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GeographyNCERT Class 7 · Our Environment

Our Changing Earth

The earth's surface is endlessly reshaped by endogenic forces from within (plate movement, earthquakes, volcanoes) and exogenic forces on the surface (rivers, sea waves, glaciers, wind) that erode and deposit material to build landforms.

⏱ 7 min readGS-I6 sections4 memory tricks
Why this matters for UPSC

Physical geography — geomorphic processes, earthquakes and landforms — is a Prelims staple: expect match-the-following on landform versus agent (river/glacier/wind/sea), erosional-versus-depositional classification, and earthquake terms (focus, epicentre, P/S/L waves, Richter scale). For Mains it anchors GS-I physical geography (geomorphology; fluvial, coastal, aeolian and glacial landforms), while the Bhuj earthquake and preparedness feed GS-III disaster management.

Understand the chapter

Plate Movement — The Engine Within

The lithosphere is broken into several large and small rigid slabs called lithospheric plates, which carry the continents and the ocean floor. These plates drift extremely slowly — just a few millimetres a year — driven by circular convection currents of molten magma in the mantle. The classic NCERT activity, in which a paper pellet rises with warming water and sinks with cooler water, models this convective motion. Plate movement is the ultimate cause of earthquakes, volcanoes and mountain building.

  • Lithospheric plates: rigid, irregularly-shaped slabs of crust carrying continents and ocean floor.
  • Driving force: circular convection of molten magma inside the earth.
  • Speed: a few millimetres per year — slow but continuous.

Endogenic vs Exogenic Forces

Earth movements are classified by the source of the force that causes them. Endogenic forces act in the interior of the earth (endo = inside), while exogenic forces work on the surface (exo = outside). Endogenic forces operate either suddenly (earthquakes, volcanoes — causing mass destruction) or slowly as diastrophic forces that build mountains over long periods. Exogenic forces continuously wear down the landscape through erosion and rebuild it through deposition.

  • Endogenic = interior forces; Exogenic = surface forces (endo/exo + genic = origin).
  • Endogenic split: sudden (earthquake, volcano) and diastrophic/slow (mountain building).
  • Exogenic agents: rivers, wind, sea waves and glaciers — erosional and depositional.

Volcanoes and Earthquakes (Sudden Endogenic Forces)

A volcano is a vent (opening) in the earth's crust through which molten material — magma/lava — along with gases and ash erupts suddenly. An earthquake is the vibration of the earth's surface caused when lithospheric plates move; the point inside the crust where the movement starts is the focus, and the point on the surface directly above it is the epicentre. Seismic vibrations spread outward from the epicentre as waves, and damage is greatest near the epicentre, decreasing outward.

  • Volcano parts: magma chamber, vent, crater, lava, gases and ash.
  • Focus = underground origin of seismic energy; Epicentre = surface point above focus.
  • Three seismic waves: P (longitudinal), S (transverse), L (surface); S-waves pass only through solids.
  • Measured by a seismograph; magnitude on the Richter scale (7.0+ = major).

Weathering, Erosion and Deposition

The landscape is continuously worn away by two distinct processes. Weathering is the breaking up of rocks on the earth's surface in place, whereas erosion is the wearing away and removal of the landscape by agents like water, wind and ice. The eroded material is transported and eventually deposited elsewhere; this erosion–transport–deposition cycle creates the planet's varied landforms.

  • Weathering: in-situ breaking of rocks (no transport).
  • Erosion: wearing away plus transport by water, wind, ice.
  • Deposition: dropping of transported sediment, building new landforms.

Work of a River

A river both erodes and deposits as it flows from highland to sea. In its upper course it cuts waterfalls where it tumbles over hard rock; on the plains it swings into large bends called meanders, whose loops eventually cut off to form ox-bow (cut-off) lakes. When it floods, the river spreads fine sediment to build a fertile floodplain with raised banks called levees, and near the sea it splits into distributaries whose combined deposits form a delta.

