geophysical phenomena

How earthquakes, tsunamis, volcanic activity, cyclones and related phenomena are generated, and why the argument about them is now less about physics than about exposure, vulnerability, prediction limits and land use.

What it is

Geophysical phenomena are the processes by which energy stored in or reaching the Earth is released, altering the crust, the oceans, the atmosphere and, at the outer edge, the magnetosphere. They fall into three families. Endogenic phenomena draw on the planet's internal heat and are organised by plate tectonics: earthquakes concentrated along plate margins, volcanic activity at divergent boundaries, subduction zones and hotspots, and tsunamis generated when a submarine earthquake, landslide or volcanic collapse displaces a column of water. Exogenic atmospheric phenomena draw on solar heating and the Earth's rotation: tropical cyclones, tornadoes, cloudbursts. A third set originates beyond the Earth — the auroras, produced when charged particles carried by the solar wind and by coronal mass ejections are funnelled along geomagnetic field lines towards the poles and excite atmospheric oxygen and nitrogen, giving the greens, reds and purples of the aurora borealis and aurora australis.

The mechanisms are specific and a candidate should be able to state them. An earthquake originates at a focus, radiates primary, secondary and surface waves, and is measured for energy by moment magnitude and for felt effects by intensity scales. Tsunamis require vertical displacement of the sea floor, typically at a subduction zone, and travel as long-wavelength shallow-water waves that are barely noticeable in the deep ocean but shoal dramatically on continental shelves. Tropical cyclones require sea surface temperatures of roughly 26.5 degrees Celsius through a layer some 50 to 60 metres deep, a pre-existing low-pressure disturbance, sufficient Coriolis force — hence their absence within about five degrees of the equator — weak vertical wind shear, and a moist mid-troposphere; they are heat engines converting latent heat of condensation into rotational kinetic energy. Tornadoes need strong low-level wind shear and steep instability, which is why the plains inland of the Gulf of Mexico, where warm moist Gulf air undercuts dry air off the Rockies and cold air from the north, produce most of the world's recorded twisters.

Institutionally, the subject is anchored in India by the India Meteorological Department, which serves as the Regional Specialised Meteorological Centre for tropical cyclones over the north Indian Ocean; the National Centre for Seismology and the Geological Survey of India; the Indian Tsunami Early Warning Centre run by INCOIS at Hyderabad within the UNESCO-coordinated Indian Ocean tsunami warning system; the seismic zonation of the country into four zones under the Bureau of Indian Standards code IS 1893; and the Disaster Management Act of 2005 with the National Disaster Management Authority and the National Disaster Response Force. The conceptual bridge between geography and governance is the distinction between hazard, the physical event; exposure, what lies in its path; and vulnerability, the capacity of the exposed to withstand and recover. Disaster risk is the product of the three, and only the hazard is geophysical.

Why it is contested

The first argument is about causation, and it decides where money goes. One framing treats loss as a function of the hazard: a great earthquake, a super cyclone, an unprecedented cloudburst. The other holds that hazards become disasters only through development choices — unregulated construction on soft alluvium, encroachment on urban drainage, settlements on toe-cut slopes, and poverty that leaves people unable to evacuate or rebuild. The Latur earthquake of 1993 was moderate in magnitude but lethal because of heavy stone-and-mud roofs; the Bhuj earthquake of 2001 killed in multi-storey buildings far from the epicentre. If loss is chiefly a hazard problem, the response is better science and stronger structures. If it is chiefly a vulnerability problem, the response is housing, land tenure, enforcement and social protection — politically much harder.

The second is about prediction and the allocation of scientific effort. Tropical cyclone track and landfall forecasting has improved markedly, and India's cyclone death toll has fallen sharply from the Odisha super cyclone of 1999 to recent storms. Earthquake prediction, in the sense of stating time, place and magnitude in advance, remains beyond reach, and most seismologists regard it as unlikely; what is available is probabilistic hazard assessment, microzonation and building codes. Cloudbursts, glacial lake outburst floods and rapid cyclone intensification sit awkwardly in between — physically understood but occurring at scales too fine for current observation networks in mountainous terrain. The contest is whether scarce budgets should chase better forecasting or accept forecast limits and invest in resilience that works regardless of warning.

