Lesson 1

EARTH SCIENCE: EXOGENIC PROCESSES

Exogenic Processes

• Definition: Exogenic Processes refer to geological processes that occur above the Earth’s surface, involved in the modification and transformation of landforms.

• Impact: Exogenic processes contribute to both the building up and tearing down of Earth’s surface features.

Constructive Processes

• They are processes that build up features on Earth’s surface.

• Examples of constructive processes:

  • Formation of Barrier Islands and Beaches.

  • Notable locations:

  • Buntod Reef Marine Sanctuary (Masbate)

  • Masasa Beach (Tingloy, Batangas)

Destructive Processes

• They are processes that tear down features on Earth’s surface.

Weathering

• Weathering: The process of breaking down rocks into smaller particles such as sand, clay, gravel, and other fragments, which includes disintegration and decomposition.

Types of Weathering

• Three main types of weathering:

  1. Physical (mechanical) weathering

  2. Chemical weathering

  3. Biological weathering

A. Physical Weathering

• Definition: Physical weathering is caused by the effects of changing temperatures on rocks, leading to their fragmentation.

• Types of Physical Weathering:

  1. Abrasion

  • Occurrence: When rock surfaces are frequently exposed to elements like water, wind, and gravity, leading to wear.

  1. Freeze-thaw

  • Occurrence: Water seeps into cracks in rocks, freezes and expands, ultimately fracturing the rock. This is observed in mountainous regions such as the Alps.

  1. Exfoliation

  • Occurrence: Cracks develop parallel to land surfaces due to pressure reduction during uplift and erosion.

B. Chemical Weathering

• Definition: Chemical weathering involves changes in the composition of rocks due to chemical reactions.

• Types of Chemical Weathering:

  1. Carbonation

  • Process: Carbon dioxide dissolves in rainwater forming weak carbonic acid that dissolves limestone in cracks.

  1. Acidification

  • Process: Acid rain reacts with stones, causing surface wear and softening of rock compositions. Organisms like lichens also contribute to this process.

  1. Hydrolysis

  • Definition: Breakdown of rocks by acidic water to produce clay and soluble salts, mainly through interaction with acid rain.

  1. Hydration

  • Process: Reaction of water with rocks alters their chemical structure. Example: Water $H<em>2O$ interacts with $CaSO</em>4$ (calcium sulfate), yielding $CaSO<em>4 + 2 H</em>2O$ (calcium sulfate dihydrate), converting anhydrite to gypsum.

  1. Oxidation

  • Process: Breakdown of rocks through reactions with oxygen and water, often resulting in rust-colored weathering on iron-rich rocks.

Comparison: Physical Weathering vs. Chemical Weathering

• Physical Weathering: Involves disintegration or disaggregation of rocks without changing their chemical composition.

• Chemical Weathering: Involves decomposition of rocks through chemical reactions that transform them into new substances.

C. Biological Weathering

• Definition: Biological weathering occurs when rocks are weakened by biological agents such as plants and animals.

• Processes:

  • Plant roots penetrate through rocks, creating fractures and eventually leading to rock breakage.

  • Biological Weathering by Physical Means:

  • Example: Burrowing animals like shrews, moles, and earthworms excavate and move rock fragments to the surface.

  • Biological Weathering by Chemical Compounds:

  • Some organisms produce acidic substances that react chemically with rocks, contributing to slow disintegration.

Erosion

• Definition: Erosion refers to the geological process where earth materials are worn away and transported by natural forces such as wind, water, ice, and gravity.

Agents of Erosion

1. Erosion by Water:

   • Changes shape of coastlines through constant wave action against the shore.

2. Erosion by Wind:

   • Carries dust, sand, and volcanic ash across different terrains.

3. Erosion by Ice:

   • Glacial movement may erode land by dragging materials as they slowly advance downhill.

4. Erosion by Gravity:

   • Loose materials are pulled down slopes, commonly referred to as mass movement.

Mass Wasting

• Definition: Mass wasting refers to the movement of rock, soil, or regolith downward due to gravity.

Triggers of Mass Wasting

1. Over-steepened slope: Increased weight from rainwater acts as a lubricant for weathered materials.

2. Water: Presence of water can trigger mass wasting through saturation of materials.

3. Earthquakes: Vibrations that can dislodge rocks and sediment, contributing to mass wasting.

4. Vegetation Removal: Lack of plant cover allows loose particles to become unstable and contribute to mass movement.