In order to understand how glaciers move one must understand the physical properties of ice. Ice can have both brittle and plastic properties. When subjected to large strain rate, ice will fracture (causing crevasses in glaciers), when the strain rate is small and constant, it can bend. If you've ever played with silly putty you've seen another material that has the same response to changes in strain rate. Water is on of the few substances for which pressure lowers the temperature of transition from liquid to solid such that at the bottom of ice sheets and glaciers (where pressure from the overburden is large) the melting point is subzero. This means that glaciers and ice sheets can have a water layer beneath them which helps them to flow by providing a lubricating film of water which allows the glacier to slide. Below are two experiments that can be done in the home to illustrate how ice flows.

Flubber Experiments: Approximating ice flow and the influences on flow speed.

Materials: Flubber PVC pipe (cut in half lengthwise) saran wrap cooking oil sandpaper ruler protractor freezer/microwave

Flubber Recipe:

Simply combine the two mixtures and work through the hands for several minutes until a consistent texture results. Drain any excess water. Flubber is easy to make and fun to work with and does not stick to hair or skin once formed (glue may stick to hands while working the Flubber to its correct consistency), however the Borax and glue are toxic and should not be ingested. We therefore advise against allowing young children to play with Flubber unsupervised. Flubber can be stored for several weeks in an air-tight bag (e.g. zip-lock). Re-work some warm water into the Flubber to return it to a desired consistency.

Download this worksheet to run your flubber experiments. Be sure to check out this website where there are movies of flubber flow.

Ice Experiments: Deformation of ice (brittle and ductile).

Materials: Mason's hammer shallow pan cup piece of cloth heavy metal key piece of brick or some other heavy object 6 ice cubes

1. Wrap two ice cubes in a piece of cloth. Use the hammer and hit the ice cubes several times. Open the cloth and notice what has happened to the ice cubes. Place the fragments of ice into a cup and wait two or three minutes. Notice what has happened to the ice. Record your observations.

What happened when you hit the ice with a hammer?

What happened when you allowed pieces of ice to touch one another in the cup?

What two properties of ice do hitting ice and allowing pieces of ice to touch one another demonstrate?

2. Place two ice cubes in a shallow pan. Put a piece of brick or another heavy object on one ice cube. Wait two or three minutes. Notice which ice cube melts faster. Also notice where the melting seems to be taking place. Record your observations.

Does ice with a weight on it seem to melt faster or slower than ice without a weight on it?

Where does the most melting seem to take place when ice has a weight on it?

How is ice with a weight on it like ice at the bottom of a glacier? Do you think the movement of a glacier begins at the top of the glacier or the bottom? Why?

3. Place two more ice cubes in a shallow pan. Place a heavy metal key or top of one ice cube. Put the pan in the freezer and leave it overnight. Examine the ice and notice the location of the key. Record your observations.

Where in the ice did you find the key?

How do you think ice flows around an object?

Sources:

L. Douglass, D. Ellis, & M. Magnoli (l985) Experiences in Earth-Space Science. Illinois: Laidlaw Brothers, Publishers.
L. Stearns and Erich Osterberg, "Modeling the Malaspina", Department of Geological Sciences, University of Maine, Orono.