Transcript Between a rock and a hard place

 You must know and be able to describe and explain:
 Physical weathering
 Freeze-thaw
 Exfoliation
 Chemical weathering
 Limestone solution
 Igneous
 Sedimentary
 Metamorphic
 Formed by fire – magma
in the interior of the
Earth
 Formed by the cooling of
lava or magma
 Examples – Basalt and
Granite
 Made up of small
particles transported by
water, ice and wind
 As more sediment
accumulates the weight
causes the rock to form
 Weak rock generally
 Examples – Sandstone,
clay, limestone and chalk
 Originally igneous or
sedimentary rock which
have been altered by heat
and/or pressure
 Example
 Limestone into Marble
 Clay into Slate
 All the Granite rocks in the UK are found to the north
and west of the Tees-Exe line
 The rock which forms tors is that which remains after
the surrounding rocks have been weathered and
carried away.
 Where tors occur, the joints in the granite are wider
apart than in the rock around them
 Freeze-thaw weathering can operate more effectively
and blocks of rock break off more quickly where the
joints are close together, because there are more cracks
in the rock for the water to fill
 Each time the water freezes and expands within a
joint, more pressure is put on the surrounding rock
and the crack widens.
 Where there are fewer joints, it takes longer for the
blocks of rock to be broken off and the block are left
upstanding as Tors
 Reservoirs
 Poor grazing land for Cattle and Sheep
 Dartmoor – Ponies
 Building materials and gravestones
 In the Uplands of England and Wales
 The Yorkshire Dales – Malham and Ingleton
 Peak District near Castleton
 These rocks are very susceptible to chemical
weathering
 Limestone pavements – flat surfaces of bare rock
broken up into separate block
 The flat surfaces of the blocks are clints and the gaps
are grykes
 Rivers disappear underground either through small
holes in the rocks called sink holes or down larger
holes with a funnel shape above called swallow holes
 Underground limestone is full of holes
 Forms large chambers, caves and caverns
 Stalactites made of lime hang down from the roofs like
long icicles
 Stalagmites are the thicker columns built up from the
floor
 Good for sheep farming – grazing the short turf-like
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grass which grows
Limestone landforms are attractive to visitors – tourist
attractions – Gift shops in Castleton etc
Farmers can ear extra income from campsites and bed
and breakfasts
Used as a building material – St. Paul’s Cathedral
When crushed it can be used for fertiliser
Used a cleanser in many industries – power stations
Quarrying
 Chalk is a soft, white, porous form of limestone composed of the
mineral calcite. It is relatively resistant to erosion so forms tall
steep cliffs where chalk ridges meet the sea e.g. Beachy Head
along the south coast of England
 Chalk is porous which means that water can pass through and be
stored in the pore spaces between the particles of rock. When it
rains, water infiltrates into the chalk layers and saturates the
chalk. The upper level of saturation is called the water table.
 Many water companies drill boreholes into the chalk rock to
supply water to nearby settlements.
 Chalk forms distinctive landscapes with steep escarpments
and gentle dip slopes. The hills may have dry valleys which
show the characteristics of a river valley but have no water
flowing along them. The North and South Downs in south-east
England (UK) show all these features
 There are two requirements before an escarpment can
be formed:
 Alternate outcrops of different types of rocks. One rock
needs to be soft and the other needs to be more resistant
to erosion
 Beds of rock dip at an angle to the ground surface.
Instead of being horizontal, the beds were tilted by
earth movements so that they lie at an angle to the
surface
 The clay is eroded more quickly than the chalk
 As the clay is eroded down into the vale, the chalk is
left standing up because of its greater resistance
 The scarp slope forms a prominent feature where the
layer of chalk reaches the surface
 The dip slope is more gentle following the tilt of the
beds of rock
 Settlement - see Fulking case studies
 Good for pasture and training racehorses
 Good building material
 Underground water supply – called aquifers