Constructive and Destructive Processes

Constructive ForcesConstructive Forces

A.A. A constructive force is on that build A constructive force is on that build up the Earth’s surface.up the Earth’s surface.

B. Examples: B. Examples: 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: Deposition

Constructive Forces: Volcanic Mountain Building

Destructive ForceDestructive Force

A. A destructive force is one that destroys or breaks A. A destructive force is one that destroys or breaks down the Earth’s surface.down the Earth’s surface.

B. Examples:B. Examples: 1.1. Weathering- a process that causes the breakdown Weathering- a process that causes the breakdown

of rock.of rock.2.2. Erosion- weathering and wearing away of rock Erosion- weathering and wearing away of rock

into sediment.into sediment.3.3. Deforestation-clearing land of trees (South Deforestation-clearing land of trees (South

America and Taiga Forest)America and Taiga Forest)4.4. Strip mining- clearing land to extract coal or other Strip mining- clearing land to extract coal or other

valuable minerals from the ground (West Virginia).valuable minerals from the ground (West Virginia).5.5. Volcanic Eruptions (Mount St. Helens)Volcanic Eruptions (Mount St. Helens)

Destructive Forces- DeforestationDestructive Forces- Deforestation Deforestation is brought about by the following:Deforestation is 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 people;people;

development of cash development of cash crops and cattle ranchingcrops and cattle ranching, , both of which earn money for tropical countries;both of which earn money for tropical countries;

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

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