Tuvalu consists of nine separate islands: six atolls and three reef islands. An atoll typically consists of several islets: Tuvalu has a total of 124 islands and islets. Each island is surrounded by a coral reef. Tuvalu's small, widely scattered atolls have poor soil and a total land area of only about 26 square kilometres (10 square miles) making Tuvalu the fourth-smallest country in the world. The sea level at the Funafuti tide gauge has been rising at a rate of 3.9 mm per year, and it has been determined that rising sea levels are causing more wave energy to be transferred across reef surfaces, which has tended to push more sand onto island shorelines, increasing islands’ land area. Over a recent four-decade period, there was a net increase in the land area of the islets of 2.9% (73.5 h