- PacIOOS data and tools
- NOAA Pacific Islands Fisheries Science Center (PIFSC)
- NOAA Coral Reef Ecosystem Program (CREP)
- Total population: 161,785 (2015 est.)
- Hagatna (Capital): 143,000 (2014)
- Chamorro: 37.3%
- Filipino: 26.3%
- Mixed: 9.4%
- Caucasian: 7.1%
- Chuukese: 7%
- Korean: 2.2%
- Other Pacific Islander: 2%
- Chinese: 1.6%
- Palauan: 1.6%
- Japanese: 1.5%
- Pohneian: 1.4%
- Other Asian: 2%
- Other: 0.6%
- GDP per capita: $30,500 (2013 est.)
- Land area: 549 km2
- EEZ area: 218,000 km2
- Political status: Organized, unincorporated territory of the United States
- Economy: Tourism and military spending
- Max elevation above sea level: 406 m
- Island minerals: Aggregate, limestone
The Chamorro people first occupied Guam and may have migrated there from the Malay Archipelago. In 1521, Ferdinand Magellan was the first Westerner to visit Guam. Miguel Lopez Legaspi claimed Guam and several Mariana Islands for Spain in 1565; colonization began a few years later but was not well established until 1688. Most of the native Chamorro population died from disease and war during the following three centuries. U.S. forces took Guam in 1898 during the Spanish-American War, and it was ceded to the United States by Spain that year. Guam was under administration by the U.S. Navy until 1941, when it was captured by the Japanese. It was retaken by the United States three years later, and the U.S. Navy then renewed administration of the island.
The Guam Organic Act of 1950 conferred U.S. citizenship on the people of Guam and established local self government. At that time, the Department of the Interior took over administrative responsibility for Guam. Military installations on Guam are some of the most strategically important in the Pacific region. As the westernmost U.S. Territory, Guam is west of the International Date Line, and is one day ahead of the United States. Hence the slogan: “Where America’s Day Begins.”
Guam is the largest island in Micronesia and is the southernmost of the Mariana Islands. The northern half of Guam is composed of a relatively flat coralline limestone plateau about 260 m above sea level, whereas the southern part is mountainous volcanic terrain with elevations up to 406 m (Mount Lamlam). Guam is largely surrounded by a fringing reef, but at the southern tip of Guam, a barrier reef and Cocos Island enclose Cocos Lagoon. Apra Harbor, located along the west-central coast, is a large lagoon bounded by Cabras Island on the north and the Orote Peninsula on the south.
Guam is in the southernmost part of the volcanic arc that includes the Mariana Islands and many associated seamounts, several of which are volcanically active. The north-central part of the Guam EEZ is occupied by this volcanic arc. The Mariana Arc started to develop about 40 million years ago by subduction of the Pacific Ocean crust underneath the Philippine Sea crust. Volcanic activity has occurred at various places along the arc since that time. To the south and southeast of Guam is the Mariana Trench, which has its deepest expression within the Guam EEZ—in fact, this is the deepest location in the global ocean. The trench is partly filled with sediment.
East of the Mariana Trench is the sediment-covered Pacific Ocean abyssal plain with several large Cretaceous (>65 million years old) seamounts that protrude through the sediment. The underlying crust in this area is Jurassic in age (>142 million years old) and is the oldest part of the Pacific Ocean crust. West of the Guam-Mariana Arc is the mostly sediment-covered Philippine Sea floor (a back-arc basin) with numerous seamounts, ridges, and basins that are less than 20 million years old. In the part immediately west of the Mariana Arc is the Mariana Trough, an active back-arc spreading ridge. The West Mariana Ridge is a remnant (inactive) volcanic arc that separates the Mariana Trough from the Parece Vela Basin abyssal plain farther to the west, in the northwesternmost part of the Guam EEZ.