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Pacific Golden Plover Pluvialis fulva © Ian Montgomery http://www.birdway.com.au

Guam, officially the Territory of Guam, is an island in the western Pacific Ocean and is an organized, unincorporated insular area of the United States. It is one of five U.S. territories with an established civilian government. The island's capital is Hagåtña (formerly Agana). Guam is the largest and southernmost of the Mariana Islands.

Guam lies between 13.2°N and 13.7°N and between 144.6°E and 145.0°E, and has an area of 209 square miles (541 km2), making it the 32nd largest island of the United States. It is the southernmost island in the Mariana island chain and is the largest island in Micronesia. This island chain was created by the colliding Pacific and Philippine tectonic plates. The Mariana Trench, a deep subduction zone, lies beside the island chain to the east. Challenger Deep, the deepest surveyed point in the Oceans, is southwest of Guam at 35,797 feet (10,911 m) deep. The highest point in Guam is Mount Lamlam, which is 1,332 feet (406 m). The island of Guam is 30 miles (48 km) long and 4 mi (6 km) to 12 mi (19 km) 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 Mariana Islands, Guam is not volcanically active. However, due to its proximity to Anatahan, vog 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.

The climate is characterized as tropical marine. The weather is generally hot and very humid with little seasonal temperature variation. The mean high temperature is 86 °F (30 °C) and mean low is 76 °F (24 °C) with an average annual rainfall of 96 inches (2,180 mm). The dry season runs from December through June. The remaining months constitute the rainy season. The months of January and February are considered the coolest months of the year with night time temperatures in the mid to low 70's and generally lower humidity levels. The highest risk of typhoons is during October and November. They can occur, however, year-round. An average of three tropical storms and one typhoon pass within 180 nautical miles (210 mi/330 km) of Guam each year. The most intense typhoon to pass over Guam recently was Super Typhoon Pongsona, with sustained winds of 125 miles per hour, which slammed Guam on December 8, 2002, leaving massive destruction.

Ecological issues

From the seventeenth through nineteenth centuries, the Spanish introduced pigs, dogs, chickens, the Philippine deer (Cervus mariannus), black francolins, and water buffalo. Water buffalo, known as carabao locally, have cultural significance. Herds of these animals obstruct military base operations and harm native ecosystems. After birth control and adoption efforts were ineffective, the U.S. military began cullling the herds in 2002.

Other introduced species include cane toads imported in 1937, the giant African snail (an agricultural pest introduced during WWII by Japanese occupation troops) and more recently frog species which could threaten crops in addition to providing additional food for the brown tree snake population. Reports of loud chirping frogs, known as coquí, that may have arrived from Hawaii have led to fears that the noise could threaten Guam's tourism. An infestation of the coconut rhinoceros beetle (CRB), Oryctes rhinoceros, was detected on Guam on September 12, 2007.