Transcript Characteristics of carboniferous limestone

Properties of carboniferous limestone
1. What is limestone formed from?
2. How is Limestone formed?
4. When was it formed?
5. What are the properties of Limestone. Is
it impervious or pervious?
6. Where can you find limestone
landscapes?
7. What is the other name for limestone
scenery?
Copy the Karst Scenery diagram. Include
the labels.
Describe what happens to the stream along
it’s course. Where does it go? What may
happen to the caves in the future?
Describe the inside of the limestone cave.
8. Draw and label the Limestone Scenery
diagram opposite using half a page of your
textbook.
How can water make a hole in the rocks?
Carboniferous limestone features
Carboniferous limestone is formed from the remains of organic matter, usually seashells
and plants. It is made of calcium carbonate.
It was formed under the sea 220-280 million years ago. It is a hard, grey sedimentary
rock, with a large number of joints (vertical cracks) and bedding planes (horizontal
cracks)
Carboniferous limestone produces distinctive karst scenery. These areas have mainly
been shaped by the action of water. Water attacks the many joints and bedding planes in
the rock, through the chemical weathering processes of carbonation and solution. The
two best areas of carboniferous limestone in Britain are the Yorkshire Dales and the Peak
District.
Limestone pavements are large areas of exposed limestone. When the overlying rock
was eroded the pressure release on the limestone below caused it to crack even more.
Limestone pavements are characterised by large gaps between the rock, called grikes.
The remaining blocks of rock are called klints.
Limestone cliffs or scars are produced at the edge of the area of limestone. Often near
vertical and highly jointed.- Swallow holes and sink holes are where rivers flow down
into the rock. Sink holes are relatively small, whilst swallow holes are larger. Both have
been formed either by the constant chemical attack of the water on the joints in the
limestone, or by the collapse of a cavern below.
Caverns are underground caves that have been hollowed out by the action of
underground streams and by carbonation and solution. They have three distinctive
features. Stalactites hang from the roof of the cavern, and are basically lime deposits.
Stalagmites grow from the floor, and are also lime deposits. Where a stalactite and
stalagmite have joined you get a pillar.
Underground streams flow down through the limestone carving out caverns, until the y
reach the impermeable layer of rock below the limestone layer. Once at this point the
stream flows under the limestone until it re-emerges. This is called resurgence. Gorges are created where the roof of a large underground cavern falls in, to create a
steep sided gorge with a river running in the bottom.
Dolines are formed when the roof of a small underground cave falls in. The ground
above the cave subsides into it causing an indentation on the surface.- Dry valleys, such
as Cheddar Gorge, were formed in periglacial times, when the ground froze, so the rivers
ran over the surface of the limestone rather than flowing down through it. These rivers
carved out steep sided valleys. Once the climate had warmed again the rivers
disappeared underground leaving a dry valley behind. These also are common features
of Chalk landscapes.
Uses of a carboniferous
limestone areas
Poor, thin soils mean that the only type
of farming possible in limestone areas
is sheep grazing
The tourist industry is a very
important source of income to
limestone areas. Most people come to
walk in the hills and see the
spectacular karst sceney. The local
people are cashing in on this by
opening café’s, guest houses and other
tourist facilities.
Limestone is an excellent building stone, and has
been used in some very well known buildings, such
as the Houses of Parliament. Obviously this mean
that there are often a large number of quarries.Limestone, whether crushed or used as lime, can
be very useful in a number of areas. It is used as
an industrial cleanser, farmers use it as fertiliser
and it forms an important ingredient in cement
making.
Malham ia a small dales village north of Skipton and Gargrave in the beautiful Yorkshire Dales National Park. Besides being the inspiration for Charles Kingsley's
classic children's novel, The Water Babies, the area around Malham is perhaps most famous as featuring some of the finest (and most spectacular) limestone
scenery in the country.
Attractions of special interest include:
Malham Cove
Malham Cove is a huge natural limestone cliff which was once the scene of a spectacular prehistoric waterfall. The valley above the cove is now dry, with the river
having found an alternative route through an undiscovered cave system deep underground. However, at the foot of the cliff, a small stream called Malham
Beck rises from a submerged cavern, which is still being explored by cave divers.
Gordale Scar
A great limestone gorge some 400 feet (150 m) deep, Gordale Scar is believed by many geologists to be the remains of a huge underground cavern whose roof
collapsed around the time of the last ice age. Gordale Beck cascades down the ravine in two spectacular waterfalls, one of which pours through a natural arch
in the rock above. A short scramble takes visitors (at their own risk !) up the tufa* deposits at the side of the first waterfall into the top section of the gorge,
which leads out onto Malham Moor.
* = Tufa is a smooth limestone deposit usually formed when water containing calcium carbonate passes over exposed rock. Besides Janet's Foss, other examples of
this type of deposit can be seen at Janet's Foss (see below).
