Waterfalls

Waterfalls in areas of massive limestone are usually found at swallow holes, where a stream or river cascades down into subterranean drainage systems. Massive limestones do not support rivers and waterfalls over long distances.

Surface rivers in Yorkshire are usually confined to non-limestone rocks, such as the area of shale, sandstone and grit that overlies the limestones of the Pennines of the Dales. These streams flow over the edge of the impermeable rock onto the limestones, but quickly disappear into the cave system below.

However, in some areas such as Wensleydale and Dentdale, several rivers flow across the limestone landscape and drop over waterfalls and rapids. In fact it is often the limestone that creates the waterfalls. How can we explain this?

Aysgarth Falls

Aysgarth Falls

In Wensleydale there are rocks that geologists call the 'Yoredale facies'. Here, layers (beds) of sandstone and shale are found sandwiched between beds of limestone.

The sandstones and shales are less permeable than limestone, and the River Ure can flow over and erode them.

The limestone beds are harder than the sandstone and shales, withstand erosion and form steps in the river's course, creating waterfalls.

Aysgarth Falls is one of the more famous, and here the River Ure tumbles over three flights of small waterfalls.

Hardraw Force

Hardraw Force

Hardraw Force, at Hawes at the head of Wensleydale, is another famous waterfall. Here the river flows over the sandstones and shales of the Yoredale facies until it reaches a thick, hard limestone, which creates a spectacular waterfall, said to be the highest unbroken waterfall in Britain.

Hardraw Force is not as high as some waterfalls, like Gaping Gill, but they are subterranean features.

The water plunges 30 m over the limestone onto more sandstones and shales below.

Goredale Scar

Goredale Scar

Goredale Scar formed a high waterfall at the end of the last ice age, where a huge step had been created by movement of the Craven Fault.

This step is at the end of a deep gorge, which was eroded at the time when the glaciers were in retreat.

Today the much smaller Goredale Beck cascades down the ravine in two waterfalls, one of which pours through a natural arch. It is interesting that tufa is being deposited here.

Malham Cove

Malham Cove

Some of the most spectacular waterfalls would have been seen towards the end of the last ice age, when the ground was frozen or when the water table was high.

Water from melting ice fields and glaciers cut deep gorges, some of which end at huge steps in the hillside like at Malham Cove. This is where the Craven Fault runs through the rocks.

Movement along the fault has created these high cliffs over which the water once flowed. The valleys around the cliffs are now dry, their river systems having found an alternative route underground.

Thornton Force

Thornton Force

Thornton Force is located on the River Twiss, near Ingleborough, where the waterfall plunges over Carboniferous limestone onto Ordovician sandstones below.

Here, earth movement along the Craven Fault has created a large, cliff-like step over which the water tumbles.

The Craven Fault is a series of geological fault lines which cut through the rocks along the southern part of the Yorkshire Dales National Park.

The fault often marks the boundary between the higher limestone area and the lower ground to the south and west. Movement along this fault is also reponsible for the high cliffs at Malham Cove and Goredale Scar.