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Physical Geography: Weathering - Coggle Diagram
Physical Geography: Weathering
Weathering is the breakdown or decay of rocks on or near the Earth’s surface
The causes of weathering include rocks exposed to:
Water
Gases in the atmosphere
Changes in temperature
Release of pressure from overlying layers of rock
Three types of weathering:
Mechanical
Mechanical weathering occurs when rocks are physically broken down into smaller pieces called regolith
Also known as physical weathering
Types of mechanical weathering:
Freeze-thaw action
Temperatures rise above (day) and fall below freezing (0°C) (night)
Plentiful supply of water
Most pronounced at higher altitudes
Day: water seeps into cracks or fissures in rocks
Night: water freezes and expands by 9 per cent straining surrounding rock
Over time: rocks crumble and break down
Scree, e.g. Great Sugar Loaf, Co. Wicklow
Also known as frost action, frost shattering
Exfoliation
Also known as onion peeling or onion layer weathering
Large diurnal temperature range
Rock expands during the heat of the day and contracts at night
Exerts pressure on the rock and the outer layers of the rock shatter
Example: Yosemite National Park, USA
Chemical
Chemical reaction when rocks come into contact with water
Changes composition
Breakdown of rock
Occurs in regions where the climate is warm and wet
Carbonation
Most common type of chemical weathering
Rainwater mixes with carbon dioxide, forms weak carbonic acid
Dissolves certain minerals in rocks, e.g. limestone
Limestone permeable
Weak carbonic acid combines with calcium carbonate in limestone, creating calcium bicarbonate (soluble)
Example: The Burren, Co. Clare
Hydrolysis
Introduction of water into the minerals in granite
Cementing agent feldspar absorbs water
Feldspar converts into Kaolin clay and breaks down
Particles of granite no longer held together, disintegrates
Most active in warm humid climates
Example: Leinster Batholith
Biological
The agents of biological weathering are plants, animals and humans
Biological weathering occurs when tree roots or animals widen spaces within the rock/soil
Humans can weather rocks, for example, by quarrying and mining
Case Study: Distinctive rock landscape – Granite in the Wicklow Mountains
Granite is the main rock type
Granite is subject to both physical (mechanical) and chemical weathering
An igneous rock composed of minerals such as quartz, feldspar and mica
Granite rock exposed due to pressure release of overlying layers of metamorphic rocks
Caused horizontal fractures in outside layers of the granite
Lines of weakness exposed to freeze-thaw action and hydrolysis
Created rounded gently sloping hills
Tors also created, rectangular shaped flat rocks stacked on top of each other