TOPIC 11 & 12

Where are nivation hollows located?

In the Northern Hemisphere on a slope that faces northeast. This orientation is most protected from the warming effects of the sun.

Where does pore ice develop?

In the pore spaces between soil and sediment particles where liquid water can accumulate and freeze.

What is permafrost?

Permafrost is a condition where a layer of soil, sediment, or rock below the ground surface remains frozen for a period greater than a year.

When creating periglacial landforms, what element is not necessary?

Permafrost.

Where are taliks found in areas with continuous permafrost areas? Why?

Under lakes because of the ability of water to store and vertically transfer heat energy.

Many periglacial regions are...

Underlain by permafrost and it influences geomorphic processes acting in this region of the world.

What is a closed talik?

Unforzen ground that is found within a mass of permafrost.

What is a through talk?

Unfrozen ground that is exposed to the ground surface and to a larger mass of unfrozen ground beneath it.

Where does water go during the development of these features? Describe what happens next.

Water migrates under some type of pressure from unfrozen parts of the soil to the ice mass. Then the liquid water comes in contact with the segregated ice mass it freezes, enlarging the feature.

How are ice wedges believed to be formed? What is the rate of growth?

When a seasonal crack in the ground forms in the winter. At first the crack is several millimeters wide and about a meter deep.

Where are exposed rock outcrops common?

Periglacial regions of the world.

What two ingredients does the development of the hollow require?

1.) A snow patch that returns to the same area year after year 2.) A slope to allow for erosional transport of material out of the developing depression.

What percentage of the world is permafrost found in?

25% of the Earth's non-glaciated land surface.

What is gelifluction?

A form of solifluction where the moving materials slide over a slick permafrost layer.

What is the name of a common feature created by nivation?

A nivation hollow.

What are surface soils and sediments in a periglacial environment frequently influence by?

A variety of a different types of ground ice.

What is an open talik?

An area of unfrozen ground that is open to the ground surface but otherwise enclosed in permafrost.

What do snow patches that persist through the warm season create?

An environment for physical weathering at their margins.

What do most deposits of permafrost have? Describe it.

An upper active layer that is between 1 to 3 meters thick. This active layers is subject to a cyclic thaw during the summer season.

Describe needle ice.

Consists if groups of narrow ice slivers that are up to several centimeters long. They normally form in moist soils when temperatures drop below freezing overnight.

Describe continuous permafrost.

Continuous permafrost exists over the landscape as an uninterrupted layer.

Where were periglacial areas located?

At the periphery of past Pleistocene glaciers.

What is the critical temperature for the development of frost induced proctoring?

Between -4 and -15 degrees celcius.

By what are periglacial areas influenced?

By frost action.

What are the five types of permafrost?

Continuous permafrost, discontinuous permafrost, sporadic permafrost, alpine permafrost, and subsea permafrost.

Why is it that each winter new cracks form in the ice wedge?

Contraction.

What are ice wedges?

Downward narrowing masses of ice that are between 2-3 meters wide at the base and extend below the ground surface up to 10 m.

What can needle ice do on sloped surfaces?

Enhance soil creep by moving soil particles at right angles to the grade.

How do many forms of segregated ice exist? What are they sometimes called while in this form?

Extensive horizontal layers. They are sometimes called ice lenses.

What can cause the fracturing of rock along natural bedding planes and joints leading to rockfalls?

Extreme variations in temperature. Mainly due to frost wedging and insolation weathering.

What is alpine permafrost?

Found at higher elevations in areas outside where continuous or discontinuous permafrost is common.

What are the three processes of nivation?

Frost weathering at the margins of snow patches; meltwater erosion; and gelifluction.

Describe subsea permafrost.

Frozen ground that exists in the sediments beneath seawater. Larges areas of subsea permafrost exists along the northern coastal edge of Russia, Alaska, and parts of northern Canada.

What does repetition of thawing allow?

Further fracturing because the liquid water us able to fill newly developed cracks.

What does the discharge of most streams in periglacial regions do?