  • Erosional: waterfall, meander.
  • Depositional: floodplain, levees, delta.
  • Ox-bow lake: abandoned meander loop cut off from the river.
  • Delta: sediment fan built where distributaries meet the sea.

Work of Sea Waves, Glaciers and Wind

Three other exogenic agents sculpt distinctive landforms. Sea waves erode coasts into sea caves, which enlarge into sea arches, then stacks (isolated walls) and steep sea cliffs, while depositing sediment as beaches. Glaciers — 'rivers of ice' — bulldoze rock and soil, gouge hollows that become mountain lakes, and dump debris as moraines. In deserts, wind erodes rock bases to leave mushroom rocks (narrow base, wide top) and deposits sand as dunes, with very fine wind-blown sand forming loess (large deposits in China).

  • Coastal erosion sequence: sea cave → sea arch → stack → cliff; beach = deposition.
  • Glacial: moraine (deposition), mountain lakes (erosion).
  • Wind: mushroom rock (erosion), sand dune and loess (deposition).

Key terms

Lithospheric plates
Rigid, irregularly-shaped slabs of the earth's crust carrying continents and ocean floor, moving a few mm/year.
Endogenic forces
Forces originating in the earth's interior — e.g., earthquakes, volcanoes and mountain building.
Exogenic forces
Surface forces that erode and deposit material — rivers, wind, sea waves and glaciers.
Diastrophic forces
Slow endogenic movements that build mountains over long periods of time.
Focus
The point inside the crust where an earthquake originates (source of seismic energy).
Epicentre
The point on the surface directly above the focus, where damage is usually greatest.
Weathering
The in-situ breaking up of rocks on the earth's surface, without transport.
Erosion
The wearing away and removal of the landscape by water, wind and ice.
Ox-bow lake
A crescent-shaped cut-off lake formed when a meander loop is abandoned by a river.
Loess
Very fine, wind-deposited sand spread over large areas, notably in China.

Must-know facts exam-ready

  • Lithospheric plates carry continents and ocean floor and move just a few millimetres a year, driven by convection of molten magma.
  • Endogenic forces act inside the earth; exogenic forces act on its surface (endo = inside, exo = outside, genic = origin).
  • Endogenic forces are either sudden (earthquakes, volcanoes) or slow diastrophic forces that build mountains.
  • A volcano is a vent in the earth's crust through which molten material (lava), gases and ash erupt suddenly.
  • Focus = the earthquake's origin inside the crust; epicentre = the surface point directly above it; damage is greatest near the epicentre.
  • Three earthquake waves: P (longitudinal), S (transverse) and L (surface); S-waves pass only through solids.
  • Earthquakes are recorded by a seismograph and rated for magnitude on the Richter scale; 7.0+ is a major earthquake.
  • Bhuj (Kutch, Gujarat) earthquake struck on 26 January 2001 and measured 6.9 on the Richter scale (per NCERT).
  • Weathering breaks rocks in place; erosion wears away and transports material — together with deposition they build landforms.
  • River landforms: waterfall and meander (erosional); ox-bow lake, floodplain, levees and delta (depositional).
  • Coastal erosion runs sea cave → sea arch → stack → sea cliff; beaches are depositional; glaciers ('rivers of ice') deposit moraines.
  • Wind makes mushroom rocks (narrow base, wide top) and sand dunes; very fine wind-blown sand forms loess, with large deposits in China.

Memory tricks remember it for good

ENDO = INside, EXO = exit/OUTside
Endo-genic = forces born INside the earth (earthquakes, volcanoes, mountain-building); Exo-genic = forces working OUTside on the surface (rivers, wind, ice, sea).
💡 Never mix up which forces are interior versus surface, or which landforms each produces.
'Wild Monkeys Often Flee Long Distances'
Waterfall → Meander → Ox-bow lake → Floodplain → Levee → Delta.
💡 Recall river landforms in order from the upper course down to the river mouth.
'Cats Always Scratch Cliffs'
sea Cave → sea Arch → Stack → Cliff (all erosional); Beach is the depositional odd-one-out.
💡 Recall the coastal erosion sequence and remember a beach is depositional.
P-S-L: 'Pretty Slow, Last'
P = Primary (longitudinal), fastest, through solids/liquids/gases; S = Secondary (transverse), slower, only through solids; L = surface waves, slowest but most destructive.
💡 Recall the three earthquake waves by speed and destructiveness.

