Geography - Rocks and Landscapes

Classification of Rocks

• Rocks found on the Earth's surface actually come from inside the Earth -
• so they tell us a lot about the Earth's interior.
• They are classified
• (organised) into three main groups: igneous rocks, sedimentary rocks and
• metamorphic rocks.
• Rock Types
• Igneous rock
• Sedimentary rock
• Metamorphic rock
• 

Igneous Rock

• Igneous rocks are formed by magma
• from the molten interior of the Earth. When magma erupts it cools to
• form volcanic landforms. If magma cools inside the Earth it forms intrusive rock, which may later be exposed by erosion and weathering.
• Examples of igneous rocks include basalt and granite.
• https://www.youtube.com/watch?v=nHEzJQzDH80 (Enclavar)

Metamorphic Rock

• Metamorphic rocks have been subjected to tremendous heat and/or
• pressure, causing them to change into another type of rock. They are
• usually resistant to weathering and erosion and are therefore very
• hard-wearing.
• Examples of metamorphic rocks include marble, which originates from limestone, slate, which originates from clay, and schists formed from sandstone or shale (sedimentary rocks).
• https://www.youtube.com/watch?v=ckypDmkbhb8 (Enclavar)

Sedimentary Rock

• Sedimentary rocks are formed from sediments that have settled at the
• bottom of a lake, sea or ocean, and have been compressed over millions
• of years. The sediment comes from eroded rocks carried there by rivers
• or ice, and from the skeletons of sea creatures.
• Examples of sedimentary rocks include sandstone, limestone, chalk and clay.
• https://www.youtube.com/watch?v=G0ru-kLpedo (Enclavar)

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.
• 

Freeze-thaw Weathering

• When rock is exposed to weather
• conditions it becomes subject to processes, such as freeze-thaw
• weathering, that cause it to change and break down.
• Freeze-thaw weathering
• The freeze-thaw weathering process is also known as frost shattering.
• Water - eg from rainfall or melting snow and ice - becomes trapped in a crack or joint in the rock.
• If the air temperature drops below freezing, the water will freeze and expand by 9-10 per cent putting pressure on the rock.
• The ice will melt when the temperature rises above freezing.
• If this process happens repeatedly, the rock will weaken and eventually shatter into angular fragments.
• The fragments may then be deposited as scree at the foot of a slope.
• It is most effective where the temperature fluctuates around 0°C, eg on north-facing high altitude slopes in Snowdonia.
• Igneous Processes and Products
• The Rock Cycle
• The Rock Cycle
• Types of Rock