It exhibits particular temporal patterns. Most of the flow tends to occur during a period of weeks when snowmelt occurs. The discharge patterns of these streams may also show wide fluctuations that are timed diurnally. This is unlike temperate and tropical streams where discharge is taking place throughout the year. The concentration of discharge in a short period leaves some peculiar features. These short-lived streams tend to have poorly developed shallow braided channels. When discharge is suddenly reduced, large quantities of gravel and boulders are left on the landscape where the flow was taking place. The final unique characteristic of periglacial streams is that their channels can be beaded with deep pools. Beaded channels develop when a stream passes over a network of ice wedges. Thermal properties of the flowing water cause the ice wedges to melt producing pools.

Where are most masses of segregated ice found?

Just below the active layer.

What happens to the crack 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. The freezing of the water results in a volumetric expansion of about 9%. This expansion than increases the width and depth of the fracture.

What are taliks?

Localizes unfrozen layers of ice that are located on top, underneath, or within masses of permafrost.

What is segregated ice? Why do they grow where they grow?

Masses of almost pure ice that grow within permafrost. They grow here because of liquid water diffusion.

What happens if a snow patch is on a grade?

Meltwater along the base of the snow patch will transport the weathered rock fragments downslope. They can also insolate the soil and sediments that ay underneath it.

What can each cycle of ice addition be identified as?

Narrow layers called foliations.

Describe a nivation hollow.

Nivation hollows have been known to develop under snow patches in just a few seasons.

Which three forms of processes tend to dominate in periglacial environments?

Nivation; eolian erosion and deposition; and fluvial erosion and deposition.

Describe sporadic permafrost.

Occurs where small islands of permafrost are scattered in generally unfrozen areas.

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Pingos are ice-cored hills with a height between 3 to 70 meters and a diameter between 30 to 1000 meters (Figure 10ag-9). Most pingos are circular in shape. Smaller pingos tend to have a curved top. Large ones usually have exposed ice at their top and the melting of this ice often forms a crater. Sometimes the craters are filled with water forming a lake. The ice at the core of pingos is thought to accumulate because of cryostatic pressure and artesian groundwater flow. The development of a cryostatic pingo begins with a lake with no permafrost beneath it (talik). The lake then gradually fills in with sediment and invading permafrost isolates the remaining water in the lake's sediments. Continued inward and downward freezing of the old lake sediments generates enough pressure to move pore water upward. This pore water then begins to freeze to form a segregated mass of ice at the core of the developing pingo. Artesian pingos develop when a supply of groundwater is channeled to a particular location where it freezes just below the ground surface. Some pingos are still actively growing. The maximum rates of vertical growth of young pingos can be as high as 1.5 meters per year. The dating of pingos has reveled that these features are generally less than 10,000 years old. Many small ones in the Arctic have ages that are less than a few hundred years old. Scientists estimate that several thousand exist in the periglacial regions of the Northern Hemisphere.

What is the most common form of ground ice?

Pore ice.

What are the common depths of permafrost?

Several hundred meters.

What two elements contract temperatures dropping way below 0 degrees celsius?

Soil and ice (like other solid materials)

What can extreme cold temperatures cause during this season?

Soil contraction.

Needle ice plays an active role in the loosening of what? How?

Soil for erosion. It tends to move small rocks upward to the soil surface.

What are the four occurring forms of mass movement?

Solifluction, gelifluction, frost creep, and rockfalls.

What can some ice wedges do in arid cold environments? What are these called?

Some ice wedges can accumulate quantities of wind blown sand within their winter cracks. These are called sand wedges.

What is a characteristic of periglacial areas? What do they often do?

Strong winds. They often more large quantities of loose sediment and soil (especially in the summer, due to increases in steam discharge, drying of sediments, and the melting of depositional features - including sand dunes, loess accumulations, and sand sheets).

What can water diffusion be caused by?

Temperature and pressure gradients, gravity, and by the movement of groundwater under pressure.

What does the quantity of the deposit indicate?

That the frost weathering process operates over andover again in repreated cycles of freeze-thaw.

What can larger bodies with taliks underneath them do?

They can store and transfer more heat energy downward.

What are the temperatures at the margins of the snow? What is the result of this?

They fluctuate between above and below 0 degrees celsius diurnally. As a result, water in the cracks of rocks located by the snow changes from liquid to solid many times, creating a mass of small fragments.

What is the vertical extent of the taliks found under lakes related to?

The depth and volume of the overlying water body.

What are types of modification in a periglacial environment?

The displacement of soil materials, migration of groundwater, and the formation of unique landforms.

