Periglacial Processes and landforms Flashcards
What are the ice action periglacial processes?
Freeze thaw weathering- crack in rocks fill with water. When temperature drops, water freezes and expands causing the rock to shatter
Frost Heave- Water in the ground freezes and expands. This pushes the ground surface up, churning the soil. Large stones are pushed towards the surface
Ground ice- This usually consists of Ice wedges where melted water in summer fills up cracks in the ground. In winter this water freezes & expands, widening the cracks (freeze-thaw on a giant scale)
What is Solifluction?
When the active layer melts and becomes saturated. It begins to slide downhill if on a slope. It looks like a mudflow. Solifluction literally means ‘flowing soil’. It flows downhill as a solifluction lobe.
What is Ground Contraction?
The re-freezing of the active layer during severe winters causes the soil to contract. The ground can sink.
What is freezing of groundwater?
Where the cold temperatures cause freezing of any water held underground. This leads to the formation of ice cores beneath the surface (small frozen lakes)
What is Aoelian processes (wind)?
Wind transports a lot of periglacial material due to the lack of vegetation and dry nature of the ground (lots of dust storms)
What is Patterned ground?
Patterned ground is the collective term for a number of fairly small-scale features of periglacial environments. As a result of frost-heave, large stones eventually reach the surface and that the ground surface is domed. The stones then move radially, under gravity, down each domed surface to form a network of stone polygons, typically 1–2 m in diameter
What is stone polygons and garlands (patterned ground)?
These are patterned ground formed by frost heave and ground ice. On the flat, polygons are formed, and on slopes stone stripes are formed
What are ice wedges and how are they formed?
Downward narrowing masses of ice that are between 2 to 3 meters wide at the base and extend below the ground surface up to 10 meters. They form when a seasonal crack in the ground forms in the winter. At first, the crack is several millimeters wide and about a meter deep. When temperatures warm up in the summer, liquid water from the active layer fills the crack. This water then refreezes because the fracture extends into the sub-zero permafrost. This expansion then increases the width and depth of the fracture.
What are the two types of pingos and how do they form?
Open System Pingos
These are found where the permafrost is quite thin, especially in valley bottom locations. Water from the surrounding slopes collects in the valley bottom under gravity, freezes & expands. Because the permafrost is thin, it is easily pushed up by the expansion of ice below.
These are most common in East Greenland.
Closed System Pingos
These often form on the sites of small lakes. As permafrost advances under the lake in winter, it squeezes the talik beneath the lake into a mound. The lake drains away leaving a dome shaped hill on the surface
What are solifucation lobes?
A type of mass movement. In summer the active layer of permafrost melts and begins to flow where it is on a slope. This creates tongue-like features called solifluction lobes. These look like mudflows
What are scree slopes (Talus)?
Scree slopes develop at the base of exposed cliffs. Weathered fragments of rock fall off the cliff and form a large unstable pile of boulders below. The cliff is weathered by freeze thaw action and the scree slope is the debris created