Gordale Scar
Malham Tarn
Set high above the village on Malham Moor, Malham Tarn is a large lake formed by glaciation in the last ice age, made famous as the setting for Charles Kingsley's
classic children's novel, The Water Babies.
Today, despite the wildness of its location, Malham Tarn attracts many visitors to its nature reserve, where a pleasant walk leads along the shoreline to Tarn House, a
remote country house which now houses a National Trust visitor centre.
Malham Tarn
Water Sinks
At the south end of Malham Tarn, the infant River Aire sets off on its long (and complicated) journey to the North Sea. The journey is complicated because, just a few
hundred yards from leaving the tarn, the river mysteriously vanishes through deep fissures in its limestone bed at a place called, quite appropriately, Water
Sinks.
For many years, it was believed that this river was the same as Malham Beck, reemerging further down the valley at the base of Malham Cove (i.e. the most obvious
course, simply tracing the route of the dry valley which leads from Water Sinks down to the cove itself). However, this is not the case, as flourescene dye tests
have now proved that the river disappearing underground at Water Sinks does not actually reemerge until much further downstream, at a place now called
Aire Head Springs south of Malham village, and near to Bell Busk ! [Malham Beck, meanwhile, appears to originate at another location on Malham Moor, before
also disappearing underground to resurface at Malham Cove.]
It is clear that, whatever routes are actually taken by these streams underground, an extensive network of cave systems lies waiting to be discovered, despite the
efforts of cave divers to penetrate the depths of the submerged boulder crawl beneath Malham Cove.
Janet's Foss, and Janet's Cave
A picturesque waterfall due south of Gordale Scar, Janet's Foss is where Gordale Beck cascades over a tufa* capped limestone outcrop into a deep pool in a wooded
limestone gorge. On the far bank is Janet's Cave, a dark hole which actually leads nowhere.
From Janet's Foss, Gordale Beck flows through woods and then open fields before meeting up with Malham Beck, just south of the village. Further downstream, this
tributary meets the stream issuing from Aire Head Springs (actually the infant River Aire) on its journey down towards Skipton.
The Dry Valley of Watlowes
Below Water Sinks, and above Malham Cove lies a deep limestone canyon known as the Dry Valley, or Watlowes Valley. Whatever underground route the streams of
Malham Moor now take, Watlowes Valley was almost certainly carved out by the glacial overspill from Malham Tarn flowing to what was once England's
highest waterfall at Malham Cove. Now the valley is dry, but contains some most impressive limestone features, with plenty of exposed and weathered rock.
Above the Dry Valley
Malham village
Malham village itself lies in a broad valley called Malhamdale, which further downstream becomes known as Airedale. The huge precipice of Malham Cove dominates
Characteristics of Granite
Granite is made up of three minerals: quartz, feldspar and mica. It
is a hard, crystalline rock, which is very resistant to erosion. It is an
intrusive igneous rock. The main processes that affect it are freezethaw and hydrolysis. A good example area to use in Great Britain is
Dartmoor.
Granite landforms
The main granite landforms are tors, which can be found on moors
such as Dartmoor and Bodmin Moor. Tors are blocks of granite
that have weathered slower than the granite around them, because
they have less joints and faults.
The Formation of Tors on Dartmoor:
The granite seen on Dartmoor originated as a granite batholith,
under the surface of the earth. A batholith is an area of molten rock
that has cooled very slowly within the crust, creating a rock with
large crystals.- Over time the material above the batholith was
weathered and removed by rivers and glaciers. As this material was
removed there was a reduction of pressure on the granite as there
was less above it. This caused it to crack creating joints and bedding
planes.- Where the joints were close together the most rapid
weathering occurred, and quickly broke down the rock. However
there were also areas where there were very few joints and so
slower weathering occurred.
The main form of weathering is freeze-thaw.- As this process continued
over millions of years, the overlying material was totally removed,
leaving behind the tors and valleys seen on Dartmoor.
Uses of a Granite Area
Granite areas themselves have limited economic uses. The soil is
usually poor and thin, so little farming takes place, probably just
some sheep and cattle grazing. Because granite is impermeable,
and the soil is poor, areas such as Dartmoor are ideal sites for
reservoirs. Historically granite areas were mined, especially in the
South-West, for things such as copper, tin and arsenic. Nowadays
quarrying occurs, taking away china clay for pottery and of course
granite itself, which is used in building (an excellent example being
the city of Aberdeen, which is known as “the Granite City”).
Granite is also used for things such as hearths, fireplaces, and
ravestones.Tourism is increasingly becoming important in granite
areas. Many tourists just come to take in the fresh air and beautiful
scenery, but the towns and villages of these areas are trying to cash
in by opening guesthouses, cafes and other tourist facilities. The
Northern half of Dartmoor is also used as an army firing range, with
a large camp based just outside of Okehampton. The military uses
of the moor have caused conflicts with local farmers, residents and
tourists.
