Mount Melbourne

Template:Short description Template:Featured article Template:Use dmy dates Template:Use shortened footnotes Template:Infobox mountain

Mount Melbourne is a Template:Convert ice-covered stratovolcano in Victoria Land, Antarctica, between Wood Bay and Terra Nova Bay. It is an elongated mountain with a summit caldera filled with ice with numerous parasitic vents; a volcanic field surrounds the edifice. Mount Melbourne has a volume of about Template:Convert and consists of tephra deposits and lava flows; tephra deposits are also found encased within ice and have been used to date the last eruption of Mount Melbourne to Template:Nobreak. The volcano is fumarolically active.

The volcano is part of the McMurdo Volcanic Group, and together with The Pleiades, Mount Overlord, Mount Rittmann and the Malta Plateau forms a subprovince, the Melbourne volcanic province. The volcanism is related both to the West Antarctic Rift and to local tectonic structures such as faults and grabens.Template:Efn Mount Melbourne has mainly erupted trachyandesite and trachyte, which formed within a magma chamber; basaltic rocks are less common.

Geothermal heat flow on Mount Melbourne has created a unique ecosystem formed by mosses and liverworts that grow between fumaroles, ice towers, and ice hummocks. This type of vegetation is found at other volcanoes of Antarctica and develops when volcanic heat generates meltwater from snow and ice, thus allowing plants to grow in the cold Antarctic environment. These mosses are particularly common in a protected area known as Cryptogam Ridge within and south of the summit caldera.

DescriptionEdit

Mount Melbourne lies in North Victoria Land,Template:Sfn facing Wood Bay of the Ross Sea. To the southeast lies Cape Washington and due south lies Terra Nova Bay; Campbell Glacier runs west from the volcanoTemplate:Sfn and Tinker Glacier lies north of the volcanic field.Template:Sfn The seasonalTemplate:Sfn Italian Mario Zucchelli Station lies Template:Convert from the volcano;Template:Sfn the 5th Chinese station in Antarctica (due to be completed in 2022),Template:Sfn Template:Sfn the Korean Jang Bogo Station,Template:Sfn the German Gondwana Station Template:Sfn and a neutrino detector are also in the area.Template:Sfn Mount Melbourne was discoveredTemplate:Sfn and first recognized as a volcano by James Ross in 1841Template:Sfn and named after William Lamb, 2nd Viscount Melbourne, who was then the prime minister of the United Kingdom.Template:Sfn The volcano and its surroundings were investigated by New Zealand-based parties in the 1960s, by German ones in the 1970s and 1980s and by Italian-based parties in the 1980s and 1990s.Template:Sfn The volcanoTemplate:Sfn and its summit can be accessed from the stations by helicopter.Template:Sfn

VolcanoEdit

File:Mount Melbourne From Terra Nova Bay.png

Mount Melbourne as seen from Zucchelli Station

Mount Melbourne is an elongated stratovolcano Template:Sfn Template:Efn formed by lava flows and tephra fall depositsTemplate:Efn, with gentle slopes.Template:Sfn The volcano is uneroded and forms a coneTemplate:Sfn with a base area of Template:Convert.Template:Sfn Viewed from afar, Mount Melbourne has a nearly perfect cone-like profile that has drawn comparisons to Mount Etna in Italy and Mount Ruapehu in New Zealand.Template:Sfn Lava domes and short lava flows form the summitTemplate:Sfn while volcanic mounds, cones,Template:Sfn domes and scoria cones dot its flanks;Template:Sfn Template:Convert from the summitTemplate:Sfn is a large parasitic vent on the north-northeastern slope,Template:Sfn which generated several lava flows.Template:Sfn Part of the edifice rises from below sea level.Template:Sfn Pyroclastic flow depositsTemplate:Snda rarity for Antarctic volcanoesTemplate:Sndhave been reported.Template:Sfn The total volume of the edifice is about Template:Convert.Template:Sfn

