A couple making a trek over the lava of volcano Piton de la Fournaise. Reunion Island is formed by two volcanoes stratum mainly basaltic composition, juxtaposed on the ocean floor and partially emerged: the Piton des Neiges northwest, oldest and extinct 20,000 years ago, culminating at 3070 m. The Piton de la Fournaise is an active volcano that formed on the southeast side of the first and reaches 2631m altitude. The total volume emerged island km3 represents 0.8 x103 to be 1/32 of the total volume of the overall structure. Taking into account the hidden volume in the monoclinal fold of the plate, the part above represents only one hundredth of the total volume. The first eruptive events on the ocean floor at 4000 m depth are estimated occurred 4-5 my ago, the Piton des Neiges has now reached about 7000 m in height from the bottom of the ocean.