Learning focus
Use this simulation to help students explain how temperature influences both the speed of glacier movement and the relative contributions of internal deformation and basal sliding.
Students should understand that a cold-based glacier can still move through internal deformation. As ice warms, it deforms more readily; when the bed reaches its local pressure melting point, basal sliding may also occur. Internal deformation continues in warm-based glaciers.
Getting started
Open Glacier scale and leave Labels and Start guide switched on for the first demonstration. The start guide shows the original marker positions, making displacement easier to follow.
Use Start, Pause, the step button or the timeline to inspect the movement. ½× playback is useful for the crystal close-ups. Reset returns the experiment to a paused start while keeping the selected conditions.
Changing temperature, water pressure or the main tab starts a fresh, paused experiment. Switching between Side view and Bird’s-eye view in the Temperature lab preserves the current conditions and progress.
Suggested teaching sequence
1. Compare warm-based and cold-based glaciers
Start the two glaciers together in Glacier scale. Ask students to follow the lowest marker first, then the surface marker.
In the cold-based example, the lowest marker remains fixed while the ice above it moves. In the warm-based example, the lowest marker moves over the rock, and the surface moves farther still. Use this to distinguish movement at the bed from deformation within the glacier.
Ask: “What evidence shows that the warm-based glacier is both sliding and deforming?”
Expected response: The lowest marker moves relative to the fixed rock marker, showing sliding. The markers above it travel different distances, showing internal deformation.
2. Connect glacier movement to processes within the ice
Use Between crystals and Within a crystal to establish these distinctions:
| Process | What students should look for |
|---|
| Intergranular deformation — between crystals | Neighbouring ice crystals change position relative to one another at their boundaries. |
| Intragranular deformation — within a crystal | Slip within the crystal lattice changes the shape of an individual crystal. |
| Basal sliding — at the glacier bed | Glacier ice moves over the ground beneath it. |
Emphasise that the crystal-scale processes contribute to the deformation of solid ice. They interact in real glaciers; the separate screens help students distinguish where each process occurs.
Ask: “Where is movement happening in each view: between crystals, inside a crystal or between the glacier and its bed?”
Use the colder and warmer examples to compare how much change occurs over the same interval.
3. Investigate the effect of temperature
Open Temperature lab and compare Very cold, Near melting and At PMP. Ask students to predict the outcome before each run, then compare the same point on the timeline.
Direct attention to the internal deformation and basal sliding bars. Students should identify that:
- Internal deformation increases as the model ice warms, even before the bed reaches PMP.
- Basal sliding becomes available at PMP.
- Both processes contribute to movement in the warm-based example.
At PMP, change Basal water pressure and repeat the comparison. Students can see that a warm bed does not produce one fixed sliding speed or guarantee that sliding contributes most of the movement.
The control represents water pressure, rather than simply the amount of meltwater. In real glaciers, drainage efficiency affects this pressure; more meltwater does not always produce faster sliding.
4. Compare movement through depth and across width
Pause a run and switch between the two viewing angles.
Side view shows how movement varies through the glacier’s depth. In this model, the surface travels farther than the ice beneath it.
Bird’s-eye view shows surface movement across the glacier’s width. The centre travels farther than the sides, producing a marker line that bows downstream. Resistance from the valley sides helps explain slower movement near the margins.
At PMP, both ends of the marker line also move downstream in the simulation. The gold ice-margin markers move, while the white triangles on the rock remain fixed as references. The centre still travels farther because internal deformation adds more movement there.
Ask: “How does each viewing angle help explain a different part of the glacier’s velocity pattern?”
Important points to reinforce
- PMP means pressure melting point. The temperature scale shows the difference from the local melting point. For example, −5°C means 5°C below PMP, not necessarily an absolute ice or air temperature of −5°C.
- Frozen to the bed does not mean the entire glacier is stationary. Ice above the bed can deform.
- Warm-based glaciers still undergo internal deformation. Sliding is an additional contribution.
- Intergranular and intragranular deformation are not exclusive to warm or cold ice.
- Fastest movement does not mean greatest deformation at that location. Avoid describing the surface as the place where deformation must be greatest simply because it moves fastest.
Interpreting the model
The coloured bars show an illustrative movement index, not speed in metres per year. Mint represents internal deformation and gold represents basal sliding. The values describe contributions to centre-line surface movement; they do not divide deformation into separate intergranular and intragranular percentages.
Slope, thickness and stress are held constant so students can focus on temperature and basal conditions. Crystal diagrams and displacements are exaggerated. The warm bird’s-eye example assumes sliding margins; actual margin conditions vary, and real glaciers can contain both cold and temperate regions.
Suggested follow-up task
“Explain how warming a glacier towards its pressure melting point can change both its rate of movement and its predominant movement mechanism.”
Ask students to support their explanation with observations from the glacier-scale view, one crystal close-up and the Temperature lab.