GLACIER MOVEMENT OVER A BEDROCK RIDGE AS SEEN AT MENDENHALL GLACIER, JUNEAU, ALASKA

Over the past decade, the rapid retreat of the Mendenhall Glacier, Juneau, Alaska has exposed a large schist ridge or "rib" striking approximately 160 (an 82 degree angle to the valley wall). The relatively unweathered stoss face of this rib offers the opportunity to develop a mathematical model to approximate the changing ice flow as a function of ice thickness through abundant striations trending from 140 to 230 degrees. The stoss face of this rib consists of a series of stoss and lee features. The striations reveal a repetitive pattern of changing ice flow up each of these features.

Using a tape and compass method, striation and joint plane data were collected along numerous transects approximately perpendicular to the strike of the form. Using this data, a physical model was developed to explain the plastic flow of the glacier over the ridge. More importantly, this data was used to develop and check a simple mathematical model of the affects of such an obstacle on glacier flow. This model utilizes velocity equations previously developed by others and the properties of adding vectors to crudely predict direction of flow at any point of one of these smaller stoss and lee features.