Surface Features
The 'classic limestone walk' is a circular 10 km route from the field centre on the north side of Malham Tarn to the village of Malham, UK via Watlowes Valley and back again via Gordale Scar.
Small surface depressions called shakeholes, which are 1-3m deep and 3-5m across, form as a result of the subsurface collapse of limestone. Shakeholes are very common throughout the Yorkshire Dales. Larger depressions are called dolines.
Streams flowing from higher impermeable slopes sink into the ground when they reach permeable limestone. During dry spells all water sinks very quickly on reaching the limestone, through sinkholes. In wetter conditions water flows a greater distance across the limestone as underground channels and chambers fill up. Large sinkholes are called 'swallowholes' or 'potholes'. Gaping Gill, Alum Pot and the Buttertubs are well-known examples.
Dry valleys are valleys without streams. Watlowes Valley is an excellent example. It was formed originally by a subglacial meltwater stream which existed during the last major Ice Age. After the ice retreated, the valley was further developed by a meltwater stream flowing across the limestone while it was frozen solid. Watlowes Valley is a particularly good example of a dry valley because it has a textbook profile - the south-facing side is less steep than the north-facing side. This results from the weathering and mass movement processes that have operated in the post-glacial period.
A limestone pavement is an area of almost bare, flat rock and is arguably the most fascinating feature of any area of carboniferous limestone. They develop after the rock has been exposed by the scouring action of an ice sheet or glacier. Existing joints are subsequently exploited by the action of chemical weathering carbonation to form deep grykes and rounded blocks called clints. Grykes have a habitat of their own, which encourages the growth of shade-loving ferns such as hart's tongue and Dog's Mercury. During the last Ice Age, Malham Cove - the most spectacular feature in the Yorkshire Dales - was a waterfall comparable in size to the Horseshoe Falls of Niagara. At the end of the Ice Age the limestone, which had been frozen solid, once again became permeable, allowing the water to disappear through its joints. Now Malham Cove is a high cliff (83m high) - it is completely dry, and a great attraction to rock climbers.
A gorge is a steep-sided valley, generally formed in a limestone area as the result of the collapse of a roof above a cave system. Gordale Scar is an excellent example.
Read more about this topic: Carboniferous Limestone
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