Quaternary Geomorphology and Climate Change: Terminology for UPSC Geography Optional

Quaternary geomorphology studies the last 2.58 million years, when repeated ice ages and warm interglacials pushed ice sheets, sea level, rivers, lakes and deserts back and forth and left most of today’s landscapes. Its vocabulary covers the time scale, the orbital pacemaker, ice loading of the crust, sea-level change, relict lakes and channels, the archives that record climate and the methods that date them.

Read each entry for the definition, then the mechanism, dated examples and sketch. UPSC has asked about the impact of the Pleistocene ice age on the crust (2013) and the karewas of Kashmir (Paper II, 2025); both entries are written to answer length. Dates follow the current International Commission on Stratigraphy chart.

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The Quaternary Time Scale

Quaternary

The Quaternary is the youngest period of the Cenozoic Era, beginning 2.58 million years ago and continuing today, marked by the onset of large, repeated Northern Hemisphere glaciations. The International Commission on Stratigraphy fixed its base in 2009 at the Monte San Nicola section, Sicily, close to the Gauss–Matuyama magnetic reversal; it comprises the Pleistocene and Holocene epochs.

• Revised base: older books place the start at about 1 or 1.8 million years ago; the 2009 decision moved it down to 2.58 million years to include the first major ice-sheet growth.
• Causes of the cold: long-term fall in atmospheric carbon dioxide, closure of the Isthmus of Panama and the uplift of the Himalaya and Tibet, which Maureen E. Raymo and William F. Ruddiman (1992) linked to faster chemical weathering drawing down carbon dioxide.
• Geomorphic character: the period’s landforms are overprinted many times, so most present landscapes are Quaternary in detail even where their bedrock framework is far older.
• Indian record: Himalayan moraines and terraces, the karewas of Kashmir, the loess of the Kashmir valley, the dunes of the Thar and the alluvium of the Indo-Gangetic plain.
• Don’t confuse with: the proposed Anthropocene, which was rejected as a formal epoch in 2024, leaving the Holocene as the current unit.

Pleistocene

The Pleistocene is the first epoch of the Quaternary, from 2.58 million to 11,700 years ago, in which ice sheets repeatedly grew over North America, northern Europe and high mountains and then retreated, in some fifty glacial–interglacial cycles. It is divided into the Gelasian, Calabrian, Chibanian and Upper (Late) Pleistocene stages.

• Stages: Gelasian (2.58–1.80 million years), Calabrian (1.80–0.774 million), Chibanian (0.774–0.129 million; ratified in 2020 with its reference section in Chiba prefecture, Japan, at the last reversal of the Earth’s magnetic field) and the Upper Pleistocene (0.129 million to 11,700 years), whose formal name is not yet ratified.
• Rhythm: glaciations followed a 41,000-year beat until the Mid-Pleistocene Transition, about 1.2–0.8 million years ago, after which longer, colder cycles of about 100,000 years dominated.
• Old versus new scheme: the four Alpine glaciations of Albrecht Penck and Eduard Brückner (Günz, Mindel, Riss, Würm) and the four of North America are simplifications; deep-sea oxygen isotopes reveal dozens of cycles.
• Examples: the Laurentide ice sheet over Canada; in India, Pleistocene glaciers in the Himalaya and Karakoram and the sequence of the Kashmir karewas.

Holocene (Greenlandian, Northgrippian and Meghalayan ages)

The Holocene is the present epoch of the Quaternary, beginning 11,700 years before AD 2000 at the end of the Younger Dryas cold phase and defined in a Greenland ice core (NGRIP2) in 2008. In June 2018 the International Commission on Stratigraphy divided it into three ages: the Greenlandian, the Northgrippian and the Meghalayan.

• Indian significance: the Meghalayan is the first unit of the geological time scale defined in India, by a stalagmite from Mawmluh Cave near Sohra (Cherrapunji) whose oxygen isotopes record the weakening of the monsoon (see speleothems).
• Key features: relatively stable warm climate, sea level rising to near its present position by about 7,000–6,000 years ago, the spread of farming and the growth of deltas.
• Debate: some geologists objected that the younger boundaries rest on climatic events that were regional rather than global.

Glacial and interglacial periods

A glacial period is a cold phase of the Quaternary, lasting tens of thousands of years, when large continental ice sheets spread, sea level falls and climatic belts shift towards the equator; an interglacial period is a warm phase between glacials, with ice cover similar to or smaller than today’s.

