Transcript Waterfall - Coolgeography

Robert Mckeegan
Jonathon Knox
James Hennessy
References:
•Essential As Geography (Stanley Thrones)
•Geography in Focus
•Encarta Premium
•Google Images (France)
•http://www.nps.gov/ (United State National Park)
Potholes
Waterfalls
Interlocking Spurs
River Valleys
Rapids
Potholes
Term: A Circular depression on a river bed carved out of solid rock
How: The Drilling Action as pebbles are caught in currents and Whisked around in a
small cracks or Hollow. Over time the potholes increases in size due to lateral and
horizontal erosion on the bed of the pothole and the bank. This is a form of Corrasion.
Where: Commonly found near Waterfalls and Rapids, This is because the Hydraulic
Action is a significant process due to the rivers increased discharge.
Waterfall
Term: Sudden step in a River long Profile
How: The sheer force of Hydraulic Action results in a band of less resistant soft rock
being eroded or undercut, as neighbouring hard rock cannot be eroded as quickly its
forms a steep step.
As the Hard Rock is not eroded as quickly, and the soft rock recedes upstream, this
results in a layer of hard rock overhanging the plunge pool. As the Waterfall recedes
upstream causing steep-sided gorge to be formed.
Waterfalls Case Study: High Force
At High Force, the River Tees falls in a single
sheet some 20m into the swirling pool below. Two
types of rock can be seen at the fall; the lower has
horizontal layers and forms part of the
carboniferous limestone.
The upper has dark colored rocks has vertical
joints within it making it denser than the underlying
limestone. In fact it’s an outcrop of igneous
dolerite. The Tees also boasts Caldron Snout
which is a series of cascades with a total drop of
60m.
Image: High Force, River
Tees
An Example of a Plunge Pool
Example of Steep Sided Gorge
Rapids
When rocks of varying resistances cut across a valley a series of smaller steps may
form rapids. Rapids are associated with very disturbed turbulent water
Example of rapids are: Yukon Rapids, Yukon Territory (Northern Canada)
V-Shaped Valleys
V-shaped valleys have steep valley walls with
narrow valley floors. In cross section it has a "V"
shape. They are created by fast flowing rivers with
steep gradients. As rivers flow downhill quickly,
they remove more sediment from the bottom of
the stream channel than from the sides. This
process is called down cutting. It can be
compared to a knife cutting through a cake. The
resulting landform is a narrow canyon with a fast
flowing river and little bank, or floodplain, on the
river sides. An example of such a valley is found in
Grand Canyon National Park and Black Canyon of
the Gunnison National Park.