LIMESTONE SCENERY Read the relevant section in the booklet that complements these slides. We will not be referring to the booklet all the time. These slide-shows are all on the Prepwork folder if you wish to copy any notes from them; we will not be stopping in class for you to do this
Limestone scenery comes in two forms;- Surface features Underground features
Limestone Pavement (Clints and Grikes) Dry Valleys Scars Gorges Pot holes, sink holes, swallow holes, shake holes Resurgents (springs) LIMESTONE - SURFACE FEATURES
Limestone Pavement - scraped clear of soil by repeated glaciation. Now the acid rain can get at it!
CLINT CLINT GRIKE GRIKE Limestone pavement, showing its characteristic clints (blocks) and grikes (gaps).
Some of BHS pupils on the pavement beside Malham Cove.
Watlowes, an example of a dry valley - carved by glacial meltwater, when the underground passages were choked with permafrost. Note also the scars, scree and limestone pavements. pavement scar scree
A scar is the name for a mini-cliff at the edge of the limestone plateau.
Upper Gordale, a good example of a gorge. Gorges are formed by the collapse of a cave system’s roof. (Not to be confused with river gorgesstudied atS.Grade)
The Verdon Gorge in southern France. Spot our two canoes?
Gaping Gill - Britain’s second deepest pot-hole. Can you see BHS pupils?
Gaping Gill has been formed over millions of years - the result of chemical weathering enlarging a vertical joint in the limestone. It is over 110 metres deep.
It is formed by soil being dribbled into a joint and a depression forming. Sometimes the soil seals the joint and it can accumulate moisture. These are sometimes called ‘Dew ponds’. A shakehole This is a shake-hole.
Boundary between limestone and impermeable rock. Resurgence (spring), where the water returns to the surface. The arrow denotes the flow of the new river.
Malham Cove, once a huge waterfall, but now virtually dry. Note the resurgence (spring) at the base of the cliff. In places this Great Scar limestone is 600ft. thick, representing 50 million years of sea-bed deposition - at about 1 inch every 2000 years!
Now watch the first part of the video about the surface features explained so far. Tape 87, programme 1, zero until 9mins 21 seconds.
Caverns Tunnels, passages and sumps Underground lakes and waterfalls Flowstone features Dripstone features-stalactites, stalagmites and pillars. LIMESTONE -UNDERGROUND FEATURES
Caverns are underground caves. In them, lakes can form; but they don’t last long as water percolates through the rock at sumps. Passages are eroded by the solution of limestone, usually along bedding planes and joints.
These flowstone deposits can vary widely in shape and colour - the colour often due to minerals such as iron, copper, lead or manganese in the water. This is called a curtain stone.
In a process known as gas diffusion, water saturated with dissolved Calcium Carbonate enters a cave through joints in the roof. As it does so, it loses some CO2 and, helped by evaporation, this causes some Calcite (the pure form of the mineral) to precipitate out - forming a variety of underground dripstone features. Copy this text
Stalactites grow down from the cave roof…on average about one inch every 500 years.
Now watch the second part of the video about the underground features explained so far. Tape 87, programme 1, 9 mins 21 seconds until 19 mins 30 seconds. END