Constructive and Destructive Forces: Forces that Change the

Surface of the Earth

Constructive Forces: build up the Earth’s surface; they add land

• Analogy: Bob the Builder– He builds things; he

does not destroy them.

Examples of Constructive Forces

1.1. Mountain building Mountain building

2.2. Deposition of sedimentDeposition of sediment

3.3. Volcanic EruptionVolcanic Eruption

August 2006 brought two new things to the Tonga Islands in the South Pacific. One was a raft of lightweight, frothy volcanic rock—pumice—floating on the ocean surface. The other was a new island emerging out of the water

Constructive Forces: Volcanic Mountain Building

Destructive Forces: destroy the earth’s crust; they remove land

• Analogy: Rob the Destroyer– He destroys things.

Examples of Destructive Forces

1.1. Weathering-Weathering- a process that causes the a process that causes the breakdown of rock.breakdown of rock.

2.2. ErosionErosion- weathering and wearing away of rock - weathering and wearing away of rock into sediment.into sediment.

3.3. DeforestationDeforestation-clearing land of trees (South -clearing land of trees (South America and Taiga Forest)America and Taiga Forest)

4.4. Strip mining-Strip mining- clearing land to extract coal or clearing land to extract coal or other valuable minerals from the ground (West other valuable minerals from the ground (West Virginia).Virginia).

5.5. Volcanic EruptionsVolcanic Eruptions (Mount St. Helens) (Mount St. Helens)

Destructive Forces: Deforestation

• Brought about by the following:Brought about by the following:

– conversion of conversion of forests and woodlands to forests and woodlands to agricultural landagricultural land to feed growing numbers of to feed growing numbers of peoplepeople

– development of cash development of cash crops and cattle crops and cattle ranchingranching, both of which earn money for , both of which earn money for tropical countriestropical countries

Destructive Forces: Deforestation

– commercial loggingcommercial logging (which supplies the (which supplies the world market with woods such as meranti, world market with woods such as meranti, teak, mahogany and ebony) destroys trees as teak, mahogany and ebony) destroys trees as well as opening up forests for agriculturewell as opening up forests for agriculture

– felling of trees for felling of trees for firewood and building firewood and building materialmaterial; the heavy lopping of foliage for ; the heavy lopping of foliage for fodder; and heavy browsing of saplings by fodder; and heavy browsing of saplings by domestic animals like goats.domestic animals like goats.

CONSEQUENCES OF DEFORESTATIONCONSEQUENCES OF DEFORESTATION

• Carbon Cycle:Carbon Cycle: When forests are cleared, and the trees are either When forests are cleared, and the trees are either burnt or rot, this carbon is released as CO2. This leads to an burnt or rot, this carbon is released as CO2. This leads to an increase in the atmospheric CO2 concentration. CO2 is the major increase in the atmospheric CO2 concentration. CO2 is the major contributor to the greenhouse effect.contributor to the greenhouse effect.

• Water Cycle:Water Cycle: With removal of part of the forest, the region cannot With removal of part of the forest, the region cannot hold as much water. The effect of this could be a drier climate. hold as much water. The effect of this could be a drier climate.

• Soil erosion:Soil erosion: With the loss of a protective cover of vegetation more With the loss of a protective cover of vegetation more soil is lost.soil is lost.

• Silting of water courses, lakes and dams:Silting of water courses, lakes and dams: This occurs as a result This occurs as a result of soil erosion. of soil erosion.

• Extinction of species:Extinction of species: which depend on the forest for survival. which depend on the forest for survival. Forests contain more than half of all species on our planet - as the Forests contain more than half of all species on our planet - as the habitat of these species is destroyed, so the number of species habitat of these species is destroyed, so the number of species declines .declines .

• Desertification: Desertification: The causes of desertification are complex, but The causes of desertification are complex, but deforestation is one of the contributing factors.deforestation is one of the contributing factors.

Weathering and Erosion

Strip Mining

Deforestation