The last time I wrote an article for Volcanocafe it was a guest post about the Galapagos Islands, but now I’m a new member of the Volcanocafe writing team (a little bit more about me later).
Deep in the South Atlantic Ocean lies an archipelago of uninhabited volcanic islands, the South Sandwich Islands. A British overseas territory located within the sub-Antarctic region. The South Sandwich Islands consists of 11 islands, they are Zavodovski, Visokoi, Leskov, Candlemas, Vindication, Saunders, Montagu, Bristol, Bellingshausen, Cook, and Thule all formed as a result of the subduction of a part of the South American Plate underneath the Scotia Plate as well as numerous seamounts. Because of the remote location of the islands and the volatile nature of the seas and climate, human expeditions are very rare so we have to almost always rely on satellite imagery for observations subject to weather.
The age of the subducting oceanic crust ranges from 27 million years old in the south to 80 million years old to the north. The East Scotia Ridge spreading centre cuts through the Scotia Plate from the northern part of the island arc, to the south forming the minor tectonic plate, the South Sandwich Plate. The Protector Seamounts forms the northenmost Volcanic centre of the island arc with the Scoresby Seamount being the northernmost volcano of the arc. Nelson Seamount is the southernmost volcano of the island arc, located to the south of the Kemp and Adventure Calderas. The Kemp and Adventure Calderas are other undersea volcanoes which are located to the southwest of the Southern Thule Islands. The volcanoes of the South Sandwich arc are predominately of Basaltic or Basaltic-Andesitic composition with minor amounts of Andesite, Dacite, or Rhyolite.
Out of the historical eruptions ever recorded in the South Sandwich Islands since 1819 there may have been many more than we think, just that these islands are very rarely visited given their remote location and hostile environment. But now, thanks to modern satellite technology we’re able to monitor the volcanic activity more often today. Historical eruptions in the South Sandwich Islands have occurred at the Protector Shoal Seamount, Mount Curry on Zavodovski Island, Lucifer Hill on Candlemas Island, Mount Michael and the northern flank on Saunders Island, Mount Belinda on Montagu Island, Mount Sourabaya and the west flank on Bristol Island, and the south flank of Bellingshausen Island. Other forms of volcanic activity observed includes fumaroles on Zavodovski Island, Leskov Island, Visokoi Island, Candlemas Island, and Bellingshausen Island, and also geysers and hot pools on Candlemas Island, and undersea hydrothermal venting on the Kemp and Adventure Calderas as well as the summits of the E2 and E9 segments in the East Scotia Ridge spreading centre.
The South Sandwich Islands are also home to a large colony of penguins especially of the Chinstrap and Adelie species. Species of seals and whales, as well as skuas are also present around the islands.
PROTECTOR SEAMOUNTS GROUP
The Protector seamounts make up the northernmost volcanic centre of the South Sandwich arc. They consist of Protector Shoal, Nimrod Bank, Endurance, Bisco, Tula, JCR, Quest caldera, and Scoresby. Because they all lie beneath the surface of the sea, not a lot is known about them. However, temperature readings from submersible dives on Scoresby and Quest caldera suggest that hydrothermal activity is occurring on these vents. Protector Shoal, a rhyolite volcano which is located on the south end of Nimrod Bank at -55m had it’s only historical eruption in 1962 when a large amount of pumice was ejected forming a pumice raft which drifted towards New Zealand.
Zavodovski is the northernmost island of the South Sandwich chain and is made up out of Basalt. The 551m high Mount Curry stratovolcano occupies the western side of the island while a lava platform makes up the eastern side of the island and to a lesser extent, the southern end of the island. Olivine-basalt is present on the east cliffs. Persistent fumarolic activity occurs at the summit and the crater of Mount Curry and is said to have been active since first sighted by explorer Fabian Gottlieb von Bellingshausen in 1819. An eruption was observed by Bellingshausen in 1819 and although no confirmed eruptions had been reported until 2016, it is likely that many eruptions may have occurred since it’s discovery. A possible sighting of a lava flow was observed in 1830. During 30th March 2016, a fishing vessel sighted an eruption which produced an ash plume that drifted east.
Leskov Island is a small cresent shaped island located west of Visokoi Island and southwest of Zavodovski Island. Made up entirely of Two-pyroxene andesite the island has a diameter of 900m long and 400m wide. A remnant of an eroded volcano, Crater Bay to the northeast side of the island is the main eruptive centre. No historical eruptions have been known on Leskov Island although fumarolic activity along the summit ridge was observed in 1911 and 1964.
