Only five percent of the islands' land area is arable land; permanent crops cover another 20%. Deforestation (only small portions of the original forests remain), largely as a result of the continued use of wood as the main fuel source, is a serious problem; as a consequence of cutting down the forests, the mountainous terrain of Futuna is particularly prone to erosion. There are no permanent settlements on Alofi because of the lack of natural fresh water resources.The two island groups lie about 260 km apart: