Glaciers: Past and Present in the Jackson Hole Valley
Teton Glacier from Teewinot Summit
Alpine glaciers, such as the ones found in the Teton mountain range, have played a crucial role in shaping the breathtaking landscape we admire today. Approximately 23,000 years ago, during the period known as the Pinedale Glaciation, the glaciers reached their maximum extent. By around 10,000 years ago, most of the Yellowstone region was ice-free, signaling the conclusion of the Pleistocene epoch. From 1400 to 1850, North America experienced a minor climatic shift, ushering in the Little Ice Age and supporting the growth of alpine glaciers. During this period, glaciers once again advanced down the mountains, eroding rock and debris from their cirques. Acting as powerful bulldozers, glaciers left behind moraines—debris piles—along their edges as they moved.
Recessional Moraine of Teton Glacier from Disappointment Peak
In the photograph provided above, the recessional moraine formed by the activity of the Teton glacier during the little ice age is visible from Disappointment Peak. These moraine features serve as vital indicators for scientists to measure historical glacier retreats and advances. Notably, the Teton Glacier stands out as one of the largest in the American Rockies. The information collected from this location plays a critical role in enhancing our comprehension of the contemporary climate change dynamics on our planet.
Geomorphology of the Jackson Hole valley is nothing short of fascinating. The surrounding landscape is a natural classroom in many facets. It shows us evidence of powerful forces that have created what we see today. At surface level, there are few agents of change as effective as glaciers. During the Pleistocene, or the last ice age, much of Jackson Hole was inundated by enormous rivers of ice.
Starting about 2.5 million years ago, the earths climate began to shift towards a sustained period of cold temperatures that lasted until about 15,000 years ago. During this time there were many periods of glacial advance and retreat. Our discussion is relevant to the most recent of those periods, the Bull Lake, and Pinedale glaciations. The Bull Lake glacial period lasted roughly 70,000 years, from 200,000 to 130,000 years ago. The smaller Pinedale spanned about 20,000 years, from 30,000 to 10,000 years ago.
In the photo above, you can see the maximum extent of the Pinedale glacial period highlighted by the white outline. Known as a terminal moraine, it is as far as the glaciers from that period ever expanded.
Highlighted in red are some the few remaining preservations of Bull Lake moraine depositions. Something that is very apparent with these is the obvious interruption to the continuity of this older moraine. A result of cottonwood creek boring its way through the moraine and creating an outwash plain in the gap as it meanders back and forth over time.
Knowing the fundamentals of these land altering mechanisms allows one to draw conclusions about events, and timeline, that created what is seen around us in Grand Teton National Park, and the surrounding region.