High Force Waterfall, River Tees by Sebastian Desando |
| The High Force waterfall is on the River Tees near Middleton-in-Teesdale,
Tees Valley, England. It has a hight of 20 metres (70 ft). It occurs
where the River Tees has created a vertical drop due to differential
erosion causing brown, peaty waters to cascade over the Whin Sill
which is a tough, dense and hard, resistant band of dolerite, an igneous
rock. It is formed because the hard cap rock at the top is being undermined
by the softer Carboniferous limestone underneath. The high content
of acid drawn from the peat reacts with the limestone and so corrosion
is an important process of erosion and so is hydraulic power, attrition
and abrasion. This causes an overhang that eventually collapses into
the plunge pool. This fallen angular bed load is smoothed and rounded
into boulders by the process of hydraulic power. The waterfall gradually
recedes and forms a narrow, steep, vertical sided gorge of recession
because the harder rock is not as affected by weathering as softer
limestone. |
 |
| The dolerite above the Carboniferous limestone is harder
and denser and so not as easily eroded by predominantly hydraulic
power. The limestone is softer and eroded by the peaty brown waters
of the River Tees. Therefore corrosion plays an important part in
the quicker erosion of the limestone along with the other processes
of hydraulic power, attrition and abrasion. The igneous rock is undermined
by the softer sedimentary rock and this causes an overhang that will
eventually fall into the plunge pool and the fallen angular bed load
is smoothed and rounded into boulders by the process of hydraulic
power and attrition. The boulders will be transported by traction.
The waterfall gradually recedes and forms a narrow, steep gorge of
recession because the harder rock is not as affected by weathering
as softer limestone |
| The waterfall is in the upper course of the river and
so vertical erosion is most prominent. The boulder-strewn gorge is
eroded by hydraulic action and the smoothed boulders are transported
downstream by traction. Eventually, after being entrained they are
deposited downstream and the river bed becomes deeper due to the vertical
erosion. The waterfall gradually recedes upstream and forms a narrow,
steep gorge of recession due to the hard dolerite not being as affected
by weathering. The cap rock is undermined by the limestone due to
the resistance to erosion of the higher doleritic limestone. It eventually
collapses creating rocks in the river bed which are eventually rounded
into boulders that will eventually be deposited downstream onto the
river banks or delta and are continually eroded and being used in
erosional processes of the river. |
The waterfall will carry on receding gradually and being
undermined up the river until the 1.5km band of dolerite is absent.
Here the river has a gentle constant gradient because the erosion
is taking place equally as all the rock is of the same type –
limestone. This would cause a v-shaped valley because the limestone
is more easily affected by weathering, the opposite to dolerite that
causes rigid, almost square-like sides. On the other hand, if the
water hits more dolerite, it will keep causing an even steeper and
sharper gorge of recession. However, over a much longer period of
time the gorges will become v-shaped valleys.
|
|