Geomorphic Processes

Definition

Geomorphic processes are the external and internal forces that bring about changes to the Earth's crust by forming and reshaping its surface.

Explanation

• Endogenic Forces: Come from deep within the Earth (heat, volcanic activity, tectonic plate movements) and build things up (mountains, plateaus, rifts).
• Exogenic Forces: Powered by the sun and gravity (running water, wind, glaciers, waves) and wear things down (smoothing high points, filling low points).
• Denudation: Collective term for exogenic geomorphic processes (weathering, mass movements, erosion, transportation) that strip the Earth bare and recycle materials.

Definition

Weathering is the mechanical breakdown and chemical alteration of rocks at or near the Earth's surface in-situ (on-site without relocation).

Explanation

• Physical / Mechanical Weathering: Breaking into smaller pieces without chemical change (e.g., frost wedging).
• Chemical Weathering: Minerals react with water, oxygen, or acids, changing into different substances (e.g., rusting).
• Biological Weathering: Plants, animals, and microbes break down rocks (e.g., tree roots cracking concrete).

Examples

• Frost wedging in high mountain ranges.
• Rusting and softening of limestone monuments due to acid rain.

Real-Life Uses

Civil engineers evaluate weathering of slope shales prior to highway construction to apply protective meshes, shotcrete, or proper drainage.

Definition

Mass movement is the down-slope movement of rock, regolith, and soil under the direct influence of gravity.

Explanation

• Creep: Extremely slow movement of soil, tilting fence posts over years.
• Slump: Rapid, rotational slide along a curved surface.
• Landslide & Debris Flow: Fast, catastrophic mass movement triggered by rains or earthquakes.

Examples

• Tilting of telephone poles on hillsides.
• Highway blockages from mudslides following tropical storms.

Real-Life Uses

Urban planners use slope stability maps to avoid construction on hazardous, unstable sea cliffs and steep mountain ridges.

Definition

Erosion is the physical removal and transportation of weathered rock and soil materials from one location to another by mobile agents.

Explanation

• Active agents include running water (rivers/streams), wind, glaciers, and ocean waves.
• Involves both detachment and transportation of fragmented materials.

Examples

• A rushing river cutting into banks and carrying mud downstream.
• Wind blowing away topsoil from overgrazed farm fields.

Real-Life Uses

Agricultural experts use contour plowing and cover crops to prevent severe soil erosion and preserve long-term farmland fertility.

Definition

Deposition is the laying down or dropping of transported rock debris, sand, and soil when the transporting agent loses velocity or energy.

Explanation

• Occurs when energy drops (e.g., rivers reaching flat plains, winds hitting barriers).
• Builds new landforms by accumulating sediments, usually sorted by size.

Examples

• River deltas forming at the mouth of the sea.
• Sand dunes accumulating in deserts around wind obstructions.

Real-Life Uses

River engineers manage artificial levees, dams, and dredging systems to regulate sediment buildup and maintain reservoir water storage capacities.

Major Geomorphic Environments

• Fluvial (Running Water): Creates V-shaped valleys, waterfalls, meanders, floodplains, and deltas.
• Glacial (Moving Ice): Creates U-shaped valleys, horns, arêtes, cirques, and moraines.
• Arid (Wind): Creates yardangs and sand dunes in dry desert settings.
• Coastal (Waves & Tides): Creates sea caves, arches, stacks, spits, and barrier islands.
• Karst (Groundwater Solution): Creates sinkholes, disappearing streams, caves, stalactites, and stalagmites in soluble carbonate rocks.

Comparison Table

• GIS (Geographic Information Systems): Software to map terrain, analyze stability, and model floods.
• Remote Sensing: Satellite imagery tracking coastal erosion and glacier retreat in real-time.
• LiDAR: Airborne laser scanning creating 3D models to detect fault lines and assess landslide risks.
• UAVs / Drones: Inspecting precarious cliffs and post-disaster zones safely.

1. Stream Discharge Formula:

Q = A x V
(Q = Discharge, A = Cross-sectional area, V = Mean velocity)

2. Universal Soil Loss Equation (USLE):

A = R x K x LS x C x P
(A = Annual soil loss; R = Rainfall erosivity; K = Soil erodibility; LS = Slope length/steepness; C = Cover management; P = Support practices)

Problem 1: Calculating River Discharge

Problem: A mountain stream has a cross-sectional channel area of 20 m² and a mean velocity of 1.5 m/s. Calculate the stream discharge.

Step 1: Identify values: A = 20 m², V = 1.5 m/s
Step 2: Formula: Q = A x V
Step 3: Substitute: Q = 20 x 1.5
Step 4: Calculate: Q = 30 m³/s
Final Answer: The stream discharge is 30 cubic meters per second.

Problem 2: Rate of Weathering and Lowering

Problem: A granite outcrop is lowered by 0.02 mm/year. How many years to lower it by 10 cm?

Step 1: Convert units: 10 cm = 100 mm.
Step 2: Rate = 0.02 mm/year.
Step 3: Time = Total depth / Rate.
Step 4: Time = 100 mm / 0.02 mm/year = 5000 years.
Final Answer: It will take 5,000 years.

The Shifting Cliffs of the Pacific Coast

Scenario: Cliffside Village, built on soft sandstone cliffs, experienced severe base erosion from ocean winter waves and top-side saturation landslides from heavy rains.

