Geology Lab Assignment

Glacial Processes.docx

Name: _______________________________

G205: Glaciers

A glacier is a body of ice and snow that moves under the influence of gravity and its own weight. Evidence that a glacier is moving includes crevasses, flow features on the surface of the glacier, and a stream emerging from the terminus of the glacier filled with ground rock called glacial flour.

All glaciers consist of two parts. The upper part is perennially covered with snow, and is referred to as the zone of accumulation. The lower part is the zone of ablation, where calving, melting, and evaporation occur. If, over a period of time, the amount of snow a glacier gains is greater than the amount of water and ice it loses, then the glacier will expand or advance. If the amount of water and ice a glacier loses is greater than the amount of snow it gains, then the glacier will shrink or retreat. This is referred to the mass balance of the glacier.

Figures 13.7 and 13.8 (11th)/13.3 and 13.4(10th)/Figures 13.1 and 13.2 (9th) in your lab manual show some of the unique landscape features created by mountain (also called valley) glaciers. Figures 13.15 and 13.16 show common features created by continental glaciers. Glaciers, especially valley glaciers, can be thought of as “rivers” of ice. In many ways, the rules governing stream flow also govern the flow mechanism of glacial ice. Just as flowing water will naturally seek out the lowest elevation, so will glaciers. Once the glacial ice of a valley glacier begins to flow downslope, the glacier occupies a valley that was formerly cut by stream erosion, thus changing its shape form a “V”-shaped stream valley to a “U”-shape profile that is flat at the base but very steep along the valley walls.

This lab examines the landscapes associated with both types of glaciers, and also the response of glaciers to climate change.

Part 1: Glacier Movement – Deformation or Basal Sliding?

Glacier Model

Materials:

10 ml Borax powderAirtight container or zip-lock bag
325 ml warm waterChute made from PVC pipe or cookie sheet
250 ml white glueTape/Rubber Bands
2 mixing bowlsRuler
Mixing spoonTimer
Food coloring (optional)Plastic drinking straw or spray bottle and water

Process:

1. Make the glacier gak (already made, but you can make it at home, too):

a. In the first mixing bowl, combine 200 ml warm water and 250 ml glue. Stir until well mixed.

b. In the second mixing bowl, combine 125 ml warm water and 10 ml of Borax powder. Stir until the powder is fully dissolved.

c. Combine the contents of the two mixing bowls. Stir until a single glob forms and cleans the sides of the bowl.

d. Optional: use food coloring to create different gak colors. Put half of the glob back into the first mixing bowl and add a few drops of food coloring. Knead the mixture, wearing rubber gloves to prevent staining your hands with the food coloring, until it is well mixed. Use the alternating colors in the experiment or smush the strips together to form a single striped glob of gak.

Experiment #1

1. Prop up one end of the PVC pipe chute (with books, rocks, etc.) so the glacier will be able to flow downhill. Think about the angle of repose from the mass wasting lab when deciding on how steep the chute might need to be.

3. Place the entire “glacier” at the top of the chute. Use the dry erase marker to mark the position of the front end of the glacier (the terminus), and the right and left sides of the glacier.

4. Set your timer for 5 minutes.

5. At the end of 5 minutes, mark the new location of the glacier terminus.

6. Take the chute down and place on a level surface to prevent further forward movement.

7. Measure and record the distance the glacier traveled from start to finish at the center, the left side, and the right side of the glacier. Repeat to obtain an average. Record the results in the table below. Determine the velocity of the three sections using the distance traveled from the table above and the elapsed time of 5 minutes. Don’t forget to convert minutes to seconds. Record the values in the table below.

Distance traveled by the glacial model (cm)
First Trial (cm)Second Trial (cm)Average (cm)Velocity (cm/sec)
Right side
Center
Left Side

8. When the glacier model initially flowed, what shape did the front of the glacier take (sketch it)?

9. What part of the glacier flowed fastest? Why?

10. Does this experiment more closely approximate glacial movement by deformation of the ice or by basal sliding?

11. What are your predictions for how the glacier will flow when a little water is added to the chute added compared to the first time you ran the experiment?

Experiment #2

1. Set up the experiment again, marking the terminus of the glacier.

13. Poke the plastic drinking straw through the glacier, as close to the top of the glacier as possible. Add 5 ml of water through the straw to simulate meltwater seeping down through the glacier. Alternatively, lightly mist the chute with water from the spray bottle.

14. Set your timer for 5 minutes.

At the end of 5 minutes, measure the distance the glacier traveled from start to finish at the center, the left side, and the right side of the glacier. Repeat and record the results in the table below. Determine the velocity of the glacier with basal water. Record the values in the table below.

Distance traveled by the glacial model (cm)
First Trial (cm)Second Trial (cm)Average (cm)Velocity (cm/sec)
Right side
Center
Left Side
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