IB Geography C.2.2 Periglacial Processes and Landscape Features Notes

The Active Layer Controls Periglacial Movement

1. Periglacial environments experience intense frost action around the margins of present or former ice sheets, commonly where permafrost underlies a seasonally thawed active layer.
2. The active layer thaws from the surface in summer but remains underlain by frozen ground, so meltwater may be trapped above an impermeable permafrost table.
3. Repeated seasonal freezing and thawing therefore controls soil movement, drainage and landform development.

Freeze-Thaw, Frost Heave and Solifluction Move Material

1. Freeze-thaw weathering breaks jointed rock when water freezes, expands and repeatedly widens cracks until angular fragments detach.
2. Frost heave occurs when ice lenses grow in fine sediment and lift stones or soil upward as water migrates towards the freezing front.
3. Differential heave and thaw sorting can organize stones into circles, polygons or stripes according to slope and sediment conditions.

1. Solifluction moves the saturated active layer slowly downslope when thawed surface material rests on frozen, impermeable ground.

Thermokarst Develops When Ground Ice Thaws

1. When ice-rich permafrost thaws, the loss of ground-ice volume causes uneven subsidence that forms hollows, ponds and disrupted drainage.
2. Water collecting in a thaw hollow absorbs solar energy and transfers heat to surrounding frozen ground, which can enlarge the depression through positive feedback.

1. Drainage can later empty a thermokarst lake if erosion connects it to a lower channel, showing that thaw does not produce one fixed landscape pathway.

Pingos Record the Growth of Ground Ice

1. A pingo forms when freezing groundwater expands or when water is forced beneath a growing ice core, pushing overlying sediment into a rounded hill.
2. Closed-system pingos commonly develop in drained lake basins as surrounding permafrost advances inward, while open-system pingos receive groundwater moving under hydraulic pressure.

1. When the ice core melts, the summit may collapse and leave a crater or pond that records the former pingo.

Warming Alters Periglacial Process Rates

1. A deeper active layer can increase slope movement, damage infrastructure and expose stored organic carbon to decomposition.
2. Thawing permafrost may initially increase water supply but later improve drainage or cause lake loss, so hydrological effects vary with ground-ice content and topography.
3. Landscape response is spatially uneven because snow cover, vegetation, sediment type, aspect and local hydrology control how heat reaches frozen ground.

Periglacial Landforms Reveal Ground Conditions

1. Patterned ground indicates repeated frost sorting, pingos indicate groundwater and ground-ice growth, and thermokarst indicates the loss of ice-rich permafrost.
2. Interpreting these features requires linking visible form to subsurface water, ice and temperature conditions.