The island was formed millions of years ago when a pair of volcanoes sank beneath the ocean leaving only their twin peaks above sea level. The lava remains of the southern volcano eventually fused with the older northern crater. This crater's limestone top had been formed underwater during a long period by an extensive coral polyp community.

Southern Guam is made up of volcanic hills, which rise to a maximum height of 1,334 feet above sea level. But, measured from its base at the bottom of the Marianas Trench, Mount Lamlam is the highest mountain in the world. Rivers cut through this terrain and high waterfalls abound The central and northern sections of the island consist of a limestone plateau as high as 600 feet with steep cliffs dropping down to a narrow coastal shelf. The towering cliffs are tunneled with caves formed by the relentless and pounding surf.

Apra Harbor is considered one of the region's finest commercial ports. It is also a favorite spot for divers and snorkelers. It is one of the few commercial ports in the world featuring a spectacular live reef with an abundant population of colorful fish and other forms of marine life.

The Port Authority of Guam, the largest harbor in the Pacific between the Philippines and Hawaii, services more than 1,000 vessels in Apra Harbor. Presently, 12 steamship lines serve the abundance of cargo shipped through Guam's port. The International Maritime Commission recognizes Guam as having one of the most efficient port operations in the world.

A majority of hotel, business, and residential centers are on the western side of the island facing the tranquil Philippine Sea. A drive along the eastern coast boasts breathtaking views of the Pacific Ocean thundering against the narrow coastal shelf.

Land Area

Guam covers an area of 212 square miles (549 square km), and is about 30 miles (48.39 km) in length with a width of 8 1/2 miles (13.71 km) at the northern tip and a maximum width in the south of 11 1/2 miles (18.55 km).

Topography

A majority of the island is surrounded by a coral table reef with deep water channels. The coastline, areas are characterized by sandy beaches, rocky, cliff lines, and mangroves. Shaped like a footprint, Guam was formed by the union of two volcanoes; a limestone plateau in the northern and southern sections of the island. The relatively flat north is home to a majority of Guam's population and businesses, while in the south, cascading waterfalls, seldom visited hiking trails, and an abundance of lush agricultural lands laid to the aura of a relaxed and laid back island lifestyle.

Location

Guam is the southernmost and largest of the islands in the Mariana archipelago, a group of 15 islands located within approximately three hours of major Asian cities. Included are selected cities and their distances from Guam Manila, Philippines, 1,597 miles 12,555 km) west Tokyo, Japan. 1,558 miles (2,493 km) south-southeast; Seoul, Korea, 1,992 miles (2,590 km) southeast; Taipei, Taiwan, 1,246 miles (2,077km) northwest; and, Hong Kong 2,026 miles (3,376 km) northwest.

Guam lies 13 degrees 38 minutes North latitude and 144 degrees 44 minutes East longitude . The island is the western most territory of the United States and 15 hours ahead of the Eastern Seaboard Time Zone. Hence, the popular slogan is often used: Guam, Where America's Day Begins.

Climate

As in most tropical islands in the western Pacific, the weather on Guam is warm throughout the year with less humidity from November through March. The mean annual temperature near sea level is about 81 F (27.2 C) with monthly means ranging from 80 F (26.7 C) in January to a little over 82 F (27.8 C) in June. Rarely does the temperature exceed 90 F (32.2 C) during the daytime hours or fall below 70 F (21.1 C) at night. The relative humidity commonly exceeds 84 percent at night throughout the year, but the average monthly humidity hovers near 66 per cent.

Guam's climate is characterized by two distinct seasons a dry season from January to May, and a rainy season from July to November: June and December are bansitional months. The mean annual rainfall varies from about 80 inches in the central and coastal lowlands up to 110 inches on the uplands in southern Guam. A wide variation in rainfall can occur from year to year. In 1952, for example, a maximum of 145.5 inches was recorded, while the minimum rainfall recorded was 60.42 inches three years later.

The easterly trade winds, usually between 4 and 12 miles per hour (mph), are dominant throughout the year. Only occasionally do winds exceed 24 mph, except during major tropical storms or typhoons small scale storms, or squalls, can occur at any time and with little notice. The likelihood of typhoons is greatest during July through September, but they can occur during any month of the year.

Air Quality

Guam's air quality is one of the cleanest in the world and generally free from Air Pollution despite the high concentration of human activity in Guam's downtown metropolitan area, favorable meteorological conditions, in particular the nearly constant, northeast trade winds, have prevented the build-up of any significant amount of pollutants.

Water Quality

The island's ground water and ocean water resources have the rare advantage of being free from the pollution discharges similar to its neighboring continental land masses. The result Guam's water quality remains consistently pure. Water quality is regularly monitored for compliance with federal and local standards.