Traps to avoid

  • Focus vs epicentre: the focus is the underground origin of the quake; the epicentre is the surface point above it — UPSC routinely swaps the two.
  • Erosional vs depositional: beach, floodplain, levee, delta, sand dune, loess and moraine are DEPOSITIONAL; waterfall, meander, sea cave/arch/stack/cliff and mushroom rock are EROSIONAL.
  • Ox-bow lakes are made by rivers (cut-off meanders), not by glaciers or deserts — a standard NCERT MCQ distractor.
  • Volcanoes and earthquakes are endogenic (sudden); they are NOT exogenic — only rivers, wind, sea waves and glaciers are exogenic.
  • Mushroom rocks have a NARROW base and WIDE top (wind erodes the lower part more) — not the other way round.
  • Seismograph is the instrument; the Richter scale measures magnitude (energy released) — magnitude is not the same as the damage/intensity felt at the surface.

Exam focus

🧠 Prelims angles

  • Match-the-following: landform ↔ agent (river/glacier/wind/sea) and classifying each as erosional or depositional — the core NCERT exercise pattern.
  • Earthquake terms: focus, epicentre, seismograph, Richter scale, and P/S/L waves — especially that S-waves cannot travel through the liquid outer core.
  • Force classification: endogenic vs exogenic, and sudden vs diastrophic movements.
  • World waterfalls: Angel Falls (Venezuela, highest), Niagara (Canada–USA border), Victoria (Zambia–Zimbabwe border).
  • Aeolian features: mushroom rocks and sand dunes in deserts; loess with large deposits in China.
  • Bhuj earthquake static facts: 26 January 2001, Gujarat (Kutch), 6.9 on the Richter scale (per NCERT).

✍️ Mains angles GS-I

  • How do endogenic and exogenic forces together shape the earth's surface? (GS-I geomorphology)Define both, contrast sudden/diastrophic build-up with erosion–deposition wearing-down, illustrate with landforms, and conclude with the idea of dynamic equilibrium.
  • 'Earthquakes cannot be predicted, but their impact can be minimised.' Discuss disaster preparedness. (GS-III)Anchor in Bhuj 2001; cover structural (quake-resistant design) and non-structural (zoning, awareness, drills) measures; cite the NDMA and the Disaster Management Act, 2005.
  • Examine the economic significance of fluvial landforms like floodplains and deltas. (GS-I)Explain sediment deposition, levee and floodplain fertility, and delta agriculture, balanced against recurrent flood risk.
Practice Geography questions from this syllabus →

Last-minute revision tick as you recall

  • Plates move a few mm/year via magma convection.
  • Endogenic = inside (earthquakes, volcanoes, mountains); Exogenic = surface (river, wind, ice, sea).
  • Focus = origin in crust; Epicentre = surface above focus; damage max at epicentre.
  • Seismograph measures; Richter scale = magnitude; 7.0+ major.
  • Bhuj quake: 26 Jan 2001, 6.9 Richter, Gujarat (Kutch).
  • River order: waterfall → meander → ox-bow → floodplain/levee → delta.
  • Sea erosion: cave → arch → stack → cliff; beach = deposition.
  • Glacier = 'river of ice' → moraine; wind → mushroom rock, dune, loess (China).
  • Weathering = breaking rocks in place; Erosion = wearing away + transport.

Distilled from NCERT Class 7 · Our Environment for UPSC. Always cross-check facts with the original NCERT.