Presentation on theme: "Limestone Features Miss James Higher. Limestone scenery exposure of very extensive limestone pavements may be partly an example of the stripping of soil."— Presentation transcript:
Limestone Features Miss James Higher
Limestone scenery exposure of very extensive limestone pavements may be partly an example of the stripping of soil by moving ice during the last glaciation period more than 10,000 years ago
Limestone Blue area Carboniferous Limestone Yorkshire Dales
Limestone consists mainly of calcium carbonate. There are several different types of limestone including Chalk, Jurassic and Carboniferous. The Carboniferous Limestone can be attacked by the weathering process of carbonation. Think about chemical weathering. This weathering contains a very distinctive type of landscape, with both surface and underground features. The most distinct landscape of this kind is found in the Yorkshire Dales. Here the limestone forms upland areas, capped by impermeable rocks above, and separated by flat-floored and steep- sided glaciated valley’s called dales. Glaciers covered this area and as well as sculpting the valley’s, also removed loose rock and soil to expose the limestone which was then more open to chemical weathering.
CaCO3 + H2O + CO2 = Ca(HCO3)2 Calcium carbonate + Water + Carbon dioxide = Calcium bicarbonate Impressive!
Limestone Surface and rain water do not flow far on exposed limestone, but infiltrate rapidly into the rock and soil. Where a joint or intersection of joints has been greatly weathered or dissolved water can pass down through the limestone Carboniferous limestone is a sedimentary rock formed in the Yorkshire Dales around 300 million years ago. These rocks were laid down on the sea bed and made up of layers of ancient corals and skeletons of sea creatures living in the shallow seas at that time.
Joints and Bedding Planes This is hard grey rock, laid down in layers on the sea bed. It occurs in massive blocks bordered by horizontal bedding planes and vertical joints. These bedding planes and joints make the rock permeable i.e. water can pass through it.
Clints and Grikes
These are flat areas of exposed limestone. Surface soil was probably removed by the glaciers. Carbonation weathering has enlarged joints to give wide gaps called grikes. The stones left are called clints. Some are 0.5m wide and 2m deep.
Swallow holes In the Yorkshire Dales, streams flow on impermeable rock on higher hillsides. When the streams reach the limestone, they usually only flow for a short distance before disappearing underground at a swallow hole (sink hole). These develop at the intersection of major joints which have been widened by solution. This can be seen at Gaping Ghyll in the Yorkshire Dales.
Stalagmites, stalactites & Pillars
Groundwater may become saturated with calcium bicarbonate in solution. Water continually drips from cave ceilings. Some water evaporates to leave a thin film of calcium carbonate (lime). Overtime a narrow stalactite may grow down from the roof of the cave. The drip of water then drops to the cave floor and evaporates from there which makes a stalagmite. If these join a pillar is formed. In Yorkshire caves stalactites grow at around 7.5mm per year.
Carboniferous limestone areas often have near vertical rock cliffs along the sides of valley’s. These cliffs are known locally as scars. They are susceptible to frost shattering (physical weathering) on exposed joints and may have scree at their base. Extremely steep sided valley’s are called gorges. Are formed by caves collapsing.
Caves/Gorges During the meltwater phase of the last ice age, underground streams eroded vast caverns as huge volumes of water travelled through the limestone. Sometimes the roofs of these caverns can collapse exposing the "underground stream" in a very steep sided gorge.