• Duration: in the last million years, glacials of about 80,000–90,000 years alternated with interglacials of about 10,000–30,000 years.
• Last Interglacial (Eemian, marine isotope stage 5e): about 129,000–116,000 years ago, slightly warmer than today, with sea level several metres higher; its beaches stand above present sea level on stable coasts.
• Last glacial: from about 115,000 to 11,700 years ago, culminating in the Last Glacial Maximum.
• Indian expression: glacial phases brought a weaker summer monsoon, active dunes in the Thar and advanced Himalayan glaciers; interglacials brought a stronger monsoon, lakes and river aggradation.
• Don’t confuse with: stadials and interstadials, which are shorter oscillations within a glacial.

Stadial and interstadial

A stadial is a short cold phase, lasting centuries to a few thousand years, within a glacial or at its end, during which glaciers readvance; an interstadial is a short warm phase within a glacial that is too brief or too cool to count as an interglacial.

• Evidence: Greenland ice cores record about 25 abrupt Dansgaard–Oeschger warmings in the last glacial, named after Willi Dansgaard and Hans Oeschger, each a jump of several degrees within decades followed by slow cooling; Hartmut Heinrich (1988) identified layers of ice-rafted debris from iceberg armadas in North Atlantic sediments (Heinrich events).
• Examples: the Bølling–Allerød interstadial (about 14,700–12,900 years ago) and the Younger Dryas stadial that followed it.
• Indian link: Arabian Sea sediments and cave records show monsoon fluctuations that mirror these North Atlantic swings.
• Geomorphic imprint: recessional moraines, readvance moraines and short-lived dune activity.

Milankovitch cycles

Milankovitch cycles are the periodic variations in the Earth’s orbit and axial tilt that change the seasonal and latitudinal distribution of sunlight and act as the pacemaker of glacial–interglacial cycles. Milutin Milanković calculated them from the 1920s, and James D. Hays, John Imbrie and Nicholas Shackleton (1976) found their periods in deep-sea sediments.

• Eccentricity: the orbit’s departure from a circle, with cycles of about 100,000 and 405,000 years.
• Obliquity: the tilt of the axis, varying between about 22.1° and 24.5° over about 41,000 years; it is now about 23.4°.
• Precession: the timing of perihelion relative to the seasons, with a climatic cycle of about 19,000–23,000 years; it strongly paces the Indian and East Asian monsoons.
• Mechanism: glaciation begins when cool Northern Hemisphere summers at about 65°N fail to melt the winter’s snow; feedbacks from ice albedo and carbon dioxide (about 180 parts per million in glacials against 280 in interglacials) amplify the small orbital signal.
• Unsolved: why the dominant rhythm shifted from 41,000 to about 100,000 years at the Mid-Pleistocene Transition.
• Sketch: three sine curves of different period, eccentricity, obliquity and precession, summed into an insolation curve.

Last Glacial Maximum

The Last Glacial Maximum is the most recent time of maximum global ice volume, about 26,000–19,000 years ago, when ice sheets covered much of North America and north-western Eurasia, sea level stood about 120–130 m below today and global mean temperature was roughly 6 °C lower.

• Ice sheets: Laurentide and Cordilleran over North America, Fennoscandian over northern Europe, British–Irish and Patagonian; permanent ice covered about a quarter of the land.
• Consequences: exposed continental shelves and land bridges (Beringia, Sundaland, Doggerland); expanded deserts and loess; lower snowlines on tropical mountains.
• Indian conditions: the shallow Palk Strait was dry land joining India and Sri Lanka; rivers cut down across the exposed shelf; the monsoon was weak and Thar dunes active; Himalayan glaciers advanced, though their maxima were often out of step with the global maximum.
• Carbon dioxide: about 180–190 parts per million.
• Sketch: a map of the Northern Hemisphere with ice-sheet outlines and the shoreline at 120 m below present.

Ice, Crust and Sea Level

Pleistocene glaciations and their impact on the crust

The impact of Pleistocene glaciations on the crust is the set of vertical movements, sea-level changes and drainage changes produced when ice sheets up to about 3 km thick loaded the continents and later melted. The ice pressed the crust into the mantle, lowered world sea level by locking up water and rearranged rivers, lakes and climatic belts.

