Weathering and Mass Movement

• Weathering


  The breaking down of rocks and other materials on the Earth's surface.
• Erosion


  Processes by which rock, sand, and soil are broken down and carried away.
• Mechanical weathering


  The type of weathering in which rock is physically broken into smaller pieces
• Example of mechanical weathering and explain


  Freeze-thaw action, occurs in mountainous areas

  -Water seeps into rock cracks during the day

  -At night temperatures fall and the water in the cracks freezes and expands by 9%, putting pressure on the rock

  -Continues over time, causing rock to weaken and pieces to break off (scree)

  Example: Croagh Patrick
• Chemical weathering


  The process that breaks down rock through chemical changes
• Example of chemical weathering and explain

  Carbonation

  -Atmosphere contains carbon dioxide

  -Rainwater mixes with carbon dioxide to from a weak carbonic acid

  -Has an effect on limestone as it is 80% calcium carbonate

  -Carbonic acid reacts with calcium carbonate and dissolves the limestone.

  Example: The Burren, Co. Clare
• Karst landscape


  an area of exposed limestone.
• Surface features of a karst landscape

  Limestone Pavement

  Swallow Hole
• Limestone pavement + formation

  Large area of exposed limestone

  -Rainwater falls onto limestone and passes through vertical joints (cracks)

  -Carbonation makes the joints wider by dissolving the limestone, until they look like gaps called grikes

  -The blocks left between the grikes are called clints

  
• Swallow hole + formation

  Hole in a limestone area where water goes underground.

  -River begins flowing underground along the bedding planes

  -The river helps to form underground karst features like passages and caves.
• Underground karst features


  Caves and Cavers

  Stalactites

  Stalagmites

  Pillar
• Caves and caverns


  naturally formed underground chambers. As rivers flow underground, they enlarge the passages through carbonation and hydraulic action

  Example: Ailwee Caves in the Burren, Co. Clare
• Stalactites


  icicle shaped features that form on cave ceilings.

  -As water seeps through the rock it takes dissolved limestone with it

  -This water eventually reaches the roof of a cave or cavern

  -The drops evaporate and leave behind deposits of pure limestone called calcite

  -Over time this forms a stalactites
• Stalagmites


  Upside-down icicle shapes on the floor of a cave/cavern

  -Drops of water seep through the rock and fall on the ground

  -The water evaporates and leaves deposits of calcite directly below stalactites

  -This eventually forms stalagmites
• Pillar


  When a stalactite and stalagmite meet and join
• Mass movement


  the downhill movement of rock and soil because of gravity
• Factors affecting mass movement

  Gradient

  Vegetation

  Water content

  Human activity

  Animals
• Types of mass movement

  Soil creep

  Bog bursts

  Mudflows

  Landslides

  Avalanches
• Soil creep


  Movement of soil down a slope under the influence of gravity

  -Slowest form of mass movement

  -Trees grow at an angle, fences bend, poles tilt, walls crack
• Bog bursts


  When a mass of bog or peat moves down a slope after a period of heavy rainfall.
• Mudflows


  When soil and regolith become saturated after heavy rainfall and move downslope like a river of mud. Very fast

  -Can also occur after volcano eruption (lahar). This is when meltwater (melted by extreme volcano heat) mixes with ash soil and rock fragments.
• Landslides


  Rapid movement of earth materials downhill.
• Avalanche


  Rapid movement of snow and ice downslope.

  -Occurs when snow is too heavy to hold
• Controlling mass movement


  -Plant vegetation to stabilise soil

  -Steps built to trap moving material

  -Restrict overgrazing

  -Controlled explosions make large avalanches less likely