Sri Lanka is a 65,610 km² tropical island off India's south-east tip, built like a stepped pyramid: a central massif rising to 2,524 m at Pidurutalagala, ringed by lower plateaus and a broad coastal plain. Two monsoons divide it into a rain-soaked south-western wet zone and a much larger dry zone to the north and east, which is why its ancient kingdoms were built around reservoirs.
The island sits between roughly 6° and 10° north of the equator, about 430 km long from Dondra Head in the south to Point Pedro in the north and some 225 km at its widest. Nearly all of it is Precambrian crystalline rock, part of the same continental block as southern India. The easiest way to read it is to start at the top and walk downhill.
Pidurutalagala and the Roof of the Central Massif
The central highlands occupy the south-central part of the island, a block of mountains about 65 km across that most Sri Lankan geography textbooks describe as the top step of three. The usual division puts the lowest step, or peneplain, between sea level and about 125 m, the middle one between about 125 m and 750 m, and the highest above 750 m. Steep escarpments separate them, and the classic explanation is uplift in stages, with erosion planing each level flat before the next lift.
The summit of the whole structure is Pidurutalagala, also called Mount Pedro, at 2,524 m. It rises directly above Nuwara Eliya, a hill station developed by the British from the late 1820s that sits at roughly 1,870 m. Here the mean temperature is about 16 °C, less than two-thirds of Colombo's, and ground frost is possible on clear nights between January and March.
Adam's Peak (Sri Pada) is not the highest, but it stands on the south-western edge of the massif and rises almost sheer from the lowlands. To the north, the Knuckles Range is a detached outlier, cut off from the main block by the Mahaweli valley around Kandy. In 2010 UNESCO listed the Peak Wilderness, Horton Plains and the Knuckles together as the Central Highlands World Heritage Site.
Horton Plains and the Drop at World's End
Just south of Pidurutalagala, the massif flattens into Horton Plains, a grassland plateau at about 2,100 to 2,300 m with patches of cloud forest. The national park covers only about 31 km², but it is the headwater of three of the island's major rivers: the Mahaweli flowing north and east, the Kelani flowing west to Colombo, and the Walawe flowing south. Rainfall is above 2,000 mm a year, and frost is common in February.
The plateau ends abruptly on its southern side at World's End, a cliff that drops about 870 m to the tea estates and villages of the middle step below. By late morning the view usually disappears into cloud. It is the clearest illustration of the stepped-peneplain idea: a near-vertical wall between two almost level surfaces. For trails and wildlife, see our guide to Horton Plains.
Where the Rain Falls: Two Monsoons and Two Zones
The massif splits the island's climate in two, because it stands in the path of both monsoon winds. From roughly May to September the south-west monsoon blows in off the Indian Ocean, and its moisture is wrung out on the windward, south-western slopes. Colombo receives around 2,400 mm a year and parts of the western hills more than 4,000 mm, while the north and east, in the rain shadow, stay hot and dry.
From about December to February the wind reverses. The north-east monsoon brings rain to the north and east, but it is weaker and less reliable. Between the two, the inter-monsoon months of March to April and October to November bring afternoon thunderstorms everywhere, and October-November is often the wettest period island-wide, as depressions and cyclones track in from the Bay of Bengal. Our explainer on how monsoons work covers the mechanics of this reversal.
The result is the island's basic division. The wet zone, the south-western lowlands and the western hills, gets about 2,500 mm or more and rain in most months; it is roughly a quarter of the land but holds most of the population and the bulk of the tea and rubber. The dry zone, around two-thirds of the island across the north, north-central and east, gets about 1,200 to 1,900 mm, concentrated in the north-east monsoon, followed by a long drought. A narrow intermediate zone lies between them, and the far north-west around Mannar and the south-east around Hambantota are semi-arid, with under 1,200 mm. Farmers name their two rice seasons after the monsoons: Maha, the main season, runs roughly September to March on north-east monsoon rain, and Yala, the smaller one, runs roughly April or May to August and in the dry zone depends almost entirely on stored water.
Down the Mahaweli: 335 km from the Hills to Trincomalee
Sri Lanka's rivers radiate from the massif like spokes, mostly short and steep, but one dwarfs the rest. The Mahaweli Ganga, 335 km long, rises in the Horton Plains and Hatton area, swings north past Kandy in a deep valley, then turns east and north-east across the dry zone to reach the sea at Koddiyar Bay, beside the deep natural harbour of Trincomalee. Its basin drains roughly a sixth of the island.
