Geomorphic Processes

Introduction

1. 1.Geomorphic processes are the physical and chemical processes that shape the Earth's surface (geomorphology = study of landforms). These processes are driven by two types of forces:
2. 2.Endogenic forces — forces from within the Earth (internal)
3. 3.Exogenic forces — forces from outside the Earth (external), mainly solar energy and gravity

The continuous action of these forces creates, modifies, and destroys landforms over geological time.

Endogenic Processes

Endogenic processes originate from the Earth's interior and are driven by geothermal energy (heat from radioactive decay and residual heat from Earth's formation).

• 1. Diastrophism — movements of solid rock (without melting):
• Epeirogenic movements: slow, vertical movements of large land masses (uplift or subsidence). Example: isostatic rebound after glaciers melt.
• Orogenic movements: horizontal forces that build mountains through folding and faulting. Example: Himalaya formation.

• 2. Volcanism — movement of molten material (magma):
• Intrusive volcanism: magma cools and solidifies inside the Earth, forming intrusive igneous rocks (e.g., batholiths, dykes, sills, laccoliths).
• Extrusive volcanism: magma reaches the surface (as lava) through volcanic eruptions, forming extrusive igneous rocks (e.g., basalt).

• 3. Earthquakes — sudden vibrations of Earth's crust:
• Generated at fault lines or subduction zones
• Classified by depth: shallow focus, intermediate focus, deep focus earthquakes

Endogenic processes generally build up the Earth's surface — creating mountains, plateaus, and volcanic landforms.

Exogenic Processes

Exogenic processes are driven by solar energy and gravity, and they generally break down and level the Earth's surface. They include:

1. Weathering: the breaking down of rocks in place (no movement of material).
2. Mass Movement / Mass Wasting: movement of weathered material downslope under gravity.
3. Erosion: removal and transport of weathered material by agents (water, wind, ice, waves).
4. Deposition: laying down of transported material.

Weathering

Weathering is the in-situ (in place) disintegration and decomposition of rocks. There is NO transportation of material in weathering alone.

• A. Physical (Mechanical) Weathering — breaks rocks without changing their chemical composition:
• Block disintegration (temperature changes cause rock to crack)
• Exfoliation (onion-skin peeling of rocks due to thermal expansion and contraction)
• Frost action / Frost wedging: water freezes in cracks, expands by about 9%, and widens the crack
• Salt crystallisation: salt crystals grow in pores and crack rocks
• Biological weathering (roots of plants crack rocks)

• B. Chemical Weathering — changes the chemical composition of rocks:
• Solution: minerals dissolve in water (e.g., limestone dissolves in rainwater containing CO2 — carbonic acid)
• Hydration: minerals absorb water and expand (e.g., feldspar becomes clay)
• Oxidation: oxygen reacts with minerals (e.g., iron rusts — iron oxide formation)
• Carbonation: CO2 + water = carbonic acid (H2CO3), which dissolves carbonate rocks (karst landscapes)
• Hydrolysis: water chemically reacts with silicate minerals breaking them down

• C. Biological Weathering — caused by living organisms (plants, animals, bacteria):
• Roots pry open cracks
• Organic acids from decomposing matter dissolve minerals
• Burrowing animals loosen soil

• Factors affecting Weathering:
• Climate: warm and humid climates favour chemical weathering; cold and dry climates favour physical weathering
• Rock type: different minerals weather at different rates
• Time: longer exposure = more weathering

Mass Movements

Mass movement is the downhill movement of weathered material under gravity without the help of a transporting medium. Types include:

• Soil Creep: extremely slow, imperceptible movement of soil down slopes
• Solifluction: slow flow of water-saturated soil (common in permafrost areas)
• Earthflow: movement of saturated soil and regolith
• Mudflow / Debris flow: rapid flow of water-saturated mud
• Landslide / Rockfall: sudden, rapid sliding or falling of large rock masses
• Slump: backward rotation of a soil/rock mass along a concave surface

Erosion, Transportation, and Deposition

These are the final stages of the exogenic cycle:

• Erosion: detachment of material from bedrock by moving water, wind, ice, or waves
• Transportation: material is carried away by the agent
• Deposition: when energy of the agent decreases, material is deposited

Erosion and deposition create specific landforms studied in Chapter 6 (Geomorphic Landforms).

• Weathering vs Erosion: Weathering = breaking down in place (no movement). Erosion = removal and transport. These are different processes. Do not use them interchangeably.
• Physical vs Chemical weathering: Physical breaks rocks mechanically (frost wedging); Chemical changes mineral composition (oxidation, carbonation). Same climate does NOT favour both equally.
• Mass movement is NOT erosion — material moves under gravity, not by a fluid agent. Though they can co-occur.
• Endogenic vs Exogenic: Endogenic = builds up; Exogenic = breaks down. The landscape at any point reflects the balance between these two sets of forces.

Geomorphic processes are divided into endogenic (internal) and exogenic (external) processes. Endogenic processes (diastrophism, volcanism, earthquakes) build up the Earth's surface. Exogenic processes (weathering, mass movement, erosion, deposition) break down and redistribute material. Weathering is the first step — breaking rocks in situ — and is of three types: physical, chemical, and biological. Mass movements are driven by gravity on slopes. Together, these processes continuously reshape the landscape.