islets—which rise to a height of above sea level—share a common geologic origin, and consist of sand deposits and limestone rock set atop a coral reef. According to the path of the International Date Line, the atoll is the easternmost point of land on Earth. Three islets make up the bulk of Caroline's land area: Nake Islet () at the north, Long Islet () at the northeast of the lagoon, and South Islet () at the southern end. The other islets, most of which were named during a 1988 ecological survey conducted by the naturalists Cameron and Angela Kepler, fall into four groups: the South Nake Islets, the Central Leeward Islets, the Southern Leeward Islets, and the Windward Islets. The island is vulnerable to erosion by spring tides, storms, and strong winds; storms have caused smaller islets to sometimes appear or disappear, and the shapes of larger ones to become altered. The lagoon, roughly in size, is shallow—it is at most in depth—and is crossed repeatedly by narrow coral heads and patch reefs. Reef flats generally extend over from the shore—although some sources report them to extend more than from land—and make boat landings perilous except at high tide. There are no natural landings, anchorages, or deep water openings into the lagoon; water that spills into it over shallow channels at high tide is contained within the surrounding reef and remains stable despite ocean tides. Most landings are made at a small break in the reef at the northeast corner of South Islet. There is no standing fresh water on Caroline Island, but Nake Islet and South Islet have underground freshwater aquifers and freshwater lenses. The underground water supply on Nake attracted Polynesian settlers, but the first European explorers to reach the atoll searched in vain for drinking water; wells were built to tap drinking water for later temporary settlements. Little is known about the island's existing freshwater lenses. Soils are of poor quality, dominated by coral gravel and sand, with organic content present only within stable, forested island centers. Guano deposits make island soil, where it does exist, nitrogen-rich. Like the rest of Kiribati, Caroline Island enjoys a tropical maritime climate which is consistently hot and humid, with air temperatures that relate closely to sea temperature. Across Kiribati average temperatures vary no more than 1 °C from season to season. There is no weather station located at Caroline. During