Three small elongated islands up to 2.3 km (1.4 miles) in length are all that remains of Maug volcano. The islands form the northern, western, and eastern rims of Maug’s largely submerged caldera. The highest point reaches 227 meters (745 feet) above sea level and the caldera has an average submarine depth of about 200 meters (656 feet). The natural harbor contains a twin-peaked central lava dome that rises up from the seafloor to within a few fathoms of the surface. This perfect natural harbour often shelters dolphins near the southern entrance. The truncated inner walls of the caldera on all three islands show expose lava flows and pyroclastic deposits that are cut by radial dikes. East Island has been used to grow coconut palms and the interior is vegetated providing nesting sites for several bird species. In fact, eleven seabirds, two shore birds and three land birds (the Marianas Megapode, Micronesian Starling and White-collared Kingfisher) are known to be found on Maug.