This should be the last general article on volcanic regions of Antarctica. While I try hard to never say never, we will have (hopefully) covered the majority of recently active volcanic regions on the continent. That being said, we never know what is actually around the next bend on the Information Highway so anything is possible regarding future articles.
The last major active volcanic region in Antarctica is adjacent to Marie Byrd Land, and follows the West Antarctica Rift System (WARS) to the north, across the Ross Sea and down the western edge of the Transantarctic Mountains.
The two major parts of this region are the Ross Sea and Victoria Land. The Ross Sea is a huge embayment that separates Marie Byrd Land from Victoria Land. The Transantarctic Mountains are relatively close to the ocean which in turn has pushed most of the volcanic activity to the coast and into the sea.
Like Marie Byrd Land, WARS is the major tectonic driver of activity in this region. Unlike Marie Byrd Land, there is not a massive permanent ice sheet across the region, although it is well glaciated.
Volcanic activity is grouped into four adjoining volcanic provinces. From south to north they are the Erebus Volcanic Province, Melbourne Volcanic Province, Hallett Volcanic Province, and Balleny Islands Volcanic Province. The Balleny may or may not constitute another volcanic province as the sources conflict. The islands are most certainly volcanic in origin. Finally, the floor of the ocean offshore Ross Sea which also is an extension of the WARS is littered with seamounts of volcanic origin.
New Zealand claims the Ross Sea region. Americans operate a pair of research facilities on Ross Island (home of Mount Erebus), Scott Station and McMurdo Station.
The Ross Sea was discovered in 1841. Due to its location, the interaction of the continental shelf, the abyss, the ice shelf off Marie Byrd Land, and the winds off the ice cap over the interior, it supports a rich array of marine life including whales, penguins, and a very healthy variety of their food sources (various forms of krill). Interestingly enough, there are not lot of seals present.
Circulation of waters is dominated by the polynya process, where slow moving, nutrient rich, relatively warm, salty circumpolar deep water moves upslope. The warmer, food-rich waters support the significant wildlife near the ice shelf. Colder water flows downslope back into the abyss. There is a katabatic wind off the ice sheet which tends to keep the area between the toe of the ice shelf and the sea ice mostly clear of ice for a part of the year.
Explorers hunted seals to provide food for crews and dogs, but they were not hunted industrially like seals on the opposite side of the continent and farther up the Antarctic peninsula. Population has ranged 2,000 – 3,000 over the last half century and is currently closer to the lower number.
On the other hand, the amount of krill available makes the Ross Sea a very good whaling location, particularly for the massive blue whales. While whales were seen in early expeditions, they were not actively hunted until the 1920s when a large number of blue whales were taken. Other whales present in large numbers are Minke whales and Orca. Industrial whaling stopped by 1986.
Erebus Volcanic Province
The first of four volcanic provinces of this part of Antarctica is called the Erebus Volcanic Province. There is some confusion as Erebus is combined with the Melbourne Volcanic Province to describe the McMurdo Volcanic Group. To make things worse, if you do a Google search on Melbourne Volcanic Province, you end up with a number of hits in Oz near Melbourne. For our purposes, I will keep the discussion here in Antarctica, and not conflate the volcanic provinces on the two continents.
The province includes Ross Island with Mount Erebus, Mt Terror, Mt Bird and the Hut Point Peninsula. Farther south are the Dailey Islands, White Island, Black Island and the peninsula with Mt. Discovery and Mt. Morning. Volcanism in this province started as early as 40 – 35 Ma.
Erebus is currently active, with both a lava lake and Strombolian eruptions on a continuous basis. It dates less than 1.3 Ma. Erebus is nearly 3,800 m high and is one of the four major volcanoes forming Ross Island. There have been at least two caldera forming eruptions over the life of Mount Erebus, the most recent was late Pleistocene. The active crater is around half a kilometer in diameter and contains an active lava lake which has existed since the volcano was discovered in 1841. Activity ramps up at times to larger Strombolian explosions which eject bombs onto the crater rim. Mount Erebus erupts phonolites and trachyte – basalt mixtures. Its plumbing system is open and stable, in place for as long as the last 17,000 years.