The third is attribution. Rising sea surface temperatures are observed, and there is a defensible physical expectation that warmer oceans and a moister atmosphere will favour more intense cyclones, heavier extreme rainfall and higher storm surge riding on higher mean sea level. But the frequency record is confounded by improved satellite detection, and the intensification of individual storms cannot simply be read off the trend. The stakes are not academic: attribution underpins claims for compensation, and the loss-and-damage funding agreed in recent climate negotiations turns on whether harm can be traced to warming caused elsewhere. Tectonic and volcanic hazards, by contrast, have no climate signal at all, and conflating them with climate-driven change is a common analytical error.

The fourth is land use, where the trade-offs are sharpest. The Himalaya is a young, seismically loaded and slope-unstable range across which India seeks roads, tunnels, hydropower, pilgrimage access and tourism income for states with few other revenues. Geologists have warned that valley-floor construction, tunnelling and reservoir loading raise landslide, subsidence and flood risk, as episodes at Kedarnath, in the Rishiganga valley, in Sikkim's Lhonak lake basin and at Joshimath have been read to show. On the coast, cyclone and tsunami safety argues for setback lines, dune and mangrove protection and restricted construction, while fishing communities need to live near the sea, ports and tourism need the shore, and coastal states resent regulation drafted centrally. Every safety measure has an identifiable loser.

The competing positions

The engineering and growth position, held broadly by infrastructure ministries, state governments in the Himalaya and the north-east, and much of the construction sector, is that hazard is a constraint to be designed around, not a veto. Codes, embankments, seawalls, cyclone shelters, tunnels and better drainage allow economic activity in risky places; withholding roads and power from mountain districts imposes a permanent poverty penalty in the name of a probabilistic risk.

The vulnerability and rights position, associated with disaster-studies scholarship, civil liberties and fishworkers' organisations, and reflected in the global shift towards disaster risk reduction under the Sendai Framework, holds that the poor die in disasters because they are poor. Its priorities are secure housing and tenure, enforced building bye-laws for the informal sector, social protection after events, and participation of affected communities in decisions about relocation, which is otherwise experienced as eviction.

The ecosystem-based position argues that mangroves, coastal dunes, wetlands, natural drainage and forested slopes attenuate surge, absorb runoff and stabilise ground more cheaply and durably than concrete, and that hard structures often transfer risk downstream or along the coast while creating a false sense of safety.

The forecasting and technocratic position, represented by the IMD, INCOIS, the National Centre for Seismology and the space agency, points to demonstrated returns: dense Doppler radar, ocean buoys, satellite observation and a functioning tsunami warning chain have already saved large numbers of lives, and the frontier lies in higher-resolution modelling and last-mile dissemination.

The federal and fiscal position, voiced by state governments, is that hazard is local but resources are central; that response funds arrive faster than mitigation funds; and that mitigation, which is politically invisible when it works, is chronically underfunded relative to relief, which is visible.

The global equity position, advanced by small island states and by India in climate negotiations, is that the countries most exposed to intensifying storms and sea-level rise contributed least to the cause, and that adaptation finance and loss-and-damage support are obligations rather than charity.

How it developed

The intellectual foundation was laid in stages: the continental drift hypothesis in the early twentieth century, palaeomagnetic and oceanographic evidence for sea-floor spreading around the mid-century, and the synthesis into plate tectonics in the late 1960s, which for the first time explained the distribution of earthquake belts, volcanic arcs, mid-ocean ridges and mountain chains within a single framework, and which also explains the slow reconfiguration of continents and ocean basins over geological time. Instrumental seismology added magnitude scales, the first widely used one in the 1930s and the moment magnitude scale later, as it became clear that earlier scales saturated for great earthquakes.

