 Aerial view of Bridgeman Island | |
  Bridgeman Island Location of Bridgeman Island Show map of Antarctica Bridgeman Island Bridgeman Island (Antarctic Peninsula) Show map of Antarctic Peninsula | |
| Geography | |
|---|---|
| Location | Antarctica |
| Coordinates | 62°03′S56°45′W / 62.050°S 56.750°W /-62.050; -56.750[1] |
| Archipelago | South Shetland Islands |
| Total islands | 2 |
| Length | 0.9 km (0.56 mi) |
| Width | 0.6 km (0.37 mi) |
| Highest elevation | 240 m (790 ft) |
| Administration | |
| Administered under theAntarctic Treaty System | |
Bridgeman Island is one of theSouth Shetland Islands inAntarctica. It is an almost circular,volcanic island marked by steep sides, measuring 900 by 600 metres (3,000 ft × 2,000 ft) with a maximum elevation of 240 m (787 ft) high, lying 45 kilometres (28 mi) east ofKing George Island.
It is surrounded by steep cliffs and consists mostly of lava flows andscoria, subdivided in two geological units. Bridgeman Island is the emergent portion of a larger volcano in theBransfield Strait, which contains numerous volcanoes includingDeception Island and numerousseamounts. The island formed during thePleistocene; there is evidence of an eruption in 1821 that generated a probabletuff cone west of Bridgeman Island, which has now disappeared.
Antarctica features numerous volcanoes, 12 of which (e.g.Mount Melbourne,Mount Erebus,Mount Berlin,Deception Island) are known to be active or potentially active. A peak in volcanic activity took place during theJurassic, when the ancient continentGondwana broke up.[2]
Bridgeman Island lies in the easternBransfield Strait,[2] 45 kilometres (28 mi) away fromKing George Island.[3] The strait separates theSouth Shetland Islands (including King George Island) to the northwest from theAntarctic Peninsula to the southeast. There are a number of mostly submarine volcanoes; from northeast to southwest these include: Gibbs Rise, Spanish Rise, G Ridge, Bridgeman Rise (with Bridgeman Island), Hook Ridge,Orca volcano, Three Sisters, Edifice A, Deception Island (with the eponymous island) andSail Rock with the eponymous island.[3][4] The volcanoes produce mainlybasaltic rocks with a characteristicsodium-rich composition.[5] Apart from discrete volcanoes,hydrothermal phenomena, highheat flow andearthquakes occur in the Bransfield Strait.[5] The line Deception Island-Bridgeman Island coincides with the axis of the Bransfieldrift.[6] The origin of Bransfield Strait took place during the last 4 million years and is linked to the cessation ofsubduction off the Antarctic Peninsula, although the exact mechanism through which the strait opened is unclear.[7]
Bridgeman Island is slightly elongated in north–southeast direction, measuring 900 by 600 metres (3,000 ft × 2,000 ft). It is surrounded on all sides by highcliffs,[5] especially on the almost vertical western side, and lacks beaches andraised beaches except for a narrowgravelly beach on the eastern side. The inner parts of the island are flat[8] and undulating; the highest peak reaches an elevation of 240 metres (790 ft).[5] The terrain was often covered with snow.[9] A small islet lies off its northern tip.[1] It has been described as a remnant of astratovolcano.[10]
Bridgeman Island consists entirely of volcanic rocks and lacks volcaniclandforms.[2] The rocks are subdivided in three units, the southeastern Lower Unit consisting of thin lava flows andscoria, the central Upper Unit formed by scoria and thick lavas, and the western unit that is formed by fragments from both other units. Below sea level, Bridgeman Island extends to a depth of 1,200 metres (3,900 ft), forming the 10 by 15 kilometres (6.2 mi × 9.3 mi) Bridgeman Rise. The volcano is the second-most voluminous volcano of the Bransfield Strait,[5] with a peak-to-bottom height of 1.7 kilometres (1.1 mi).[10] It separates the deep basin of the Bransfield Strait into an eastern and central segment,[11] and its position may coincide with a boundary between segments of the Bransfield rift.[12] Around Bridgeman Island, there are submarine mounds andvolcanic plugs that rise to a depth of 45 metres (148 ft) below sea level;[13] otherwise, the localbathymetry is sparsely known.[14] Hydrothermal activity has been recorded between Deception Island and Bridgeman Island, as well as east of Bridgeman Island.[15]
