Geology of War in the Pacific National Historical Park, Guam

Geodiversity is the full range of a park's geologic resources — rocks, minerals, sediments, fossils, landforms and the processes that shape them — together with its soils. The National Park Service's Geodiversity Atlas, produced by the Geologic Resources Inventory, collects that information for education, geoconservation and the joint management of each park's living and non-living resources.

The park

• War in the Pacific National Historical Park is on Guam, an unincorporated U.S. territory in the western Pacific.
• Established on August 18, 1978, it covers about 822 hectares (2,031 acres) in seven units, from the summit of Mount Tenjo to submerged war relics on offshore coral reefs.
• It honors all who served in the Pacific Theater of World War II. Guam held a strategic position, and its 1944 liberation by American forces was a major struggle. The park preserves landing beaches, pillboxes, caves, foxholes, gun emplacements and historic structures from those battles.

Geologic setting

Guam's geology is the stage for those World War II stories. The park's rocks are young, Cenozoic volcanic and sedimentary rocks, from the Eocene–Oligocene to the present:

• The Alutom and Umatac volcanic rocks record Guam's early life as part of a still-active island arc; Guam's own volcanoes are quiet now, and activity has shifted to the Northern Mariana Islands.
• The Alifan and Mariana limestones began forming before the island rose from the sea and now cap Guam's highest peaks — evidence of long uplift as the Pacific and Mariana plates converge.
• The limestones support unique limestone forests and hold classic karst features: caves, pinnacles and blind valleys.

A swimmer over a reef. Image from the National Park Service's page.

Maps and reports

Part of the Geologic Resources Inventory map of War in the Pacific. Image from the National Park Service's page.

The Geologic Resources Inventory produces digital geologic maps and reports for more than 270 natural resource parks. Each park's report — covering its geologic history, setting, and features and processes — is a useful summary for college or AP geology and earth science students and teachers. All are available through the NPS DataStore.

Sources

Based on "NPS Geodiversity Atlas—War in the Pacific National Historical Park, Guam," National Park Service; a work of the United States government in the public domain.