A quick revision squeeze of this chapter for right before the exam: endogenic-exogenic forces and gradation, diastrophism and volcanism, the three types of weathering, the forms of mass movement and the five types of landslide, the agents of erosion and deposition, and the five factors of soil formation. Full notes are available separately for detailed reading.
1 Six definitions to learn by heart
The reduction of relief differences through erosion is called Gradation.
To strip off or to uncover: all exogenic geomorphic processes (weathering, mass wasting, erosion, transportation) are together called Denudation.
The flaking off of more or less curved sheets from over a rock, leaving a smooth, rounded surface: this is a result, not a process.
The process by which weathering concentrates valuable mineral ores (iron, manganese, copper) is called Enrichment: important for the national economy.
The direct, gravity-driven transfer of rock debris down a slope; no geomorphic agent (water/ice/wind) is directly involved, which is why it does not come under erosion.
Pedology is soil science, and a pedologist is a soil scientist.
2 Endogenic vs exogenic forces
| Force | Source | Effect | Examples |
|---|---|---|---|
| Endogenic | Radioactivity, rotational-tidal friction, primordial heat | Elevates/builds up parts of the surface | Diastrophism, volcanism |
| Exogenic | Sun’s energy + gradients created by endogenic forces | Tries to even out relief (gradation) | Weathering, erosion, deposition, mass movement |
3 The four parts of diastrophism
| Process | Identity |
|---|---|
| Orogeny | Mountain building through severe folding; affects long narrow belts |
| Epeirogeny | Uplift/warping of large parts of the surface; continent building |
| Earthquakes | Relatively minor, local movements |
| Plate tectonics | Horizontal movement of crustal plates |
Orogeny is mountain-building; epeirogeny is continent-building: don’t swap the two.
4 The three types of weathering
| Type | Processes/causes |
|---|---|
| Chemical weathering | Solution, carbonation, hydration, oxidation, reduction: reduce rock to a fine (clastic) state |
| Physical (mechanical) weathering | Gravitational forces (overburden pressure, load, shearing stress); expansion forces due to temperature changes, crystal growth or animal activity; water pressure from wetting-drying cycles |
| Biological weathering | Movement/growth of organisms transferring minerals and ions; burrowing, root pressure, and human ploughing create new surfaces |
5 Mass movement: three forms and five types of landslide
The three forms of mass movement: (1) Heave (2) Flow (3) Slide.
| Landslide category | Identity |
|---|---|
| Slump | Slipping of rock debris units WITH a backward rotation |
| Debris slide | Rapid rolling/sliding of debris WITHOUT backward rotation |
| Debris fall | Nearly a free fall of earth debris from a vertical or overhanging face |
| Rockslide | Sliding of individual rock masses along bedding/joint/fault surfaces (to substantial depth) |
| Rock fall | Free fall of rock blocks away from the slope (from superficial layers only) |
Landslides are more frequent in the Himalayas than the Western Ghats because the Himalayas are more tectonically active: the Western Ghats are comparatively stable and made of harder rocks, so don’t reverse this.
6 Agents of erosion and deposition
Climate-controlled agents: running water, glaciers, wind. Agents not controlled by climate: waves (work at the coastal region) and groundwater (controlled by the lithological character of the region).
7 The five factors of soil formation
| Factor | Type | Effect |
|---|---|---|
| Parent material | Passive | Determines the soil’s texture, structure and mineral-chemical composition |
| Topography | Passive | Thin soil on steep slopes, deep/thick soil in flat areas |
| Climate | Active | Precipitation-evaporation and temperature variation determine the pace of soil development |
| Biological activity | Active | Adds humus, moisture-retention capacity, and nitrogen (via nitrogen fixation, e.g. Rhizobium) |
| Time | Passive (also the book’s “third important controlling factor”) | Determines the maturity of soil and the development of its profile |
Early stages of soil formation: weathered mantle/deposit forms → colonisation by bacteria-mosses-lichens → growth of minor grasses-ferns → growth of bushes-trees.