GEOLOGY 445 - GLACIAL GEOLOGY

Lab 8 - Glaciofluvial Landscapes

Introduction

Below glacial firnlines, water takes on an increasing importance in shaping the glacial landscape.  Subglacially such shaping is, in all but cases of glacial stagnation, erased by subsequent glacial flow.  At and beyond glacial margins, however, glaciofluvial landforms are preserved.

Problem

Select a glaciated region (mountains are generally easier than plains, simply because of the ease of recognizing the glacial margin).  Find the topographic maps relevant to the region.  Draw generalized maps and detailed longitudinal profiles of lastglacial (Pinedale / Wisconsinan - equivalents) glaciofluvial features, and show their relationship to the modern river.  Include older (Bull Lake / Illinoian - equivalents) if evident.  Look for ~50 km without tributaries.

Suggested rivers:  Clark Fork of the Yellowstone (MT/WY), Tongue River, Big Goose Creek (Sheridan, WY), Clear Creek (Buffalo, WY), Owl Creek (Thermopolis, WY), Little Popo Agie (S of Lander, WY), Big Sandy Creek (Farson, WY), Blacks Fork (Granger, WY), North Platte (CO/WY), Yampa (Craig, CO), Rio Grande (Alamosa, CO).

Suggestions

For a base map for generalized mapping, consider photocopying a 1:250,000 (or 1:100,000) topographic map.  To recognize the remnants of former terraces, 1:24,000 maps will be required.  The detailed longitudinal profiles will require the use of intermediate as well as master (bold) contour lines. 

Consider the discussions of the evolution of terraces downstream from the Madison 'Slide and along lower Jack Creek.  We will also discuss in lab the landforms of the Paradise Valley (web page under construction).  Be alert for the effects of bedrock canyons (consider Hyalite/Middle Creek, south of Bozeman, MT, for example) on the long profile of aggradation/degradation.

Discussion

In your discussion, consider the following questions:

• How far downstream from the glacier terminus was the glacial presence felt?
• What was the approximate volume of glaciofluvial sediment deposition?
• How long did it take for the terrace to migrate that far (and how could you tell)?

As always, explain your results, discuss their implications, and explicitly state all necessary assumptions in the analysis.