Understanding Rocks, Weathering, and Limestone Landscapes
Rock Types: Igneous, Sedimentary, and Metamorphic
1. Igneous Rocks: Formed from volcanic activity. They are made of tiny crystals that formed as the volcanic rock cooled down. Examples include granite and basalt.
2. Sedimentary Rocks: These rocks are laid down in layers. They are made of other rocks that have been eroded and transported, or from the remains of plants and animals. Examples include limestone, chalk, and coal.
3. Metamorphic Rocks: These are rocks that have been changed due to intense heat and pressure. Examples include marble and slate.
Weathering Processes: Physical, Chemical, and Biological
1. Physical Weathering: This occurs when rocks are broken into smaller pieces by physical processes. It often happens in areas of bare rock where there is no vegetation to protect the rock from the weather.
1.1 Freeze-Thaw (Frost Shattering): This is common when the temperature fluctuates around freezing point and where exposed rocks have many cracks. Water enters the cracks, freezes, expands, and then thaws, exerting pressure that causes the rock to break into smaller pieces.
1.2 Exfoliation (Onion Weathering): This occurs in very warm climates where exposed rocks are repeatedly heated and cooled.
Scree: The accumulation of broken rocks at the foot of a cliff, deposited by physical weathering.
2. Chemical Weathering: This happens when water and air activate chemical changes that cause rock to decompose and rot. Chemical reactions are most intense in warm and wet climates. Limestone solution is an example of chemical weathering.
3. Biological Weathering: This occurs when tree roots penetrate and widen cracks in a rock, or when acids released by decaying vegetation attack the rock.
National Parks and Quarrying: Benefits and Disadvantages
Benefits of Quarrying
- Quarrying provides jobs and increases local income, often in areas with limited employment.
- Local roads are improved to accommodate increased traffic.
- Local councils receive revenue from quarry firms.
- Quarries provide raw materials that support the national economy.
Disadvantages of Quarrying
- Spoil heaps, scarred hillsides, and quarry buildings are eyesores.
- Heavy lorries cause noise, raise dust, and block narrow country lanes.
- Blasting operations cause noise, dust, and vibrations.
- Local water supplies may be polluted.
- Disused quarries may flood and become dangerous.
- When quarries close, they leave a scarred landscape, derelict buildings, and a loss of jobs.
- Farmland and wildlife habitats are lost.
Escarpments and Chalk Landscapes
Escarpments have a steep scarp slope and a more gentle dip slope. Rivers and streams are usually absent on chalk itself. In contrast, surface drainage, with rivers emerging from springs at the junction of permeable and impermeable rocks, is often abundant in the vales.
Dry valleys are another characteristic landform of chalk areas. These valleys are believed to have formed during the Ice Age when the ground was frozen, causing it to act as an impermeable rock. Although dry valleys in chalk have steep sides, they are not as steep as those found on Carboniferous limestone.
Limestone: Chemical Weathering, Structure, and Permeability
1. Chemical Weathering: Rainwater contains carbon dioxide in solution. Although it is a weak acid, it reacts with rocks that include calcium carbonate, like limestone.
2. Rock Structure: Limestone is a sedimentary rock, which means it was laid down in layers. Each layer is separated by a bedding plane.
3. Permeability: Carboniferous limestone is not porous, unlike chalk, which is.
Definitions of Limestone Features
- Limestone: A sedimentary rock made by the remains of shells and marine skeletons on the sea bed.
- Gryke: A deep and narrow groove caused by chemical weathering on an exposed limestone surface.
- Clint: A small ridge or flat-topped block found on an exposed limestone surface.
- Escarpment: A ridge that has a steep slope on one side and a gentle slope on the other.
- Karst: An area of Carboniferous limestone scenery with extensive underground drainage.