San Benedicto Island
Encyclopedia
San Benedicto, formerly Santo Tomás, is an uninhabited island, and third largest island of the Revillagigedo Islands
, located in the Pacific
at 19°18′16"N 110°48′52"W.
It is 4.8 km by 2.4 km in size, with an area 10 km². It is of volcanic
origin. It has two prominent peaks. The tallest peak, Bárcena, rises to a height of 332 meters (1,089 feet) near the southern part of the island. It forms a typical volcanic crater
. It is located between the remains of two older craters, Herrera in the middle of the island and the Montículo Cinerítico ("Ash Heap") in the southwest. There is no permanent source of freshwater
.
Barcena's only historic eruption began around 8:30 AM on August 1, 1952, from the El Boquerón vent. In a severe Vulcanian eruption
of magnitude 3 on the Volcanic Explosivity Index
scale, pyroclastic flow
s rolled over the island. Soon the entire island was covered in ash and pumice
up to 3 m (10 ft ) high. Ejecta
filled the valley between Herrera crater and Montículo Cinerítico, and by August 14 had formed a cone some 300 m (over 1000 ft) high. After some months with little activity, a second series of eruptions began on November 1, 1952. On December 8, the magma
broke through the cone's southeastern base and started to flow into the sea. This continued to about February 24, 1953. By March 9, 1953, most activity had subsided, except fumarole
s in the crater and at the rift in its base; the lava
was hard but still retained much heat. By late 1953, the volcano was dormant again.
and terrestrial fauna
of San Benedicto, much like it had happened on Krakatoa
in 1883. The fauna included the endemic San Benedicto Rock Wren
which became extinct around 9 AM on August 1. It is unusual for an extinction to be recorded with such precision, and in this case it was only possible because observers were offshore, documenting how the island was blasted with ejecta.
However, once the volcanic activity had died down by the spring of 1953, seabird
s returned to the island for the breeding season. They roosted only north of Herrera crater, where the ash cover had already began to erode
away. A few Gecarcinus planatus land crab
s were present also, having either managed to survive the eruption or, more probably, recolonized the island; their larva
e live in the ocean. Still, the island was devoid of plant life.
By late 1953, rain had removed the ash and pumice deposits in the steeper places of northern San Benedicto. At least half the previously-recorded plant taxa were again present. Numerous seabirds were found breeding, most north of Herrera but a colony of Blue-footed Boobies was present in the ditch between Herrera and Barcena.
fauna of San Benedicto is nowadays composed entirely of seabirds. It appears that the Revillagigedo population of Western Ravens also bred on San Benedicto before the 1952 eruption, but any such population was wiped out and ravens are not found - except maybe as very rare vagrants - on San Benedicto today.
Its position on the northeastern edge of the archipelago makes San Benedicto the north(east)ernmost location where several seabirds of the tropical Eastern Pacific come to breed. Taxa breeding on San Benedicto are:
The nearly extinct Townsend's Shearwater
(Puffinus auricularis) does not seem to breed on San Benedicto, but can sometimes be seen feeding offshore. Given that there are no invasive species
on San Benedicto and also no predators apart from the frigatebirds, the island might be highly suitable for establishing a new colony. Indeed, it bred here before the 1952 eruption; shearwaters are highly conservative in choosing their breeding locations, which explains why San Benedicto has not yet been recolonized.
Vagrants of other species, such as Brown Pelican
s, Red-tailed Hawk
s, Osprey
s, Barn Swallow
s and Bay-breasted Warbler
s may occasionally visit the island but ultimately move on or perish, finding San Benedicto still too barren to support a resident population. Migrant
wader
s, such as Hudsonian Curlews and Wandering Tattler
s, use San Benedicto for brief stopovers more regularly.
s and grass
es, with the occasional subshrub
s and vine
s. It does not appear that any went extinct due to the 1952 eruption. The local plant life contains several Revillagigedo endemics shared with Clarión: Bulbostylis nesiotica, Cyperus duripes and Perityle socorrosensis. The taxonomic status of the local Euphorbia anthonyi is not fully resolved. Other plants on San Benedicto are Aristolochia islandica, Cenchrus myosuroides, Eragrostis diversiflora, Erigeron crenatus, Ipomoea pes-caprae ssp. brasiliensis (Beach Morning Glory) and Teucrium townsendii.
and other pelagics. An area called "The Boiler" is where divers commonly interact with the rays. Divers have also spotted tiger shark
s, Galapagos shark
s, silky shark
s, and humpback whale
s here. Since there is no public airport on the island, divers visit here aboard dive vessels. The most popular months to visit are between November and May when the weather and seas are calmer.
Revillagigedo Islands
The Revillagigedo Islands or Revillagigedo Archipelago are a group of four volcanic islands in the Pacific Ocean, known for their unique ecosystem...
