The island is characterized by its gentle relief in the northern half of the island and a mountain range in the southern half composed of several phonolitic peaks with altitudes between where there is a patch of primary rainforest. The difference in geomorphology and terrain between the two sides, results in differentiated bioclimatology, has influence in the distribution of major types of ecosystems of the island, such as lotic (river) systems in the area of the massif and its valleys and lentic (lake) systems in the northern plains area.