📌 Key Points
- The earth's crust consists of several large and small, rigid, irregularly-shaped lithospheric plates that carry continents and the ocean floor
- Lithospheric plates move very slowly (a few millimetres per year) due to the movement of molten magma inside the earth
- Endogenic forces act in the interior of the earth (Endo = inside); they produce sudden movements (earthquakes, volcanoes) and slow movements
- Exogenic forces work on the surface of the earth (Exo = outside); they include weathering and erosion
- A volcano is a vent (opening) in the earth's crust through which molten material erupts suddenly
- Earthquakes are vibrations caused by the movement of lithospheric plates; Focus = underground origin point; Epicentre = surface point above focus
- Earthquakes cannot be predicted, but impact can be minimised through preparedness: shelter under tables/desks, stay away from windows/mirrors
- Weathering = breaking up of rocks (no transport); Erosion = wearing away of landscape by agents like water, wind, and ice (involves transport)
- River landforms: Waterfall (steep angle over hard rocks) → Meanders (bends in plains) → Oxbow lake (cut-off meander) → Floodplain & Levees (flooding deposits) → Distributaries & Delta (near sea)
- Floodplains are formed by deposition of fine soil (sediments) when river overflows; raised banks are called levees
- Distributaries are streams that branch out from the main river near the sea; collection of sediments from all mouths forms a delta
- Sea wave erosion sequence: Cracks → Sea Caves (hollow caves) → Sea Arches (only roof remains) → Stacks (only walls remain) → Sea Cliff (steep vertical coast)
- Beaches are formed by deposition of sediments by sea waves along the shores
- A glacier is a large mass of ice continuously moving over land; it erodes by bulldozing (creating hollows/lakes) and deposits glacial moraines
- Wind erosion creates mushroom rocks in deserts (narrower base, wider top - because wind erodes lower section more)
- Sand dunes: low hill-like structures formed when wind deposits heavier sand nearby; Loess: fine, light sand carried over long distances (found in China)
📘 Important Definitions
⚠️ Common Mistakes
✗ Wrong: Confusing focus and epicentre
✓ Correct: Focus is INSIDE the earth's crust (where the earthquake starts). Epicentre is ON the surface (directly above the focus). Focus = underground, Epicentre = surface.
✗ Wrong: Using weathering and erosion interchangeably
✓ Correct: Weathering only breaks rocks in place (no movement). Erosion involves wearing away AND transporting material by agents like water, wind, and ice.
✗ Wrong: Confusing tributaries and distributaries
✓ Correct: Tributaries JOIN the main river (bringing water in). Distributaries BRANCH OUT from the main river near the sea (splitting water out).
✗ Wrong: Mixing up sea arches and stacks
✓ Correct: Sea arches still have the ROOF intact (arch shape). Stacks are formed AFTER the roof breaks - only the walls remain standing.
✗ Wrong: Confusing magma and lava
✓ Correct: Magma is molten rock INSIDE the earth. When it erupts and comes to the surface through a volcanic vent, it is called lava.
✗ Wrong: Thinking sand dunes and loess are the same
✓ Correct: Sand dunes are formed from heavier sand deposited nearby when wind stops. Loess is very fine, light sand carried over long distances (found in China).
📝 Exam Focus
These questions are frequently asked in CBSE exams:
🎯 Last-Minute Recall
Close your eyes and try to recall: Key definitions, formulas, and 3 common mistakes. If you can recall 80% without looking, you're exam-ready!