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 moved 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.
Carboniferous limestone is a very permeable rock through which rain water or river water can pass through very easily. A chemical reaction occurs and a mineral called calcite is formed. The water becomes slightly acidic in nature and breaks down the rock into many different shapes and sizes.
Waterfalls normally only occur in areas with rich geology and varying rock strata. The types of waterfall are shown below:
Ledge waterfall: Water descends vertically over a vertical cliff, maintaining partial contact with the bedrock.
Block/Sheet: Water descends from a relatively wide stream or river.
Classical: Ledge waterfalls where fall height is nearly equal to stream width, forming a vertical square shape.
Curtain: Ledge waterfalls which descend over a height larger than the width of falling water stream.
Plunge: Fast moving water descends vertically, losing complete contact with the bedrock surface.[The contact is typically lost due to horizontal thrust of the water before it falls. It always starts from a narrow stream.
Punchbowl: Water descends in a constricted form and then spreads out in a wider pool.
Horsetail: Descending water maintains good contact with bedrock most of the time.
Slide: Water glides down maintaining continuous contact.
Ribbon: Water descends over a long narrow strip.
Chute: A large quantity of water forced through a narrow, vertical passage.
Fan: Water spreads horizontally as it descends while remaining in contact with bedrock.
Cascade: Water descends a series of rock steps.
Cataract: A large, powerful waterfall.
Segmented: Distinctly separate flows of water form as it descends.
Frozen: Any waterfall which has some element of ice.
In order to log a find against this earthcache you will need to visit the given coordinates and answer the following questions.
1) What type of waterfall do you think the waterfall here is? Please explain your answer.
2) Notice the overhang of limestone, please describe the course of the water along the limestone and explain to me how the cave has formed. 3) This waterfall has a large plunge pool that has been eroded by the waterfall into the limestone. Using your knowledge of limestone permeability, do you think this plunge pool will be here in a million years or do you think it will eventually have formed another cave?
Please email your answers to me via my geocaching profile. You do not need to wait for a reply before logging this earthcache.