Welcome to Yordas Cave, a fine example of a solution formed cave.
The Yorkshire Dales is an area with a geology of primarily limestone. This limestone is Carboniferous limestone. This means it was formed in a tropical sea which covered the UK 359 million years ago. This would have occured in the Dinantian sub period of the Carboniferous era. Carboniferous limestone is a sedimentary rock made of calcium carbonate. It is generally light-grey in colour, and is hard. It was formed in warm, shallow tropical seas teeming with life. The rock is made up of the shells and hard parts of millions of sea creatures, some up to 30 cm in length, encased in carbonate mud. Fossil corals, brachiopods and crinoids are very much in evidence as components of Carboniferous limestone; indeed the rock is full of fossils.
Carboniferous limestone has horizontal layers (beds) with bedding planes, and vertical joints. These joints are weaknesses in the rock, which are exploited by agents of both denudation and weathering. They also lead to the most important characteristic of Carboniferous limestone - its permeability. Water seeps through the joints in the limestone. This creates a landscape that lacks surface drainage but which has all manner of characteristic surface and subsurface features. The Carboniferous Limestone has been folded and faulted by massive Earth movements which can be seen by the fact that the rocks are now above sea-level and no longer horizontal. There are other types of limestone which include Sugar, but they are formed in different conditions to Carboniferous limestone.
Limestone's technical name is Calcium Carbonate and when water percolates through the cracks and weaknesses in the rock. This chemical reaction is known as solution and the water dissolves some of the chemicals in the limestone. When the water evaporates, this leaves deposits known as calcite or flowstone.
Yordas Cave is a solutional cave formed in Lower Carboniferous limestone. Yordas Beck normally sinks at the top of the gorge, and reappears from a passage near the top of Yordas Pot. From the base of the shaft it follows the passage down to the Chapter House waterfall, before disappearing in confined passages at the end of the Main Chamber. In flood conditions a lake can rise in the Main Chamber up to 2 metres (6 ft 7 in) deep, before the water is able to flow out of the show cave entrance. The underground stream next appears in Kingsdale Master Cave, and it resurges at Keld Head 2.7 kilometres (1.7 mi) down the valley. The Main Chamber is several hundred thousand years old, and was formed by solution under phreatic conditions before the Kingsdale valley had formed and allowed it to drain. The square profile of the chamber has resulted from rock collapses from joints. A number of different false floors which may still be seen clinging to the walls indicate that the cave was subject to cycles of deposition and re-excavation during the recent ice ages.
The images above show the formation of the cave. A phreatic cave formation is a cave which is formed through the action of water under pressure below the water table. Over time, the water starts to reach the cutting process of cave formation where a channel develops. This has now become the vadose stage of cave formation.
The action of water is still ongoing as the cave matures:
As water saturated with calcium carbonate drips through the ceiling of a cave, successive rings of calcite crystals form a tiny tube or straw stalactite. Straws no more than 2-3mm thick have been known to grow to a length of several metres.
If the straw is blocked, the water then is forced to flow down the outside of the tube, and calcite deposits thicken the tube into the traditional carrot shaped stalactite.
Water saturated with calcium carbonate dripping on the floor builds stalagmites, which in time may join stalactites to form columns.
Variations in the minerals dissolved in the water and the speed of its movement can produce a range of cave formations ranging from gracefully curving flowstone curtains to convoluted helictites.
In order to log a find against this earthcache you will need to answer some questions when you visit the coordinates given. You shouldn't answer these questions in your log, you will need to send them to me via my geocaching profile. You do not need to wait for a reply from me to log the cache
You will need to go inside the cave to answer these questions. The cave has a wide but short entrance. A head torch or torch is encouraged. There is no immediate risks or dangers of going inside the cave as it is a historic victorian show cave, but the risks of caving are still there so exercise caution at all times.
1) How high and wide do you think the Main Chamber is? I only expect an estimate of its dimensions. What does this main chamber tell you about its phreatic formation?
2) Which part of the cave would you class as the vadose stage of cave formation? Explain your answer.
3) Describe the flowstone waterfall inside the cave and comment on its texture.
4) Can you see any stalactites or stalagmites or columns? Do you think they are the same mineral as the flowstone?
Pictures of the inside of the cave are encouraged but not compulsory.
My thanks again must go the Yorkshire Dales National Park Authority for their permission for this cache.