Weird and Wonderful of Nature: The Earth’s Weathering

Physical weathering includes the action of ice and frost and the effect of plants and animals. When water gets into crack in rock, it freezes and expands. This expansion can expansion can exert a force up to 635 kg/cm2 (1400lb/sq in). With repeated freezing and thawing cracks gradually enlarge to the point at which pieces of rock break off. The process, known as ice- or frost-wedging, is most pronounced on mountains, where the daily cycle of freezing and thawing, even in summer, creates large accumulations of rock rubble, called talus or scree, around the base of steep slopes.

Weird and Wonderful of Nature: The Earth’s Weathering

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By Mr Ghaz, October 2, 2010

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Weird and Wonderful of Nature: The Earth’s Weathering

Core fact: Weathering is the gradual breaking down of rock exposed at the Earth’s surface. Joints and fissures in rock let in and water and facilitate the process.

Physical forces such as ice and tree roots break up large expanse of rock into smaller pieces, and expose the surface to attack from acids dissolved in water and from oxygen in the air.

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Water and oxygen react with veins of minerals in rock to produce areas of weakness.

Weathering exposes deposits of areas and minerals in rock, and creates the sediment that forms soil.

Physical Forces

 

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Physical weathering includes the action of ice and frost and the effect of plants and animals.

When water gets into crack in rock, it freezes and expands. This expansion can expansion can exert a force up to 635 kg/cm2 (1400lb/sq in). With repeated freezing and thawing cracks gradually enlarge to the point at which pieces of rock break off. The process, known as ice- or frost-wedging, is most pronounced on mountains, where the daily cycle of freezing and thawing, even in summer, creates large accumulations of rock rubble, called talus or scree, around the base of steep slopes.

 

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Plant and tree roots get into surface cracks in rock, where they can exert a force so strong that it widens a crack, opening it up to chemical weathering.

Large animals contribute by stepping on or crushing stones and pebbles. Even earthworms help to break up rock fragments.

The Power of Ice

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Ice- wedging is particularly active in mountains, where meltwater from snow seeps into cracks then freezes and expands at night.

Slow Disintegration

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In Bryce Canyon, USA, weathering has accentuated the differences in rock types, and landslides and erosion have removed the resulting debris, leaving an exotic array of rock shapes.

Exfoliation Domes

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When an area of igneous rock is uncovered by the erosion of overlying rock layers, the pressure on it is reduced and the rock expands upwards. The outer layer of granite expands ore than the rock underneath and labs break off, forming an exfoliation dome. Stone Mountain in Georgia and El Captain in Yosemite were formed this way. A combination of exfoliation and erosion by glaciers produced Half Dome in Yosemite.

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Yosemite: Half Dome rises more than 1200m (4000ft) above the Valley floor.

Chemical Forces

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Chemical weathering occurs when water or air come into contact with rock surfaces. For example, acids dissolved in water attack soluble rock such as limestone, while oxidation works on iron-rich rocks such as basalt. These processes change the mineral content in rock into other, often softer, minerals, many of which are soluble in water and get washed away, most weathering happens within a few metres of the Earth’s surface. Heat speeds up the rate of chemical reactions.

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Granite Boulders: Edges and corners weather faster than flat surfaces, and all boulders gradually develop a rounded shape, like these in the Namib Desert.

Onion-Skin Weathering

 

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In arid where rock surface are exposed to high daytime temperature and low night- time ones, the surface

Layers expand in the day and contract at night. Eventually, the outermost the rock beneath and breaks off, in a process known as onion- skin weathering. The Devil’s Marbles in Australia were formed by this process.

Making Soil

 

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Much of the Earth’s surface is covered with a blanket of disintegrated and decomposed rock and mineral fragments produced by weathering. Where this is mixed with water, air and decayed plant and animal remains (humus), soil forms. The mineral content of the bedrock determines the nutrient richness of the soil produced.

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The soil- forming process works from the surface downwards, and variations in composition and texture evolve at different depths. A vertical section through the layers is called a soil profile.

Tie-Breaker

Q: What common metal gives much sandstone their red color?

A: Iron. In fact, it is rust (iron oxide) that makes the rock red. Oxygen in water combines with iron in rock to form a red rust, known as hematite, or a yellow rust, called limonite.

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14 Responses to “Weird and Wonderful of Nature: The Earth’s Weathering”
  1. Katien Says...

    On October 2, 2010 at 12:58 pm

    Interesting topic with great pictures.


  2. webseowriters Says...

    On October 2, 2010 at 2:14 pm

    An interesting share


  3. margaridab Says...

    On October 2, 2010 at 3:50 pm

    Good article and beautiful photos!


  4. mukech Says...

    On October 2, 2010 at 10:24 pm

    Nice post..informative …


  5. nobert soloria bermosa Says...

    On October 3, 2010 at 1:51 am

    another wonderful presentation


  6. GodsGrace Says...

    On October 3, 2010 at 2:43 am

    Good Post


  7. CHAN LEE PENG Says...

    On October 3, 2010 at 5:06 am

    Nature made me wondering that it’s a perfect sculptor. :-)


  8. zulfiqarali5 Says...

    On October 3, 2010 at 10:48 am


  9. albert1jemi Says...

    On October 3, 2010 at 11:15 am

    great work


  10. Mark Gordon Brown Says...

    On October 3, 2010 at 11:26 am

    good information and awesome pictures!


  11. papaleng Says...

    On October 5, 2010 at 2:27 am

    lovely photos and a very informative post.


  12. revivor Says...

    On October 13, 2010 at 2:10 pm

    weathering has always intrigued me – worth looking at everywhere you go (especially your pics, though!!)


  13. helen Says...

    On January 8, 2012 at 8:09 pm

    its amazing


  14. NDABAKURANYE Theogene Says...

    On May 8, 2012 at 2:35 pm

    This teach us well about physical geography


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