Summary
Summary Surface forces (geomorphology) - Grade 9
Surface forces (geomorphology) for grade 9. There are spaces (blocks) for drawing diagrams.
[Show more]
Seller
Follow
Content preview
Surface forces that shape Earth- Earth’s surface = worn away by natural forces (wind, rain, frost, waves)
o shapes all of natural landforms.
- Humans also contribute to the shaping of Earth’s surface (building, mining, farming)
Weathering
- Weathering --> the wearing away of rocks and soil by the action of the weather.
- Three types:
o Physical weathering – frost and temperature
o Chemical weathering – chemicals weaken rock.
o Biological weathering – plants/animals
Physical weathering
- Involves physical processes (ice, water, and temperature change)
o Freeze thaw action
o Exfoliation
- Freeze thaw action
o Water collects in cracks in rocks.
o The water freezes from the top of the crack downwards
o Cannot expand up because top is frozen, so it expands sideways putting pressure on the
rock (ice = 9% bigger volume than water)
- Exfoliation (peeling away of layers of rock)
o Big changes in temperature between day and night cause the outer layer of the rock to
expand and contract.
o Weakens outer layer causing it to ‘peel-off’.
Chemical weathering
- Changes chemical composition of rocks ∴ weakening and breaking it.
- Different types:
o Carbonation
o Oxidation
o Hydrolysis
- Carbonation
o Water in atmosphere and CO2 come into contact and form carbonic acid (H2CO3)
o Acid comes into contact with rocks containing calcium carbonate (CaCO 3)
o Rain changes insoluble calcium carbonate into soluble calcium bicarbonate
▪ Dissolves in rainwater and washes away.
1
, - Oxidation
o Occurs in rocks containing iron (rusting)
o Water contains O2 which reacts with iron to form iron oxide.
o Changes structure of rocks making it weaker ∴ it breaks down more easily.
- Hydrolysis
o Silicates in rocks absorb water and change into clay.
o Clay washes out of rock.
o Rock becomes unstable and may crumble.
Biological weathering
- Plants grow in cracks in rocks causing them to expand.
- Animals burrow and dig in soil ∴ exposing rocks and weakening the soil.
- Plants and animals contain chemicals that cause chemical weathering.
- Lichen (green/red) grows on rocks.
o Roots penetrate between grains in rock.
o Produces acid that breaks down minerals in rock.
Erosion and deposition
- Erosion --> wearing away of land through natural forces (movement)
- Deposition --> the depositing of materials created by weathering and erosion (on land)
Rivers
- River flows over the land, it carries weathered materials called a load (sand, stones, and silt)
o Load (sand and stones) bounce along the bottom of river wearing away the riverbed and
sides)
o Load piece sizes get smaller as journey continues as force of river wears away the rocks.
Upper course of river
- Waterfalls and rapids
o Waterfall is a sudden drop in a rivers gradient.
River flows over bands of The river undercuts the harder River forms a plunge pool below
harder and softer rock rock leaving an overhang whilst the waterfall. Overhang rocks
the sifter rock is more quickly eroded collapse into the plunge pool
o Rapids are where the water flows faster in a river’s course (without sudden drop in height
2
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through EFT, credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying this summary from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller citygirl04. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy this summary for R150,00. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
53068 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy summaries for 14 years now