A Template:Convert Template:Sfn crater or caldera Template:Sfn sits at the top of the volcano. The highest point of the volcano lies east-northeast of the caldera and reaches Template:Convert elevation.Template:Sfn Template:Efn The caldera has an incomplete rim and is filled with snow, leaving a Template:Convert depression.Template:Sfn The rim of the caldera is covered by volcanic ejecta including lapilli and lava bombs, probably the products of the most recent eruption,Template:Sfn which overlie a Template:Convert layer of pumice lapilli.Template:Sfn Three small, nested cratersTemplate:Sfn formed by phreatomagmatic eruptions occur on the southern rim of the summit caldera.Template:Sfn Pyroclastic fall deposits crop out in the northern rim of the calderaTemplate:Sfn and there are more alternating lava-tephra sequences elsewhere in the summit region. There is evidence of past structural instability (collapse structures) on the eastern and southeastern flanks,Template:Sfn and an arcuate (with the shape of an arc) Template:Convert scarp on the eastern flank appears to be an incipient sector collapse.Template:Sfn

Except for geothermal areas, the ground is bouldery.Template:Sfn Some of the coastal areas around the volcano are ice-free and rocky.Template:Sfn Frost heave has been observed in the summit region.Template:Sfn Small creeks flow down the eastern flank of Mount Melbourne;Template:Sfn they are fed by meltwater during summer and quickly disappear when the snow is gone.Template:Sfn

GlaciationEdit

The mountain is covered with permanent ice, which extends to the coastTemplate:Sfn and leaves only a few exposures of the underlying rock;Template:Sfn Template:Sfn rocky outcrops are most exposed on the eastern flank.Template:Sfn The caldera hosts a névé that generates a westward-flowing glacier.Template:Sfn An icefall lies northwest of the caldera.Template:Sfn Glaciers emanating from snowfields on the volcano have deposited moraines;Template:Sfn these and tills from both Pleistocene Template:Efn and Holocene Template:Efn glaciations crop out at Edmonson Point.Template:Sfn

Tephra layers crop out in ice cliffs Template:Sfn and seracs Template:Sfn and testify to recent eruptions,Template:Sfn including the one that deposited the ejecta and lapilli pumice units on the summit.Template:Sfn Tephra bands are also found in other glaciers of the region.Template:Sfn They form when snow accumulates on top of tephra that fell onto iceTemplate:Sfn and in the case of Mount Melbourne they indicate eruptions during the last few thousand years.Template:Sfn Volcanic sediments from Mount Melbourne are also found in Terra Nova Bay.Template:Sfn The Campbell Glacier carries glacial erratics derived from Mount Melbourne.Template:Sfn

Volcanic fieldEdit

File:MountMelbourneMap.jpg

Topographic map of Mount Melbourne (1:250,000 scale) from USGS Mount Melbourne

Mount Melbourne is surrounded by a volcanic fieldTemplate:Sfn consisting of 60 exposed volcanoes,Template:Sfn which have the form of scoria cones and tuff rings with hyaloclastite deposits, lava flows and pillow lavas. Some of these volcanoes formed under ice.Template:Sfn The volcanic field forms a peninsula which is separated by steep faults from the Transantarctic Mountains to the north.Template:Sfn Among these volcanoes is Shield Nunatak southwest from Mount Melbourne,Template:Sfn a subglacial volcano, now exposed, that may have formed during the last 21,000 to 17,000 years.Template:Sfn The Cape Washington ridge consists mostly of lava, including pillow lava, overlaid by scoria cones,Template:Sfn and is the remnant of a shield volcano.Template:Sfn Edmonson Point is another volcanic complex in the volcanic field that formed partly while interacting with glaciers and partly through phreatomagmatic activity.Template:Sfn Other volcanoes in the field are Baker Rocks, Oscar Point and Random Hills.Template:Sfn These volcanoes are aligned mainly in a north–south direction,Template:Sfn with palagonitized Template:Efn outcrops that expose dikes.Template:Sfn Perfectly preserved scoria cones occur at Pinckard Table north of the volcanic field, while Harrow Peak is a heavily eroded lava plug.Template:Sfn The total volume of volcanic rocks is about Template:Convert Template:Sfn and their emplacement apparently altered the path of the Campbell Glacier.Template:Sfn

GeologyEdit

File:Map of West Antarctic Rift (WARS).svg

West Antarctic Rift system in the Ross Sea; red dashed line is the margin of the rift.

