Northern Guam geospatial information server

Coastal geomorphology in northern Guam

The coastal zone of northern Guam exhibits three distinct morphologies.

Sheer cliffs dominate much of the coast. They reach up to 180 m in height and are fronted with narrow to no coastal benches and narrow-to-absent fringing reefs. The cliffs occupy almost the entire east coast of northern Guam from Pago Bay to Tagua Point in the north, and long stretches of the west coast, notably from Hilaan Point to Uruno Point, accounting altogether for 68% of the total coastline.

Retreated cliffs are the second fundamental type of coastal morphology. In places, cliffs have retreated up to 300 m inland and run parallel to the coast. Such cliffs are fronted by long linear beaches behind fringing reefs. This type of coastline is found between Uruno Point and Mergagan Point, in the long linear beaches of Falcona, Uruno, Ritidian, and Jinapsan, and accounts for 12% of the total coastline.

Embayments are the third type of coastline and form in places where sheer cliffs arch back inland. The arching cliffs define broad embayments with adjacent crescent-shaped beaches or deeply-enscalloped embayments enclosing isolated beaches and well-developed fringing reefs. Broad embayments are found in Tanguisson and Tarague, and occupy 11% of the total coastline. The deep embayments of Hågatña, Tumon, and Haputo bays occupy another 9%. The Sasajyan embayment on the east coast of northern Guam is a deep embayment similar to Tumon in size and shape, but is elevated several meters above the modern sea level, and its coastal edge is delineated by a low cliff line without beach deposits.

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