Now
that I have outlined the key terms that I think were quite handy to know when
talking about periglacial environments, I am now going to move onto periglacial
processes.
One
of the main periglacial processes is mass movement. This
is due to the periglacial environment: the thawing and freezing of water
throughout the year which leads to water lying above the permafrost, low
temperatures meaning that water cannot evaporate and a lack of vegetation so
the soil cannot properly hold the soil together. However, this mass movement
term is very broad and it can be narrowed down to a more specific process:
Solifluction – This is the slow, downslope movement of
saturated soil and sediment. As the ice thaws into water, it cannot infiltrate
the hard ground below it and so begins to move on the surface, typically
downslope moving material with it. This process can be seen as it can create
lobes which are semi-mixed surface deposits.
The
diagram above shows the process of solifluction as well as showing the lobes
that can be created with a visual example of these forms.
Frost heave – this is the upward and outward movement of the
ground surface which is caused by the formation of ice within the soil. Ice
crystals develop in the winter when the active layer of the permafrost freezes
and these expand upwards at the soil surface. Stones which are in the soil cool
down much quicker than the surrounding soil and so ice forms here much faster.
As this water freezes it expands and pushes the stone upwards. This process
continues until the stone eventually reaches the surface. Soil and stones that
are pushed up in this manner eventually form small domes and the stones located
on top of these domes will eventually move down slope via processes of mass
movement.
Nivation – This is a process that occurs underneath patches
of snow, in hollows of rock. Frost action that occurs beneath the snow (mainly
cycles of freeze-thaw weathering) gradually wears away and eventually shatters
this underlying rock. In the spring when thawing takes place, mass movement
carries away these deposits of weathered rock. Periodic freeze-thaw weathering
causes the creation of nivation hollows.
Frost shattering – This occurs as a result of continuous cycles of
freeze-thaw weathering and the wet conditions of the active layer. Water enters
into cracks and joints in the rock and as the temperature drops, the water
freezes causing it to expand and therefore puts pressure on the rock, weakening
it. When the ice thaws, it contracts. This continuous process will eventually
weaken the rock to the point that it shatters.
Aeolian processes – Due to the lack of vegetation in periglacial
environments, the soil is more prone to wind action. This can produce a loess (for
example in northern China
I
found it difficult to find diagrams of each of these processes. However, when
teaching them it might be good to get the students to draw their own diagrams
of each of these processes. This would aid in their learning by not only
writing down the processes but by drawing them and so it might help with
remembering them. It could also be turned into some form of game; putting up my
own diagrams of the different processes around the room and getting students to
move around the room and guessing which processes go with which diagram. Then
afterwards, getting them to sit down and volunteer what they thought each
process was and why. This would help to engage the students and might also help
quieter students as they would have had a chance to discuss with others and so
may help give them more confidence with volunteering answers in a class
discussion.
In
my next post I will look at the different periglacial landforms that may be
created as a result of these different processes.
Links
used:
http://www.slideshare.net/pdxmas/periglacial-processes-presentation
- slides on periglacial processes
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