, located in the Pacific
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...
at 19°18′16"N 110°48′52"W.
It is 4.8 km by 2.4 km in size, with an area 10 km². It is of volcanic
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
origin. It has two prominent peaks. The tallest peak, Bárcena, rises to a height of 332 meters (1,089 feet) near the southern part of the island. It forms a typical volcanic crater
Volcanic crater
A volcanic crater is a circular depression in the ground caused by volcanic activity. It is typically a basin, circular in form within which occurs a vent from which magma erupts as gases, lava, and ejecta. A crater can be of large dimensions, and sometimes of great depth...
. It is located between the remains of two older craters, Herrera in the middle of the island and the Montículo Cinerítico ("Ash Heap") in the southwest. There is no permanent source of freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
.
1952/53 volcanic eruption
Vulcanian eruption
The term Vulcanian was first used by Giuseppe Mercalli, witnessing the 1888-1890 eruptions on the island of Vulcano. His description of the eruption style is now used all over the world for eruptions characterised by a dense cloud of ash-laden gas exploding from the crater and rising high above the...
of magnitude 3 on the Volcanic Explosivity Index
Volcanic Explosivity Index
The Volcanic Explosivity Index was devised by Chris Newhall of the U.S. Geological Survey and Stephen Self at the University of Hawaii in 1982 to provide a relative measure of the explosiveness of volcanic eruptions....
scale, pyroclastic flow
Pyroclastic flow
A pyroclastic flow is a fast-moving current of superheated gas and rock , which reaches speeds moving away from a volcano of up to 700 km/h . The flows normally hug the ground and travel downhill, or spread laterally under gravity...
s rolled over the island. Soon the entire island was covered in ash and pumice
Pumice
Pumice is a textural term for a volcanic rock that is a solidified frothy lava typically created when super-heated, highly pressurized rock is violently ejected from a volcano. It can be formed when lava and water are mixed. This unusual formation is due to the simultaneous actions of rapid...
up to 3 m (10 ft ) high. Ejecta
Ejecta
Ejecta can mean:*In volcanology, particles that came out of a volcanic vent, traveled through the air or under water, and fell back on the ground surface or on the ocean floor...
filled the valley between Herrera crater and Montículo Cinerítico, and by August 14 had formed a cone some 300 m (over 1000 ft) high. After some months with little activity, a second series of eruptions began on November 1, 1952. On December 8, the magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
broke through the cone's southeastern base and started to flow into the sea. This continued to about February 24, 1953. By March 9, 1953, most activity had subsided, except fumarole
Fumarole
A fumarole is an opening in a planet's crust, often in the neighborhood of volcanoes, which emits steam and gases such as carbon dioxide, sulfur dioxide, hydrochloric acid, and hydrogen sulfide. The steam is created when superheated water turns to steam as its pressure drops when it emerges from...
s in the crater and at the rift in its base; the lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...
was hard but still retained much heat. By late 1953, the volcano was dormant again.
Ecology
The eruption wiped out - at least temporarily - all floraFlora
Flora is the plant life occurring in a particular region or time, generally the naturally occurring or indigenous—native plant life. The corresponding term for animals is fauna.-Etymology:...
and terrestrial fauna
Fauna
Fauna or faunæ is all of the animal life of any particular region or time. The corresponding term for plants is flora.Zoologists and paleontologists use fauna to refer to a typical collection of animals found in a specific time or place, e.g. the "Sonoran Desert fauna" or the "Burgess shale fauna"...
of San Benedicto, much like it had happened on Krakatoa
Krakatoa
Krakatoa is a volcanic island made of a'a lava in the Sunda Strait between the islands of Java and Sumatra in Indonesia. The name is used for the island group, the main island , and the volcano as a whole. The island exploded in 1883, killing approximately 40,000 people, although some estimates...
in 1883. The fauna included the endemic San Benedicto Rock Wren
San Benedicto Rock Wren
The San Benedicto Rock Wren is a small extinct passerine which was endemic to San Benedicto Island in the Revillagigedo Islands off Mexico. It was a subspecies of the Rock Wren.-Extinction:...
which became extinct around 9 AM on August 1. It is unusual for an extinction to be recorded with such precision, and in this case it was only possible because observers were offshore, documenting how the island was blasted with ejecta.
However, once the volcanic activity had died down by the spring of 1953, seabird
Seabird
Seabirds are birds that have adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations...
s returned to the island for the breeding season. They roosted only north of Herrera crater, where the ash cover had already began to erode
Erode
Erode is a city, a municipal corporation and the headquarters of Erode district in the South Indian state of Tamil Nadu.It is situated at the center of the South Indian Peninsula, about southwest from the state capital Chennai and on the banks of the rivers Cauvery and Bhavani, between 11° 19.5"...
away. A few Gecarcinus planatus land crab
Land crab
Gecarcinidae is a family of true crabs that are adapted for terrestrial existence, commonly known as land crabs. Similar to all other crabs, land crabs possess a series of gills. In addition, the part of the carapace covering the gills is inflated and equipped with blood vessels. These organs...
s were present also, having either managed to survive the eruption or, more probably, recolonized the island; their larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e live in the ocean. Still, the island was devoid of plant life.
