The island is 63 kilometres (39 miles) long; 45 kilometres (28 miles) wide; and covers 2512 square kilometres (970 square miles). It is similar to the island Hawaii insofar as both are located above hotspots in the Earth's crust.
The Piton de la Fournaise, a shield volcano on the eastern end of Réunion Island, rises more than 2631 metres (8632 ft) above sea level and is sometimes called a sister to Hawaiian volcanoes because of the similarity of climate and volcanic nature. It has erupted more than 100 times since 1640 and is under constant monitoring. It most recently erupted on 4 April 2007. The lava flow from this eruption has been estimated at 3 million m3 (about 4 million cubic yards) per day. The Piton de la Fournaise is created by a hotspot volcano, which also created the Piton des Neiges and the islands of Mauritius and Rodrigues.
The Piton des Neiges volcano, the highest point on the island at 3070 metres (10,069 ft) above sea level, is north west of the Piton de la Fournaise. Collapsed calderas and canyons are south west of the mountain. Like Kohala on the Big Island of Hawaii, the Piton des Neiges is extinct. Despite its name, snow (French: neige) practically never falls on the summit.
The slopes of both volcanoes are heavily forested. Cultivated land and cities like the capital city of Saint-Denis are concentrated on the surrounding coastal lowlands.
Réunion also has three calderas: the Cirque de Salazie, the Cirque de Cilaos and the Cirque de Mafate. The last is accessible only by foot or helicopter.