Visokoi Island consists of a single stratovolcano, Mount Hodson and is predominately made up out of Basalt with lesser amounts of Basaltic-andesite. Much of the island is covered in permanent ice although the coastal areas can be ice free during summer. Basaltic-andesites were found at Irving Point on the east coast of the island. Scoria cones dot the lower flanks of Mount Hodson. Vapour has been observed on odd occasions in the past coming from the summit but nothing more could be confirmed. A fumarole on the north coast was reported in 1930. Although there had been no historical eruptions confirmed it is possible that some eruptive activity may have occurred up to almost the present day.
Candlemas Island has a distinction between the southern part of the island, and the northern peninsula. The southern part of the island is older than the northern peninsula and it consists of an ice covered volcanic edifice with two peaks on the east side, Mount Andromeda and Mount Perseus. The volcanic edifice of the southern part of the island is made up out of porphyritic basalt although some dacitic obsidian fragments were found on the northern cliffs. The edifice is eroded to the east but lavas dipping towards the west suggest that a former summit vent once occupied the area beyond the eastern coast. The northern peninsula of the island is younger but is more low lying and is made up out of andesite and dacite, it consists of lava fields and a younger volcano, Lucifer Hill. It is likely to have started out as a seperate island before eventually merging with the south. Gorgon Pool and Medusa Pool occupy the area which connects the northern peninsula with the southern part of the island. Eruptions on Lucifer Hill occurred in 1823 and in 1911. A lot of the lava fields around Lucifer Hill is said to have formed during recent times. In 1953-54 a glowing lava field was observed and in 1964 steam was reported to have been issuing from the youngest lava flow. Geysers and hot pools were observed on occasions during the 20th century. The Lucifer Hill Volcano currently displays persistent fumarolic activity while no eruptive nor fumarolic activity has ever been observed on the southern part of the island.
Vindication Island is located very close west-southwest of Candlemas Island and the two islands are seperated by a shallow shelf. Vindication is smaller than Candlemas Island but has been largely reduced by erosion and is bounded by high cliffs. The island is made up of porphyritic basalt with lesser amounts of basaltic-andesite and smaller amounts of palagonite-tuff on on the north coast. Quadrant Peak on the western side of the island may have been part of a once principal eruptive centre of the island. No volcanic activity of any form has been observed on Vindication Island.
Saunders Island is made up out of basalt and it lies midway within the South Sandwich island arc. While the 991m high glacier covered Mount Michael Volcano dominates the island, the north coast consists of Blackstone Plain, a low lying lava platform and the south east consists of a small cluster of parasitic cones, Ashen Hills. Cordelia Bay is located to the northeast. Two seamount chains are present to the northwest and southwest of the Saunders Island platform. Vitric palagonite-tuff is present at Nattriss Point while basaltic-andesite is present at Yellowstone Crags and olivine-basalt is present on Blackstone Plain. A 500m wide crater is present on the summit of Mount Michael with a smaller older crater to the southeast. The first observed eruption came in 1819 and a lava flow on the north flank was said to have occurred during the end of the 19th century. Eruptions on Mount Michael have been occurring on a regular basis since 1995. Vapour emissions have been repeatedly reported. Satellite data suggests that the occasional lava lake activity has occurred.
Montagu Island is the largest island in the archipelago and has a more broad shaped profile, it is almost entirely covered by ice. The Mount Belinda central cone is also the highest point on the island at 1370m. At least three small parasitic cones lie at the edge of the high plateau. A secondary volcano, Mount Oceanite lies at the southeast edge of the island. The island is almost entirely made up out of basalt though palagonite-tuff is present in the cliffs behind Horsburgh Beach on the west-southwest of the island. No eruptive nor fumarolic activity has been observed on the island until 2001 when Mount Belinda erupted. The eruption of Mount Belinda lasted until 2007, when a lava flow reached the north coast of the island within that time. Unconfirmed eruptions may have been detected between 1995 and 1998.
Glacier covered Bristol Island is located near the Southern Thule Islands group, near the southern end of the island arc. This largely porphyritic basaltic island consists of prominent peaks, Mount Sourabaya, Mount Darnley, and Havfruen Peak. A ridge runs from the inland east, down to the north coast of the island. Freezland Rock, Wilson Rock, and Grindle Rock which lie off the western tip of the island (Turmoil Point) may be remnants of a former volcano. Andesite and palgonite-tuff is present on Freezland Rock. Historical eruptions have occurred in 1823, 1935, 1936, 1950, 1956, and 2016. While most of the eruptions occurred from the summit vents (more likely Mount Sourabaya), the 1956 eruption occurred on the west side of the island close to Turmoil Point. The most recent eruption on Bristol Island occurred on Mount Sourabaya during April-August 2016 when satellite imagery picked up on thermal anomalies, eruption plumes, and two branches of lava flows which advanced to the west and to the north-northwest of Mount Sourabaya.