In a periglacial environment...

The effects of freezing and thawing drastically modify the ground surface.

What are the effects of isolation?

The effects of isolation can raise the temperature of these materials to above freezing when combined with seeping water from melted snow.

What are characteristics of erosion and deposition related to?

The importance of freeze-thaw action, the presence of strong winds, and that fact that the warm season is very short.

What else does frost action affect?

The landscape (these and even the ones that were not at the margin of ancient glaciers).

What is nivation?

The localized form of erosion associated with isolated patches of snow that remain through the summer season.

What characterizes locations that have a periglacial environment?

The presence of large quantities of angular, fractured rock. The angular nature of these deposits suggests that the process responsible for the rock fracturing is the crystallization of water.

What controls the growth of segregated ice?

The pressure exerted by overlying sediments.

Describe the process of the forming of a nivation hollow?

The process begins with a patch of snow. Around the edges of this patch, physical weathering and frost heaving begins to separate particles for erosion. Running water then picks up the loose particles and carries them off. Material is also removed from the developing hollow by gelifluction. As the summer season progresses, the patch of snow reduces in size and the excavation of material continues inward. Enlargement of the hollow involves several different mechanisms. Sometime in the following year, the boundary of the snow mound and depression will once again be inline and frost weathering will eat away at the hollow's edge. The edge of the hollow is also preferentially eroded because the micro-slope creates localized instabilities and focuses the entrainment potential of flowing water.

What happens when the sediments are thawed and saturated?

The sediments may begin moving by gelifluction if a slope exists.

What is solifluction? Gives details about this process.

The slow downslope flow of soil and sediment that is saturated with water. This process can occur on very shallow grades. This common sign of this form of mass movement is the presence solifluction lobes and tongue-like semi-mixed surface deposits. In periglacial environments, solifluction is confined to times when temperatures are well above zero and free liquid water is available in the active layer. Solifluction is very common when surface sediments are poorly drained and quite saturated with water.

What is frost creep?

The slow downslope movement of soil and sediments because of frost heaving a thawing. The process begins with the freezing of the ground surface elevating particles at right angles to the slope. The particles are elevated because cold temperatures cause water in between particles to freeze and expand. In the warm season, thawing cause the ice to convert back to liquid water and the contracting surface drops the particles in elevation. This drop, however, is influenced by gravity causing the particle to move slightly downslope.

What is going on at the same time of the re-freezing crack (soon-to-be ice wedge?

The soil layers adjacent to the developing ice wedge are pushed outward and upward creating a slight hill at the surface. This, and the re-freezing process, cause the ice wedge to increase in size with each passing year.

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The surface of periglacial areas is often characterized by the presence of ground materials arranged in a variety of symmetrical, geometric shapes. These features are collectively known as patterned ground. Shapes of patterned ground can include stripes, steps, circles, polygons, and nets. Sometimes one pattern can morph into another shape. Researchers have discovered that a single process cannot explain the various forms observed. Many of these features appear to be caused by freeze-thaw action selectively moving coarse particles to the edge of the shape or to its surface. Some polygon forms seem to be caused by the same thermal processes that create ice wedges. Yet, other types of pattern ground still remain not fully explained. Palsas are low permafrost mounds with cores of layered segregated ice and peat (Figure 10ag-8). They are normally 1 to 7 meters high, 10 to 30 meters wide, and 15 to 150 meters long. They are also most common at the southern margin of the discontinuous permafrost zone. Palsas are believed to form when areas of reduced snow cover allow frost to penetrate more deeply into an unfrozen peat bog. This frost freezes the water in the peat forming an initial ice layer. The layer then grows in size over time as water migrates under some type of pressure from unfrozen parts of the peat to the surface of the growing ice mass.

How can closed taliks form?

When lakes fill in with sediment and become bogs. With the removal of the open water, summer solar radiation is now being received by a surface with a lower specific heat and poor vertical heat transfer. As a result, soil near the surface begins to freeze solid encasing a zone of unfrozen soil in permafrost. Closed taliks can also form because of goundwater flow.

Where does permafrost occur?

Wherever the meal annual ground temperature is less than 0 degrees celsius.

Describe discontinuous permafrost.

Zones of permafrost with numerous scattered small thawed areas. It usually exists as an extensive marginal zone at the edge of continuous permafrost.