(a) Explain the causes of glacial lake outburst flood. (10 marks) (b) What is solifluction? What are its impacts? (10…

(a) GLOFs

Glacial lake outburst floods (GLOFs) occur when water stored in moraine-dammed or ice-dammed lakes is released suddenly. The main cause is dam failure: as lakes grow, hydrostatic pressure weakens moraine; internal erosion or piping creates tunnels, while overtopping during heavy rain or glacial melt scours the dam. Seismic activity can crack moraines or trigger rock/ice avalanches into the lake, producing displacement waves. Ice avalanches and calving into ice-dammed lakes raise water levels rapidly. Climate warming intensifies these triggers by increasing glacial melt, lake expansion and debris supply; in the Himalayas, South Lhonak Lake in Sikkim, long monitored as a rapidly growing and vulnerable lake, breached in October 2023. The 2013 Kedarnath floods, in which the moraine-dammed Chorabari Lake breached after extreme rainfall on fresh snow, showed how glacial melt, rainfall and riverine processes can combine into catastrophic downstream flooding. The breach can destroy bridges and villages downstream. Thus GLOFs are a chain: storage, trigger, dam breach, and high-velocity debris-laden outflow.

(b) Solifluction

Solifluction is the slow, downslope creep of water-saturated soil or regolith over a frozen or impermeable permafrost table. In periglacial and alpine zones, summer thawing of the active layer increases pore-water pressure, while the underlying frozen ground prevents drainage. The saturated mass becomes plastic and flows under gravity, often as lobes or sheets. Repeated freeze-thaw cycles consolidate the material, producing terraced slopes, lobate deposits, and degraded hillside stability. Its impacts are practical as well as geomorphic: it blocks natural drainage, redirects streams, and increases landslide susceptibility. In Ladakh and Arunachal Pradesh, solifluction can undermine roads, bridges, and settlements on thawing slopes, especially where permafrost is disturbed by construction or warming. It also reduces agricultural land by burying or eroding fertile topsoil. Hence solifluction is not merely surface creep; it is a freeze-thaw-driven mass movement that reshapes cold-region landscapes and threatens infrastructure.

(c) Nappes

Nappes form in orogenic belts where intense compressional tectonics cause extreme crustal shortening. When a thickened crust is squeezed, large rock masses detach along low-angle thrust faults and are transported over underlying strata. The process begins with folding; continued compression can produce recumbent folds, whose limbs flatten and break into thrust sheets. Gravity sliding assists movement, especially when weak layers such as shale, evaporite, or fault gouge act as detachment surfaces. In the Helvetic nappes of the Alps, Mesozoic–Palaeogene sedimentary cover was detached from its crystalline basement along weak shale and evaporite horizons and thrust northward over younger foreland strata. In the Himalaya, the Almora nappe of Kumaon (with the Ramgarh nappe) is a classic example: crystalline and sedimentary thrust sheets were transported southward over the Lesser Himalayan sequences along low-angle thrusts, their root zone lying near the Main Central Thrust (the MCT itself is a major thrust fault rather than a nappe). The result is a stacked, imbricate structure in which older rocks lie above younger ones, recording mountain-building by thrusting and gravitational collapse.

(d) Air masses and winds

Air masses are large, uniform air bodies; local winds are pressure responses to their interaction with land, sea, and relief. When an air mass crosses a contrasting surface, it is thermally modified: maritime tropical (mT) air over heated land becomes unstable and fuels convectional winds, while continental tropical (cT) air over cooler water stabilizes. In India, monsoon reversal is driven mainly by differential heating and ITCZ migration, with cT air over the subcontinent and mT air over the Indian Ocean, not by continental polar air. Orographic channeling converts air-mass flow into local winds: the Bora forms when cold continental polar air banked up over the Dinaric Alps spills down as a katabatic fall wind onto the Adriatic, and the Mistral is cold northerly polar air funnelled through the Rhône valley behind a cold front. In north India the Loo is the surface expression of hot, dry cT air in May–June. Sea and land breezes arise when adjacent surfaces warm or cool an air mass, creating daily pressure cells. Thus air masses provide the thermal and moisture background, while local winds redistribute heat and moisture at smaller scales.

(e) Waves, currents, tides

Ocean waves, currents, and tides differ in energy source, motion, and scale. Waves are oscillatory surface motions generated mainly by wind energy; water particles move in near-circular orbits, so waves transfer energy rather than large volumes of water. Ocean currents are sustained horizontal movements of water masses, driven by wind stress, density differences, and pressure gradients; they transport heat, salt, and nutrients. The Southwest Monsoon Current of the north Indian Ocean is a wind-driven seasonal current that reverses with the monsoon, whereas thermohaline circulation is density-driven and global. Tides are periodic vertical and horizontal water movements caused by gravitational pull of the Moon and Sun; they are predictable, rhythmic, and not dependent on wind. Their semidiurnal or diurnal periods are fixed by Earth-Moon-Sun geometry. Tidal ranges vary with basin shape, as in the Gulf of Khambhat, where funneling amplifies high tides. Thus waves are short-period oscillations, currents are mass transport, and tides are astronomical vertical pulsations.