Mount Melbourne is part of the McMurdo Volcanic Group, which includes the active volcano Mount Erebus.Template:Sfn This volcanic group is one of the largest alkaline volcanic Template:Efn provinces in the world,Template:Sfn comparable with that of the East African Rift,Template:Sfn and is subdivided into the Melbourne, the Hallett and the Erebus volcanic provinces.Template:Sfn The volcanic group consists of large shield volcanoes mainly near the coast, stratovolcanoes and monogenetic volcanoes Template:Sfn which formed parallel to the Transantarctic Mountains.Template:Sfn

Volcanic activity of the McMurdo Volcanic Group is tied to continental rifting Template:Sfn and commenced during the Oligocene.Template:Efn Template:Sfn It is unclear whether this is caused by a local hotspot beneath the area or mantle convection in the area of the West Antarctic Rift.Template:Sfn The latter is one of the largest continental riftsTemplate:Efn on Earth but little known and possibly inactive today. The Ross Sea and the Victoria Land Basin developed along this riftTemplate:Sfn and were deeply buried, while the Transantarctic Mountains were rapidly uplifted during the last fifty million yearsTemplate:Sfn and are on the "shoulder" of the rift.Template:Sfn The line separating the two is a major crustal suture, with large differences in elevation and crustal thickness across the suture.Template:Sfn Many of the volcanoes appear to have formed under the influence of fault zones in the area,Template:Sfn and increased activity in the last thirty million years has been correlated to the reactivation of faults.Template:Sfn

Mount Melbourne is part of a volcano alignment that includes The Pleiades, Mount Overlord,Template:Sfn Mount Rittmann Template:Sndall large stratovolcanoesTemplate:Sfn Template:Sndwhich with the Malta Plateau form the Melbourne province of the McMurdo Volcanic Group.Template:Sfn In addition, this province consists of numerous smaller volcanic centres, volcanic intrusions and sequences of volcanic rocks,Template:Sfn and it has been active for the past twenty-five million years.Template:Sfn Volcanic edifices buried under sediment are also part of the Melbourne province, including a cone southeast of Cape Washington, which has a size comparable to that of Mount Melbourne.Template:Sfn

Mount Melbourne and its volcanic field are over a basement of Precambrian Template:Efn to Ordovician Template:Efn age, which consists of volcanic and metamorphic rocks of the Wilson Terrane.Template:Sfn The volcano is at the intersection of three geological structures: the Rennick Graben of Cretaceous Template:Efn age, the Victoria Land Basin and the PolarTemplate:Nbs3 magnetic anomalyTemplate:Efn.Template:Sfn The Terror Rift in the Victoria Land BasinTemplate:Sfn runs between Mount Melbourne and Mount ErebusTemplate:Sfn and appears to be related to their existence.Template:Sfn Mount Melbourne appears to lie in a graben; the marginal faults on the eastern flank of Mount Melbourne are still active with earthquakes.Template:Sfn North–south-trending faulting may also be responsible for the trend in edifice structure,Template:Sfn and strike-slip faulting takes place on the eastern flank.Template:Sfn Recent offset on faultsTemplate:Sfn and Holocene coastal uplift in the area indicates that tectonic activity is ongoing.Template:Sfn

Tomographic studies have shown an area of low seismic velocity at Template:Convert depth under the volcano, which may be due to temperatures there being Template:Convert hotter than normal.Template:Sfn Anomalies underneath Mount Melbourne are connected to similar anomalies under the Terror Rift.Template:Sfn These anomalies above Template:Convert depth are focused under Mount Melbourne and the neighbouring Priestley Fault.Template:Sfn A low gravity anomaly over Mount Melbourne may reflect either the presence of low-density volcanic rocks or of a magma chamber under the volcano.Template:Sfn