• Glacio-isostatic depression: the crust sank beneath the ice by up to several hundred metres, about a third of the ice thickness, as mantle rock flowed away (see glacio-isostasy).
• Peripheral forebulge: the displaced mantle raised a bulge beyond the ice margin; its collapse since deglaciation is lowering the land along the Netherlands, southern England and the Atlantic coast of the USA.
• Post-glacial rebound: unloading lets the crust rise; the northern Gulf of Bothnia still rises by about 1 cm a year and Finland gains several square kilometres of land annually, while the highest post-glacial shoreline on Sweden’s High Coast stands about 286 m above sea level.
• Glacio-eustasy: sea level fell about 120 m at the Last Glacial Maximum, exposing shelves and land bridges and making rivers incise; the post-glacial rise then drowned their lower valleys.
• Hydro-isostasy: the returning water loaded the ocean floor, tilting continental margins.
• Drainage diversion: ice fronts pushed the Missouri and Ohio into their present courses and the Anglian ice sheet diverted the Thames to its present valley about 450,000 years ago; proglacial lakes and overflow channels formed, and the Great Lakes were scoured and later released by the ice.
• Pluvial and periglacial belts: pluvial lakes (below) filled basins such as the Great Basin, and a periglacial belt with permafrost extended across southern England and central Europe.
• Faulting and seismicity: rapid rebound reactivated faults, such as the Pärvie fault of northern Sweden, and still triggers intraplate earthquakes in eastern Canada and Fennoscandia.
• Indian dimension: India lay beyond the great ice sheets, but it felt the eustatic fall on its shelves, glacial advances in the Himalaya and Karakoram and lake formation in the Kashmir basin.
• Sketch: two panels, an ice sheet depressing the crust with a forebulge beyond, then the ice gone, the crust rebounding and a flight of raised beaches on the coast.

Eustasy (glacio-eustasy and tectono-eustasy)

Eustasy is a worldwide change of sea level caused by a change in the volume of ocean water or in the capacity of the ocean basins, as distinct from local vertical movement of the land. Eduard Suess introduced the term in 1888; relative sea level at any coast combines eustatic change with local uplift or subsidence.

• Glacio-eustasy: growth and melting of ice sheets changed sea level by about 120 m over each 100,000-year cycle; during deglaciation it rose by more than 1 cm a year at times.
• Tectono-eustasy: changes in the volume of mid-ocean ridges and basins alter sea level slowly, over millions of years; fast spreading in the Cretaceous raised sea level far above today’s.
• Steric change: warming expands seawater, a major part of present rise.
• Present trend: global mean sea level rose about 0.20 m between 1901 and 2018, and by about 3.7 mm a year in 2006–2018.
• Indian example: relative sea-level rise in the Sundarbans exceeds the global rate because the delta is also subsiding.
• Don’t confuse with: isostasy, which moves the land rather than the sea (see isostasy versus eustasy); eustatic falls drive rejuvenation.

Raised beaches and marine terraces

A raised beach is a former beach, with its sand, shingle and shells, now standing above the reach of present waves; a marine terrace is a raised wave-cut platform with its old cliff behind it. Both record a relative fall of sea level through land uplift, a higher former sea level or both.

• Isostatic cause: glacial rebound lifted flights of beaches around the Gulf of Bothnia, Hudson Bay and western Scotland.
• Tectonic cause: coral terraces on the Huon Peninsula, Papua New Guinea, lifted by steady uplift, give one of the best sea-level records of the last glacial cycle; single earthquakes lift shorelines in one step.
• Eustatic cause: Last Interglacial beaches stand a few metres above present sea level on stable coasts.
• Indian examples: the Saurashtra coast of Gujarat carries raised beaches and marine terraces with Pleistocene limestones; the December 2004 earthquake raised parts of the North Andaman coast by about a metre, exposing coral reefs (see earthquakes).
• Sketch: a coastal section with a present beach, a raised beach ridge and a higher wave-cut platform with a fossil cliff (see coastal landforms).

Drowned (submerged) valleys and submerged forests

Drowned valleys are river valleys flooded by the sea when post-glacial sea level rose about 120 m between roughly 20,000 and 7,000 years ago; submerged forests are the rooted stumps and peat of woodland that grew on low coastal land before the same rise and now lie in the intertidal zone or below the sea.

