10°30′S 105°40′E, the island is about 19 kilometres in greatest length and 14.5 km in breadth. The total land area is 135 square kilometres, with 138.9 km of coastline. The island is the flat summit of an underwater mountain more than 4,500 metres (14,800 ft) high, which rises from about 4,200 m (13,780 ft) below the sea and only about 300 m (984 ft) above it. The mountain was originally a volcano, and some basalt is exposed in places such as The Dales and Dolly Beach, but most of the surface rock is limestone accumulated from coral growth. The karst terrain supports numerous anchialine caves. The summit of this mountain peak is formed by a succession of tertiary limestones ranging from the Eocene or Oligocene up to recent reef deposits, with intercalations of volcanic rock in the older beds.
Steep cliffs along much of the coast rise abruptly to a central plateau. Elevation ranges from sea level to 361 m (1,184 ft) at Murray Hill. The island is mainly tropical rainforest, 63% of which is national park land. The narrow fringing reef surrounding the island can be a maritime hazard.
Christmas Island lies 2,600 kilometres northwest of Perth, Western Australia, 500 km (310 mi) south of Indonesia, 975 km ENE of the Cocos (Keeling) Islands, and 2,748 km west of Darwin, Northern Territory. Its closest point to the Australian mainland is 1,560 km from the town of Exmouth, Western Australia.
Christmas Island has 80 kilometres of shoreline but only small parts of the shoreline are easily accessible. The island’s perimeter is embodied by sharp cliff faces, making many of the island’s beaches difficult to get to. Some of the easily accessible beaches include Flying Fish Cove (main beach), Lily Beach, Ethel Beach, and Isabel Beach, while the more difficult beaches to access include Greta Beach, Dolly Beach, Winifred Beach, Merrial Beach, and West White Beach, which all require a vehicle with four wheel drive and a difficult walk through dense rainforest.
As Christmas Island is located toward the southern edge of the equatorial region, climate is tropical and temperatures vary little throughout the months. The highest temperature is usually around 29 °C (84 °F) in March and April, while the lowest temperature is 23 °C (73 °F) and occurs in August. There is a dry season from July to November with only occasional showers. The wet season is between November and May, and includes monsoons, which are downpours of rain at random times of the day. Tropical cyclones may also occur in the wet season, bringing very solid winds, rain and enormous seas. These tropical cyclones only happen occasionally, for most of the time during the wet season is damp, subside weather.