Pinedale Glaciation

Over the course of the last few days, we have observed many features that resulted from glaciation. There are two recent glaciers that impacted the Colorado Rockies region. 

First, there was the Bull Lake Glacier which occurred from about 160-130 thousand years ago, and it covered most of the Eastern Rockies region. After this, the Pinedalce Glacier occurred from around 70-13 thousand years ago. During this time period, several valley glaciers merged and moved along lower landscapes, which then formed the Cordilleran Ice Sheet.

Our first encounter with the features of the Pinedale Glacier was with Glacial Boulder, near Inspiration Point in Yellowstone National Park. Glacial Boulder is a prime example of an erratic. Erratics are rocks or boulders, that are transported via a glacier, and deposited in another environment. Glacial Boulder has a 60 foot diameter, and a height of about 16 feet 4 inches. It is a granite erratic, composed of quartz (SiO2), Microcline (KAlSi3O8), hornblende (Ca2(Mg,Fe,Al)5(Al,Si)8O22(OH)2), and some biotite (K(Mg,Fe)3(AlSi3O10)(F,OH)2). 

While looking at the Tetons there are three distinct features that form from valley glaciers. One feature is a u-shaped valleys, which are valleys shaped in a "U". Another feature is an arête, which are narrow, sharp ridges. The last feature are horns, mountains with a sharp, pyramid-like peak. There are three glaciers that are on the Tetons, the Teton glacier, the Teepee and the Middle-Teton glacier. These glaciers have lost 25 percent of their total surface area within the last 40 years. Also at the base of the Tetons are glacial deposits called end moraines. These end moraines are composed of unesorted sediments called till and are deposited by the receding of the Pinedale glacier. One way to tell that there is a moraine is there is a line off pine trees which grow along the moraine due to its low permeability.