By late 1953, rain had removed the ash and pumice deposits in the steeper places of northern San Benedicto. At least half the previously-recorded plant taxa were again present. Numerous seabirds were found breeding, most north of Herrera but a colony of Blue-footed Boobies was present in the ditch between Herrera and Barcena.
Fauna
The vertebrateVertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
fauna of San Benedicto is nowadays composed entirely of seabirds. It appears that the Revillagigedo population of Western Ravens also bred on San Benedicto before the 1952 eruption, but any such population was wiped out and ravens are not found - except maybe as very rare vagrants - on San Benedicto today.
Its position on the northeastern edge of the archipelago makes San Benedicto the north(east)ernmost location where several seabirds of the tropical Eastern Pacific come to breed. Taxa breeding on San Benedicto are:
- Wedge-tailed ShearwaterWedge-tailed ShearwaterThe Wedge-tailed Shearwater, Puffinus pacificus is a medium-large shearwater in the seabird family Procellariidae. It is one of the shearwater species that is sometimes referred to as a Muttonbird, like the Sooty Shearwater of New Zealand and the Short-tailed Shearwater of Australia...
, Puffinus pacificus (or Ardenna pacifica) - easternmost breeding site - Western Red-billed TropicbirdRed-billed TropicbirdThe Red-billed Tropicbird, Phaethon aethereus, also known as the Boatswain Bird is a tropicbird, one of three closely related seabirds of tropical oceans.-Distribution and habitat:...
, Phaethon aethereus mesonauta - possibly northernmost breeding site - Northern Blue-footed BoobyBlue-footed BoobyThe Blue-footed Booby is a bird in the Sulidae family which comprises ten species of long-winged seabirds. The natural breeding habitat of the Blue-footed Booby is tropical and subtropical islands off the Pacific Ocean, most famously, the Galápagos Islands, Ecuador.- Etymology :The name booby...
, Sula nebouxii nebouxii - possibly northernmost breeding site - Nazca BoobyNazca BoobyThe Nazca Booby, Sula granti, is a booby which is found in the eastern Pacific Ocean, namely on the Galápagos Islands where it can be seen by eco-tourists, and on Clipperton Island...
, Sula granti - possibly northeasternmost breeding site - East Pacific Red-footed BoobyRed-footed BoobyThe Red-footed Booby, Sula sula, is a large seabird of the booby family, Sulidae. As suggested by the name, adults always have red feet, but the colour of the plumage varies. They are powerful and agile fliers, but they are clumsy in takeoffs and landings...
, Sula sula websteri - northernmost breeding site of this doubtfully distinct subspeciesSubspeciesSubspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one... - Northeast Pacific Brown BoobyBrown BoobyThe Brown Booby is a large seabird of the booby family, Sulidae. The adult brown booby reaches about in length. Its head and upper body are covered in dark brown, with the remainder being a contrasting white. The juvenile form is gray-brown with darkening on the head, wings and tail...
, Sula leucogaster brewsteri - northernmost breeding site - East Pacific Great FrigatebirdGreat FrigatebirdThe Great Frigatebird is a large dispersive seabird in the frigatebird family. Major nesting populations are found in the Pacific and Indian Oceans, as well as a population in the South Atlantic....
, Fregata minor ridgwayi - northernmost breeding site of this doubtfully distinct subspecies
The nearly extinct Townsend's Shearwater
Townsend's Shearwater
Townsend's Shearwater, Puffinus auricularis, is a rare seabird of the tropics from the family Procellariidae.Its relationships are unresolved. Its closest relatives are probably, but not certainly, the Hawaiian Shearwater and possibly the Manx Shearwater...
(Puffinus auricularis) does not seem to breed on San Benedicto, but can sometimes be seen feeding offshore. Given that there are no invasive species
Invasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
on San Benedicto and also no predators apart from the frigatebirds, the island might be highly suitable for establishing a new colony. Indeed, it bred here before the 1952 eruption; shearwaters are highly conservative in choosing their breeding locations, which explains why San Benedicto has not yet been recolonized.
