Northern Guam geospatial information server

Beaches in northern Guam

Beaches are coastal deposits of loose sandy sediment. They are important natural habitats and some of Guam’s most beautiful scenery. In northern Guam, beach sand is almost entirely biogenic: it is composed of disintegrated calcium carbonate shells of marine organisms. Observing this speckled white-to-tan sand under magnification reveals grains that are pieces of corals and calcareous algae, mollusk shells, echinoderm fragments, etc. Sand in some areas, notably Jinapsan Beach, consists largely of star-shaped foraminiferal tests (tiny shells of single-celled organisms).

Beaches in northern Guam correspond to two distinct geomorphic types. Some are long, linear beaches that extend parallel to the cliffline (e.g., Ritidian). They are protected from waves only by narrow reefs and exhibit comparatively high-energy conditions. Others are short, somewhat crescent-shaped beaches contained within prominent bays (e.g., Tumon). They are behind wide, well-developed reefs and are consequently relatively quiet settings.

The Pacific side of northern Guam lacks sandy shore. Its steep coastal slopes and exposure to nearly constantly rough seas has not favored the development of reefs that could protect the coast and allow accumulation of beach sand.

Beaches are generally barren. Very few plants can grow in loose and salty coastal sand. Vines such as Ipomoea pes-caprae and Canavalia spp. may extend from their roots in the backshore and creep seaward to take advantage of unshaded, open space on the beach. Near the water, beach sand is locally cemented by natural processes into hard deposits known as beachrock. They are usually coated with slippery films of algae. Green algae, especially Ulva, occasionally bloom in the intertidal zone.

Text above is slightly modified from "Environments of Guam" by Danko Taborosi, David R. Burdick, Claudine M. Camacho, Frank Camacho, published by BessPress, 2013.


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