(a) Define 'speleothem'. Discuss the various forms and features of speleothems. (10 marks) (b) What are the high altitude…

(a) Speleothems Speleothems are secondary mineral deposits formed in caves by precipitation from water, mainly calcium carbonate (calcite/aragonite) from limestone dissolution, sometimes gypsum or silica. Dripping water loses CO2, raising pH, so CaCO3 precipitates. Stalactites hang from ceilings as icicle-like formations, formed by dripping water; stalagmites rise from floors where drops splash; when they meet they form columns. Flowstones are sheet-like draperies on walls/floors from thin films; helictites are twisted, gravity-defying forms due to capillary forces and crystal growth.

Features include concentric growth bands, calcite crystals, and paleoclimate proxies. In India, Meghalaya caves such as Mawmluh and the Borra and Belum caves of Andhra Pradesh show such deposits, and a Mawmluh stalagmite defines the start of the Meghalayan Age (4,200 years ago). Their morphology records past rainfall, temperature, and hydrology; speleothem oxygen isotopes help reconstruct monsoon variability. Speleothems are fragile and are damaged by tourism, artificial lighting and changes in cave microclimate.

(b) High-altitude hazards High-altitude environmental hazards are physical and physiological risks above roughly 2,500–3,000 m, where lower barometric pressure, thin air, intense radiation, cold, and unstable terrain combine. Hypoxia causes acute mountain sickness, high-altitude pulmonary/cerebral oedema; Everest and K2 expeditions record deaths from AMS and exhaustion. Strong UV increases snow blindness and skin damage. Cold injuries include frostbite and hypothermia, especially in Siachen Glacier’s extreme winds and sub-zero temperatures. Avalanches, seracs, crevasses, rockfall, and wind-scoured ridges create terrain instability; Ladakh tourism incidents show risks from sudden weather and unprepared trekkers. Altitude also reduces oxygen availability, impairs judgement, and increases fatigue. Glacial lake outburst floods add a further hazard, as in the South Lhonak GLOF in Sikkim (October 2023), and remote terrain delays rescue.

(c) Pollution dome A pollution (dust) dome is a dome-shaped mass of polluted air over a city, held in place by the circulation of the urban heat island. On calm days warm air rises over the city centre, spreads outward aloft, sinks at the cooler edges and flows back inward near the ground, so pollutants are recycled rather than dispersed. A capping inversion, often a high-pressure subsidence inversion, limits the dome from above, and a regional wind stretches it downwind into a pollution plume. Stable air, weak winds, and topography prevent vertical mixing, so vehicular, industrial, biomass, and dust emissions accumulate. In Delhi, winter inversion, crop-residue burning, and cold stable air create smog domes; Mexico City’s basin topography and subsidence produce persistent ozone and particulate layers. Impacts include respiratory and cardiovascular illness, especially for children and elderly, reduced visibility and school closures. The dome cuts incoming sunshine by day but traps outgoing long-wave radiation at night, keeping city nights warmer.

It can persist for days, especially in winter, under stable high pressure, when cold air pools in valleys and plains. Because pollutants cross city and state boundaries, control needs regional coordination, as under the National Clean Air Programme.

(d) Coral bleaching Coral bleaching occurs when stressed corals expel or lose their symbiotic zooxanthellae, the dinoflagellates that provide colour and most of their energy through photosynthesis. The main trigger is thermal stress: even 1–2°C above summer maxima for weeks can damage the symbiosis, exposing the white skeleton. Nutrient pollution, sedimentation, low light, disease, and ocean acidification weaken corals and reduce recovery. Repeated mass bleaching on the Great Barrier Reef (2016, 2017, 2020, 2022, 2024) and the fourth global bleaching event declared by NOAA in April 2024 showed climate-driven mortality; in India, Gulf of Mannar and Palk Bay reefs have experienced bleaching and degradation, and Lakshadweep reefs bleached in 2024. Bleached corals survive if stress ends, but repeated events cause mortality, loss of fish habitat, reduced coastal protection, and biodiversity decline.

(e) Soil horizons Well-developed soils show distinct horizons formed by weathering, organic accumulation, and translocation. The O horizon is organic litter and humus; A is topsoil with mixed mineral and organic matter, high biological activity. E is an eluvial horizon where fine clay, iron, and organic matter are leached out, leaving paler sandy material. B is illuvial, receiving clay, sesquioxides, or organic matter; in Podzols it is a spodic horizon with illuvial Fe/Al and organic matter, while in Alfisols/Ultisols it may be argillic. C is weathered parent material; R is bedrock. In India, laterite soils show thick red B horizons rich in iron/aluminium, alluvial soils have young A-C profiles, and black soils (Vertisols) are deep and clayey but show weak horizon differentiation because shrink-swell cracking churns the profile. These profiles reveal climate, vegetation, and time. Their thickness and colour also indicate drainage and erosion history.