Vagrants of other species, such as Brown Pelican
Brown Pelican
The Brown Pelican is the smallest of the eight species of pelican, although it is a large bird in nearly every other regard. It is in length, weighs from and has a wingspan from .-Range and habits:...
s, Red-tailed Hawk
Red-tailed Hawk
The Red-tailed Hawk is a bird of prey, one of three species colloquially known in the United States as the "chickenhawk," though it rarely preys on standard sized chickens. It breeds throughout most of North America, from western Alaska and northern Canada to as far south as Panama and the West...
s, Osprey
Osprey
The Osprey , sometimes known as the sea hawk or fish eagle, is a diurnal, fish-eating bird of prey. It is a large raptor, reaching more than in length and across the wings...
s, Barn Swallow
Barn Swallow
The Barn Swallow is the most widespread species of swallow in the world. It is a distinctive passerine bird with blue upperparts, a long, deeply forked tail and curved, pointed wings. It is found in Europe, Asia, Africa and the Americas...
s and Bay-breasted Warbler
Bay-breasted Warbler
The Bay-breasted Warbler, Dendroica castanea , is a New World warbler. They breed in northern North America, specifically in Canada, into the Great Lakes region, and into northern New England....
s may occasionally visit the island but ultimately move on or perish, finding San Benedicto still too barren to support a resident population. Migrant
Bird migration
Bird migration is the regular seasonal journey undertaken by many species of birds. Bird movements include those made in response to changes in food availability, habitat or weather. Sometimes, journeys are not termed "true migration" because they are irregular or in only one direction...
wader
Wader
Waders, called shorebirds in North America , are members of the order Charadriiformes, excluding the more marine web-footed seabird groups. The latter are the skuas , gulls , terns , skimmers , and auks...
s, such as Hudsonian Curlews and Wandering Tattler
Wandering Tattler
The Wandering Tattler, Tringa incana , is a medium-sized wading bird. It is similar in appearance to the closely related Gray-tailed Tattler, T. brevipes...
s, use San Benedicto for brief stopovers more regularly.
Flora
A mere 10 plant taxa have been recorded from San Benedicto, containing mainly herbHerb
Except in botanical usage, an herb is "any plant with leaves, seeds, or flowers used for flavoring, food, medicine, or perfume" or "a part of such a plant as used in cooking"...
s and grass
Grass
Grasses, or more technically graminoids, are monocotyledonous, usually herbaceous plants with narrow leaves growing from the base. They include the "true grasses", of the Poaceae family, as well as the sedges and the rushes . The true grasses include cereals, bamboo and the grasses of lawns ...
es, with the occasional subshrub
Subshrub
A subshrub or dwarf shrub is a short woody plant. Prostrate shrub is a similar term.It is distinguished from a shrub by its ground-hugging stems and lower height, with overwintering perennial woody growth typically less than 10–20 cm tall, or by being only weakly woody and/or persisting...
s and vine
Vine
A vine in the narrowest sense is the grapevine , but more generally it can refer to any plant with a growth habit of trailing or scandent, that is to say climbing, stems or runners...
s. It does not appear that any went extinct due to the 1952 eruption. The local plant life contains several Revillagigedo endemics shared with Clarión: Bulbostylis nesiotica, Cyperus duripes and Perityle socorrosensis. The taxonomic status of the local Euphorbia anthonyi is not fully resolved. Other plants on San Benedicto are Aristolochia islandica, Cenchrus myosuroides, Eragrostis diversiflora, Erigeron crenatus, Ipomoea pes-caprae ssp. brasiliensis (Beach Morning Glory) and Teucrium townsendii.
Visiting information
San Benedicto Island is a popular scuba diving destination known for underwater encounters with dolphins, sharks, giant manta raysManta ray
The manta ray is the largest species of the rays. The largest known specimen was more than across, with a weight of about . It ranges throughout waters of the world, typically around coral reefs...
and other pelagics. An area called "The Boiler" is where divers commonly interact with the rays. Divers have also spotted tiger shark
Tiger shark
The tiger sharks, Galeocerdo cuvier, is a species of requiem shark and the only member of the genus Galeocerdo. Commonly known as sea tigers, tiger sharks are relatively large macropredators, capable of attaining a length of over . It is found in many tropical and temperate waters, and is...
s, Galapagos shark
Galapagos shark
The Galapagos shark is a species of requiem shark, family Carcharhinidae, found worldwide. This species favors clear reef environments around oceanic islands, where it is often the most abundant shark species...
s, silky shark
Silky shark
The silky shark is a species of requiem shark, family Carcharhinidae, named for the smooth texture of its skin. It is one of the most abundant sharks in the pelagic zone, and can be found around the world in tropical waters. Highly mobile and migratory, this shark is most often found over the edge...
s, and humpback whale
Humpback Whale
The humpback whale is a species of baleen whale. One of the larger rorqual species, adults range in length from and weigh approximately . The humpback has a distinctive body shape, with unusually long pectoral fins and a knobbly head. It is an acrobatic animal, often breaching and slapping the...
s here. Since there is no public airport on the island, divers visit here aboard dive vessels. The most popular months to visit are between November and May when the weather and seas are calmer.