REUNION, known also by its former name BOURBON, an island and French colony in the Indian Ocean, 400 m. S.E. of Tamatave, Madagascar, and 13o S.W. of Port Louis, Mauritius. It is elliptic in form and has an area of 97o sq.m. It lies between 2o° and and 22' S. and 55° 15' and 54' E.
The coast-line is little indented, high and difficult of access and the harbours are usually sunken craters. The narrow coast-lands I to 3 km. wide are succeeded by hilly ground which gives place to mountain masses and tableland, which occupy the greater part of the island. The main axis runs N.W. and S.E., and divides the island into a windward (E.) district and a leeward (W.) dis trict, the dividing line being practically that of the watershed. The whole relief is very complex owing to vulcanicity. First was formed a mountain whose summit is approximately represented by Piton des Neiges (10,069 ft.), an immense denuded crater, and at a later date another crater opened towards the E., piling up the mountain mass of Le Volcan. The oldest erupted rocks belong to the type of the andesites ; the newest are varieties of basalt. The two massifs are united by high tablelands. In the older massif the most striking features are now three areas of sub sidence—the cirques of Salazie, Riviere des Galets and Cilaos which lie N.W. and S. of the Piton des Neiges. The first, which may be taken as typical, is. surrounded by high almost perpendicu lar walls of basaltic lava. Towards the S. lies the vast stratum of rocks which, on November 26, 1875, suddenly sweeping down from the Piton des Neiges and the Gros Morne, buried the little village of Grand Sable.
The second massif, Le Volcan, is cut off from the rest of the island by two "enclosures," each about Soo or 600 ft. deep. The outer enclosure runs across the island in a north and south direc tion; the inner forms a kind of parabola with its arms stretching E. to the sea and embracing not only the volcano proper but also the great eastward slope known as the Grand Brille. The 3o m. of mountain wall round the volcano is perhaps unique in its astonish ing regularity. It encloses an area of about 4o sq.m. known as
the Grand Enclos. There are two principal craters, each on an elevated cone,—the more westerly, now extinct, known as the Bory Crater (8,612 ft.), after Bory de St. Vincent, the geologist, and the more easterly called the Burning Crater or Fournaise (8,294 ft.). The latter is partially surrounded by an "enclosure" on a small scale with precipices 200 ft. high. Eruptions, though not infrequent (thirty were registered between 1735 and 186o), are seldom serious; the more noteworthy are those of 1745, 1778, 1791, 1812, 186o, 1870, 1881. After 4o years of inactivity Four naise was in eruption for four months from Dec. 1925 to April 1926. Hot mineral springs are found on the flanks of the Piton des Neiges: the Source de Salazie, 2,86o ft. above sea-level, has a temperature of 90° F, and discharges water impregnated with bicarbonate of soda, carbonates of magnesium, lime, iron, etc.; that of Cilaos is 3,65o ft. above the sea with a temperature of 100° ; and that of Mafate 2,238 ft. and 87°.