The Mahaweli's significance is that it carries wet-zone rain into the dry zone. That was the logic of the Accelerated Mahaweli Development Programme launched in the late 1970s, which built the Kotmale, Victoria, Randenigala and Rantembe dams in the hills and diverted water through tunnels and canals to new irrigated settlements on the northern plains. The same dams now supply a large share of the island's hydroelectricity. The second-longest river, the Malvathu at about 170 km, flows the other way, north-west past Anuradhapura to the Gulf of Mannar.
Tanks of the Dry-Zone Plains
Below the hills, the lowest step of the island is a gently undulating plain studded with isolated granite inselbergs. Sigiriya, the rock fortress built by King Kashyapa in the fifth century, is the best known, a sheer-sided lump rising about 180 m above the forest; its story and gardens are covered in our Sigiriya site guide. But the more important human landscape here is made of water.
Because dry-zone rain arrives in a few months and then stops, the kingdoms of Anuradhapura (from about the 4th century BC) and Polonnaruwa (11th to 13th centuries AD) were built on stored water. Sinhala calls a reservoir a wewa; the British called them tanks. Thousands of small village tanks were arranged in cascades down shallow valleys, each catching the overflow of the one above, a system FAO now recognises as a Globally Important Agricultural Heritage System. The great royal tanks were on another scale: Minneriya, credited to King Mahasena; Kala Wewa, built under King Dhatusena in the fifth century and linked to Anuradhapura by the Jaya Ganga canal, around 87 km long with a famously gentle gradient; and the Parakrama Samudra at Polonnaruwa, the "Sea of Parakrama", built under Parakramabahu I in the 12th century. Many still irrigate rice, and in the dry season Minneriya's receding shore draws hundreds of wild elephants.
The Coastal Rim, Adam's Bridge and the 2004 Tsunami
The outermost ring is a coastal belt mostly under 30 m, about 1,340 km long, with sandy beaches, lagoons and mangroves. It is palm-fringed and crowded in the south-west, broken by long lagoons such as Batticaloa's in the east, and scrubby in the semi-arid corners. The Jaffna Peninsula in the far north is different again: flat Miocene limestone with no rivers, farmed on groundwater.
Off the north-west coast, Mannar Island points toward India. Between Talaimannar and Dhanushkodi on India's Pamban Island, the narrowest crossing of the Palk Strait is only about 29 to 30 km, much of it spanned by Adam's Bridge (Rama Setu), a chain of limestone shoals and sandbanks about 48 km long in water mostly 1 to 3 m deep. In the last ice age, with sea level far lower, the island was joined to India across this shelf, which is why so much of its wildlife is shared with the south of the subcontinent.
The coast is also the island's most exposed edge. On 26 December 2004, the tsunami from the magnitude 9.1 Sumatra-Andaman earthquake crossed the Bay of Bengal in about two hours and struck the eastern and southern shores. More than 30,000 people died in Sri Lanka, Ampara and Batticaloa districts worst of all, and near Peraliya a wave overturned a crowded passenger train.
Sri Lanka and Tasmania: Two Islands of Almost the Same Size
The most revealing comparison is with Tasmania, whose main island of Tasmania covers about 64,500 km², within 2 percent of Sri Lanka. Both lie off the tip of a much larger landmass across a shallow strait that was dry land during the last glacial period: Bass Strait for Tasmania, Palk Strait for Sri Lanka. Both have an upland core and a stark rain-shadow divide. Tasmania's west coast, facing the Roaring Forties, takes well over 2,000 mm of rain a year, while Hobart, in the east, gets only around 600 mm.
The differences are as instructive. Tasmania sits at about 40° to 43° south, its highest peak, Mount Ossa, reaches only 1,617 m, roughly 900 m lower than Pidurutalagala, and its Central Plateau was scoured by ice sheets, which left hundreds of glacial lakes. Sri Lanka's highlands were never glaciated. Tasmania's rain comes from one prevailing wind all year; Sri Lanka's comes from two monsoons blowing from opposite directions, so each side of the island takes its turn as the wet side. And about 22 million people live in Sri Lanka against roughly 575,000 in Tasmania, a gap that owes much to tropical warmth, two rice seasons and 2,000 years of tank irrigation. For the other half of the comparison, our Tasmania island guide walks through its own mountains, coasts and wilderness.