Geography 10Video on Weathering and SoilsMs. Ripley
Name:______
Weathering Video Notes
- Cleopatra’s Needle an ancient Egyptian monument moved to N. York in 1880
- All of the rocks are affected from weathering.
- Most rocks are formed below the earth’s surface. There the rocks are “weathered”. Weathering happens every where on the planet.
- Granite – heavily weathered – it’s soft, crumbles easily and it’s decomposing.
- Breaking of rock into fragments – physical fragmentation of rock – mechanical weathering. Rocks are usually cracked b/c of tectonic activity.
- Joints – pressure release.
- Rock below surface – layers of earth. Surface erosion forces the rock upwards. Rock has to crack into sheets.
- Exposed by erosion – plates detach themselves and go layer by layer (like stripping an onion).
- Burst water pipes in winter. Effects of this pressure on roads – frigid winter – water freezes and expands heaving up the road surface. When water gets into the cracks – it expands and extending the cracks. Spires of granite.
- Shows landscape.
- Mechanical weathering – natural break up of rock at the earth’s surface. Chunk of granite can be broken up by tectonic activity. But it doesn’t change the composition of the rock. Exposes the rock by breaking into smaller pieces. Drier climate – won’t break down as much.
- Chemical weathering – drastic effect – water in the ground and moisture in the air.
- As rain falls, it dissolves carbon dioxide producing weak carbonic acid. It picks up more acids and decomposes limestone and other rocks. Rainfall gradually dissolves limesteons. It actually destroys or changes the compositions. Rusting on a nail – changing what the rock actually is. Iron binded with oxygen – oxidized – rust.
- Because water is an important agent – amount of water is crucial. Climate wet moist climate – a lot more chemical weathering and the rocks.
- Weathering in the tropics – warm and damp – lots of water – fast weathering
- Desert – slow weathering due to lack of moisture.
- Only a few minerals are stable at the earth’s surface. Minerals that are most unstable – those that form the highest temperatures. Most stable – low temp.
- Granite – unlettered – I can’t break this rock apart. Quartz hasn’t weathered. But granite that is falling apart – it’s weathering the fastest and it’s turned into clay. I can break this rock apart b/c it’s starting to decompose. That will fall into the sedimentary system.
- Sediment is washed away by streams. Sandstone will form. Silt may harden as siltstone.
- Man has accelerated – carbon dioxide, sulphur dioxide – by burning of fossil fuels and forests – these gases combine with rain water. Serious global problem. Acid rain. Sulphur dioxide by power plants and cars. Sulphuric acid. Auto exhaust – excess acids in rainfall – reek havoc on trees and plants. Striking effect of acid rain – destruction of woodlands. Acid precipitation with continued industrial pollution – the process compounds.
Soils – Video and Questions
- Weathering – can break rocks into soil. We couldn’t survive without soil.
- Why is soil important?
1) Provides an anchorage for plants
2) Provides soluble nutrients for plant roots.
3) Home for microscopic animals which breakdown dead organic material
4) Harbours bacteria
- Soil is the foundation of the food chain depends.
Humus – rich organic material. Fertile soils.
A horizon – Topsoil – dark, rich with humus which holds nutrients and water
B horizon – Subsoil – layer where dissolved minerals collect light in color.
C horizon – weathering bedrock
- In South America - Most nutrients are locked up in the trees – clearcut and you lose the nutrients.
- People have damaged soils in the Great Plains of the USA by:
(1) Deep plowing in a dry climate
(2) Lack of crop rotation
(3) Overgrazing by beef cattle - Soil erosion be stopped by:
(1) Crop rotation – gives the soil a break
(2) Plant windbreaks (hedges, shelter belts)
(3) Shallow and infrequent tilling
(4) Use a watering system to moisten the soil and maintain plant growth