Answer the following in about 150 words each: (a) Describe the concept of 'Altiplanation'. (10 marks) (b) What are the important…

(a) Describe the concept of 'Altiplanation'

Altiplanation refers to a complex periglacial geomorphic process that produces flat, step-like terraces or structural benches, known as altiplanation or goletz terraces, on mountaintops and upper valley slopes. The process is driven by the interaction of freeze-thaw weathering (gelifraction), nivation, and mass wasting.

During the warmer periods of the periglacial cycle, snow patches accumulated in hillside hollows induce intense nivation along the backwall. Gelifraction shatters the bedrock, causing the steep backwall scarp to retreat headward. Concurrently, the frost-shattered debris is evacuated downslope across the terrace floor (tread) through solifluction, gelifluction, and meltwater slopewash. Repeated seasonal cycles lead to the lateral expansion of planar treads backed by frost-riven scarps. Over time, coalescing terraces reshape high-altitude relief into stepped landscapes. These landforms are characteristically developed in permafrost and periglacial environments such as the Rocky Mountains, the Tien Shan, and parts of eastern Siberia.

(b) What are the important factors responsible for airmass modifications?

Airmass modification occurs when an airmass migrates from its source region and undergoes thermodynamic and dynamic transformations due to new underlying boundary conditions. The primary factors include:

Surface properties dictate the exchange of heat and moisture. A cold, dry continental polar (cP) airmass passing over a warm ocean undergoes rapid sensible heating and moisture influx, transforming into an unstable maritime polar (mP) airmass. Trajectory and path length determine the magnitude of modification; prolonged transit over contrasting surfaces enhances the depth of the modified layer. Topography and surface roughness induce frictional convergence, mechanical turbulence, and forced orographic uplift, disrupting stability. Vertical mixing and thermodynamic stability govern whether heating from below triggers deep convection or cooling from below creates a low-level temperature inversion. Lastly, residence time and seasonality control the flux of incoming solar radiation, establishing the rate and vertical extent of transformation.

(c) Discuss the hazards associated with rise of sea-surface temperature

The rise in Sea Surface Temperature (SST) under global warming disrupts ocean-atmosphere coupling, precipitating several severe marine and terrestrial hazards.

Elevated SSTs above the critical 26.5°C threshold enhance latent heat transfer, leading to the rapid intensification of tropical cyclones, as witnessed in the rising frequency of extremely severe cyclonic storms over the Arabian Sea and Bay of Bengal. Marine heatwaves trigger widespread coral bleaching by disrupting the symbiotic relationship between corals and zooxanthellae, threatening biodiversity in regions like Lakshadweep and the Gulf of Mannar. Furthermore, thermal expansion of ocean water, coupled with polar ice melt, accelerates global sea-level rise, increasing coastal erosion and inundation in vulnerable deltas such as the Sundarbans. Elevated temperatures also cause ocean deoxygenation and stratification, disrupting primary productivity, shifting pelagic fish distributions, and destabilizing traditional marine fisheries.

(d) Gene pool centres are 'Good Hope' for biodiversity conservation. Elucidate

Gene pool centres, conceptualized by Nikolai Vavilov as geographic centres of origin and diversity of cultivated plants, represent critical reservoirs of genetic variations necessary for ecological resilience and food security.

These centres harbor extensive populations of Crop Wild Relatives (CWR) and primitive landraces that possess evolutionary adaptations to abiotic stresses such as drought, salinity, and temperature extremes, as well as biotic resistance to emerging pests. In India, megadiversity zones spanning the Western Ghats, Eastern Himalaya, and the Indo-Burma region act as primary and secondary gene centres for staple crops, including rice (Oryza sativa), millets, and pulses. Conserving these centres facilitates in-situ conservation, allowing natural selection and continuous evolution of germplasm against climate change. They also supply irreplaceable genetic materials to ex-situ repositories, like the National Bureau of Plant Genetic Resources (NBPGR), providing the foundational biological capital needed for future crop breeding and ecosystem restoration.

(e) Describe how ecosystem services of Himalaya are essential for Highland-Lowland sustainability in Asia

The Himalayan mountain system provides critical provisioning, regulating, and supporting ecosystem services that sustain downstream highland-lowland socio-ecological systems across Asia.

As the "Water Tower of Asia," the Himalayan glaciers and snowfields regulate the perennial flow of major transboundary river systems—including the Indus, Ganga, and Brahmaputra—which sustain agricultural productivity, industrial demand, and domestic water supplies for over a billion people in the Indo-Gangetic plains. Climatologically, the range acts as an orographic barrier that intercepts the Southwest Monsoon, ensuring widespread precipitation across South Asia, while blocking freezing Central Asian katabatic winds during winter. The dense Himalayan forests regulate the hydrological cycle by facilitating groundwater recharge and mitigating downstream flood peaks. Furthermore, the mountain range drives vital sediment fluxes, replenishing fertile alluvial soils across the downstream plains, while its rich biodiversity corridors preserve ecological stability across connected river basins.