High Force Reservoir
LO: To describe the formation
of a waterfall and gorge using
High Force as an exemplar
High Force is the tallest waterfall in the
UK
Waterfalls happen where there are layers of hard and soft
rock.
In the case of the River Tees, water flows over hard
(resistant) rock ie whinstone. The softer, limestone rock
beneath is vertically eroded more quickly to leave a small
step in the channel. The erosional processes are abrasion,
corrosion and hydraulic action.
Over time, the small step in the softer limestone rock
continues to erode to form a vertical drop between the two
layers of Whinstone rock. A waterfall has now been formed.
Due to the height that the water now falls, strong currents
and high pressure erode the river bed at the base of the
waterfall, creating a plunge pool. Material is swirled around
and the plunge pool becomes deeper and larger. An
example is High Force (21.5 metre drop).
Transportation methods
TRACTION
Match up the transportation methods
with the correct description and draw
a diagram to show it.
Particles of rock are dissolved in the water and
carried along without being seen.
SALTATION
Large boulders and rocks are ‘rolled’ along the
bed of the river.
SUSPENSION
Smaller pebbles and stones are ‘bounced’ along
the bed of the river.
SOLUTION
Smaller particles of silt and sand are held within
the water and transported along in the flow of
water.
Erosion processes
ABRASION
The sheer force of the water removed
material from the bed and banks of the river.
SOLUTION
Material is rubbing against the bed and
banks of the river wearing them away.
ATTRITION
Some rock such as calcium carbonate
dissolve in the water if it is slightly acidic.
HYDRAULIC EROSION
The load itself being carried, bang into each
other and break up and become smaller
and smaller.
A WATERFALL
How is a waterfall
formed?
What do you notice
about the diagram?
Many waterfalls form when
rivers meet a band of softer less
resistant rock after flowing over
a relatively hard resistant rock.
The softer rock is worn away
more quickly, and the harder
rock undercut.
The overhead hard rock forms
an overhang, which will
eventually collapse, to form a
deep plunge pool.
This process is repeated causing
the waterfall to retreat
upstream creating a gorge in its
wake.
Model answer
Waterfalls occur where there are alternate layers of hard and
soft rock in the landscape. In the case of the River Tees,
water flows over hard (resistant) rock ie whinstone. The
softer, limestone rock beneath is vertically eroded more
quickly to leave a small step in the channel. The erosional
processes are abrasion, corrosion and hydraulic action. Over
time, the small step in the softer limestone rock continues to
erode to form a vertical drop between the two layers of
Whinstone rock. A waterfall has now been formed. Due to
the height that the water now falls, strong currents and high
pressure erode the river bed at the base of the waterfall,
creating a plunge pool. Material is swirled around and the
plunge pool becomes deeper and larger. An example is High
Force (71 feet/21.5 metre drop).