• Formation: rivers graded to the low glacial sea cut valleys across the exposed shelf; the rising sea invaded them as estuaries and rias and buried coastal forests in marine silt.
• Examples: Chesapeake Bay, the drowned lower valley of the Susquehanna, USA; Doggerland beneath the southern North Sea; stumps exposed at low tide at Borth, Cardigan Bay, Wales.
• Indian examples: a submerged forest was found below low-tide level during nineteenth-century excavation of the Prince’s Dock in Mumbai; buried channels on the western continental shelf mark rivers of the glacial low stand; drowned valley mouths on the Konkan coast are treated as rias.
• Significance: these features date the post-glacial rise and preserve archives of past vegetation.

Relict Landscapes and Indian Archives

Pluvial lakes

Pluvial lakes are lakes that expanded, or formed, in basins that are now dry or saline, during periods of higher effective moisture caused by greater rainfall, lower evaporation or shifted storm tracks. Their shorelines, beach ridges, tufa and lake sediments survive as relict landforms.

• Examples: Lake Bonneville, which covered about 50,000 km² of Utah and was about 300 m deep, studied by Grove Karl Gilbert (1890), with the Great Salt Lake as its remnant; Lake Lahontan, Nevada; Mega-Lake Chad in the African Humid Period.
• Timing: in the western USA the lakes peaked in the late glacial, when storm tracks shifted south; in the Sahara and the Thar they peaked in the early and middle Holocene, when the monsoon was strongest.
• Indian examples: Sambhar, Didwana and Lunkaransar in Rajasthan were fresh or larger in the early Holocene; Lunkaransar had dried by about 5,500 years ago.
• Geomorphic evidence: terraced shorelines on basin slopes, deltas at old lake levels and overflow channels.
• Sketch: a basin section with a small present salt lake and a series of higher shoreline benches.

Karewas

Karewas are flat-topped tablelands of lake, river and glacial-outwash sediments (clay, silt, sand and gravel, with lignite bands and a loess cover) that flank the Kashmir valley. They were laid down from the late Pliocene through the Pleistocene in a large lake basin ponded when the rising Pir Panjal range blocked the valley’s drainage.

• Location: best developed on the Pir Panjal (south-western) side of the valley, in Budgam, Pulwama and Shopian districts, with smaller karewas on the north-eastern flank and in the Bhadarwah valley of Doda district; Kashmiris call them wudar.
• Formation: uplift of the Pir Panjal impounded the valley; rivers and meltwater streams filled the lake with fine lake beds alternating with outwash gravels through glacial–interglacial swings; the Lower Karewa (Hirpur Formation) was later folded and tilted by continued uplift, and the Upper Karewa (Nagum Formation) carries more outwash and loess; the lake drained as the Jhelum cut its gorge near Baramulla, and streams dissected the deposits into terraces.
• Palaeoclimate archive: pollen, loess–palaeosol layers, fossil vertebrates and magnetic reversals in the karewas record Himalayan uplift and glacial cycles, including drying as the rising Pir Panjal cut off monsoon moisture.
• Economic significance: well-drained, flood-free, frost-tolerant karewa soils carry saffron around Pampore, Pulwama district, the heart of Kashmir saffron (granted a geographical indication tag in 2020), with almonds, apples, walnuts and other orchards; lignite and brick clay are also worked.
• Threats: karewa soil is excavated as fill for roads, railway embankments and construction, and urban expansion is eating into saffron land.
• Sketch: a cross-section of the Kashmir valley with the Pir Panjal on one side, tilted karewa terraces above the Jhelum floodplain and the Baramulla gorge as the outlet.

Palaeochannels (Ghaggar–Hakra, the “Saraswati”)

A palaeochannel is an abandoned river course, visible on the surface or buried beneath younger sediment, preserved as a linear belt of sand and gravel; palaeochannels are detected from satellite imagery, soil tone, geophysical surveys and boreholes, and dated by luminescence.

• Ghaggar–Hakra: a broad valley across Haryana, Rajasthan and Cholistan now carries only the seasonal Ghaggar. Luminescence dating published in 2017 indicates that the Sutlej abandoned it between about 15,000 and 8,000 years ago, so the Harappan cities along it grew beside a monsoon-fed river in an older valley; its identification with the Vedic Saraswati remains debated.
• Uses: palaeochannels are productive aquifers and are mapped for groundwater recharge; they guide archaeology; and rivers can reoccupy them during floods and avulsions (see avulsion).
• Other examples: abandoned courses of the Kosi across its megafan and of the Yamuna on the Haryana plain.
• Don’t confuse with: a misfit stream, a small modern river inside a valley made by a larger one.