CompositionEdit

Trachyandesite and trachyte are the most common rocks on Mount Melbourne, with basalt being less commonTemplate:Sfn and mostly occurring around its base. The rocks define a mildly alkaline suiteTemplate:Sfn rich in potassium, unlike the rocks elsewhere in the volcanic field. The rest of the volcanic field also features alkali basalts, basanite and mugearite. Phenocrysts include aegirine, amphibole, anorthoclase, augite, clinopyroxene, fayalite, hedenbergite, ilmenite, kaersutite, magnetite, olivine, plagioclase and sanidine.Template:Sfn Template:Sfn Template:Sfn Gneiss,Template:Sfn granulite, harzburgite, lherzolite and tholeiite xenoliths are found in the volcanic fieldTemplate:Sfn and form the core of many lava bombs.Template:Sfn Inclusions in xenoliths indicate that the gaseous components of the Mount Melbourne volcanic field magmas consist mainly of carbon dioxide.Template:Sfn The rocks in the volcanic field have porphyritic to vitrophyric textures.Template:Sfn

The trachytes and mugearites formed through magmatic differentiation in a crustal magma chamberTemplate:Sfn from alkali basalts,Template:Sfn defining an alkali basalt-trachyte differentiation series.Template:Sfn Basalts were mainly erupted early in the history of the volcano.Template:Sfn During the last hundred thousand years the magma chamber became established; this allowed both the differentiation of trachytes and the occurrence of large eruptions.Template:Sfn A gap in the rock spectrum ("Daly gap") with a scarcity of benmoreite and mugearite has been noted at Mount Melbourne and other volcanoes in the region.Template:Sfn There is no agreement on which processes contributed to petrogenesis in the Mount Melbourne volcanic fieldTemplate:Sfn but diverse mantle domains and assimilation and fractional crystallization processes appear to have played a role.Template:Sfn The magmatic system that feeds Mount Melbourne appears to have a composition distinct from the one associated with the Mount Melbourne volcanic field.Template:Sfn

Hydrothermal alteration has affected parts of the summit area, leaving yellow and white deposits that contrast with the black volcanic rocks.Template:Sfn Template:Sfn Hydrothermal sinter deposits have formed in geothermal areasTemplate:Sfn from past liquid water flow.Template:Sfn Clay containing allophane, amorphous silica and feldspar are found in the summit area.Template:Sfn

Eruption historyEdit

Mount Melbourne was active beginning 3.0–2.7Template:Nbsmillion years ago.Template:Sfn Template:Sfn Activity has been subdivided into an older Pliocene Cape Washington stage, an early Pleistocene Random Hills stage, the Shield Nunatak stage that is 400,000 to 100,000 years old,Template:Sfn and the recent Mount Melbourne stage.Template:Sfn Volcanic activity migrated north from Cape Washington towards the Transantarctic Mountains and eventually became centralized at Mount Melbourne.Template:Sfn During the last hundred thousand years Mount Melbourne has produced about Template:Convert of magma.Template:Sfn The earliest records of the volcano noted its young appearance.Template:Sfn

Mount Melbourne volcanic fieldEdit

Ages obtained on the Mount Melbourne volcanic field include 2.96 ± 0.20Template:Nbsmillion years,Template:Sfn 740,000 ± 100,000 years and 200,000 ± 40,000 years for Baker Rocks, 2.7 ± 0.2Template:Nbsmillion years and 450,000 ± 50,000 years for Cape Washington, 74,000 ± 110,000 years and 50,000 ± 20,000 years for Edmonson Point, less than 400,000 years for Markham Island, 745,000 ± 66,000 years for Harrows Peak, 1.368 ± 0.090Template:Nbsmillion years for Pinkard Table, 1.55 ± 0.05Template:Nbsmillion years, 431,000 ± 82,000 and 110,000 ± 70,000 years for Shield Nunatak, and 2.5 ± 0.1Template:Nbsmillion years for Willows Nunatak.Template:Sfn Template:Sfn The northeastern parasitic cone formed after the bulk of the volcano and appears to be younger than the summit.Template:Sfn

Radiometric dating has shown that the appearance of a landform at Mount Melbourne is not indicative of its age; some well preserved vents are older than heavily eroded ones.Template:Sfn On the other hand, a lack of proper margins of error and lack of details on which samples were dated has been problematic for radiometric dating efforts.Template:Sfn

