Glaciers: Periglacial Landforms/landscapes Flashcards
What are the periglacial landforms and landscapes?
- patterned ground
- ice wedges
- pingos
- terracettes
- blockfields
- thermokarst
- solifluction lobes
What is patterned ground?
the active layer refreezes in winter.
- frost heave of stones in and underneath the active layer. Ice lenses exist within permafrost, and grow by repeated freezing and thawing. Capillary action (movement of water) draws more water to the ice lens, so grow more. When ice lens expands, stones around the ice lens are shunted upwards. Larger stones roll down due to their weight and fine sediment fills the space to stop larger rocks. Polygons appear on flat surfaces, or stripes on steeper inclines (where the rocks roll downhill). They last a medium amount of time as they can be disrupted
What’s an example of patterned ground?
one example of them is the ‘stone rings’ in Svalbard.
What are ice wedges?
meltwater infiltrates small cracks in the permafrost during the summer and expands when freezing (frost action) - expands by approx 9%, widening and deepening the crack. This process repeats through the cycle of winter and summer and leaves a large ice wedge - which is likely to last a medium amount of time as temps must stay consistently cool.
What’s an example of ice wedges?
One example is the Banks Island in Canada.
What are pingos?
when permafrost is thin, water seeps into ground and freezes, pushing up the overlying sediment/ground (e.g. frost heave of an ice lens). This is an open and discontinuous pingo.
- A Closed (continuous) pingo forms under a lake, where permafrost is insulated and melts. The lake will eventually dry up or freeze - leaving unfrozen ground. An ice lens will develop through capillary action when temps drop and water groups together, permafrosts then frost heaves the unfrozen ground upwards, creating a mound. These pingos last a medium amount of time as warmer temps melt the ice lens
What’s an example of a pingo?
An example of a pingo is Pingo National Landmark, Canada.
What are terracettes?
frost heave pushes particles of soil upwards, which usually fall downhill through the process of creep (downslope movement of soil, slowly). However, vegetation can block the soil from falling, meaning it stays behind in a step shape - described as terraces. They last a short-medium amount of time, as thawing of the soil will disrupt the frost heave.
What’s an example of terracettes?
One example is the Kingston near Lewes, The South Downs.
What are blockfields?
a rock strewn landscape caused by extensive frost action of the landscape. Lasts a medium to long amount of time as loose rocks can be displaced by weathering.
What’s an example of blockfields?
One example is Broad Crag, The Lake District
What’s thermokarst?
Marshy, boggy wetlands caused when permafrost melts. Any ice lenses within the ground originally, or landforms such as pingos would melt and collapse. This can leave holes in the ground (topographic depressions), which will also fill with meltwater. These can last a short-medium amount of time as will dry up when temps rise.
What’s an example of thermokarst?
One example is Hudson Bay Lowlands, Canada.
What are solifluction lobes?
when the active layer thaws (melts in summer) excessive lubrication reduces friction between the soil particles so Solifluction occurs, where tongue-shaped lobes of soil fall down a Slope. Even on slopes as shallow as 2 degrees. Normally tends to last a short-medium amount of time
What’s an example of solifluction lobes?
one example is Seward Peninsula, Alaska
