Geology of Puerto Rico

Shaded relief image of Puerto Rico

Image of Puerto Rico taken by NASA.

Puerto Rico is composed of Jurassic to Eocene volcanic and plutonic rocks, which are overlain by younger Oligocene to recent carbonates and other sedimentary rocks. Most of the caverns and karst topography on the island occurs in the northern Oligocene to recent carbonates. The oldest rocks are approximately 190 million years old (Jurassic) and are located at Sierra Bermeja in the southwest part of the island. These rocks may represent part of the oceanic crust and are believed to come from the Pacific Ocean realm.

Puerto Rico lies at the boundary between the Caribbean and North American plates. This means that it is currently being deformed by the tectonic stresses caused by the interaction of these plates. These stresses may cause earthquakes and tsunamis. These seismic events, along with landslides, represent some of the most dangerous geologic hazards in the island and in the northeastern Caribbean. The most recent major earthquake occurred on October 11, 1918 and had an estimated magnitude of 7.5 on the Richter scale. It originated off the coast of Aguadilla and was accompanied by a tsunami.

Lying about 110 miles (120 km) north of Puerto Rico in the Atlantic Ocean at the boundary between the Caribbean and North American plates is the Puerto Rico Trench, the largest and deepest trench in the Atlantic. The trench is 1,090 miles (1,754 km) long and about 60 miles (97 km) wide. At its deepest point (named Milwaukee Depth), it is 27,493 feet (8,380 m) deep. At this trench the North American plate is being subducted by the Caribbean plate. This subduction zone is responsible for the volcanism of the West Indies to the southeast of Puerto Rico. A major transform fault extends from the Puerto Rico trench along the northern coast of Puerto Rico and on through the Cayman Trough to the coast of Central America. Approximately 50 miles ESE of Fajardo, Puerto Rico, past the island of Vieques and approximately 20 miles south of Saint Thomas in the US Virgin Islands, can be found the Virgin Islands Trough, which in places exceeds 14,000 feet in depth.

Geology of the United States by political division

States	Alabama Alaska Arizona Arkansas California Colorado Connecticut Delaware Florida Georgia Hawaii Idaho Illinois Indiana Iowa Kansas Kentucky Louisiana Maine Maryland Massachusetts Michigan Minnesota Mississippi Missouri Montana Nebraska Nevada New Hampshire New Jersey New Mexico New York North Carolina North Dakota Ohio Oklahoma Oregon Pennsylvania Rhode Island South Carolina South Dakota Tennessee Texas Utah Vermont Virginia Washington West Virginia Wisconsin Wyoming

Federal district	Washington, D.C.

Insular areas	American Samoa Guam Northern Mariana Islands Puerto Rico U.S. Virgin Islands

Geology of North America

Sovereign states	Antigua and Barbuda Bahamas Barbados Belize Canada Costa Rica Cuba Dominica Dominican Republic El Salvador Grenada Guatemala Haiti Honduras Jamaica Mexico Nicaragua Panama Saint Kitts and Nevis Saint Lucia Saint Vincent and the Grenadines Trinidad and Tobago United States

Dependencies and other territories	Anguilla Aruba Bermuda Bonaire British Virgin Islands Cayman Islands Curaçao Greenland Guadeloupe Martinique Montserrat Puerto Rico Saint Barthélemy Saint Martin Saint Pierre and Miquelon Saba Sint Eustatius Sint Maarten Turks and Caicos Islands United States Virgin Islands

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Geology of Puerto Rico

See also