TephraEdit

Tephra found at the Allan Hills,Template:Sfn in Dome C Template:Sfn and in the Siple Dome ice cores may come from Mount Melbourne.Template:Sfn Some marine tephra layers originally attributed to Mount Melbourne may instead come from Mount Rittmann,Template:Sfn and many tephra layers in the area have compositions that do not match these from Mount Melbourne.Template:Sfn There are additional tephra layers attributed to the volcano:

Tephra layers less than 500,000 years old in the Frontier Mountain and Lichen Hills blue-ice areas have been attributed to volcanoes in the Mount Melbourne volcanic province.Template:Sfn
A tephra layer less than 30,000 years old in a sediment core from the Ross Sea has a composition indicating that it was erupted at Mount Melbourne. Its deposition has been used to infer that that part of the western Ross Sea was ice-free at that time.Template:Sfn
A tephra layer found in the Ross Sea has been interpreted as originating from an eruption of Mount Melbourne 9,700 ± 5,300 years ago.Template:Sfn
In the Talos Dome ice core record, two tephra layers emplaced 2,680 and 5,280 years ago have compositions similar to these of Mount Melbourne.Template:Sfn
Tephra layers at Siple Dome indicate eruptions at Mount Melbourne in 304Template:NbsCE,Template:Sfn which deposited substantial amounts of sulfate on the ice sheet.Template:Sfn
A tephra layer at Siple Dome dated to 1810Template:NbsCE might have been erupted by Mount Melbourne, but its attribution is less certain than for the 304Template:NbsCE tephra.Template:Sfn

Mount Melbourne properEdit

The Edmonson Point ignimbrite is a trachytic ignimbrite that crops out at Edmonson Point. It consists of three units of ash-supported, lapilli- and pumice-rich deposits with intercalated breccia lenses that reach a thickness of Template:Convert. They are two ignimbrite units separated by a base surge deposit. Faulting has offset the sequences, which are intruded by dikes.Template:Sfn The Edmonson Point ignimbrite was produced by large Plinian eruptions Template:Sfn and is about 115,000 years old.Template:Sfn The eruption deposited tephra into the Ross Sea,Template:Sfn and correlative tephra layers were found in the Talos Dome ice core.Template:Sfn

After this ignimbrite, a series of dikes gave rise to the Adelie Penguin Rookery lava field. This lava field, which probably formed subglacially, is made up by numerous blocky lava flows with glassy margins that reach a thickness of Template:Convert and are formed by hawaiite Template:Sfn and benmoreite.Template:Sfn They were fed through numerous dikes, which also gave rise to small scoria cones and spatter cones, and were emplaced non-contemporaneously.Template:Sfn A tuff cone rises from the lava field and is formed by monogenetic volcano ejecta, including lava bombs encasing granite fragments and bombs large enough to leave craters in the ash they fell in.Template:Sfn Ropy basalt lava flows with an uncertain source vent, and a undissected scoria cone rise above the lava field and complete the Edmonson Point system.Template:Sfn The Adelie Penguin Rookery lava field was erupted about 90,000 years ago,Template:Sfn and its emplacement may have been accompanied by the emission of tephra recorded in the Talos Dome ice core.Template:Sfn The eruptions of the last 120,000 years probably caused the anomalous thinning of the Campbell Glacier during that time, which is unlike the behaviour of other Antarctic glaciers.Template:Sfn

Rocks at the summit have ages of between 260,000 and 10,000 years.Template:Sfn Template:Sfn Individual eruptions have been dated to 10,000 ± 20,000, 80,000 ± 15,000, 260,000 ± 60,000 and 15,000 ± 35,000 years ago.Template:Sfn Highly imprecise ages of late Pleistocene to Holocene age have been obtained from the ejecta layer on the summit.Template:Sfn One large eruption took place 13,500 ± 4,300 years ago.Template:Sfn Three cryptotephra layers in Edisto Inlet (close to Cape Hallett) have been attributed to eruptions that took place between 1,677 and 1,615 years before present;Template:Sfn a tephra layer from Roosevelt Island dates to the same time.Template:Sfn These eruptions probably took place on parasitic vents of Mount Melbourne. Two more parasitic eruptions took place in the same timeframe.Template:Sfn

