Because of the low elevation, the islands that make up this nation are vulnerable to the effects of tropical cyclones and by the threat of current and future sea level rise. The highest elevation is 4.6 metres (15 ft) above sea level on Niulakita, which gives Tuvalu the second-lowest maximum elevation of any country (after the Maldives). The highest elevations are typically in narrow storm dunes on the ocean side of the islands which are prone to overtopping in tropical cyclones, as occurred with Cyclone Bebe, which was a very early-season storm that passed through the Tuvaluan atolls in October 1972. Cyclone Bebe submerged Funafuti, eliminating 90% of structures on the island. Sources of drinking water were contaminated as a result of the system's storm surge and the flooding of the sources of fresh water.