Candlemas Island is a small uninhabited island of the Candlemas Islands in the South Sandwich Islands. It is one of about a dozen islands that make up the South Sandwich island arc, a chain of volcanoes in the Southern Ocean that was discovered in 1775 by James Cook. The volcanism is caused by the subduction of the South American Plate beneath the Sandwich Plate. The island is remote and rarely visited due to the often hostile weather conditions, but is populated by penguins and seabirds, which form large breeding colonies.
The island consists of two parts. The southeastern part is older and consists of the heavily glaciated volcanoes Mount Andromeda - with elevation the highest point of the island - and Mount Perseus, and shows no evidence of recent activity. The northwestern part features the younger scoria cone complex Lucifer Hill, which is surrounded by lava flows. Some of the lava flows may have been emplaced during the 20th century. The older rocks consist mostly of basalt and basaltic andesite, while the younger rocks are predominantly andesite and dacite; the two groups share a common magma formation process.
The Lucifer Hill complex features numerous fumaroles which emit volcanic gases. A vegetation community consisting of mosses and lichens grows around the fumaroles, with some members extending to non-fumarolic terrain.
Geography and geomorphology
Candlemas Island is one of the South Sandwich Islands, a long north–south trending island arc to the southeast of South Georgia and the Falklands. They include Zavodovski, Leskov Island, Visokoi, Candlemas and Vindication Island, Saunders Island, Montagu Island, Bristol Island and Freezland Rock, Bellingshausen Island, Cook Island and Thule Island. All the islands are small and volcanic, most showing evidence of activity during the last two centuries. They are subject to intense marine erosion. Submarine volcanoes include Protector Shoals at the northern end and Nelson and Kemp seamounts at the southern end of the island chain.
The island is also known as Lichtmess-Insel and Candelaria. It is rarely visited owing to the hostile weather and sea conditions, and the south and southeast coasts are hardly accessible; tourist vessels occasionally land on Candlemas. Longline fishing takes place in the surrounding waters. Politically, South Georgia and the South Sandwich Islands make up the UK Overseas Territory of South Georgia and the South Sandwich Islands. In 2012, a marine protected area was established in the South Sandwich Islands. The scope of the protected area was further expanded in 2019.
With dimensions of , Candlemas is the third-largest of the South Sandwich Islands and consists of a southeastern, roughly square-shaped half and an irregularly shaped northwestern half. Vindication Island to the west is separated from Candlemas by the shallow (-) wide Nelson Channel. Visokoi lies north and Saunders south of Candlemas Island.
The northwestern half consists of a complex of scoria cones named Lucifer Hill (also known as Lucifer Hills), which reach a maximum elevation of , or above sea level. Two main craters with depths of about and diameters of flank the main summit, which has a flat top. A subsidiary crater lies on the southwestern flank. They are surrounded by five lava flows, the eastern of which is old and covered with volcanic ash while the northern one is younger, with an irregular surface featuring blocks, ridges and gullies. The lava flows are morphologically aa lavas. The eastern lava flow forms Breakbones Plateau, while a northwestward extending lava flow constitutes the Vulcan Point peninsula. The southwestward and northwestward extending lava flows enclose the Tow Bay; Cauldron Pool lies just east of Tow Bay. Another unnamed pool lies at the end of Clinker Gulch on Lucifer Hill, and there are freshwater pools throughout the island. The coastline is formed by cliffs with interspersed recesses and bays.
The southeastern half is the larger and consists of an extinct and eroded stratovolcano. A north-south trending ridge has two summits, the northeastern high Mount Perseus and the southeastern Mount Andromeda; the latter is the highest point of Candlemas with or elevation. This half is asymmetric, rising from west to east, which may indicate that it is the remnant of a formerly larger volcano that was centered east of the current island. Glaciers cover most of the southeastern half of Candlemas, an area of which amounts to 40% of the island. The ice reaches thicknesses of in coastal cliff exposures. On the southern and eastern side of Candlemas, the ice descends to the sea, in the north it forms glacier tongues at elevations of surrounded by a belt of moraines around the ice edge. Streams draining meltwater have incised glacial deposits. Cliffs with heights of form most of the southern and eastern coasts, while a wide youthful coastal terrace makes up the western and northern side. Marine deposits have formed the northward extending Demon Point peninsula, which encloses Kraken Bay between the peninsula and Lucifer Hill. Shrove Point is the southeastern end of Candlemas Island, while Boot Rock juts out from the eastern coastline and Clapmatch and Carbon Points. east of the coastline is the islet Tomblin Point.
Between the two halves lies Chimaera Flats, a southwest–northeast trending sandy plain with two lagoons named Gorgon Pool and Medusa Pool. Medusa Pool is the southwestern lagoon and was connected to the sea at Sea Serpent Cove in 1964, while Gorgon Pool is the northeastern one. The configuration of Chimaera Flats is variable over time, during 1830-1927 Candlemas Island was sometimes reported to consist of three islands although visual conditions can lead to Candlemas Island being mistaken for two islands. The two halves of Candlemas Island shielded the terrain from marine erosion, thus allowing the growth of spits formed by boulders and shingles.