India's institutional development was event-driven. A national meteorological service dating from the late nineteenth century built cyclone warning capacity through the twentieth. The Odisha super cyclone of 1999 and the Bhuj earthquake of 2001 exposed the absence of a statutory framework, leading to the Disaster Management Act of 2005 and a shift in official language from relief to preparedness and mitigation. The Indian Ocean tsunami of December 2004, generated by a great subduction earthquake off Sumatra and causing over two hundred thousand deaths across the region including many thousands in India and the Andaman and Nicobar Islands, revealed that an ocean assumed to be tsunami-quiet had no warning system at all; a national tsunami warning centre followed within a few years, embedded in a regional network.

Globally, the Hyogo Framework of 2005 and the Sendai Framework adopted in 2015 moved the emphasis from response to risk reduction and to targets for reducing mortality and economic loss. Meanwhile the climate assessments, in particular the special report on the ocean and cryosphere and the sixth assessment cycle, established observed warming of the ocean, retreat of glaciers and ice sheets and rising sea level, and offered graded confidence statements about extremes. A run of mountain events — the Kedarnath disaster of 2013, the Chamoli flood of 2021, the Sikkim glacial lake outburst of 2023 and the subsidence at Joshimath — turned Himalayan hazard from a specialist concern into a mainstream political one.

Where it stands

Cyclone mortality in India has fallen dramatically while cyclone-related economic loss has risen, which is the expected signature of good warning combined with growing coastal assets. The Arabian Sea has produced a series of intense systems in recent years, unsettling the long-standing assumption that the Bay of Bengal accounts for the great majority of north Indian Ocean cyclones, though whether this is a trend or variability is unsettled. Tsunami warning works well for distant sources but the near-field problem remains: for a rupture in the Andaman or Makran zones, warning time may be minutes, which makes community drills and vertical evacuation more important than instrumentation. The central Himalayan seismic gap, a stretch that has not produced a great earthquake in the instrumental era while convergence continues at a few centimetres a year, is widely regarded as capable of one; the exposed population in Himalayan towns and in the Indo-Gangetic plain, which sits on thick sediment that amplifies ground motion, has multiplied since the last such event. Seismic microzonation exists for some cities only, and building code compliance in the informal housing sector is weak. Cloudburst and flash-flood forecasting in mountain catchments, glacial lake inventories and early warning for outburst floods, urban drainage in coastal cities, and the balance struck by successive coastal regulation notifications between protection and construction all remain open. Internationally, the loss-and-damage fund exists but its scale relative to projected need is disputed.

Taking a view

A good answer earns its marks in the first three sentences by getting the mechanism right and specific — the thermodynamic conditions for cyclogenesis, the vertical sea-floor displacement that a tsunami requires, the subduction geometry or hotspot that a volcano sits on. Vagueness here cannot be recovered later. Then move deliberately from hazard to consequence, and use the hazard–exposure–vulnerability distinction as the organising device: it converts a list of impacts into an argument about why the same magnitude produces different death tolls in different places. Indian examples should be chosen for what they demonstrate rather than mentioned in bulk.

Two traps recur. The first is treating every extreme event as a climate change event; the disciplined move is to say what warming makes more likely, in what confidence terms, and to note plainly that earthquakes, tsunamis and volcanic activity have no climate driver. The second is ending with an undifferentiated list of measures — early warning, awareness, capacity building — which reads as filler. Prioritise instead, and say why.

Taking a view here does not mean choosing between science and society. It means stating where the marginal return now lies. A defensible line is that for cyclones India has largely solved the warning problem and the binding constraint has shifted to exposure — what is built on the coast and how — while for earthquakes the reverse holds, since prediction is unavailable and the only real instrument is enforced construction quality in existing settlements. That position can be argued in two sentences, concedes what the other side gets right, and is better than balance for its own sake.