Socorro Island is a small volcanic island in the Revillagigedo Islands, a Mexican possession lying off the country's western coast. The size is 16.5 by 11.5 km, with an area of. It is the largest of the four islands of the Revillagigedo Archipelago.
Geology
The island rises abruptly from the sea to in elevation at its summit. Socorro Island is the emerged summit of a massive, predominately submarine shield volcano. The island is part of the northern Mathematicians Ridge, a mid-ocean ridge that became largely inactive 3.5 million years ago when activity moved to the East Pacific Rise. All four islands along with the many seamounts on the ridge are post-abandonment alkaline volcanoes. Socorro Island is unusual in that it is the only dominantly silicicperalkaline volcanic island in the Pacific Ocean. It most recently erupted in late January-early February, 1993, which was a submarine flank eruption off the coast from Punta Tosca. An earlier eruption was on May 21, 1951; earlier eruptions probably occurred in 1905, 1896 and 1848. The initial volcanic event probably occurred in 3090 BC +/- 500 years. Mount Evermann is the name given to the summit dome complex, in honor of ichthyologistBarton Warren Evermann. The island's surface is broken by furrows, small craters, and numerous ravines, and covered in lava domes, lava flows and cinder cones. There is a naval station, established in 1957, with a population of 250, living in a village with a church, that stands on the western side of Bahia Vargas Lozano, a small cove with a rocky beach, about 800 meters east of Cabo Regla, the southernmost point of the island. The station is served by a dock, a local helipad and Isla Socorro airport, located six kilometers to the north. There is a fresh water spring about 5 km northwest of Cabo Regla, at the shoreline of Ensenada Grayson, an inlet. This is brackish and sometimes covered by the sea at high tide. Apart from some temporary pools and maybe one that is more permanent, a small freshwater seep exists most of the time some inland at Bahia Lucio Gallardo Pavon, 800 meters NW of the naval station.
History
No evidence of human habitation on Socorro exists before its discovery by Spanish explorers. and his crew discovered an uninhabited island on 19 December 1533 and named it Santo Tomás. In 1542, Ruy López de Villalobos, while exploring new routes across the Pacific, rediscovered Inocentes and renamed it Isla Anublada due to the clouds frequently forming on the northern slopes of Mount Evermann, and again in 1608, Martín Yañez de Armida, in charge of another expedition, visited Santo Tomás and changed its name to Isla Socorro after Our Lady of Perpetual Help. At the beginning of the twentieth century, Barton Warren Evermann, director of the California Academy of Sciences in San Francisco promoted the scientific exploration of the island. The most comprehensive biological collections were obtained at this time. The volcano on Socorro was renamed in his honor. Archie Smith, an American laborer from San Diego, was abandoned on the island for one month in 1929 before being rescued by a passing fishing boat. In September 1997, Hurricane Linda passed near the island near peak intensity causing minor damage to the island.
Ecology
The lowlands of Socorro – except on the northern, more humid side – are covered with thick shrubland, consisting mainly of endemicCroton masonii and a cactus, probably Engelmann's prickly pear. Above and on the northern side, a richer vegetation occurs. This includes small trees such as Ficuscotinifolia, black cherry, and the endemic Guettardainsularis, which bear epiphytic orchids. The native land fauna is depauperate, with birds predominating and mammals absent. There is one endemic species of iguanid lizard and the land crabJohngarthia oceanica which also occurs on Clipperton Island. Sheep, cats and rodents were introduced to the island by human activity; more recently, the locustSchistocerca piceifrons has also established itself on the island. Unlike the mammals on Guadalupe Island or Clarión, their impact on the local flora was minor, but cat predation has had a drastic effect since the mid-1970s due to the fauna's island tameness, and the locusts that swarm twice a year seriously damage vegetation during that time. There have been no recorded extinctions of plants on Socorro; several birds have been drastically affected by cat predation however, and one taxon, the Socorro dove, has gone extinct in the wild. Socorro is an important breeding location for several seabirds, many of which have here one of their northernmost breeding colonies. The present status of these birds is not well known, and they presumably have suffered from cat predation. In 1953, the following taxa were present:
Being the largest of the Revillagigedo Islands and closer to mainland than Clarion, Socorro sports a rich array of endemic taxa, mainly plants and landbirds as well as lizards. Some are threatened due to the presence of feral cats.
Brickellia peninsularis var. amphithalassa, Cheilanthes peninsularis var. insularis, Nicotiana stocktonii, Spermacoce nesiotica and Zapoteca formosa ssp. rosei are near-endemics, being restricted to Socorro and Clarión. Whether Teucrium townsendii ssp. affine is the same plant as those on San Benedicto is not conclusively determined.
Visiting information
Socorro Island is a popular scuba diving destination known for underwater encounters with dolphins, sharks, manta rays and other pelagic animals. Since there is no public airport on the island, divers visit here on live-aboard dive vessels. The most popular months are between November and May when the weather and seas are calmer. November to December are popular months to visit for a good chance to dive with whale sharks.
