Geo rocks and weathering - physical and chemical

what is physical weathering?

the disintegration of rocks, producing smaller, angular fragments of the same rock

what is chemical weathering?

decomposition creates altered rock substances such as kaolinite (china clay) from granite

what are the 5 types of physical weathering?

freeze thaw

heating and cooling

salt crystal growth

pressure release (dilatation)

vegetation root action

what is the process of freeze thaw weathering?

1) when water enters cracks in rocks and freezes it expands

2) this expansion exerts pressure on the surrounding rock, gradually widening the cracks

3) repeated freezing and thawing eventually cause pieces of rock to fall off.

when freeze haw occurs what percentage does the water expand by

9%

where is freeze thaw common in?

cold climates which frequent temp fluctuations around 0^oC

when is freeze thaw most rapid?

when combined with other processes like dilation and salt crystal growth

what is the case study for freeze thaw weathering?

the Scottish Highlands, UK

• Ben Nevis

what is the process of heating and cooling?

rocks expand when heated and contract when cooled.

overtime, repeated temp changes cause stress within the rock, leading to surface peeling and cracking (exfoliation)

where is heating and cooling most effective?

in deserts where there are high diurnal temp ranges

what is essential for heating and cooling to ocur

moisture

what is the process of salt crystal growth (haloclasty)

when salty water enters cracks in rocks and then evaporates, it leaves salt crystal behind

the growth of these crystals exert pressure on the rock causing it to crack and break apart.

where is salt crystal growth common in?

costal areas and arid environments where evaporation is high

which rock type is salt crystal growth most rapid in?

chalk, followed by limestone.

what is the rate of disintegration linked to in salt crystal growth

the porosity and permeability of the rock

what evidence is there of salt crystal growth?

honeycomb weathering - found on costal cliffs at salt point state park, CA

cave formations

what is the process of pressure release? (dilatation)

happens when overlying materials like soil or rock layers are removed through erosion

the release of pressure allows the underlying rock to expand and fracture

this often leads to the formation of exfoliation sheets or domes

what is vegetation root growth?

plants grow into cracks in rocks in search of nutrients and water

as the roots grow and thicken, they exert pressure on the rock, causing it to fracture

where is vegetation root growth common in?

areas with dense vegetation, like forests

where is chemical weathering most effective?

in warm, humid climates, e.g the amazon.

what are the key aspects of chemical weathering?

• water is the key medium

• most effective is sub-surface

• amount of water is important

• deep weathering

what is hydrolysis?

minerals in rocks react with water and change properties, e.g feldspar in granite

what are the changes that occur in the rock when experiencing hydrolysis

the rock becomes weaker and more susceptible to other weathering

which environment is hydrolysis most common in?

tropical regions

what is the process of hydrolysis

solution takes away the silicic acid and potassium hydroxyl leaving behind china clay

what is the case study for hydrolysis

Dartmoor, UK -south west england

granite environment with feldspar , when rainwater seeps through cracks in rocks it reacts with feldspar to form kaoline (china clay) and produces rounded tors and sandy soils.

it also contributes to the formation of boggy areas in the moorland

what is hydration?

hydration involves the absorption of water by minerals in rocks, causing them to expand and weaken.

this process does not chemically alter the minerals composition by increases physical stress within the rock

what is an example of hydration (using rocks)

anhydrite absorbs water to form gypsum

what happens with hydration overtime

overtime, the expansion and contraction of associated with hydration can cause rock layers to crack and break apart

where is hydration most common?

in hot, arid, or semi-arid environments as well as areas subject to periodic wetting and drying

how does carbonation work?

rainfall combines with dissolved carbon dioxide to form a weak carbonic acid in the atmosphere

what is a rock example of carbonation?

calcium carbonate reacts with acid water to form calcium bicarbonate which is soluble and removed by water via solution

where is carbonation most effective

in cooler, wetter climates where CO is more easily absorbed by water

what are the features/landforns of carbonation

karsts

what is the case study for carbonation?

the Guilin region in southern china has limestone karts

Rainwater absorbs CO2 from the atmosphere forming weak carbonic acid

this acidic water reacts with calcium carbonate in the limestone dissolving it into calcium bicarbonate

what does the type of weathering refer to?

whether its physical or chemical weathering

what does the rate refer to?

how fast or slow the weathering process is

what does the peltiers diagram tell us?

it shows the variations of chemical and physical weathering with climate

what are the 5 factors affecting weathering type and rate

1) climate - temp and rainfall

2) rock type - composition and how its formed

3) rock structure - what it looks like

4) vegetation

5) relief

what are the two minerals that make up granite

quartz - more resistant

feldspar

according to the peltiers diagram where is physical and chemical weathering the strongest

physical (coldest and driest point)

chemical (hottest and wettest point)

what is the number one control of weathering?

climate - rainfall then temp

when is chemical weathering the weakest

in dry areas

what are the 3 types of rocks?

igneous

sedimentary

metamorphic

how are igneous rocks formed

from cooling magma or lava

how are sedimentary rocks formed

formed from the compaction and cementation of sediments

how are metamorphic rocks formed

formed when existing rocks are changed by heat and pressure

what is an example of each type of rock?

igneous - granite

sedimentary. - limestone

metamorphic. - marble

how does rock structure affect weathering

physical: rocks with more joints and bedding planes will allow water, roots, and air in will increase weathering

chemical: fractured rocks allow more water and chemicals to penetrate deeper enhancing chemical reactions