Submarine structure
Both Candlemas and Vindication rise from the same submarine volcano, and are named the Candlemas Islands. Around the islands the sea is less than deep, forming a wide shallow platform with numerous shoals, islets and sea stacks. They are remnants of eroded islands and include Buddha Rock, Castor Rock, Cook Rock, Pollux Rock, Santa Rock, Saw Rock, Tomblin Rock and Trousers Rock. Most of the islets lie around Vindication. Some of these rocks make up a series of shoals between the islands. The shelf itself probably formed through marine erosion and scouring by icebergs.
The volcano has a base diameter of more than at and a total volume of about . Away from the shallow platform, the slopes of the volcano drop off steeply into the deep ocean. East of Candlemas and abutting its southeastern side is a large wide submarine embayment, probably the remnant of a large sector collapse. Two other structures interpreted as landslide scars lie north and south of the shelf, which is scalloped by landslide scars. The submarine slopes have wave-like bedforms in many places. Smaller ridges emanate from the submarine volcano and are interpreted as parts of it, while chutes emanating in all directions formed through mass wasting. A submarine ridge at depth connects the group to Visokoi farther north. West of Candlemas, monogenetic volcanoes are developed on the seafloor.
Geology
East of the South Sandwich Islands, the South America Plate subducts into the more than deep South Sandwich Trench at a rate of . The volcanic arc consists of volcanoes with heights of that developed on top of the Sandwich Plate, which is produced at the East Scotia Ridge west of the arc. Both the underlying oceanic crust (8-10 million years old) and the volcanic arc appear to be young; this may explain the peculiar basalt-rich composition and small size of the volcanoes.
Composition
Volcanic rocks from Candlemas consist of basalt, basaltic andesite, andesite and dacite. The basalts and basaltic andesite define a potassium-poor tholeiitic suite, while the andesites and dacites are calc-alkaline. Phenocrysts include feldspar, olivine, plagioclase and pyroxene, and there are gabbro-like xenoliths, but unlike other South Sandwich volcanoes the lavas are mostly aphyric. Rocks from the older southeastern half are mostly basaltic, the younger northwestern half is mostly andesitic/ dacitic, one dacitic obsidian has been reported from the southeastern half. Some rocks have been weathered. Sulfur has accumulated around active fumaroles.
The basalt, which forms about 90% of all Candlemas rocks, is considered to be the primary rock, from which the andesites evolved through fractional crystallization. A contribution of melting slab rocks is likely. The rocks of southeastern Candlemas resemble these of Vindication.
Eruption history
No rocks from Candlemas Island have been dated, but the island appears to have formed in two stages. During the first stage, the southeastern half of the island formed, which today constitutes about 90% of the volume of Candlemas. Outcrops in cliffs of the southeastern half of the island feature alternating layers of porphyritic lava flows and scoria, which are intruded by dykes and sills and show evidence of later deformation. Apart from the lava flows, some deposits were originally emplaced in now-dry lagoons, others formed through fallout. Subglacial eruptions of Mount Perseus produced glacial meltwater floods. Close to Medusa Pool, some lava flows have become palagonitic. Later in the history of the island, two lava flows were emplaced on the southwestern end of the southeastern half of Candlemas; they form Carbon Point and Clapmatch Point. These flows may be analogous to historical eruptions at Tristan da Cunha. The southeastern half of the island was extensively eroded by the sea and by glaciers.
After a hiatus, volcanism shifted north of the previous volcanic centre, where eruptions in shallow water formed Lucifer Hill initially probably as a separate island. It is possible that an earlier volcano existed at the present location of Lucifer Hill, leaving pyroclastic flow deposits in the northwestern sector of the southeastern half of Candlemas Island. Lucifer Hill consists mostly of volcanic ash mixed with scoria, with blocks reaching sizes of . The oldest outcrops belong to the northern cone and are found in Clinker Gulch. The cones emitted numerous lava flows reaching thicknesses of , separated by scoria and ash eruptions. Lava flows are thick and fragmented, with surface ridges. The relative ages of the lava flows have been established from their appearance and relative grade of erosion; two southern and northern flows formed first. Then the entire eastern half of the lava flow field was emplaced. Subsequently, the southwestern lava flow was erupted from the southern vent. Last, the northwestern lava flow and lava flows on the southeastern flank were emplaced. The lava flows form wide lava deltas.
Chronology and historical reports
Unlike the first stage, which may have lasted for 1-2 million years, the second stage probably only began a few centuries or millennia ago, which might make it one of the youngest volcanoes of the South Sandwich Islands. There is no evidence of recent activity in the southeastern half of the island, other than a localized tilting in its northwestern sector that may be caused by the activity of northwestern Candlemas.