Transcript Limestone Features

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 steepsided 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.
Impressive!
CaCO3 + H2O + CO2 = Ca(HCO3)2
Calcium carbonate + Water + Carbon
dioxide = Calcium bicarbonate
Yorkshire Dales
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.
Yorkshire
Dales
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
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.
http://www.bbc.co.uk/scotland/education/int/geog/limestone/surface/their_formation.shtml
Sink/Swallow holes
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.
Gaping Ghyll
Outcrops
Stalagmites, stalactites & Pillars
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.
Gorges
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
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.