Investigation & Solution: Geomorphologists used LiDAR and drone surveys to analyze risks. The government implemented beach nourishment to absorb wave energy, installed steel rock-bolts and drainage wells to stabilize slopes, and enforced 50-meter setback zones using GIS hazard maps.

1. Which of the current geomorphic processes is characterized as an in-situ process?
   A) Erosion
   B) Weathering
   C) Deposition
   D) Mass movement
   Answer: B
   Explanation: Weathering breaks down rocks right where they are without transporting fragments away.


2. Frost wedging is a classic example of which type of weathering?
   A) Chemical weathering
   B) Biological weathering
   C) Physical weathering
   D) Solution weathering
   Answer: C
   Explanation: Frost wedging breaks rocks mechanically through freezing and expansion of water.


3. What is the primary driving force behind all mass movements?
   A) Wind velocity
   B) Running water
   C) Solar radiation
   D) Gravity
   Answer: D
   Explanation: Gravity is the sole force pulling loose earth and rock down slopes.


4. Which landform is carved primarily by glacial action?
   A) V-shaped valley
   B) U-shaped valley
   C) Sand dune
   D) Sinkhole
   Answer: B
   Explanation: Moving glaciers scour broad U-shaped valleys.


5. Deposition occurs primarily when:
   A) Transporting agents increase velocity
   B) Rocks undergo chemical weathering
   C) Transporting agents lose energy and velocity
   D) Tectonic plates collide
   Answer: C
   Explanation: Slowing agents lose carrying capacity and drop sediment load.


6. Karst topography is predominantly associated with which bedrock?
   A) Basalt
   B) Granite
   C) Limestone
   D) Sandstone
   Answer: C
   Explanation: Limestone dissolves readily in weak carbonic acid.


7. Which modern tool uses airborne laser scanning for 3D elevation models?
   A) LiDAR
   B) Sonar
   C) Thermometer
   D) Barometer
   Answer: A
   Explanation: LiDAR uses rapid laser pulses to map ground contours.


8. Wind-driven removal of loose, fine-grained desert particles is called:
   A) Abrasion
   B) Deflation
   C) Deposition
   D) Plucking
   Answer: B
   Explanation: Deflation is the removal of dry dust and sand by wind.


9. If river cross-sectional area increases while velocity remains constant, discharge will:
   A) Decrease
   B) Remain unchanged
   C) Increase
   D) Drop to zero
   Answer: C
   Explanation: Discharge (Q = A x V) is directly proportional to area.


10. Which coastal feature is formed when longshore drift blocks a bay mouth?
    A) Sea stack
    B) Spits
    C) Moraine
    D) Yardang
    Answer: B
    Explanation: Spits are elongated sand ridges extending across bays.

1. Define geomorphic processes and distinguish between endogenic and exogenic forces.
   Answer: Geomorphic processes shape the Earth's surface. Endogenic forces originate internally (tectonic/volcanic) to build up relief, while exogenic forces operate externally (solar/gravity driven) to wear down relief via weathering and erosion.


2. Explain why weathering is considered a prerequisite for erosion.
   Answer: Weathering breaks down coherent bedrock into loose fragments and weakens rock structures, making them susceptible to detachment and transport by erosion agents.


3. Describe the factors influencing mass movement rates and types.
   Answer: Key factors include slope steepness, water content (adds weight and reduces friction), vegetation cover (anchors soil), and triggering seismic events.


4. Compare and contrast V-shaped valleys and U-shaped valleys.
   Answer: V-shaped valleys are formed by fluvial vertical river erosion creating narrow channels. U-shaped valleys are carved by glaciers scouring both bottom and sides simultaneously.


5. How does groundwater create karst landforms? Give two examples.
   Answer: Slightly acidic groundwater containing carbonic acid dissolves soluble carbonate rocks like limestone over time. Examples include sinkholes and stalactites.


6. What is longshore drift and what landforms does it create?
   Answer: Longshore drift is the movement of sand parallel to the shore driven by angled waves, creating spits, tombolos, and barrier islands.


7. How does climate affect dominant weathering types?
   Answer: Hot, humid climates accelerate chemical weathering, whereas cold freezing climates promote physical weathering (frost wedging).


8. State the Universal Soil Loss Equation (USLE) and its variables.
   Answer: A = R x K x LS x C x P (Rainfall erosivity, soil erodibility, slope factors, crop cover, and support practices) used to estimate annual soil loss.


9. Discuss two modern technological tools used to monitor hazards.
   Answer: LiDAR provides high-resolution 3D terrain models, while GIS layers spatial data to model flood and landslide risks.


10. Why is geomorphology vital for civil engineering and urban planning?
    Answer: It ensures infrastructure safety by guiding stable building foundations, river flood defenses, highway slope protection, and hazard avoidance.

• Denudation Steps: Weathering ➔ Mass Movement ➔ Erosion ➔ Deposition.
• Weathering Rule: In-situ (stays put). Erosion Rule: Travels (transported).
• Environments: Fluvial, Glacial, Arid, Coastal, Karst.

Mnemonics:
- Exogenic steps: "Wild Monkeys Eat Doughnuts" (Weathering, Mass Movement, Erosion, Deposition).
- Environments: "Friendly Giants Always Crave Knowledge" (Fluvial, Glacial, Arid, Coastal, Karst).