Pohnpei, lying at 6°57′ N, 158°14′ E, is an exposed tip of a submerged volcanic mountain. A protective barrier reef surrounds Pohnpei and creates a lagoon of varying width that covers an area of roughly 207 square kilometers. A total of forty small islands of volcanic and coral origin rest on or within the reef. The landmass of Pohnpei proper is 336.7 square kilometers. The interior is covered by dense rain forests and rugged mountains, the highest of which is 778 meters, running west and northwest. A coastal plain, marked by ridges and various rivers and streams, is found to the south and east. This plain gradually gives way to mangrove swamps that hide the shoreline. To the north is a wide valley that runs toward the interior. Pohnpei is visited by heavy northeast trade winds between January and March. The island is subject to heavy rainfall throughout the remainder of the year. Precipitation along the coast averages 482 centimeters a year; the interior receives considerably more. The low-lying clouds that sit atop the mountains after a heavy rain create a majestic sight that has impressed many a visitor.