1. Constructive and Destructive Forces: Forces that Change the Surface of the Earth

2. Constructive Forces: build up the Earth’s surface; they add land Analogy: Bob the Builder –He builds things; he does not destroy them.

3. Examples of Constructive Forces 1.Mountain building 2.Deposition of sediment 3.Volcanic Eruption

4. 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 waterTonga Islands

5. Constructive Forces: Volcanic Mountain Building

6. Destructive Forces: destroy the earth’s crust; they remove land Analogy: Rob the Destroyer –He destroys things.

7. Examples of Destructive Forces 1.Weathering- a process that causes the breakdown of rock. 2.Erosion- weathering and wearing away of rock into sediment. 3.Deforestation-clearing land of trees (South America and Taiga Forest) 4.Strip mining- clearing land to extract coal or other valuable minerals from the ground (West Virginia). 5.Volcanic Eruptions (Mount St. Helens)

8. Destructive Forces: Deforestation Brought about by the following:Brought about by the following: –conversion of forests and woodlands to agricultural land to feed growing numbers of people –development of cash crops and cattle ranching, both of which earn money for tropical countries

9. Destructive Forces: Deforestation –commercial logging (which supplies the world market with woods such as meranti, teak, mahogany and ebony) destroys trees as well as opening up forests for agriculture –felling of trees for firewood and building material; the heavy lopping of foliage for fodder; and heavy browsing of saplings by domestic animals like goats.

10. CONSEQUENCES OF DEFORESTATION Carbon Cycle: When forests are cleared, and the trees are either burnt or rot, this carbon is released as CO2. This leads to an increase in the atmospheric CO2 concentration. CO2 is the major contributor to the greenhouse effect.Carbon Cycle: When forests are cleared, and the trees are either burnt or rot, this carbon is released as CO2. This leads to an increase in the atmospheric CO2 concentration. CO2 is the major contributor to the greenhouse effect. Water Cycle: With removal of part of the forest, the region cannot hold as much water. The effect of this could be a drier climate.Water Cycle: With removal of part of the forest, the region cannot hold as much water. The effect of this could be a drier climate. Soil erosion: With the loss of a protective cover of vegetation more soil is lost.Soil erosion: With the loss of a protective cover of vegetation more soil is lost. Silting of water courses, lakes and dams: This occurs as a result of soil erosion.Silting of water courses, lakes and dams: This occurs as a result of soil erosion. Extinction of species: which depend on the forest for survival. Forests contain more than half of all species on our planet - as the habitat of these species is destroyed, so the number of species declines.Extinction of species: which depend on the forest for survival. Forests contain more than half of all species on our planet - as the habitat of these species is destroyed, so the number of species declines. Desertification: The causes of desertification are complex, but deforestation is one of the contributing factors.Desertification: The causes of desertification are complex, but deforestation is one of the contributing factors.

11. Weathering and Erosion

12. Strip Mining

13. Deforestation