Bellingshausen Island is the smallest island of the Southern Thule Islands group at the south end of the island arc. It is made up almost entirely out of basaltic-andesite though palagonite-tuff is present on the northern summit crater wall. Lava fields are present on the south side of the island, and the underwater Resolution Caldera lies to the south of the island. Active fumaroles have been observed on the southern crater rim and an eruption occurred on the south side of the island sometime during the late 20th century.
Cook Island is the central island of the Southern Thule Islands group and the highest point on the island is Mount Harmer. Olivine basalt as well as andesite and dacite is present. No volcanic activity of any form has ever been observed on Cook Island.
Thule Island is the westernmost island of the Southern Thule Islands group and consists of a single stratovolcano, Mount Larsen. An ice filled caldera occupies the summit area while a lava flow emitted from a parasitic vent forms the low lying southeast tip of the island (Hewison Point). The island is eroded along the east coast and a possible underwater caldera occupies the area in Douglas Straight between the east of the island and Cook Island. Andesite and dacite, as well as olivine-basalt is present on the island while palagonite-tuff was found at the parasitic centre near Hewison Point. Steam was observed from the summit crater in 1962 indicating fumarolic activity, and ashfall was also observed on the southwest of the island indicating that an eruption took place.
KEMP SEAMOUNTS GROUP
The Kemp Seamounts group is a group of undersea volcanoes which are located to the southwest of the Southern Thule Islands, they are Adventure Caldera, Kemp Seamount, and Kemp Caldera. A group of smaller seamounts are located to the west of Kemp Caldera. According to samples collected, the Kemp Seamount is made up out of basalt and basaltic-andesite and the Adventure Caldera is made up out of basalt and dacite. Hydrothermal activity is present at the Kemp and Adventure calderas.
The Nelson Seamounts form the southernmost volcanic centre of the South Sandwich volcanic arc. According to samples collected Nelson is made up out of dacite. Not a lot is known about the Nelson Seamounts given their remote undersea location.
The South Sandwich Islands are quite an active volcanic arc though the most active volcanoes within the archipelago tend to be Mount Curry on Zavodovski Island and Mount Michael on Saunders Island. Most eruptions would most likely be of strombolian style in areas free of ice while eruptions in glacier covered areas would cause a phreatomagmatic eruption. Lava and ice interaction also occurs like the eruptions which occurred on Montagu and Bristol islands which would’ve been similar to the eruptions of Mount Veniaminof in Alaska. The past eruptions of Lucifer Hill on Candlemas Island more likely would’ve been similar to that on Nishino-shima near Japan. If Mount Hodson on Visokoi Island were to erupt from the ice covered summit crater then we would more likely see an Eyjafjallajokull style eruption. And finally if an eruption were to occur in any of the Southern Thule Islands then it would more likely come from a parasitic flank vent, surtseyan eruptions are also a possible scenario if an underwater vent eruption occurred.
Video credit: BBC Planet Earth II
My own knowledge
Global Volcanism Program
Bathymetry and geological setting of the South Sandwich Islands volcanic arc – Philip T. Leat, Peter T. Fretwell, Alex J. Tate, Robert D. Larter, Tara J. Martin, John L. Smellie, Wilfried Jokat, and Gerhard Bohrmann.
The South Sandwich Islands: III. Petrology of the volcanic rocks – P. E. Baker and D. Phil.
Bathymetry and Geological Setting of the South Sandwich Islands Volcanic Arc Side 2: The South Sandwich Islands – Philip T. Leat, Peter T. Fretwell, Alex J. Tate, Robert D. Larter, Tara J. Martin, John L. Smellie, Wilfried Jokat, and Gerhard Bohrmann.
Bathymetry and Geological Setting of the South Sandwich Islands Volcanic Arc Side 1: The South Sandwich Islands – Philip T. Leat, Peter T. Fretwell, Alex J. Tate, Robert D. Larter, Tara J. Martin, John L. Smellie, Wilfried Jokat, and Gerhard Bohrmann.
A little bit about me:
My name is René (or you can call me Ren for short) and I come from the south of England. I’m a volcanophile and a nature lover and have been so since I was a child. To date I have travelled to volcanoes in Sicily, Iceland, Mexico, Guatemala, Costa Rica, Ecuador, and the Galapagos Islands. I also like a bit of photography.
My volcano website: www.volcanoplanet.co.uk
My photography website: www.rgoadphotography.com
My blog about the South Sandwich Islands: http://southsandwichmonitoring.blogspot.co.uk/