(a) Describe the concept of 'Altiplanation'. (10 marks) (b) What are the important factors responsible for airmass modifications?…

(a) Altiplanation

Altiplanation (cryoplanation) is a periglacial process that cuts flat, step-like terraces into mountain summits and upper slopes in cold, frost-active climates.

Snow collects in hollows on a slope. Repeated freeze–thaw (frost shattering) and nivation break the rock at the back of the hollow, so the steep scarp (riser) retreats. Meltwater, solifluction and slopewash carry the debris across the terrace floor (tread) and downslope, so the tread widens as the riser recedes. Shallow permafrost holds meltwater near the surface and keeps the process going. Repeated cycles leave stepped summits. Examples are the Alaska–Yukon uplands, north-eastern Siberia (goletz terraces) and parts of the Rocky Mountains.

(b) Factors of airmass modification

An airmass changes its temperature, moisture and stability once it leaves its source region. The main factors are:

• Underlying surface and the air–surface temperature contrast, which govern heat and moisture exchange. A cold, dry continental polar (cP) airmass over warm water gains heat and vapour and turns unstable, as in lake-effect snow.
• Path length, speed and residence time: slow, long travel allows deeper change.
• Topography: uplift cools the air and releases latent heat; the lee side gets foehn-type warming.
• Radiation and season, which heat or cool the surface by day and night, summer and winter.
• Vertical mixing, subsidence and convergence, which spread, dry or lift the modified layer.

Cooling from below stabilises the air (fog, inversion); heating from below destabilises it (showers).

(c) Hazards of rising sea-surface temperature

Warm water supplies the energy and moisture that drive many ocean–atmosphere hazards.

Above about 26.5°C, tropical cyclones intensify rapidly, as Amphan (2020) did over the Bay of Bengal and Tauktae (2021) over the Arabian Sea. Marine heatwaves bleach corals by expelling their zooxanthellae, as in the Great Barrier Reef, Lakshadweep and the Gulf of Mannar. Thermal expansion of water raises sea level, worsening erosion and flooding in deltas such as the Sundarbans. Warming and stratification lower dissolved oxygen and shift fish stocks, hurting fisheries. SST changes also alter ENSO and monsoon behaviour, raising the risk of drought and floods.

(d) Gene pool centres as 'Good Hope'

Vavilov identified centres of origin and diversity of cultivated plants. These centres still hold the widest variety of crop genes.

Crop wild relatives and landraces there carry genes for drought, salinity and disease resistance that high-yielding varieties have lost. Resistance to grassy-stunt virus came into cultivated rice from wild Oryza nivara, showing how such genes protect food security. India lies in the Indo-Burma and Hindustani centres, rich in rice, pulses and citrus. They are protected in situ, as in the Garo Hills citrus gene sanctuary, and ex situ in NBPGR gene banks. The PPV&FR Act, 2001 and the Biological Diversity Act, 2002 support this. Losing these centres would close the main source of future breeding material.

(e) Himalayan ecosystem services and highland–lowland sustainability

The Himalaya supplies services on which the Asian lowlands depend.

It is the water tower of Asia: glaciers, snow and springs feed the Indus, Ganga and Brahmaputra, which support some 1.65 billion people downstream (ICIMOD). The range blocks the monsoon, giving rain to the plains, and shields them from cold Central Asian winds. Its forests and wetlands regulate stream flow, recharge groundwater and curb floods. Eroded silt renews alluvial soils and its rivers give hydropower. Biodiversity, medicinal plants and sacred landscapes add livelihoods. Lowland security therefore depends on healthy highlands. Glacier retreat and glacial-lake floods, as at Chamoli in 2021, show the risk, which is why payment for ecosystem services and mountain-sensitive planning matter.