Last eruption and present-day activityEdit

Tephrochronology has yielded an age of 1892 ± 30Template:NbsCE for the last eruption.Template:Sfn This eruption deposited a major tephra layer around the volcano, which crops out mainly on its eastern sideTemplate:Sfn and in the Aviator and Tinker Glaciers.Template:Sfn The three small craters on the rim of the Mount Melbourne summit crater formed at the end of this eruption.Template:Sfn

No eruptions have been observed during historical time,Template:Sfn and Mount Melbourne is considered to be quiescentTemplate:Efn and a low-hazard volcano.Template:Sfn Template:Sfn Ongoing deformation and seismic activity occurs at Mount Melbourne,Template:Sfn Template:Sfn and the latter may be caused either by the movement of fluids underground or by fracturing processes.Template:Sfn Icequakes caused by glacier movement also occur.Template:Sfn Geothermal activity was steady between 1963 and 1983,Template:Sfn while ground deformation commenced in 1997. This deformation was probably caused by changes in the geothermal system.Template:Sfn

Hazards and monitoringEdit

Future moderateTemplate:Sfn to large explosive eruptions Template:Sfn such as Plinian eruptions are possible.Template:Sfn The prevailing winds would transport volcanic ash eastward across the Ross Sea,Template:Sfn and the ash might affect research stations close to Mount Melbourne such as Mario Zucchelli, Gondwana and Jang Bogo.Template:Sfn The hazards of Antarctic volcano eruptions are poorly known.Template:Sfn Mount Melbourne is remote, and thus renewed eruptionsTemplate:Sfn would likely not impact any human habitations but regional environmental or even global climate impacts,Template:Sfn as well as disruptions of air travel, are possible.Template:Sfn

Italian scientists began a volcanology research program on Mount Melbourne in the late 1980s,Template:Sfn establishing a volcanological observatory in 1988.Template:Sfn In 1990 they installed seismic stations around Mount MelbourneTemplate:Sfn and between 1999 and 2001 a network of geodetic measurement stations around Terra Nova Bay, including several aimed at monitoring the Mount Melbourne volcano.Template:Sfn Beginning in 2012 Korean scientists at the Jang Bogo Station added another seismic station network to monitor the volcano.Template:Sfn In 2016–2019 geochemical, seismological and volcanological research was carried out at Mount Melbourne as part of the ICE-VOLC project.Template:Sfn

Geothermal activityEdit

Geothermal activity occurs around the summit crater, on the upper parts of the volcanoTemplate:Sfn and on the northwestern slope between Template:Convert elevation.Template:Sfn Another geothermal area exists close to Edmonson Point,Template:Sfn including fumaroles,Template:Sfn thermal anomaliesTemplate:Sfn and freshwater ponds. Their temperatures of Template:Convert are considerably higher than normal atmospheric temperatures in Antarctica.Template:Sfn The geothermal areas are visible in infrared light from aircraft.Template:Sfn Satellite images have identified areas with temperatures of over Template:Convert.Template:Sfn

Individual geothermally heated areas cover surfaces of a few hectares.Template:Sfn Typically, the soil consists of a thin sand layer with organic matter covering scoria gravel.Template:Sfn In some places, the ground is too hot to be touched.Template:Sfn Mount Melbourne is one of several volcanoes in Antarctica that feature such geothermal soils.Template:Sfn

Fumarolic landforms include ice towers,Template:Efn fumaroles,Template:Sfn ice "roofs",Template:Sfn caves in snow and firn,Template:Sfn bare ground,Template:Sfn ice hummocks surrounding fumarolic vents,Template:Sfn puddles formed by condensed water vapourTemplate:Sfn and steaming ground:Template:Sfn

