Geomorphic Processes: Rocks, Weathering & Landforms
The three types of rocks and the rock cycle, the processes of weathering and erosion, and the landforms sculpted by rivers, glaciers and wind.
Key Takeaways
- Rocks are of three types — igneous, sedimentary and metamorphic — linked by the rock cycle.
- Weathering is the in-situ breakdown of rocks; erosion involves their removal and transport.
- Each agent of erosion (river, glacier, wind, sea) creates its own erosional and depositional landforms.
Core concept
Geomorphic processes are the forces — internal (endogenic) and external (exogenic) — that shape the Earth's surface. Endogenic forces (tectonics, volcanism) build up relief; exogenic forces (weathering, erosion) wear it down. The materials they work on are rocks.
Static foundation — the three types of rock
The Three Types of Rock
| Type | How it forms | Examples |
|---|---|---|
| Igneous | Cooling and solidification of magma/lava (the 'primary' rock) | Granite (intrusive), Basalt (extrusive) |
| Sedimentary | Deposition and compaction of sediments; layered; may contain fossils | Sandstone, Limestone, Shale |
| Metamorphic | Transformation of existing rocks by heat and pressure | Marble (from limestone), Slate (from shale), Gneiss (from granite) |
The Rock Cycle
Magma cools
Molten magma solidifies to form IGNEOUS rock — the starting point.
Weathering & erosion
Rocks are broken down into sediments and transported by rivers, wind and ice.
Deposition & compaction
Sediments settle in layers and are compacted/cemented into SEDIMENTARY rock.
Heat & pressure
Deep burial subjects rocks to heat and pressure, forming METAMORPHIC rock.
Melting
Further heat melts rock back into magma — and the cycle begins again.
Weathering vs Erosion
Weathering is the breakdown of rocks in situ (no movement) — it is physical/mechanical (temperature, frost), chemical (oxidation, carbonation — creating karst/limestone caves), or biological. Erosion is the removal and transport of the weathered material by an agent (river, glacier, wind, waves). Weathering weakens; erosion carries away.
Agents of Erosion & Their Landforms
| Agent | Erosional landform | Depositional landform |
|---|---|---|
| River | V-shaped valley, gorge, waterfall, meander | Floodplain, delta, alluvial fan, levee |
| Glacier | U-shaped valley, cirque, horn, arête | Moraine, drumlin, esker, outwash plain |
| Wind | Mushroom rock, deflation hollow, yardang | Sand dunes, loess |
| Sea waves | Sea cliff, sea cave, arch, stack | Beach, spit, bar |
Prelims trap zones
- Marble = metamorphosed limestone; Gneiss = metamorphosed granite — learn the parent–product pairs.
- Weathering is in situ (no transport); erosion involves transport.
- U-shaped valleys are glacial; V-shaped valleys are fluvial (rivers).
Knowledge Check
2 questions · check your understanding
1. Marble is a metamorphic rock formed from which parent rock?
2. A U-shaped valley is characteristic of erosion by:
Prelims Pointers
- Igneous rocks form from magma; sedimentary from deposition (and contain fossils); metamorphic from heat and pressure.
- Marble is metamorphosed limestone; slate from shale; gneiss from granite.
- Weathering is 'in situ' (no movement); mass wasting and erosion involve transport.
- The Deccan Traps are basaltic (igneous) lava plateaus.
Mains Angle
- 'Weathering is the first step in soil formation and denudation.' Discuss.
- Explain how running water sculpts the landscape, from the upper to the lower course of a river.
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