Ingleborough

Limestones are affected by acidic rainwater and chemical weathering results in a number of characteristic solution features in a limestone landscape. The landscape surrounding Ingleborough serves as a good example of karst features in a single area.

Trow Gill

Trow Gill

Towards the end of the last ice age, meltwater from the retreating ice, near what is now Ingleborough, was not able to take its normal subterreanean route, because the cave system was blocked by permafrost.

Instead it rushed over the surface, down what is now Fell Beck and cascaded into Clapdale, rapidly eroding the dale floor.

When the glaciers were in retreat, huge quantities of water would have flowed through Trow Gill.

The meltwater cut down rapidly through the rock, eroding a spectacular gorge, 20 m deep in places and only 3 m wide at its narrowest.

However, the glaciers had also eroded away the valley floor, lowering the level of resurgence. For this reason, with the disappearance of the ice fields and glaciers, the water followed a new subterranean route to the new resurgence level, and Trow Gill was left 'high and dry'.

Dry valleys

Dry valley

After the limestones accumulated in the warm tropical sea of the Carboniferous climates, sands and grits were washed down from the land and deposited on top.

These sands and grits are still on top of the limestone and cap the Pennines of the Yorkshire Dales, such as at Ingleborough Hill.

Water flows over the sands and grits more easily than limestone, so rivers radiate out from Ingleborough. But as soon as they start to flow over the limestone, they disappear below ground, leaving behind a dry valley.

Crina Bottom is an example of dry valley to the south-east of Ingleborough. Further dry valleys occur north of Clapdale and a beheaded older dry valley joins Trow Gill at Foxholes, but the other dry valleys of Ingleborough are quite shallow.

During the last ice age, when the ground was frozen, Fell Beck flowed over the surface of Simon Fell, heading towards the outlet through Trow Gill. While the water flowed over the surface, it eroded a 'dendritic' system of stream channels, which can still be seen in the contours of the hillside.

Blind valleys

Marble Steps Pot

Blind valleys are one of the characteristic features of karst scenery. They carry a stream for part of their course, but then the water disappears down a sinkhole or swallow hole.

On the flanks of Ingleborough, a number of streams flow over the sandstones and shales on the summits of the hills, but disappear underground when they reach the limestone.

There are a few blind valleys on Ingleborough, but they occur where there is a cover of glacial till that allows the streams that originate on the upland areas to flow over the limestone.

Rivers that flow off Simon Fell have formed several blind valleys between Newby Moss and the Allotment, although none are large.

Fell Beck forms a blind valley where it disappears down Gaping Gill. The beck flows off the sandstone and shales onto the till, which it erodes to disappear down the swallow hole.

Downhill from Gaping Gill, there is no river to erode the till. Uphill of the swallow hole, however, the river continues to erode so that it is much lower here than on the downhill side. A cliff forms downhill of the swallow hole, facing uphill.

A little further east, the Allotment potholes and Marble Steps Pot also provide examples of blind valleys.

Sinkholes (dolines)

Gaping Gill

Ingleborough has a large number of dolines along its benches, including solution and collapse dolines and many swallow holes.

Gaping Gill is an example of a swallow hole. Here, Fell Beck, which drains Simon Fell on the eastern side of Ingleborough, cascades down the vertical shaft to the cave floor 100 m below ground.

Gaping Gill forms Britain's largest unbroken waterfall.

Limestone pavements

Limestone pavement, Moughton.

Erosion by glacial scour has resulted in the exposure of numerous limestone pavements on the benches and plateaux of the Yorkshire Dales.

On the eastern side of Ingleborough, the limestone pavement extends 8 km along Chapel-le-Dale, from Crina Bottom to Ribblehead. To the east, limestone pavements are found from Alum Pot to Norber and Moughton.

Some of the largest clints occur at Scar Close, but in other areas the clints are greatly reduced due to the widening of the grykes by acid rain. Chemical weathering has also resulted in the development of karren.

When glaciers move down valleys, the moraine they carry gouges grooves into the bare surface rock underneath. In some of the newly exposed limestone pavements of Ingleborough, striations cut by the glaciers can be seen. However, these are dissolved away by the rain within a decade or so of being exposed.

Erratics

Erratic at Norber

The glacial history of the karst of Yorkshire is reflected in the huge erratic blocks that are seen, particularly around Norber.

Here, Silurian sandstone blocks 2 m high rest on the limestone.

The erratics were carried uphill from Crummackdale by the ice. In some cases, the erratic block protects the underlying limestone from chemical weathering, and during the last 10 000 years the surrounding limestone has been lowered so that the erratics now appear to stand on limestone plinths up to 0.5 m high.

Scars

When glaciers moved down the valleys, the side of the valley was scoured and the rock plucked away to leave long cliff-like scars.

There are fine examples in the Ingleborough area, such as those of Sulber and Moughton, around Crummackdale and perhaps one of the most famous is Kilnsey Crag.

Cowside Beck
Kilnsey Crag