Ice hummocks are hollow glacial structures that encase fumaroles. They reach heights of Template:Convert and widths of Template:Convert.Template:Sfn They mainly form over colder ground and widely spaced fumarolic vents.Template:Sfn
Ice towers are widespread around the caldera, especially in the north-northwestern and south-southeastern sectors, while warm ground is more restricted. In the northern sector of the volcano, ice towers and bare ground form a southeast–northwest trending lineament.Template:Sfn Ice towers form when fumarolic gases freeze in the cold Antarctic air.Template:Sfn
Glacial caves form when geothermal heat melts ice, leaving cavities. Some of these caves are in the summit caldera and reach lengths of several hundred metres, with ceilings reaching Template:Convert height.Template:Sfn Several caves have been accessed through ice towersTemplate:Sfn or through gaps where the ice surrounding the cave rests on rock,Template:Sfn and one ice cave ("Aurora Ice Cave") was mapped in 2016.Template:Sfn

The caves and ice towers release water-vapour-rich warm air.Template:Sfn Fumarole temperatures can reach Template:Convert, contrasting with the cold air.Template:Sfn Fumaroles release gases containing excesses of volcanic carbon dioxide and methane.Template:Sfn Hydrogen sulfide gas has been detected too,Template:Sfn but only at low concentrations which do not prevent the development of vegetation.Template:Sfn Yellow deposits have been identified as sulfur.Template:Sfn

The geothermal manifestations appear to be powered mainly by steam, as there is no evidence of geothermal landforms related to liquid water flow and heat conduction is not effective enough at most sites. It is possible that underground liquid water reservoirs form in some areas, however. The steam is produced by the melting and evaporation of snow and ice, and is then channelled through rocks to the vents. Atmospheric air likely circulates underground and is heated, eventually exiting in ice towers.Template:Sfn An early theory that the ice towers formed on top of a cooling lava flow is considered improbable given the long duration of fumarolic activity; a lava-heated system would have cooled down by now.Template:Sfn

ClimateEdit

There are no detailed meteorological records of the summit region.Template:Sfn Winds blow mostly from the westTemplate:Sfn and more rarely from the northwest. Catabatic winds blow from the Priestly and Reeves valleys.Template:Sfn Precipitation is scarce. During winter, polar night lasts about three months.Template:Sfn Temperatures in the summit region have been variously reported to either not exceed Template:Convert Template:Sfn or to range between Template:Convert.Template:Sfn Seasonal temperature variation is high and reaches Template:Convert.Template:Sfn

During the Last Glacial Maximum (LGM), a marine ice sheet occupied Terra Nova Bay. The "Terra Nova Drift" was deposited between 25,000 and 7,000 years ago and is overlaid by later moraines from retreating ice during the post-LGM period.Template:Sfn During the late Holocene after 5,000 years before present, glaciers advanced again as part of the Neoglacial.Template:Sfn One minor advance occurred in the last Template:Circa years.Template:Sfn

LifeEdit

Algae,Template:Efn Template:Sfn lichens,Template:Sfn liverworts Template:Efn and mosses Template:Efn Template:Sfn grow on geothermally heated terrain on the upper parts of Mount Melbourne. Algae form crusts on the heated ground. Mosses form cushionsTemplate:Sfn and often occur around steam ventsTemplate:Sfn and under ice hummocks.Template:Sfn The moss species Campylopus pyriformis does not grow leaves on Mount Melbourne.Template:Sfn Pohlia nutans forms small shoots.Template:Sfn The two moss species form separate standsTemplate:Sfn which occur at different sites of the volcano.Template:Sfn Together with occurrences at Mount Erebus, they constitute the highest mosses growing in Antarctica.Template:Sfn Small peat deposits have been found.Template:Sfn

Vegetation is particularly common on a ridge withinTemplate:Sfn and south of the main crater, "Cryptogam Ridge".Template:Efn It features a long snow-free area with a gravelly ground, small terraces and stone stripes.Template:Sfn Soil temperatures recorded there reach Template:Convert.Template:Sfn These are the only occurrences of Campylopus pyriformis on warm ground in Antarctica.Template:Sfn

Mount Melbourne along with Mount Erebus, Mount Rittmann and Deception Island is one of four volcanoes in Antarctica known for having geothermal habitats, although other poorly studied volcanoes such as Mount Berlin, Mount Hampton and Mount Kauffman may also have them.Template:Sfn In South America, high-elevation geothermal environments similar to Mount Melbourne are found at Socompa.Template:Sfn Vegetation on geothermally heated terrain is unusual in AntarcticaTemplate:Sfn but other occurs elsewhere, including on Bouvet, Deception Island, Mount Erebus and the South Sandwich Islands.Template:Sfn

