Geomorphology

🌍 Overview

Geomorphology is the scientific study of landforms and the processes — internal (endogenic) and external (exogenic) — that create and modify them. It forms the foundation of Physical Geography in the UPSC/APPSC/TSPSC syllabus and underpins understanding of drainage systems, soils, and natural hazards.

🌐 Interior of the Earth

The Earth's interior is understood mainly through seismic wave behaviour and is divided into three broad layers:

Crust — the outermost, thinnest layer (5–70 km), divided into oceanic crust (basaltic, denser, thinner) and continental crust (granitic, lighter, thicker).
Mantle — extends to about 2,900 km depth; the upper mantle's partially molten asthenosphere is where plate tectonic movement originates.
Core — outer core (liquid, generates the Earth's magnetic field) and inner core (solid, extremely high pressure), composed mainly of iron and nickel.

🌍 Plate Tectonics

The theory of plate tectonics (building on Alfred Wegener's earlier Continental Drift theory and later seafloor spreading evidence) explains that the lithosphere is broken into several rigid plates that move over the asthenosphere. Plate boundaries are classified as:

Convergent (destructive) — plates move towards each other, forming fold mountains (e.g. Himalayas, from the Indian-Eurasian plate collision) or subduction zones with volcanic arcs and deep ocean trenches.
Divergent (constructive) — plates move apart, forming mid-ocean ridges and rift valleys (e.g. East African Rift).
Transform — plates slide past each other laterally, generating significant earthquake activity (e.g. San Andreas Fault).

⛰️ Endogenic and Exogenic Forces

Endogenic (internal) forces — originate within the Earth, including diastrophism (folding, faulting, which builds mountains and plateaus) and volcanism (which builds volcanic landforms).
Exogenic (external) forces — operate on the surface, wearing landforms down, including weathering (physical, chemical, biological breakdown of rock in place) and erosion by agents like rivers (fluvial), wind (aeolian), glaciers (glacial) and waves (coastal), each producing distinctive landforms (e.g. river meanders and oxbow lakes, sand dunes, moraines, beaches and spits).

🏖️ Major Landform Types

Mountains — fold (Himalayas), block/fault (Vosges), volcanic (Fujiyama), and residual (Aravallis, among the oldest fold mountains, heavily eroded).
Plateaus — extensive flat-topped elevated landforms, e.g. the Deccan Plateau (formed by volcanic lava flows in the Deccan Traps).
Plains — flat, low-relief land, often fertile alluvial plains formed by river deposition (e.g. the Indo-Gangetic Plain).

🎯 Exam Angle

Prelims frequently tests plate boundary types and their associated landforms/hazards, and matching specific landform examples to the process that created them. Mains rewards linking geomorphic processes to real-world consequences — e.g. how Himalayan tectonics drive seismic risk in the region, connecting Geography to Disaster Management.