Pacific Coastal & Marine Science Center
USGS Pacific Coral Reefs Website
IKONOS Quickbird satellite image
The Territory of Guam is an organized unincorporated territory of the United States. The island itself is 30 miles (48 km) long and 4 mi (6 km) to 12 mi (19 km) wide. It is the southernmost island in the Marianas island chain and is the largest island in Micronesia. Unlike many of the northern Marianas islands, Guam is not volcanically active. 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.
Human activity has significantly increased the rate of sedimentation along many areas of Guam’s coastline. These human activities are related primarily to land-management practices, including urban development, unregulated use of off-road vehicles, and illegal wildfires. The wildfires, which are intentionally set by hunters to clear lines of sight and draw in new game, remove the grasses and small trees that stabilize the soil. Typhoons strike Guam frequently, commonly dropping more than 30 cm of rain in 24 hours and flushing the unstabilized soil down to the coast and into the nearshore waters.
The USGS is working with the National Park Service on the west coast of the island to help determine the effects of sedimentation in the nearshore waters, including those of War-in-the-Pacific National Historical Park. This is especially significant because the wet season (July to December), during which time large amounts of unstabilized soil wash down to the ocean, coincides with peak coral spawning and larvae settlement. Click on the links below to learn more about these efforts.