The volcanic rocks of Bridgeman Island are formed bybasaltic andesite andsubalkalinebasalt,[16] and there is one questionable occurrence ofdacite.[17] These rocks define analuminum-rich suite[1] and share compositional traits with bothmid-ocean ridge-derived andisland arc-derived magmas.[18]Augite,diopside,olivine andplagioclase formphenocrysts.[18][19] The magmas of Bridgeman Island may have formed through the incomplete melting ofspinelperidotite, with 10–20% of the resulting melt ending up as the magma.[20] Melts derived from theslab[21] andfractional crystallization may also have played a role.[22]Hydrothermal alteration has yielded secondary minerals such ascalcite,chalcedony,hematite andlimonite, giving the rocks a deep red colour.[18]
Bridgeman Island was discovered on 21 January 1820 by the marinerWilliam Smith from theWilliam,[23] and named presumably afterCharles Orlando Bridgeman.[24] Other names include Yelena, as given byBellingshausen, the misspelling Bridgman[25] and Burning Mount or Brians Isle, by captain Richard Sherratt.[26]
The island formed throughSurtseyan eruptions and was apparently never significantly eroded byglaciers. The older volcanism is undated; a younger volcanic event occurred 63,000±25,000 years ago.[27] It is possible that either the eruptions occurred during times of low sea levels or that the island subsided over time, explaining why it was not significantly eroded by the sea.[28] The volcano may have producedtephra during theHolocene, which was identified in marinesediment cores.[2]
Bridgeman Island was the first volcano in Antarctica to be recognized as active and the first to be observed as erupting.[2] An eruption in 1821 was observed by numerous passing ships.[14] Until 2021, it was attributed toPenguin Island, which has young-looking volcanic features[3] but no clear evidence of recent activity.[29] From its discovery to 1835, the shape of the island did not change significantly,[3] although comparisons of sketches of the island during the 19th century with modern images imply that parts of the island disappeared after the 19th century.[30]
Based on observations from passing ships, it seems like the eruption commenced in January 1821 and ended at some point between 1853 and 1909.[27] From the observations, it appears that the eruption originated from what was probably atuff ring on the southwestern side of the island. Repeated explosions were seen, which belched black smoke at irregular intervals as vents shut off and reopened.[14] The crater may have reached a width of 500–600 metres (1,600–2,000 ft).[31] Accounts mention that the smoke smelled ofsulfur, deadpenguins floating in the water,[32] and of boiling water and rock so hot that it could not be touched.[33] The tuff ring or vent on the southwestern end of the island may have significantly enlarged Bridgeman Island while it existed,[28] possibly extending it by more than 2 kilometres (1.2 mi).[31] It disappeared after the eruption, probably due tomarine erosion,[27] as such shallow-water volcanoes are highly erodible.[31]
Dumont D'Urville reportedfumaroles on the western side in 1838 and thought that part of the island must have collapsed in the past.[34] There are reports of eruptions in 1838, 1839 and 1850, sometimes attributed to Penguin Island instead;[29] reports of an eruption in 1909 are false.[35]Seismic swarms in the Bransfield Strait have been localized to Orca seamount and Bridgeman Island.[36] In 2022, acoustic anomalies were identified at aseamount southeast of Bridgeman Island[37] and at a submarine depression on the same side of the island.[38] They may imply the occurrence of hydrothermal activity at Bridgeman Island.[39] However, no heated ground was reported on Bridgeman Island in 2013.[40]
Lichens andmosses grow on the island,[41] which otherwise lacks vegetation.[8]Crustaceans occur in the neighbouring sea,[42] andsnow petrels have been observed.[43]
