Underworld
This section looks at limestone formations and the physical characteristics that make them so unique
Key questions
How do limestone caves form?
What physical features are found in caves?
How do limestone caves form?
The underground caves that characterise many areas of limestone scenery are formed due to the structure and the composition of limestone and the way it interacts with water. Limestone contains both joints and bedding planes which run perpendicular to each other splitting the rock into well-defined blocks and making it permeable. Both joints and bedding planes provide lines of weakness along which water can flow and as it does so its slight acidity dissolves the limestone with which it comes into contact. At the surface the joints within the limestone pavement widen to produce features known as grykes separating the limestone blocks, clints.
Water flowing over the surface plunges down the joints which it rapidly enlarges to form swallow or sink holes. Underground the processes continue and as limestone is dissolved along the route of the submerged stream caves, caverns, waterfalls and lakes begin to form. Carboniferous Limestone in both the Yorkshire Dales and Derbyshire form spectacular caverns such as Gaping Ghyll and Titan. Eventually the underground stream may descend to an impermeable layer such as a clay and can emerge where the water table intersects with the hillside as a spring or river (a resurgence) such as the River Axe at Wookey Hole in the Mendips or the River Aire which reappears from under Malham Cove in the Yorkshire Dales. Some cave systems may also have been influenced by changes in the level of the water table and in volumes of water passing through as climate has changed.
What physical features are found in caves?
Within the caves water continues to play a crucial role in shaping the scenery and the growth of stalactites and stalagmites (speleothems). Gaping Ghyll contains extensive speleothem formations in the "Stalactite and Stalagmite Chambers".
Links
Starter
How might these caves form?
Main Activity
Watch the Limestone landscapes: formation interactive animation to see how caves form.
Read the detailed glossary of caving terms or the summary glossary of caving terms.
Watch the caving movie again or read the script using the draw what you hear document.
Draw what you hear.
You should end up with a diagram in cross section of the physical features of the imaginary cave described in the clip and the script!
Plenary
Ogof Ffynnon Ddu (Welsh for Cave of the Black Spring) is a cave located under a hillside in the area surrounding Penwyllt in the Upper Swansea Valley in South Wales.
At 308 metres (1,010 feet) deep and 48 kilometres (28 miles) long, it is the deepest cave in the UK and the second longest in Wales.
OFD (as the cave is perhaps more commonly known) was discovered in 1946.
The system is famous for its intricate maze-like structure and its impressive main stream passage. It forms the Ogof Ffynnon Ddu National Nature Reserve.
Can you find Dip Sump?
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