Geomorphology and Soil Formation - Notes

Introduction to geomorphic processes

Geomorphology defined as the study of processes that drive changes in landforms; focus on weathering, erosion, transportation, and deposition.
Key goal: understand rapid processes that change the landscape engineers work with today.
Rock-to-soil transformation is a central theme; engineers build on soil, while geomorphologists explain how soil and landforms arise from underlying processes.
NZ context highlighted: diverse landforms (glacier-fed mountains, rivers, coastlines) and the presence of earthquakes and volcanoes shape the landscape and hazards.
Learning outcomes: relate common rocks to geotechnical behavior; understand geological hazards and their engineering implications.
Reminder of reference material: Open textbook, Chapter 5 on weathering and erosion; connects to sediments and sedimentary rocks; geomorphology as a related science.
Career pathways analogy: Geotech is a subset of civil engineering; geomorphology is a subset of geology.
Real-world relevance: understanding processes helps explain formations like hills, volcanoes, rivers, beaches, and how these affect engineering design and hazard assessment.

Exogenic processes: external processes on/above the ground surface; can be slow (glaciation, river sediment buildup) or rapid (landslides).
Endogenic processes: internal Earth processes (earthquakes, faulting, volcanism, metamorphism) that shape rocks, sometimes rapidly.
Core sequence: formation of intact rock → tectonic modification (breakage, faulting, folding) → weathering (mechanical/physical and chemical) → erosion/transportation → deposition/aggregation → potential reconsolidation into new rock (sedimentary rock under pressure).
Weathering, erosion, and transport are linked steps in the rock cycle; weathering creates material, erosion moves it, deposition builds new layers that can become sedimentary rock under stress.

Weathering overview: physical (mechanical) and chemical processes break down rock; biological action can contribute.
Mechanical (physical) weathering: fragmentation of rock without altering chemical composition; increases surface area and facilitates other weathering; driven by stress and environmental conditions.
- Key principle: smaller pieces increase exposed surface area, accelerating weathering.
- Surface area example (conceptual): start with a cube of side length L=1 ext{ m}. Original surface area: 6L^2 = 6 ext{ m}^2. If broken into n=8 equal pieces (each L/2 per side), total surface area becomes 6L^2 imes n^{1/3} = 6 imes 8^{1/3} = 12 ext{ m}^2. For n=10 pieces, total area ≈ $$6 imes 10^{1/3} ext{ m}^2 \