Rocas Alijos

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overview map with detail inset Rocas Alijos-map.png
overview map with detail inset
Rocas Alijos from the East (South Rock to the left) Rocas Alijos 2.jpg
Rocas Alijos from the East (South Rock to the left)
Rocas Alijos - South Rock (left) and Middle Rock Rocas Alijos 3.jpg
Rocas Alijos - South Rock (left) and Middle Rock

Rocas Alijos, or Escollos Alijos (English: Alijos Rocks) are a group of tiny, steep and barren volcanic islets or above-water (as well as below-water) rocks in the Pacific Ocean at 24°57′31″N115°44′59″W / 24.95861°N 115.74972°W / 24.95861; -115.74972 . They are part of Comondú municipality of the Mexican state of Baja California Sur, and situated about 300 km west of the mainland. The total surface area is less than 1,000 square metres. The official area figure of 0.012 square kilometres (0.0046 sq mi). [1]

Volcano A rupture in the crust of a planetary-mass object that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface

A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.

Pacific Ocean Ocean between Asia and Australia in the west, the Americas in the east and Antarctica or the Southern Ocean in the south.

The Pacific Ocean is the largest and deepest of Earth's oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean in the south and is bounded by Asia and Australia in the west and the Americas in the east.

Comondú Municipality Municipality in Baja California Sur, Mexico

Comondú is a municipality of the Mexican state of Baja California Sur. It had a population of 70,816 inhabitants in 2010 census (INEGI). With a land area of 16,858.3 km², it is the seventh-largest municipality in area in Mexico. The municipal seat is located in Ciudad Constitución.


The group consists of three principal rocks and numerous smaller ones. South Rock, the largest of the group, is 34 meters (111 ft) high, with a diameter of only 14 meters (46 ft) (position 24°57′03″N115°44′55″W / 24.95083°N 115.74861°W / 24.95083; -115.74861 ). Middle Rock is 18 meters (59 ft) high and about 10 meters (33 ft) in diameter. North Rock, 200 meters (656 ft) north of South Rock, is 22 meters (72 ft) high, with a diameter of 12 meters (39 ft). The rocks in between those are either submerged or so low that they are barely visible among the heavily breaking waves.[ citation needed ]

The rocks seem to be known since the early Spanish history of Mexico; they can be found on a map from 1598. The first description is from 1704, by pirate John Clipperton. But only in 1791 the first exact description was made by a Spanish sailor. South Rock was climbed for the first time in 1990 by an expedition (October 31 through November 7, 1990) under the leadership of Robert Schmieder, who edited a monograph about the rocks. [2]

John Clipperton was an English privateer who fought against the Spanish in the 18th century. He was involved in two buccaneering expeditions to the South Pacific—the first led by William Dampier in 1703, and the second under his own command in 1719. He used Clipperton Island in the eastern Pacific Ocean as a base for his raids.

Robert Schmieder American scientist

Robert William Schmieder is an American scientist and explorer. Schmieder has had a multidisciplinary career, broadly divided between physics and related physical sciences, and natural science and exploration. In most of his projects, he created and led teams of both professional scientists and volunteers. His work is documented in about 100 technical publications and 10 books. Among his most significant work was the invention of laser spark spectroscopy, the formulation of nanologic, and the concept of underwater islands.

A monograph is a specialist work of writing on a single subject or an aspect of a subject, often by a single author, and usually on a scholarly subject.

The group is located at the transition zone between two major biologic provinces, at a latitude where the Pacific Current turns westward to form the North Pacific trans-oceanic current.[ citation needed ] The rocks are nesting sites of many seabirds.[ citation needed ]

The two other Mexican island groups in the Pacific Ocean that are not on the continental shelf are Guadalupe Island and Revillagigedo Islands.

Continental shelf A portion of a continent that is submerged under an area of relatively shallow water known as a shelf sea

A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water known as a shelf sea. Much of the shelves were exposed during glacial periods and interglacial periods.

Guadalupe Island island

Guadalupe Island or Isla Guadalupe is a volcanic island 250 km² and located 241 kilometres (150 mi) off the west coast of Mexico's Baja California Peninsula and some 400 kilometres (250 mi) southwest of the city of Ensenada in the state of Baja California, in the Pacific Ocean. The two other Mexican island groups in the Pacific Ocean that are not on the continental shelf are Revillagigedo Islands and Rocas Alijos. Guadalupe Island and its islets are the westernmost region of Mexico.

Revillagigedo Islands island

The Revillagigedo Islands or Revillagigedo Archipelago are a group of four volcanic islands in the Pacific Ocean, known for their unique ecosystem. They lie approximately 390 kilometres (240 mi) southwest of Cabo San Lucas, the southern tip of the Baja California Peninsula, and 720 to 970 kilometres west of Manzanillo. They are located around 18°49′N112°46′W. Technically part of the Mexican state of Colima, the islands are under Mexican federal jurisdiction.


The breeding marine avifauna of Alijos Rocks currently consists of Leach's storm-petrel (a presumed breeder, probably a few pairs), red-billed tropicbird (14 birds), masked booby (100), and sooty tern (250). The magnificent frigatebird is a regular winter visitor but probably does not breed. The Laysan albatross is currently an annual visitor to Alijos Rocks during its winter breeding season, and may start to nest there in the near future.

Red-billed tropicbird Species of seabird of tropical oceans

The red-billed tropicbird is a tropicbird, one of three closely related species of seabird of tropical oceans. Superficially resembling a tern in appearance, it has mostly white plumage with some black markings on the wings and back, a black mask and, as its common name suggests, a red bill. Most adults have tail streamers that are about two times their body length, with those in males being generally longer than those in females. The red-billed tropicbird itself has three subspecies recognized, including the nominate. The subspecies mesonauta is distinguished from the nominate by the rosy tinge of its fresh plumage, and the subspecies indicus can be differentiated by its smaller size, more restricted mask, and more orange bill. This species ranges across the tropical Atlantic, eastern Pacific, and Indian Oceans. The nominate is found in the southern Atlantic Ocean, the subspecies indicus in the waters off of the Middle East and in the Indian Ocean, and the subspecies mesonauta in the eastern portions of both the Atlantic and the Pacific Oceans and in the Caribbean. It was one of the many species described by Carl Linnaeus in his 1758 10th edition of Systema Naturae.

Masked booby Species of bird

The masked booby is a large seabird of the booby family, Sulidae. First described by French naturalist René-Primevère Lesson in 1831, the masked booby is one of six species of booby in the genus Sula. This species breeds on islands in tropical oceans, except in the eastern Atlantic; in the eastern Pacific it is replaced by the Nazca booby, Sula granti, which was formerly regarded as a subspecies of masked booby. It is also called the masked gannet or the blue-faced booby.

Sooty tern species of bird

The sooty tern is a seabird in the family Laridae. It is a bird of the tropical oceans, breeding on islands throughout the equatorial zone.

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Baja California Sur State of Mexico

Baja California Sur, officially the Estado Libre y Soberano de Baja California Sur, is the second-smallest Mexican state by population and the 31st admitted state of the 31 states which, with Mexico City, make up the 32 Federal Entities of Mexico.

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  1. Archived July 11, 2007, at the Wayback Machine .
  2. Archived May 24, 2011, at the Wayback Machine .