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Commonwealth of the Northern Mariana Islands


Land area: 549 km2
EEZ area: 218,000 km2
Political status: Organized, unincorporated territory of the United States
Population: 166,090 (July 2004, USGS), 175,877 (Jan 2008, rep)
GDP: $2.5 billion, GDPper capita: $28,860 (2007)
Ethnicity: Chamorro 37.1%, Filipino 26.3%, other Pacific islander 11.3%, white 6.9%, other Asian 6.3%, other ethnic origin or race 2.3%, mixed 9.8% (2000 census)
Economy: Tourism and Military spending
Max elevation above sea level: 406 m (SOPAC)
Island minerals: Aggregate, limestone

Island History

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.

Geologic Setting

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.

Regional Representative

Dr. Jason Biggs, PacIOOS Guam Representative
Marine Laboratory
University of Guam
Mangilao GU 96923 USA
Tel: 671.735.2175
Fax: 671.735.6767

Jason Biggs joined PacIOOS as the Guam representative in March 2008.  Jason’s commitment to the people of Guam has engendered a deeply rooted desire to do everything he can to ensure the welfare of Guam’s coastal resources.  After completing his Ph.D. in Pharmacology & Toxicology and postdoctoral research in the Biochemistry of Conus venoms, Jason returned to Guam in 2008 as the first Chamorro faculty member to join the University of Guam Marine Laboratory.  He is beginning to start a research laboratory focusing on the biochemical ecology of marine venomous molluscs, but also shares his wife’s (Laura’s) passion of providing the next generation of students with opportunities in scientific careers by creating outreach programs designed to instill awareness of, and vested interests with marine environments throughout the Pacific.

The University of Guam Marine Laboratory was established in 1970 for the purposes of serving Micronesia (Guam, CNMI, FSM, Belau, and Marshall Is.) with a research group focused entirely towards providing expertise in research, conservation, management, and education of coastal marine resources.


PacIOOS regional representatives (personal communication)
SOPAC website (www.sopac.org)
USGS Circular 1286 (http://pubs.usgs.gov/circ/2005/1286)



Please consider acknowledging PacIOOS in any distribution or publication of data as follows: Data provided by PacIOOS (www.pacioos.org), which is a part of the U.S. Integrated Ocean Observing System (IOOS®), funded in part by National Oceanic and Atmospheric Administration (NOAA) Award #NA11NOS0120039.