- San Benedicto Island
San Benedicto, formerly Santo Tomás, is the third largest island of the
Revillagigedo Islands , located at coord|19|19|N|110|49|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 1,089 feet (332 meters)GVP (2007)] 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 offreshwater .Brattstrom & Howell (1956)]1952/53 volcanic eruption
Barcena's only historic eruption began around 8:30 AMVerify source|date=November 2007 on
August 1 1952 from the El Boquerón vent. In a severeVulcanian eruption of magnitude 3 on theVolcanic Explosivity Index scale,pyroclastic flow s rolled over the island. Soon the entire island was covered in ash andpumice up to 10 ft (3 m) high.Ejecta filled the valley between Herrera crater and Montículo Cinerítico, and by August 14 had formed a cone some 1000 ft (over 300 m) high. After some months with little activity, a second series of eruptions began on November 1 1952. On December 8, themagma broke through the cone's southeastern base and started to flow into the sea. This continued to aboutFebruary 24 1953 Fact|date=November 2007. By March 9 1953, most activity had subsided, exceptfumarole s in the crater and at the rift in its base; thelava was hard but still retained much heat. By late 1953, the volcano was dormant again. [Brattstrom & Howell (1956), Mattox (2006), GVP (2007)]Ecology
The eruption wiped out - at least temporarily - all
flora and terrestrialfauna of San Benedicto, much like it had happened onKrakatoa in 1883. The fauna included the endemicSan Benedicto Rock Wren which wentextinct 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. [See photos in Brattstrom & Howell (1956)]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 toerode away. A few "Gecarcinus planatus "land crab s were present also, having either managed to survive the eruption or, more probably, recolonized the island; theirlarva 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 ofBlue-footed Boobies was present in the ditch between Herrera and Barcena.Fauna
The
vertebrate fauna of San Benedicto is nowadays composed entirely of seabirds. It appears that the Revillagigedo population ofWestern Raven s 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 Shearwater , "Puffinus pacificus" (or "Ardenna pacifica") - easternmost breeding site
* WesternRed-billed Tropicbird , "Phaethon aethereus mesonauta" - possibly northernmost breeding site
* NorthernBlue-footed Booby , "Sula nebouxii nebouxii" - possibly northernmost breeding site
*Nazca Booby , "Sula granti" - possibly northeasternmost breeding site
* East PacificRed-footed Booby , "Sula sula websteri" - northernmost breeding site of this doubtfully distinctsubspecies
* Northeast PacificBrown Booby , "Sula leucogaster brewsteri" - northernmost breeding site
* East PacificGreat Frigatebird , "Fregata minor ridgwayi" - northernmost breeding site of this doubtfully distinct subspeciesThe 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 noinvasive species on San Benedicto and also nopredator s 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. [Brattstrom & Howell (1956), BirdLife International (2007)]Vagrants of other species, such as
Brown Pelican s,Red-tailed Hawk s,Osprey s,Barn Swallow s andBay-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. Migrantwader s, such asHudsonian Curlew s andWandering Tattler s, use San Benedicto for brief stopovers more regularly.Flora
A mere 10 plant taxa have been recorded from San Benedicto, containing mainly
herb s andgrass es, with the occasionalsubshrub s andvine s. It does not appear that any went extinct due to the 1952 eruption. The local plantlife contains several Revillagigedo endemics shared with Clarión: "Bulbostylis nesiotica ", "Cyperus duripes " and "Perityle socorrosensis ". Thetaxonomic 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 ". [CMICD (2007)]Visiting information
San Benedicto Island is a popular scuba diving destination known for underwater encounters with dolphins, sharks, giant manta rays 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, andhumpback whale s here. Since there is no public airport on the island, divers visit here aboard live-aboard dive vessels such as the 112' "Solmar V" out ofCabo San Lucas, Mexico . The most popular months are between November and May when the weather and seas are calmer.Footnotes
References
*|year=2007|id=18851|title=Puffinus auricularis|downloaded=11 November 2007
* (1956): The Birds of the Revilla Gigedo Islands, Mexico. "Condor" 58(2): 107-120. doi|10.2307/1364977 [http://elibrary.unm.edu/sora/Condor/files/issues/v058n02/p0107-p0120.pdf PDF fulltext] [http://elibrary.unm.edu/sora/Condor/files/DJVU/v058n02/P0107-P0120.djvu DjVu fulltext]
* (2007): [http://altamura.ucsc.edu/pls/new/ISLA2.PUBLIC_MENU.show Plant accounts: San Benedicto] . Retrieved 2007-NOV-12.
* (2007): [http://www.volcano.si.edu/world/volcano.cfm?vnum=1401-02= Bárcena] . Version of 2007-AUG-05 . Retrieved 2007-NOV-13.
* (2006): [http://volcano.und.edu/vwdocs/frequent_questions/grp7/north_america/question1692.html [References on Isla San Benedicto] . Version of 2006-SEP-11 . Retrieved 2007-NOV-13.
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