Reading and Dating the Record

Palaeoclimate proxies

Palaeoclimate proxies are natural archives whose physical, chemical or biological properties vary with climate and can be read and dated to reconstruct past temperature, rainfall, ice volume and atmospheric composition where no instrumental records exist.

• Marine oxygen isotopes: Cesare Emiliani (1955) showed that foraminifera shells record the ratio of oxygen-18 to oxygen-16; because ice sheets store the lighter isotope, glacial oceans are richer in oxygen-18. Numbered marine isotope stages (odd warm, even cold) now exceed 100 in the Quaternary.
• Ice cores: Greenland cores cover the last glacial cycle; the EPICA Dome C core in Antarctica spans about 800,000 years, and in January 2025 the Beyond EPICA project reported ice at least 1.2 million years old. Trapped air gives past carbon dioxide and methane.
• Speleothems: uranium–thorium-dated stalagmites record monsoon rainfall through oxygen isotopes, as at Mawmluh Cave, Meghalaya.
• Pollen and lake sediments: pollen in Kashmir karewas and Thar lakes reveals vegetation and moisture; varves give annual layers.
• Other archives: tree rings of Himalayan conifers, corals, loess–palaeosol sequences and glacial moraines.
• Limits: each proxy records one season or place, needs calibration and dating, and can be disturbed by non-climatic factors.

Radiocarbon, OSL and cosmogenic-nuclide dating

Radiocarbon, optically stimulated luminescence (OSL) and cosmogenic-nuclide dating are the main numerical methods of Quaternary geomorphology: radiocarbon dates organic matter, OSL the burial of sediment grains and cosmogenic nuclides the exposure of rock surfaces to cosmic rays. Together they have replaced relative correlation of terraces, moraines and surfaces.

• Radiocarbon: developed by Willard Frank Libby in the late 1940s; carbon-14 in dead organisms decays with a half-life of about 5,730 years, giving ages up to about 50,000 years after calibration against tree rings.
• OSL: introduced by David J. Huntley and colleagues in 1985; it measures the time since quartz or feldspar grains were last exposed to sunlight, dating dunes, loess, river terraces and palaeochannels from a few hundred to more than 100,000 years.
• Cosmogenic nuclides: beryllium-10, aluminium-26 and chlorine-36 build up in exposed rock; they give exposure ages of moraines, terraces and fault scarps and basin-wide erosion rates from about 1,000 to over a million years, on principles set out by the Indian physicist Devendra Lal (1991).
• Other methods: uranium–thorium for speleothems and corals, varve and tree-ring counting, volcanic ash layers and palaeomagnetism.
• Indian examples: OSL ages of Thar dunes and Himalayan terraces; cosmogenic ages of Himalayan moraines showing glacial advances out of step with the global maximum.
• Scope: older surfaces are dated by other means (see dating of erosion surfaces).

Abrupt Climatic Events

Younger Dryas

The Younger Dryas is an abrupt return to near-glacial conditions around the North Atlantic between about 12,900 and 11,700 years ago, interrupting the warming that followed the Last Glacial Maximum. It is named after the arctic–alpine flower Dryas octopetala, whose pollen marks it in Scandinavian lake sediments, and its end defines the base of the Holocene.

• Magnitude and speed: Greenland cooled by up to about 10 °C within decades, and the cold ended with a comparable warming in about half a century.
• Cause: the favoured explanation is a weakening of the Atlantic overturning circulation after meltwater from the retreating Laurentide ice sheet freshened the North Atlantic; an extraterrestrial-impact hypothesis remains contested.
• Geomorphic imprint: glaciers readvanced, building the Salpausselkä moraine ridges of southern Finland and the moraines of the Loch Lomond readvance in Scotland; periglacial activity revived.
• Monsoon link: Asian and Indian cave records show a weak monsoon during the Younger Dryas.

Holocene Climatic Optimum

The Holocene Climatic Optimum is the warm, and in the tropics wetter, phase of the early and middle Holocene, roughly 9,000 to 5,000 years ago, when strong Northern Hemisphere summer sunlight warmed high latitudes and strengthened the African and Indian monsoons. It was neither globally uniform nor synchronous.

• Mechanism: precession placed perihelion in the northern summer, raising summer insolation.
• Effects: the African Humid Period turned the Sahara into savanna with large lakes; the Thar lakes filled and dunes were stabilised by vegetation; Himalayan and Alpine glaciers were smaller than in later centuries.
• Decline: from about 5,000 years ago the monsoon weakened, lakes shrank and dunes were reactivated in parts of the Thar and the Sahara.
• Caution: the older idea of a uniformly warmer world is not supported by all records.

