HIGHER GEOGRAPHY LITHOSPHERE

LIMESTONE SCENERY

LIMESTONE -UNDERGROUND FEATURES

• Caves and Caverns• Tunnels, passages and sumps• Potholes, sinkholes, swallow holes• Flowstone and dripstone features• Stalactites, stalagmites and

columns.

Potholes and shakeholes

• Occasionally, hollows are created on the surface of limestone. They form where drift material falls into joints which have been enlarged and widened by chemical solution. The hollows are called dolines or shakeholes.

• The shakehole is then eroded by streams and a vertical hole known as a pothole or swallow hole is formed. These holes can, in turn, be enlarged by heavy rainfall or glacial meltwater. Gaping Gill, in the Yorkshire Dales, is an example of an enlarged swallow hole.

Underground, at the bottom of Gaping Gill.BBC - Learning Zone Class Clips - Upland limestone drainage features - Geography Video

Caves, caverns, lakes, passages and sumps.

BBC - Learning Zone Class Clips - Surface features of upland limestone scenery - Geography Video

Abseiling into Jingling Pot

Phreatic Caves, which can be almost circular in shape.

Cavers exploring the Battlefield Chamber in the White Scar system.

Swallow holes and sink holes

• Swallow holes or sink holes. This is where the acidic rainwater has dissolved and widened a joint in the limestone, and surface streams disappear underground, eg Gaping Gill near Ingleborough.

Resurgence (spring), where the water returns to the surface.

Resurgence (spring), where the water returns to the surface.

Limestone solution

• The limestone solution process is also known as carbonation.

• Limestone is made of calcium carbonate. When carbon dioxide is dissolved in rainwater, it makes a weak acid called carbonic acid.

• When carbonic acid comes into contact with limestone and passes through joints and bedding planes, it reacts with the rock to form calcium bicarbonate.

• The calcium bicarbonate is soluble and is carried away in solution, gradually weathering the limestone.

• 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 features.

These flowstone or dripstone deposits can vary widely in shape and colour - the colour often due to minerals such as iron, copper, lead or manganese in the water.

Stalactites grow down from the cave roof…on average about one inch every 500 years.

Ca (HCO3)2 is known as calcium bicarbonate, and the water carries the substance, basically dissolved calcite, through the cracks of the roof of a cave. Once water comes into contact with the air inside the cave, however, some of the calcium bicarbonate is transformed back into calcium carbonate, and calcite starts to form around the crack. As water continues to drip, the length and thickness of the calcite grows, and eventually a stalactite forms on the ceiling.

Stalactites

...stalagmites grow up from the cave floor

Straw stalactites - slender, hollow and faster growing, at about one

inch every 100 years.

Straw stalactites - slender, hollow and faster growing, at about one

inch every 100 years.

The water dripping from the end of a stalactite falls to the floor of a cave and deposits more calcite into a mound. Soon enough, a stalagmite will form in a conelike shape. This is why you usually find stalactites and stalagmites in pairs, and sometimes they'll even grow together to form one big column.

Stalagmites/columns

Columns/pillars

Columns or pillarsColumns or pillars

Summary

• BBC - Education Scotland - Upland Limestone - Underground