The geothermal area at the summit of Mount Melbourne makes up Antarctic Specially Protected Area Template:Nbs118,Template:Sfn which contains two specially restricted areas around Cryptogam Ridge and some markers used in studies of volcano deformation.Template:Sfn Some algae from Mount Melbourne were accidentally transferred to Deception Island or Mount Erebus.Template:Sfn

Edmonson Point and Cape Washington have Adelie penguin and emperor penguin rookeriesTemplate:Sfn Template:Sfn and south polar skuas and Weddel seals are also found.Template:Sfn More than twenty-four lichen plus six moss speciesTemplate:Sfn (including Bryum argenteum moss) have been found at Edmonson Point,Template:Sfn as well as microbial mats formed by cyanobacteria. Nematodes and collembola complete the biota of Edmonson Point.Template:Sfn

BiologyEdit

The vegetation on Mount Melbourne grows mainly on terrain heated to temperatures of over Template:Convert, and there are gradations in vegetation type from colder to warmer temperatures.Template:Sfn There are differences between the vegetationTemplate:Sfn and bacterial communities at Cryptogam Ridge and those on the northwest slope of Mount Melbourne; distinct soils may be the reason for such differences.Template:Sfn

These communities must have reached Mount Melbourne from far away.Template:Sfn Transport was probably by wind as there is no flowing water in the region.Template:Sfn Mount Melbourne was recently active, has a polar night lasting thirteen weeks,Template:Sfn has soils containing toxic elements such as mercury,Template:Sfn is distant from ecosystems that could be the source of colonization events, and lies away from the westerlies Template:Efn, which may explain why the vegetation is species-poor.Template:Sfn Pohlia nutans may have arrived only recently on Mount Melbourne, or this volcano is not as favourable for its growth as Mount Rittmann, where this moss is more common.Template:Sfn Its colonies are less vigorous on Mount Melbourne than Campylopus pyriformis.Template:Sfn

Condensing fumarole gases and meltwater from snow form the water supply of this vegetation.Template:Sfn Mosses are concentrated around fumarolic vents as there is more fresh water available there.Template:Sfn The steam freezes in the cold air, forming the ice hummocks that act as a shelter and maintain stable humidity and temperature.Template:Sfn The geothermal heating and the availability of freshwater sets these volcanic biological communities apart from other Antarctic vegetation communities that are heated by the sun.Template:Sfn

Some bacterial species are nitrogen fixing.Template:Sfn Genetic analysis has found that some mosses at Mount Melbourne are mutating, yielding genetic variation.Template:Sfn Template:Sfn Template:Sfn The hot, wet soils at Mount Melbourne host thermophilic organisms,Template:Sfn making Mount Melbourne an island of thermophilic life on an ice-cold continent.Template:Sfn Cold-tolerant microbes coexist with the thermophiles.Template:Sfn

Other species associated with the vegetation are the protozoan Corythion dubium,Template:Sfn which is a testate amoeba Template:Sfn common in Antarctica Template:Sfn and the only invertebrate found in the geothermal habitats of Mount Melbourne,Template:Sfn actinobacteria Template:Sfn and various actinomycetes Template:Sfn and fungal Template:Efn genera.Template:Sfn Several bacterial species were first described from Mount Melbourne's geothermal terrains:

Alicyclobacillus pohliae from the northwest slope.Template:Sfn
Aneurinibacillus terranovensis from Cryptogam Ridge and also from Mount Rittmann volcano.Template:Sfn
Bacillus fumarioli from Cryptogam Ridge.Template:Sfn
Bacillus thermoantarcticus from Cryptogam Ridge,Template:Sfn later renamed to Bacillus thermantarcticus.Template:Sfn A further reclassification to Geobacillus thermantarcticus was proposed in 2012.Template:Sfn
Brevibacillus levickii from the northwest slope.Template:Sfn

NotesEdit

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ReferencesEdit

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SourcesEdit

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External linksEdit

Template:Antarctic Specially Protected Areas