4.2 ka event

The 4.2 ka event is a severe drought, lasting about two to three centuries, that began around 4,200 years ago (about 2200 BC) across the Mediterranean, the Middle East and South Asia. It marks the base of the Meghalayan Age and has been linked to the decline of Old Kingdom Egypt, the Akkadian empire and the urban phase of the Harappan civilisation.

• Evidence: oxygen isotopes in the Mawmluh Cave stalagmite; lake sediments at Kotla Dahar, Haryana, which record a weakening of the monsoon at about this time; dust and lake records across West Asia.
• Harappan debate: Harappan cities declined between about 2000 and 1900 BC and settlement shifted towards the wetter Himalayan foothills and the Ganga–Yamuna doab; many researchers link this to a gradual weakening of the monsoon over centuries, while others stress river shifts, trade decline and social change, and hedge against a single cause.
• Criticism: some palaeoclimatologists argue that the event was regional, not global, and that records of different droughts have been lumped together.
• Geomorphic imprint: shrinking lakes, reactivated dunes and reduced river flow in semi-arid belts.

Medieval Warm Period and Little Ice Age

The Medieval Warm Period was a regional warm phase, strongest around the North Atlantic, between about AD 950 and 1250; the Little Ice Age was a cooler period from about the fourteenth to the mid-nineteenth century, when mountain glaciers advanced worldwide. Neither was uniform or synchronous across the globe.

• Causes of the Little Ice Age: clusters of large volcanic eruptions, such as Tambora in 1815, which produced the “year without a summer” of 1816, and low solar activity during the Maunder Minimum (1645–1715).
• Geomorphic imprint: Alpine glaciers reached their late-Holocene maximum in the mid-nineteenth century; fresh terminal moraines of Little Ice Age age lie close to the snouts of many Himalayan glaciers.
• Present relevance: many of these moraines now dam the lakes that feed glacial lake outburst floods, as the glaciers retreat from their Little Ice Age positions.
• Medieval examples: Norse settlement of Greenland during the warm phase and its abandonment as the climate cooled.

PYQs Built on These Terms

• Referring to the location and physical formation of karewas, highlight their economic significance. (Paper II, 2025)
• Discuss the variations in nature of glaciers in India and the emerging issues due to climate change. (Paper II, 2024)
• Write short note: Impact of Pleistocene Ice age on the crust of the Earth. (2013)

Frequently Asked Questions

When did the Quaternary period begin?

It began 2.58 million years ago, the date fixed by the International Commission on Stratigraphy in 2009 to coincide with the onset of major Northern Hemisphere glaciation. Older books give about 1 or 1.8 million years. The period includes the Pleistocene and the Holocene, which began 11,700 years ago.

What is the Meghalayan Age and why is it linked to India?

The Meghalayan is the latest age of the Holocene, running from 4,250 years ago to the present. Its boundary is defined in a stalagmite from Mawmluh Cave in Meghalaya, which records the severe drought of the 4.2 ka event; it is the first geological time unit defined in India.

What is the difference between eustasy and isostasy?

Eustasy is a worldwide change in sea level caused by changes in ocean water volume, mainly from melting or growing ice sheets. Isostasy is the vertical movement of the land as the crust adjusts to loading and unloading, such as rebound after an ice sheet melts. Relative sea level at a coast reflects both.

How low was sea level during the last ice age?

At the Last Glacial Maximum, about 26,000–19,000 years ago, sea level stood about 120–130 m below today because so much water was locked in ice sheets. Continental shelves were exposed, the Palk Strait between India and Sri Lanka was dry land and rivers cut valleys across the shelf.

What are karewas and why are they famous?

Karewas are terraces of old lake and outwash deposits on the flanks of the Kashmir valley, formed when the rising Pir Panjal dammed the valley’s drainage. Their well-drained soils around Pampore grow India’s saffron, along with almonds and apples, and their layers record Himalayan climate history.

Did climate change cause the decline of the Harappan civilisation?

Climate probably contributed but was not the only cause. Cave and lake records show the monsoon weakening around the 4.2 ka event, and Harappan cities declined after about 2000 BC as people moved towards wetter regions, but river shifts, trade and social change also played a part.