Periglacial landforms

Polygonal ground and ponds on the tundra in Noatak National Preserve, Alaska, photographed from the air. — Ice-wedge polygons in Alaska's Noatak tundra. Repeated thermal contraction cracking and ice growth organise the permafrost landscape.

A suggested lesson sequence

Use these stages at your own pace. Pause for students to sketch, compare observations or lead part of the demonstration.

01
Observe
Define permafrost and distinguish ground ice from a glacier. Play a year and identify seasonal thaw above the dashed maximum active-layer depth.
Open Observe
02
Tinker
Increase Wedge development and trace the tapering ice mass. Explain winter thermal contraction, crack infilling and refreezing.
Open Tinker
03
Explain
Explain how repeated thermal cracking and refreezing build an ice wedge over many years.
Open Explain
04
Check
Choose an answer and explain your reasoning. Each question includes feedback.
Open Check

Rehearse with the model

The same scene and controls as the lab. Load it when you are ready; use Start projector for the full classroom view.

Before the lesson

Explain how repeated freezing and thawing produce ice wedges and patterned ground in cold landscapes.

Open the model before the lesson and choose a view that makes the important feature easy to see. Drag to rotate, and use the on-screen controls to change one variable at a time. The Controls panel explains the available keyboard shortcuts.

Pause the animation at a useful moment. Ask students what should happen next, then play it to test their explanation.

Guide the demonstration

Define permafrost and distinguish ground ice from a glacier. Play a year and identify seasonal thaw above the dashed maximum active-layer depth.

Increase Wedge development and trace the tapering ice mass. Explain winter thermal contraction, crack infilling and refreezing.

Discuss a common misconception

“Permafrost is simply a glacier buried beneath the soil.” Permafrost is ground that remains at or below zero degrees Celsius for at least two consecutive years. It may contain ground ice, but it need not be entirely frozen water. Seasonal thaw can affect the active layer above it, while glaciers are separate bodies of accumulated, flowing ice.

Build the explanation

Permafrost is ground that remains at or below 0 °C for at least two years. Seasonal thaw affects its active layer, while repeated thermal cracking and refreezing can build ice wedges.

Increase Wedge development and trace the tapering ice mass. Explain winter thermal contraction, crack infilling and refreezing.

The annual cycle and accumulated wedge width are separate comparisons; the width slider does not specify a growth rate.

Teaching notes

Distinguish processes in cold ground from erosion and deposition by moving glacier ice.

Explain ice wedges through repeated cracking and freezing rather than describing them as river channels.

Consider whether a landform records past cold conditions when interpreting relict features in the Cairngorms.

Check understanding

Open Check for 4 questions. Ask students to explain their choice before revealing the answer.

Return to the opening photograph. Ask students to identify one visible feature and explain which part of the model helps account for it.

Look more closely

Use these observations to connect the vocabulary to features students can identify.

Nivation

Blorenge above Llanfoist, with the shallow Cwm Craf hollow visible on its front slope. — Cwm Craf on Blorenge, Wales, has been interpreted as a former nivation hollow. Persistent snow patches can promote weathering and sediment removal without forming a moving glacier. The foreground hollow lies in a glacial moraine.

Read the definition

Blockfield

Angular rock blocks cover the summit of Foel Fras in Wales. — Blockfield on Foel Fras, Wales. Physical weathering breaks bedrock into angular fragments without changing its minerals.