Grade 8 Social Studies: Forces Shaping the Earth's Surface

Forces Shaping the Earth's Surface

Competencies

  • Learners will be able to:

    • Describe internal and external forces shaping the surface of the earth.

    • Identify landforms created by external and internal forces.

    • Explain how the earth's internal and external forces affect human life.

Key Vocabulary

Top Ten Words

  • Anticline: Upward fold in rock layers.

  • Crater: Bowl-shaped depression at the top of a volcano.

  • Exfoliation: The process of rock layers peeling off due to temperature changes.

  • Faulting: Breaking and shifting of rock layers.

  • Fold Mountains: Mountains formed by the folding of the earth's crust.

  • Magma: Molten rock beneath the earth's surface.

  • Weathering: Breaking down of rocks into smaller pieces.

  • Denudation: The process of eroding the surface layer of the earth.

Additional Key Words

  • Fissure

  • Richter scale

  • Block mountains

  • Lava

  • Seismometer

  • Earthquake

  • Normal fault

  • Stalactite

  • Epicenter

  • Reverse fault

  • Syncline

1.1 Internal Forces and Resultant Landforms

Internal Forces

  • Definition: Forces originating from within the earth that shape the earth's crust.

  • Examples of Internal Forces:

    • Folding: Bending of rock layers due to lateral pressure.

    • Faulting: Formation of cracks or fractures as a result of stress.

    • Volcanism: Movement of magma that forms volcanoes.

    • Earthquakes: Rapid shaking caused by the release of energy within the earth.

Folding

  • Definition: The bending of rock layers.

  • Types of Folds:

    • Monocline: All layers bend in the same direction.

    • Anticline: Upward fold.

    • Syncline: Downward fold.

  • Examples of Major Fold Mountains:

    • Andes (South America)

    • Rockies (North America)

    • Alps (Europe)

    • Himalayas (Asia)

    • Atlas (North Africa)

    • Cape Ranges (South Africa)

    • Australian Alps (Australia)

Faulting

  • Definition: The formation of faults or cracks in the earth's crust.

  • Main Forces:

    • Tensional Forces: Create normal faults.

    • Compressional Forces: Create reverse faults.

  • Landforms Created by Faulting:

    • Rift Valleys: Formed by the sinking of land between faults.

    • Example: East African Rift Valley.

    • Block Mountains (Horst Mountains): Formed by uplift between faults.

Volcanism

  • Definition: The process where molten rock escapes to the surface.

  • Landforms Produced:

    • Extrusive Landforms: Volcanoes, craters, and lava flows.

    • Intrusive Landforms: Batholiths, laccoliths, dykes, and sills.

  • Types of Volcanoes:

    • Active: Recently erupted.

    • Dormant: Inactive, but may erupt again.

    • Extinct: Not expected to erupt.

Effects of Volcanism on Human Life

  • Positive impacts:

    • Natural hot springs, fertile soil, geothermal energy, tourism opportunities.

  • Negative impacts:

    • Destruction from eruptions, ash clouds causing health issues, mudslides, and floods.

Earthquakes

  • Definition: Sudden shaking of the earth.

  • Causes: Movements along fault lines.

  • Key Terms to Know:

    • Focus: Origin point of the earthquake.

    • Epicenter: Point on the surface directly above the focus.

    • Seismometer: Device that measures earthquake intensity.

    • Richter Scale: Measures magnitude (0-9 scale).

1.2 External Forces and Resultant Landforms

External Forces

  • Definition: Forces acting on the earth's surface causing erosion and sediment deposition.

  • Key Processes:

    • Denudation: Wear down of landforms.

    • Weathering: Breaking down of rocks.

Weathering Types

  • Physical Weathering: Breaking of rocks without changing their chemical composition.

  • Chemical Weathering: Breakdown of rocks due to chemical reactions.

    • Important Agents: Flooding and plant influences on rock breakdown.

Erosion Types

  • Definition: Movement of weathered materials from one location to another.

  • **Types of Erosion:

    • Erosion by Water:**

    • Sheet: Broad surface layer.

    • Rill: Small channels cutting into the land.

    • Gully: Deep, wide cuts in the land.

    • Wind Erosion: Carries sand and soil in arid conditions, forming various landforms such as dunes.

1.2.3 Weather and Climate

Weather vs Climate

  • Weather: Current atmospheric conditions over a short time.

  • Climate: Long-term average atmospheric conditions.

Elements of Weather and Climate

  • Key Elements: Temperature, precipitation, pressure, wind, humidity.

Temperature and Rainfall

  • Temperature: Measured by thermometers; affected by solar radiation.

  • Rainfall Types:

    • Relief (Orographic): Caused by mountains.

    • Convectional: Driven by heat from the surface.

    • Frontal: Interaction of warm and cold air masses.

Controls of Weather and Climate

  1. Latitude: Affects insolation intensity.

  2. Altitude: Higher altitudes have lower temperatures.

  3. Distance from Sea: Coastal areas experience milder conditions than inland areas.

  4. Cloud Cover: Influences solar radiation reaching the surface.

  5. Ocean Currents: Affect temperatures of nearby regions.