Geology of Puerto Rico - AbsoluteAstronomy.com

Puerto Rico , officially the Commonwealth of Puerto Rico , is an unincorporated territory of the United States, located in the northeastern Caribbean, east of the Dominican Republic and west of both the United States Virgin Islands and the British Virgin Islands.Puerto Rico comprises an...

is composed of Jurassic

Jurassic

The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...

to Eocene

Eocene

The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...

volcanic and plutonic rocks, which are overlain by younger Oligocene

Oligocene

The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...

to recent carbonates and other sedimentary rock

Sedimentary rock

Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....

s. Most of the cavern

Cave

A cave or cavern is a natural underground space large enough for a human to enter. The term applies to natural cavities some part of which is in total darkness. The word cave also includes smaller spaces like rock shelters, sea caves, and grottos.Speleology is the science of exploration and study...

s and karst

KARST

Kilometer-square Area Radio Synthesis Telescope is a Chinese telescope project to which FAST is a forerunner. KARST is a set of large spherical reflectors on karst landforms, which are bowlshaped limestone sinkholes named after the Kras region in Slovenia and Northern Italy. It will consist of...

topography on the island occurs in the northern Oligocene to recent carbonates. The oldest rocks are approximately 190 million years old (Jurassic

Jurassic

) and are located at Sierra Bermeja

Sierra Bermeja

Sierra Bermeja is a mountain range in southwestern Puerto Rico. It covers the area from the Laguna Cartegena to the north, to the Caribbean Sea to the south. From the Boqueron Forest to the west, to La Parguera to the east. It consists of a combination of volcanic rocks, completely crossed by...

in the southwest part of the island. These rocks may represent part of the oceanic crust

Oceanic crust

Oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium...

and are believed to come from the Pacific Ocean

Pacific Ocean

The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

realm.

Puerto Rico lies at the boundary between the Caribbean

Caribbean Plate

The Caribbean Plate is a mostly oceanic tectonic plate underlying Central America and the Caribbean Sea off the north coast of South America....

and North American plate

North American Plate

The North American Plate is a tectonic plate covering most of North America, Greenland, Cuba, Bahamas, and parts of Siberia, Japan and Iceland. It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust...

s. 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 tsunami

Tsunami

A tsunami is a series of water waves caused by the displacement of a large volume of a body of water, typically an ocean or a large lake...

s. These seismic events, along with landslide

Landslide

A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...

s, represent some of the most dangerous geologic hazards

Geologic hazards

A geologic hazard is one of several types of adverse geologic conditions capable of causing damage or loss of property and life. These hazards consist of sudden phenomena and slow phenomena:Sudden phenomena include:...

in the island and in the northeastern Caribbean. The most recent major earthquake

1918 Puerto Rico earthquake

The San Fermín earthquake, also known as the Puerto Rico earthquake of 1918, was a major earthquake that struck the island of Puerto Rico at 10:14am on October 11, 1918. The magnitude for the earthquake has been reported at around 7.5 ; however, that might not be an exact number...

occurred on October 11, 1918 and had an estimated magnitude of 7.5 on the Richter scale

Richter magnitude scale

The expression Richter magnitude scale refers to a number of ways to assign a single number to quantify the energy contained in an earthquake....

. It originated off the coast of Aguadilla and was accompanied by a tsunami

Tsunami

A tsunami is a series of water waves caused by the displacement of a large volume of a body of water, typically an ocean or a large lake...

.

Lying about 75 miles (120 km) east of Puerto Rico in the Atlantic Ocean

Atlantic Ocean

The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

at the boundary between the Caribbean and North American plates is the Puerto Rico Trench

Puerto Rico Trench

The Puerto Rico Trench is an oceanic trench located on the boundary between the Caribbean Sea and the Atlantic Ocean. The trench is associated with a complex transition between the subduction zone to the south along the Lesser Antilles island arc and the major transform fault zone or plate boundary...

, 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 27493 feet (8,379.9 m) deep. At this trench the North American plate is being subducted

Subduction

In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...

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

Transform fault

A transform fault or transform boundary, also known as conservative plate boundary since these faults neither create nor destroy lithosphere, is a type of fault whose relative motion is predominantly horizontal in either sinistral or dextral direction. Furthermore, transform faults end abruptly...

extends from the Puerto Rico trench along the northern coast of Puerto Rico and on through the Cayman Trough

Cayman Trough

The Cayman Trough, is a complex transform fault zone pull apart basin which contains a small spreading ridge on the floor of the western Caribbean Sea between Jamaica and the Cayman Islands...

to the coast of Central America

Central America

Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...

See also