geography-guam mapGUAM (Chamorro: Guahan), officially the Territory of Guam, is an island in the Western Pacific Ocean and is an organized unincorporated territory of the United States. The Chamorros, Guam's indigenous inhabitants, first populated the island approximately 6,000 years ago. It is the largest and southernmost of the Mariana Islands. The island's capital is Hagatna, formerly Agana. Guam's economy is mainly supported by tourism (particularly from Japan, Korea and Taiwan) and United States armed forces bases.

Guam is located at 13.5°N 144.5°E and has an area of 210 square miles. It is the southernmost island in the Mariana Island chain and is the largest island in Micronesia. The island of Guam is 30 miles long and 4 miles to 12 miles wide. This island chain was created by the colliding Pacific and Philippine tectonic plates. The Marianas Trench lies beside the island chain to the east. Challenger Deep, the deepest point on Earth, is southwest of Guam at 35,797 feet. The highest point in Guam is Mount Lamlam, which is 1,332 feet. The island of Guam is 30 miles long and 4 miles to 12 miles wide. The island experiences occasional earthquakes due to it being on the western edge of the Pacific Plate and near the Philippine plate. In recent years, earthquakes with epicenters near Guam have had magnitudes ranging from 5.0 to 8.7. Unlike the Anatahan volcano in the northern Marianas, Guam is not volcanically active. However, due to wind direction and proximity to Anatahan, volcanic ash activity does occasionally affect Guam.

The northern part of the island is a forested coralline limestone plateau while the south contains volcanic peaks covered in forest and grassland. A coral reef surrounds most of the island, except in areas where bays exist that provide access to small rivers and streams that run down from the hills into the Pacific Ocean and Philippine Sea. The island's population is most dense in the northern and central regions.