Chalk & Clay
Characteristics of chalk and clay
Chalk:
Formed 70 to 100 million years ago, chalk is also called cretaceous limestone. It is a soft, white rock.Chalk is an example of a porous
rock, as it has pore spaces, which can store water. It does not have joints and bedding planes like carboniferous limestone.Clay:Is a
product of chemical weathering and river erosion.Clay is porous, but becomes impermeable when wet, as the particles expand and fill
the pore spaces.The main areas of chalk and clay in this country are in the South and East of the country. Places like the North and South
Downs are good examples.
Chalk and clay landforms
- Bournes are streams that occasionally flow down the dry valleys in times of prolonged wet weather, when the ground may have become
saturated. - Clay vales are the valleys between the chalk escarpments. The clay, when drained is a fertile soil suitable for a range of
farming methods. Clay vales are flat, and have a number of streams meandering through them.- Dry valleys, such as Devil’s Dyke, were
formed in periglacial times, when the ground froze, so melt water rivers ran over the surface of the chalk rather than flowing down through
it. These rivers carved out steep sided valleys. Once the climate had warmed again a dry valley was left behind. These also are common
features of limestone landscapes.- Escarpments or cuesta’s are the main landform of chalk and clay areas. Initially the layers of chalk
and clay were tilted by the collision of the African and Eurasion plates. The soft clay was then eroded faster than the more resistant chalk,
leaving escarpments (chalk hills) behind. Because of the angle of the tilt, these escarpments have two distinctive sides. The steeper side
is called the scarp slope, whilst the gently sloping side is called the dip slope. - Springs form at the bottom of the escarpment, where
the chalk meets the clay. This is why many settlements can be found along spring lines in chalk and clay areas.
Uses of a chalk and clay area
Clay is very fertile, but must be drained first. Once that has been done farming includes dairying, sheep grazing, and some arable farming. On
the chalk escarpments the main agriculture is sheep grazing.
Many settlements were built at the bottom of the scarp or dip slope, as the land was less likely to flood, there was a good water supply, and
there was good farming land nearby. Very early settlements would have been higher up the chalk escarpment for defensive
purposes.Chalk is a main ingredient in cement making, and is quarried for that purpose. Clay can be used in pottery.Underground
aquifers act as a store for water within the chalk and are used as a natural water supply for London.
Quarrying
Quarrying is one of the biggest industries in the areas where granite, limestone, chalk and clay are found.
Unfortunately these areas are, in many cases, also areas of great natural beauty and often part of a National Park.
There are therefore many positive and negative impacts of quarrying.
The impacts of quarrying
Advantages
Disadvantages
Quarries provide much needed employment opportunities in areas where jobs are often hard to come by.Noise pollution
from the blasting needed to extract rock.The increased income means that more money is likely to be put into the
local economy.Visual pollution from the quarry pit itself, as well as the buildings and slag heaps.The increase of
industry and need for access for large lorries may lead to infrastructure (roads mainly) improvements.Dust
pollution from the rock blasting.Good landscaping of the quarry site once it has been exhausted could enhance the
area’s natural beauty further.Noise and dust pollution from the many heavy lorries that will be travelling to and from
the quarry every day. These lorries may also block country roads and damage wildlife. Pollutants from the quarry
can run-off into the local rivers and cause problems for local people and wildlife. Wildlife habitats are initially lost
when the quarry opens.
Possible solutions to the problems of quarrying
Trains could be used instead of lorries, which would cut down the traffic and damage to roads.
Landscaping could be used during quarrying to diminish the visual scar, and also once quarrying has been completed,
to try to return the area to nature as best as possible.
The quarry could be restricted in size, so that it does not engulf the surrounding area.
Lines of trees can be used to reduce noise pollution and try to improve the look of the area.
The Main Weathering Process
Freeze-Thaw
Occurs in areas where the temperature regularly drops below 0°C.
Water enters cracks in the rock during the day. Overnight the temperature drops and the water freezes. As it freezes, it
expands.
The expanded ice places pressure on the rocks around it.
Over time this constant pressuring of the rock causes it to crack and split.
Exfoliation
Occurs in hot, dry climates.
The outer layer of the rock is heated by the sun during the day, causing it to expand, during the night, as the
temperature drops, the rock contracts. This constant expanding and contracting eventually leads to the outer
layers of the rock pealing away, leaving behind them rounded rocks and dome shaped outcrops.
Hydrolysis
Attacks rocks, which include feldspar crystals, the most common example being granite.
The feldspar reacts with acidic rainwater and dissolves to form kaolin (china clay).
The remainder of the rock breaks up into its individual crystals over time.
Carbonation & solution
Occurs on rocks containing calcium carbonate, such as limestone and chalk.
Rainwater and dissolved carbon dioxide mix to form a weak carbonic acid.
Calcium carbonate in the rocks reacts with the acidic water and dissolves leaving behind calcium bicarbonate.
This compound is soluble and is easily washed away by running water.