Periglacial Landforms

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  • Created on: 13-11-14 15:10
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Zoe Leek 12RSG Geography HD
Potholes are cylindrical holes drilled
into the rocky bed of a river by
turbulent high velocity water loaded
with pebbles. The pebbles become
trapped in slight hollows and
vertical eddies in the water are
strong enough to allow the
sediment to grind a hole into the
rock by abrasion (corrosion).
Attrition rounds and smooth's the
pebbles caught in the hole and helps
to reduce the size of the bed load.
Potholes can vary in the width from
a few centimetres to several metres.
They are generally found in the
upper or early ­ middle course of a river. This is where the valley lies well above base level, giving
more potential for down cutting, and where the river bed is more likely to be rocky in nature.
A Giant's kettle, also known as giant's cauldron or pothole, is a cavity or hole which appears to
have been drilled in the surrounding rocks by eddying currents of water bearing stones, gravel and
other detrital matter.
The interiors of potholes tend to be smooth and regular, unlike a plunge pool. An example is the
large pothole found in Archbald, Pennsylvania in Archbald Pothole State Park.
Rapids and Waterfalls
Waterfalls and rapids occur when there is a sudden change in the gradient of the river as it flows
downstream. Waterfalls are more dramatic features than rapids and may be a result of;
A resistant band of rock occurring across the course of the river
The edge of a plateau

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Zoe Leek 12RSG Geography HD
The rejuvenation of the area, giving the river renewed erosional power as sea level falls.
The river falls over a rock edge into a deep plunge pool at the foot of the fall, where the layers of
weak rock are excavated more quickly than the overlying resistant rock. The force of the swirling
water around the rocks and boulders enlarges and deepens the plunge pool by hydraulic action
and abrasion. This undercuts the resistant 9cap) rock above.…read more

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Zoe Leek 12RSG Geography HD
to have alternating bars of sediment on their beds and the moving water is forced to weave
around these bars. This creates alternating shallow sections (riffles) and deeper sections (pools).
The swing of the flow that has been induced by the riffles directs the maximum velocity towards
one of the banks and results in erosion by undercutting on that side. An outer concave bank is
therefore created. Deposition takes place on the inside of the bend, the convex bank.…read more

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Zoe Leek 12RSG Geography HD
The sediment load of the river is very large, as in the Mississippi and Nile rivers.
The coastal area into which the river empties its load has a small tidal range and weak
currents. This means that there is limited wave action and, therefore, little transportation
of sediment after deposition has taken place. This is a feature of the Gulf of Mexico and
the Mediterranean Sea.…read more

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Zoe Leek 12RSG Geography HD
Floodplains are created as a result of both
erosion and deposition, although the
accumulation of river deposits suggests
that they are predominantly depositional
features. They are the relatively flat areas
of land either side of the river, which form
the valley floor in the middle and lower
courses of the river. They are composed of
alluvium ­ river-deposited silts and clays.
Over time, a floodplain becomes wider and the depth of sediment accretions increases.…read more

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