Transcript Constructive and Destructive Forces: Forces that Change the

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. Mountain building
2. Deposition of sediment
3. Volcanic 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. 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)
Destructive Forces: Deforestation
• 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
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.
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.
• 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.
• 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 .
• Desertification: The causes of desertification are complex, but
deforestation is one of the contributing factors.
Weathering and Erosion
Strip Mining
Deforestation