Geologic Activities: Exogenic and Endogenic Processes

GEOLOGIC ACTIVITIES

Exogenic and Endogenic Processes
  • Exogenic Processes
    • Occur on or near the surface of Earth
    • Usually influenced or driven by gravity, water, wind, and organisms
    • In extreme cases, can wipe out the majority of organisms inhabiting that area.

WEATHERING

Definition of Weathering
  • The disintegration of rocks, soil, and minerals together with other materials through contact with Earth’s subsystems.
  • Happens even without movement or transportation.
Mechanisms of Weathering
  • Rock with crack:
    • Water enters cracks, freezes, expands the crack, and deepens it.
    • Repeated freeze and thaw breaks up rock along the joint lines.

TYPES OF WEATHERING

Mechanical (Physical) Weathering
  • The breaking down of rocks into smaller pieces without changing their chemical composition.
Chemical Weathering
  • The breakdown of rocks by chemical reactions that change the rock’s minerals into new substances.

MECHANICAL WEATHERING

Definition
  • Breakdown of rocks by mechanical forces concentrated along rock fractures.
  • Can occur due to changes in temperature and pressure.
Examples of Mechanical Weathering
  1. Ice/Frost Wedging
    • Occurs in cold climates at high elevations.
    • Water seeps into cracks in rocks and freezes, causing expansion and buildup of pressure over time, eventually breaking the rock.
  2. Root Wedging
    • Plant roots grow into cracks in rocks, expand, exert pressure which widens cracks and breaks rock.
  3. Exfoliation (Sheeting)
    • Layers of rock peel off due to pressure release when overlying material is removed.
  4. Salt Crystal Growth (Haloclasty)
    • Saltwater enters cracks in rocks, evaporates, leading to salt crystal formation and pressure buildup, eventually breaking the rock.
  5. Thermal Expansion and Contraction
    • Rocks expand in daytime heat, contract at night creating buildup of stress and causing cracks.
  6. Biological Activities
    • Animals physically break apart rocks and soil by digging and tunneling for food or shelter.

CHEMICAL WEATHERING

Definition
  • Rocks break down by chemical reactions, forming new or secondary minerals that replace the original properties of the minerals in the original rock or soil.
Examples of Chemical Weathering
  1. Oxidation
    • Minerals, especially those containing iron, react with oxygen to form new compounds like iron oxide (rust).
  2. Carbonation
    • Carbon dioxide dissolves in water to form carbonic acid, which reacts with minerals.
  3. Hydrolysis
    • Water reacts with minerals to form new minerals while dissolving some components.
  4. Hydration
    • Minerals absorb water and expand, weakening the rock (e.g., Anhydrite to Gypsum).
  5. Solution (Dissolution)
    • Minerals dissolve directly in water.

EROSION

Definition of Erosion
  • Process by which Earth’s surface is worn away by wind, water, or ice, moving rock debris or soil from one place to another.
Mechanisms of Erosion
  • Takes place during rainfall, surface runoff, flowing rivers, seawater intrusion, flooding, freezing and thawing, hurricanes, wind, and migration of animals.
  • Human activities such as deforestation, overgrazing, and mining contribute significantly.
Types of Erosion
  1. Water Erosion
  2. Wind Erosion
  3. Glacial Erosion
  4. Coastal Erosion

MASS WASTING

Definition
  • Movement of large masses of materials (rock debris, soil, mud) down a slope due to the pull of gravity.
  • Very destructive in areas with increased water flow; does not necessarily require water to occur.
Types of Mass Wasting
  1. Mudflow
    • Happens when combined soil and water flow down a slope, typically near rivers or streams
  2. Debris Flow
    • Large sediments, usually rocks of various sizes fall down the slope, not needing water to flow.
  3. Creep
    • Slow movement of soil along a curved surface, creating curved appearances and depressions.

SEDIMENTATION

Definition
  • Accumulation of materials such as soil, rock fragments, and soil particles settling on the ground.
  • Usually occurs in streams or as a result of sea erosion.
  • Over time, sediment load becomes thick and forms new layers of ground.

ENDOGENIC PROCESSES

Definition
  • Takes place within or in the interior of Earth.
  • The driving force is the thermal energy of the mantle
  • Responsible for earthquakes, development of continents, mountain building, and volcanic activities.

DIASTROPHISM

Definition
  • Movement of rock masses on the Earth’s crust involving bending, breaking, folding, and uplifting.
  • Caused by plate movements, compression, tension, uplift, and subsidence.
  • Classified as an endogenic process alongside volcanism and earthquakes.

TYPES OF ENDOGENIC PROCESSES

  1. Plate Tectonics
    • Theory stating Earth's surface is divided into structures called lithospheric plates.
Types of Plate Boundaries

  1. Convergent Boundaries (Colliding Plates)

    • Plates move toward each other; may lead to subduction or mountain formation.
    • Examples:
      • Oceanic–continental: Andes Mountains (South America)
      • Oceanic–oceanic: Mariana Trench
      • Continental–continental: Himalayas (India colliding with Asia)

  2. Divergent Boundaries (Moving Apart)

    • Plates move away from each other; magma rises creating new crust;
    • Examples: Mid-Atlantic Ridge, East African Rift Valley.

  3. Transform Boundaries (Sliding Past)

    • Plates slide horizontally past each other causing earthquakes but not mountains or volcanoes.
    • Example: San Andreas Fault (California).

MAGMATISM

Definition
  • Magma is the original material that makes up igneous rocks.
  • Magmatism occurs when magma is generated and develops into igneous (magmatic) rocks, either underground or on Earth's surface.

VOLCANISM (PLUTONISM)

Definition
  • Process that happens post-magma formation; magma escapes from the source through openings such as volcanoes or existing cracks.
  • Once magma reaches the surface of the Earth, it is termed lava.

METAMORPHISM

Definition
  • Process of changing the materials that compose a rock due to heat and pressure.
  • Changes the chemical components and geologic characteristics of the rock.
  • Note: Rocks changing due to weathering and sedimentation are not classified as undergoing metamorphism.
Types of Metamorphism

  1. Regional Metamorphism

    • Occurs over large areas due to high pressure and temperature, associated with mountain-building and plate collisions.
    • Causes compression during convergent plate boundaries or deep burial under thick layers of rocks
    • Examples: Formation of schist, gneiss, slate (from shale), Himalayan and Alps rocks.

  2. Contact Metamorphism

    • Occurs locally when rocks come into contact with magma or lava, with heat being the critical factor.
    • Examples: Marble from limestone, quartzite from sandstone, aureoles (zones of altered rock around volcanic intrusions).
Types of Metamorphic Rocks
  • Foliated Metamorphic Rocks
    • Minerals arranged in parallel layers or bands due to directed pressure, resulting in a striped appearance (e.g., slate, schist, gneiss).
  • Non-Foliated Rocks
    • Minerals are more uniform, without layering; formed mostly through contact metamorphism (e.g., marble, quartzite).

THOUGHT PROVOKING QUESTIONS

  • What drives the endogenous processes on Earth?
  • Where does the force come from?
  • Why are they called endogenous?