Reunion, an island among islands
Even today, despite the omnipresence of the media, many French people still mistakenly place Réunion in the Caribbean. And with good reason: you have to zoom, zoom and zoom again to see the island appear on a globe, in the south-western Indian Ocean, 200 km north of the Tropic of Capricorn and some 9,000 km south of mainland France. Roughly oval in shape, the island is around 70 km long and 50 km wide, with a circumference of 217 km and a surface area of 2,512 km², far behind New Caledonia (around 18,000 km²) and Corsica (8,680 km²), but ahead of Guadeloupe (1,800 km²) and Martinique (1,128 km²). Although it's a long way from the motherland, it is geographically, historically and culturally close to many other Indian Ocean islands: to the west, Madagascar is 680 km away and the African coast 1,700 km; to the north, the Seychelles are 1,800 km away and India 4,000 km; to the east, its closest neighbor is Mauritius at 180 km, followed by Rodrigues at 800 km. Beyond, there's no land on the horizon for 6,000 km, all the way to Australia; while 3,000 km to the south, a few little-known French possessions, the Terres australes et antarctiques françaises (TAAF) (French Southern and Antarctic Lands), loom large: the Crozet, Kerguelen and Amsterdam islands. Inhabited only by a handful of scientists, their administrative headquarters are on Reunion Island.
The youngest and most mountainous of the Mascarene Islands
Since the passage of Portuguese sailors in the 16th century, Réunion, along with its eastern neighbors Mauritius and Rodrigues, has formed the Mascarene archipelago. The three islands are the "last islands" in a series of reliefs formed by a single hot spot, currently located beneath Réunion, which shaped them one after the other. By way of comparison, Rodrigues, the oldest and therefore the flattest, is also the smallest. Its highest point is 398 m, and its 110 km² are home to 38,000 inhabitants. Mauritius is the next most populous, with around 1.2 million inhabitants. Its highest peak is 828 m above sea level and its surface area is 1,865 km². Finally, Réunion is the largest, the youngest and, above all, the most mountainous, with the 3,070 m-high Piton des Neiges. It is not, however, the most populous, with around 913,000 inhabitants in 2023. Nevertheless, Réunion is the most populous overseas territory, far ahead of Guadeloupe, which will be in second place with almost 376,000 inhabitants in 2023 (Insee figures).
An island shaped by lava
Réunion is a tropical, mountainous and volcanic island. Its relief is surprising, daring and phenomenally diverse: emerging from the ocean three million years ago, compared with five million years ago for Mauritius, the youngest of the Mascarene Islands has been very little smoothed, polished and softened by erosion. Roughly cut, the island was born from the projection of magma from its two volcanoes: first the Piton des Neiges, dormant for 12,000 years, then the Piton de la Fournaise, which emerged 500,000 years ago and is now one of the world's most active volcanoes. While arid expanses of dried lava carpet the slopes of La Fournaise, where only sparse vegetation grows, nature is exuberant on the rest of the island. In a few million years' time, Réunion will probably resemble Mauritius, flat and surrounded by lagoons. For the time being, only a few kilometers of coral reef have formed, sheltering superb lagoons and beautiful beaches in the west and south, while 90% of the coastline is made up of pebbles or cliffs jagged by the powerful swell of the Indian Ocean. In a few million years, we'll have even more beautiful beaches and lower mountains. Until, one day, the Garden of Eden will vanish as it came, disappearing once again to the bottom of the ocean.
