocks in North America. These rocks are primarily gneiss, schist, and granite, providing insight into the Earth's early crustal development.
2. Jackson Hole
The valley known as Jackson Hole is a grabben (a sunken block of land) that formed as a result of the same faulting process that uplifted the Tetons. The valley has gradually subsided while the mountains rose, creating a flat basin that is now home to Jackson Lake.
3. Glaciation
The landscape surrounding Jackson Lake was significantly shaped by glaciers during the Pleistocene Epoch (about 2.6 million to 11,700 years ago). During this period, large glaciers flowed from the high peaks of the Teton Range down into Jackson Hole. These glaciers carved U-shaped valleys and left behind moraines (ridges of debris) as they retreated.
- Jackson Lake itself was formed by glacial damming. The receding glaciers left moraines that blocked the flow of the Snake River, causing water to pool and form the lake. Today, Jackson Lake is one of the largest natural lakes in the region, although it has been enlarged by a man-made dam for water storage.
- Terminal moraines and other glacial features are still visible in the area, providing evidence of the massive ice sheets that once covered the landscape.
4. Sedimentation and Erosion
Over time, erosion has continued to shape the Teton Range and the surrounding landscape. The Snake River and other streams have carried sediment down from the mountains, depositing it in the valley. These sediments, along with volcanic ash from past eruptions in the region (notably from the nearby Yellowstone Plateau), have created layers of soil and sediment on the valley floor.
The geology of the Jackson Lake Overlook area provides a dramatic example of tectonic and glacial forces at work, showcasing the dynamic processes that shaped the Rocky Mountain region over millions of years.
References
Information above was referenced from the following sources:
Received permission to place from Grand Teton National Park
Activities
Go to the overlook and make observations about each of the four geological features (I have provided reference points to asssit); there is also an information board at the coordinates which provides some useful information:
- Teton Fault – Observe the mountains in the distance to the West and estimate the direction of the thrust (was it straight up or angled towards a particular direction on a compass). What does this say about the fault line?
- Grabben – Take a measurement from your GPS of the altitude that Jackson Lake sits at. From GZ and using paralax, each 1/2 inch of height represents 1,500 feet of altitude so you can use a finger as a guide to estimate the height difference between the mountains (to the West) and the Jackson valley (to the Southwest)
- Glaciation – Identify some evidence of glaciation in the landscape and explain why you think this is from glaciers. Hint you can see some in the mountains to the Northwest and West as well as the valley towards the South
- Sediment and Erosion – Identify areas of possible erosion or sediment and explain how you think they formed this way. Hint you can see some in the lake and the lakeshore as well as the mountains to the West