Weathering 5 th Ms Carr Year Geography Learning

Weathering 5 th Ms. Carr Year Geography

Learning Outcome �Understand the main causes of Weathering. �Identify the different types of weathering. �Recognise a landform created as a result of one type of weathering.

Weathering Types of Weathering

�Weathering is the breaking down of the rocks exposed on the earth’s surface. �Causes of Weathering �Water �Fluctuating Temperatures �Animals �Plants

Types of Weathering �There are three main types of weathering: �Mechanical / Physical Weathering is the break down of rocks into smaller pieces, such as Freeze-thaw action, Exfoliation, Pressure Release and Crystallisation of salts. �Chemical Weathering is when a chemical reaction occurs in the rock causing it to decompose, such as Carbonation, Hydration, Oxidation and Hydrolysis. �Biological Weathering is the break down of rocks due to the physical and/or chemical actions of living things, such as Plants, Animals and Humans.

� Four types of mechanical weathering: i. Freeze-thaw action ii. Exfoliation iii. Pressure release (unloading) iv. Salt crystallisation

� 1. Freeze-thaw action Chapter 8: Weathering § Frequent temperature change § Temperatures rise above and fall below freezing § § § § (0°C) Plentiful supply of water Most pronounced at higher altitudes Day: water seeps into cracks or fissures in rocks Night: water freezes and expands straining surrounding rock Rocks crumble and break down Scree, e. g. Croagh Patrick, Co. Mayo Also known as frost action

Mechanical Weathering Freeze-thaw Action

� II. Exfoliation § Also known as onion-peeling § 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 § e. g. the Kissing Camels, Garden of the Gods, Colorado, USA

Mechanical Weathering Onion Weathering/Exfoliation

�III. Pressure release § Also known as unloading § Denudation removes the rock material § Underlying rock is exposed and pressure is released § Outer layers of the rock expand which creates stresses on the rock § Leads to fracturing parallel to the rock surface § Sheets of rock break away from the exposed rocks along fractures

� IV. Salt crystallisation § Associated with arid climates § High temperatures cause strong evaporation § Causes the breaking down of rocks when a salt solution (i. e. water containing salt) seeps into cracks § Evaporate leaving salt crystals behind § Salt crystals expand when they are heated up, thus exerting pressure on the rock which leads to its disintegration

Mechanical Weathering Crystallisation of Salts

Chemical Weathering § Composition of rocks change § Break down of rock caused by water and acid § Occurs in regions where the climate is warm and wet

Four Types of Chemical Weathering �Carbonation �Hydrolysis �Oxidation �Hydration

Chemical Weathering �Carbonation occurs when: Carbon dioxide is absorbed by the rainwater to form weak carbonic acid. This weak acid dissolves rock, especially Limestone. Rain + Carbon Dioxide = Weak Carbonic Acid + Limestone = Calcium Bicarbonate Eg; The Burren, Co Clare

Chemical Weathering Carbonation

Chemical Weathering �Hydrolysis involves the action of the hydrogen in the rainwater on rockforming minerals, such as Feldspars. Feldspar is a mineral in granite which is converted into Kaolin by hydrolsis. Kaolin is used as pottery clay. In granite, the other minerals are resistant to hydrolysis and therefore fall out of the rock. It is more effective in hot conditions and therefore is more common in hot, wet regions.

Chemical Weathering Hydrolysis

Chemical Weathering �Oxidation occurs when a mineral in the rock chemically combines with oxygen or air. Rocks which contain iron are easily oxidised. Iron oxides in rocks and appears as reddish or orange-yellow streaks leaching from the rock.

Chemical Weathering Oxidisation

Chemical Weathering �Hydration is when the rock minerals combine with water. As the minerals hydrate they expand. This expansion puts pressure on the rock and causes it to shatter. This process is extremely similar to the process of crystallisation of salts but needs water to take place and is therefore a chemical process.

Chemical Weathering Hydration

Biological Weathering �The action of plants, animals and man can speed up both mechanical and chemical weathering. This can include burrowing animals, the growth of plant roots, quarrying and deforestation.

Landforms as a result of Weathering in the Wicklow Mountains case study � § Granite is the main rock type § Granite is subject to both physical (mechanical) and chemical § § weathering An igneous rock composed of mineral such as quartz, feldspar and mica Granite weathers – feldspar undergoes hydrolysis and forms kaolin Quartz remains as residual mineral Weathered rock becomes an ingredient of soil

� § Quartz will become eroded and its sediment is transported to the sea, along with clays § Move downslope under the influence of gravity § Wicklow Mountains are rounded and have gradual slopes § Tors have formed on the Wicklow Mountains § Wicklow Mountains had shale and sandstone § These rocks were then eroded over time, releasing downward pressure on the underlying granite

§ Granite was then able to expand upwards causing joints to appear in the rock § Joints appeared at points of weakness in the granite rock § Susceptible to hydrolysis, and the feldspar in the granite was converted to kaolin clay, as a result of chemical weathering § Freeze-thaw action continued to attack the joints § Under the extremes of diurnal temperature changes, the joints were further enlarged

§ Weathered regolith moved downslope under the force of gravity § Tors left behind upslope ‒ blocks of more resistant rock, often roughly rectangular in shape § Examples of tors are also found on Dartmoor, and Bodmin Moor, in south-west England

What type of Weathering is this? �Mechanical/Physical Weathering- Onion Weathering

What type of Weathering is this? �Chemical Weathering - Carbonation

What type of Weathering is this? �Mechanical/Physical Weathering- Freeze-thaw Action.

Keywords �Exfoliation �Carbonation �Hydration �Oxidation �Hydrolysis

Exam Questions �Choose one example of each type of weathering process and explain how it occurs. (30 m) �Weathering is the process where rock and soil is broken up and can be caused by; �Freeze-thaw action �Carbonation Describe and explain any one of these weathering processes. (30 m)