The sudden formation of circuses
Réunion Island is dominated by two peaks, the Piton des Neiges (3,070 m) and the Piton de la Fournaise (2,632 m). If the cone were perfect, the island's summit would be over 5,000 m high. But a million years ago, the magma chambers of the Piton des Neiges collapsed, forming three gigantic basins: the sumptuous cirques of Cilaos, Mafate and Salazie. Forming a cloverleaf 20 km wide and 1,500 m deep on average, these monumental crevasses with their gorges and pitons are enclosed by steep ramparts almost 1 km high, protecting a world isolated from the hustle and bustle of the coast, out of time and space. They form the heart of the national park and are listed as a World Heritage Site. The bottoms of the cirques, with their chaotic, sharp and very vertical relief, vary in altitude from 500 m to 1,500 m. Carved out by thousands of years of rainfall, the cirques are cut by ribs in which gullies and waterfalls pierce the basalt rock. In each of the three cirques, a single river concentrates the flow of water: the Rivière du Mât for Salazie, the Bras de Cilaos for Cilaos, and the Rivière des Galets for Mafate, each winding through monumental gorges. Below these three rivers, coastal plains have formed from alluvial deposits: those of Saint-Louis, Le Port and Saint-André. Comparable to a mountain torrent in (austral) winter, the Rivière des Galets can, for example, reach the flow rate of the Rhône during cyclonic periods! In fact, it has long threatened the town of Le Port, necessitating huge dyking works to secure its flow.
An island in pieces
Apart from the cirques, the outside of the island slopes steadily down from the crest to the coast, at a gradient of 8% to 9%. Landscapes and microclimates vary as you approach sea level, which has facilitated the vertical colonization of the island, planting different species according to the climate that is most favorable to them. The best example is sugar cane, which occupies all the mid-slopes, and geranium in the cooler Hauts. Urbanization also follows a curve parallel to altitude: the lower slopes are very densely populated, with most of the towns concentrated there, while the mid-slopes are moderately populated, although still expanding, while in the highlands the inhabitants are becoming rarer. The gentle landscape is nevertheless marred by deep ravines, which for a long time constituted impassable natural barriers. Thousands of often impressive bridges had to be built (keep your eyes on the road), as well as an infinite number of riffles and fords.
The main ecosystems of the island
The ocean environment: off the island, above the abyssal depths of the ocean (4,000 m), this is the domain of large predators and marine mammals. Marlins, swordfish, sailfish, bream, trevally and sharks all thrive here, giving fishermen a field day. Whales are present from July to October, while dolphins and turtles play around Reunion's coasts all year round.
The lagoon environment: small in size, the lagoon is rich but fragile. Formed over millions of years by the accumulation of the skeleton of a small animal, the polyp, the coral forms an offshore barrier, protecting a calm lagoon at 27°C where life is exuberant. A number of stunning dive sites rival the world's most famous coral reefs. Multicolored tropical fish inhabit the lagoon floor and are plentiful near the passes and along the drop-off.
Coastal regions: with temperatures varying between 23°C and 35°C throughout the year, two very distinct ecosystems are formed, depending on whether you're on the leeward (west) or windward (east) coast. In the dry west, sheltered from the mountains, the beach is covered with filaos trees, which are much more common than coconut palms. To the south, the rocky coasts are dominated by vacoas. Slightly uphill, human activities are mainly devoted to sugarcane cultivation and tropical fruit orchards (mangoes, bananas, papayas...).
Mid-altitude regions: above this altitude, forests are more numerous and crops are sparser and smaller. The forests are adorned with colored woods, tamarinds, cryptomerias and palm trees, followed by tree ferns in various shades of green, against a background of mosses that are sometimes dense and spongy. This is also the region of fragrant plants: geranium and vetiver are grown here and then distilled. Here too, depending on exposure to the trade winds and altitude, the forest is more or less dense. In the high plains, cows are raised; in the cirques, peaches, pears and vines grow.
The high mountains: as you climb, the vegetation becomes sparser. From 2,000 m upwards, forests give way to mountain grasslands, with a few ferns, gorse and heather. Higher up, the world becomes downright mineral, with bare rock... and no snow-covered fir trees on the horizon.
Volcanic lands: the volcano's territory is mainly framed by the ramparts of the Fouqué enclosure, which delimits the area, some one hundred square kilometers in size, where the lava flows. It takes several decades before vegetation begins to conquer the dried-out lava flows. At first, lichens grow on the young lava, gradually building up humus reserves that will be the breeding ground for a future forest. Water, soil and vegetation form an imprecise mixture at first, but the process is the same everywhere, depending on rainfall. On the Sainte-Rose side, the volcano is particularly watered, while on the Plaine-des-Sables side, a desert landscape dominates.
