---
title: "Plate Tectonics, Landforms & the Rock Cycle | Model Diplomat"
description: "Learn plate tectonics, the rock cycle and major landforms for UPSC Geography, with theory, mechanisms, Indian instances and exam-tuned high-yield facts."
url: "https://modeldiplomat.com/learn/lessons/upsc-geography-geomorphology-plate-tectonics-landforms-rock-cycle"
---

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Geomorphology: plate tectonics, landforms & rock cycle

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# Geomorphology: plate tectonics, landforms & rock cycle

Plate tectonics, the rock cycle and major landforms for UPSC Geography: theory, mechanisms, Indian instances and exam-tuned high-yield facts.

## From Continental Drift to Plate Tectonics

Alfred Wegener, in *Die Entstehung der Kontinente und Ozeane* (1912, expanded 1915), proposed **continental drift**: a single supercontinent, **Pangaea**, surrounded by the ocean **Panthalassa**, fragmented from the Mesozoic onward. He marshalled the jigsaw fit of the Atlantic coasts, matching *Mesosaurus* and *Glossopteris* fossils across South America, Africa, India, Antarctica and Australia, and identical Permo-Carboniferous glacial striations on these now-tropical landmasses. Wegener's fatal weakness was mechanism: his proposed driving forces (*Polflucht* and tidal forces) were dynamically inadequate, and the theory was rejected by most geophysicists until the 1950s.

The mechanism arrived through the **sea-floor spreading** hypothesis of **Harry Hess (1962, 'History of Ocean Basins')** and Robert Dietz. Hess argued that mantle convection upwells along **mid-oceanic ridges**, creating new oceanic crust that spreads laterally and is destroyed at **trenches**. The decisive proof was the **Vine–Matthews–Morley hypothesis (1963)**: symmetrical magnetic-stripe anomalies on either side of the ridge record reversals of Earth's magnetic field, confirming the conveyor-belt of crust.

## The Theory of Plate Tectonics

Synthesised c. 1967–68 (McKenzie, Parker, Morgan), **plate tectonics** holds that the **lithosphere** is divided into rigid plates—seven major (Pacific, North American, South American, Eurasian, African, Indo-Australian, Antarctic) and several minor (Arabian, Nazca, Cocos, Caribbean, Philippine, Scotia, Juan de Fuca)—gliding over the plastic **asthenosphere**. Plate motion is driven chiefly by **slab pull** and **ridge push**, with mantle convection (Holmes, 1928–29) and plume activity as deeper engines.

Three boundary types define the tectonic regime:

- **Divergent (constructive):** plates separate; new crust forms. Examples: the Mid-Atlantic Ridge, the East African Rift, Iceland.
- **Convergent (destructive):** plates collide. Ocean–continent convergence yields **subduction**, volcanic arcs and trenches (Andes, Cascades); ocean–ocean yields island arcs (Japan, Aleutians); **continent–continent** yields fold mountains—the **Himalaya**, raised by the Indian plate colliding with the Eurasian plate from c. 50 million years ago, after the breakup of Gondwana drove India northward across the Tethys Sea.
- **Transform (conservative):** plates slide past each other; crust is neither created nor destroyed. The **San Andreas Fault** is the classic case.

The **Pacific 'Ring of Fire'**, where the Pacific, Nazca, Cocos and Philippine plates subduct, concentrates \~75% of the world's active volcanoes and \~90% of earthquakes. India's own **Deccan Traps**—flood basalts erupted c. 66 million years ago over the **Réunion hotspot**—illustrate intra-plate plume volcanism, a favourite UPSC link to the Cretaceous–Palaeogene extinction debate.

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