Cape Royds and Barne date less than 1.0 Ma. Cape Royds is covered with phonolitic volcanics. It is mostly ice free and is a penguin and skua breeding ground. Weddell seals also use it as a haulout.
Mount Terror is the second major volcano constructing Ross Island. It dates between 1.3 – 1.7 Ma and tops out at 3,262 m. Like Erebus, it is also topped with what looks to be at least one caldera. The volcano is a large basaltic shield volcano with numerous pyroclastic cones and lava domes, the youngest of which date around 0.8 Ma (Terra Nova). Rocks near the rim have not been dated. Cape Crozier is the western end of the island and dates between 0.8 – 1.3 Ma. This is where the most recent volcanic rocks from Mount Terror end up.
Mount Bird is the third major volcano making up Ross Island. It is the oldest at 3.8 – 4.6 Ma. Like Terror, it is another basaltic shield volcano formed by a thick stack of basaltic lava flows. Late in the eruptive sequence, there were scoria cones and domes formed. Lava flows are phonolites.
Volcanism on White Island dates between 7.65 – 0.17 Ma. It was mostly subaerial. An early phase formed pillow breccias. There are a pair of nunataks in the southern part of the island as tuff cones. Magmatism for White Island is thought to be a result of rift-related decompression melting of previously enriched magmas.
Black Island dates between 11.2 – 1.7 Ma. It is basaltic and mostly ice free. High prevailing winds keep snow from staying put. It hosts a telecommunications facility that supports McMurdo Station some 40 km away.
Mt. Discovery dates between 5.5 – less than 1 Ma. It lies at the head of McMurdo Sound. Brown Peninsula, which dates between 2.1 – 2.7 Ma is one extension to the north, and Minna Bluff dates 12 – 6 Ma is another extension to the east. Mount Morning, which will be discussed later is connected via a saddle to the west. Mount Discovery is nearly 2,700 m high. It is constructed along the edge of the WARS.
Mt. Morning is a large shield volcano topped with a 4 m diameter caldera. While its composition is unknown, the gentle slope suggests a basaltic composition. Outcrops on the summit are phonolitic. There are a number of basaltic scoria cones on the northern slope. One of the cones is dated at 1.15 Ma. Mt. Morning dates in two pulses, the first between 18.7 – 11.4 Ma, and the second between 6.1 – 0.1 Ma. There are over 50 youthful flank vents. Major volcanic rocks are phonolites, basalts, and trachytes.
There are a pair of other neighboring onshore volcanic centers date 4 – 1.5 Ma and between 14 – less than 1 Ma.
Melbourne Volcanic Province
The next volcanic group to the south is the Melbourne Volcanic province. Unlike the other volcanoes in this region, these are on the land side of the rift and comprise a group of four relatively young stratovolcanoes associated with north to NW-trending grabens and faults in northern Victoria Land.
It is in turn divided into four subprovinces: Malta Plateau, The Pleiades, Mount Overlord, and Mount Melbourne. Activity began around 35 Ma ago. These volcanoes are considered part of the Transantarctic Mountains. Their location seems to be related to the discontinuity in plate thickness under the Mountains at 40 km, which thins to 17 – 21 km under the Ross Sea. The grabens and faults run parallel to the western and NW boundaries of the Ross Sea in line with the long axis of the mountains.
Volcanic activity appears to have begun along the faults or at their intersections. If I understand what I am reading correctly, It appears there were two surges of magmatic activity – 48 – 29 Ma for pluton and dike emplacement, and 31 – 18 Ma for the start of surface volcanism. The large stratovolcanoes Mount Melbourne and Overlord are at the intersection of regional linements. Volcanic fields are located near Edmonson Point to the east along the coast. Timing of these events varied greatly based on location. For example, there was not a significant break between the youngest plutonic activity and the oldest volcanic rocks on the Malta Plateau
The oldest dated rocks are at Mount Overlord and date 14 Ma. Mount Melbourne is the youngest, and the only one still active. There are fumaroles and hot springs in the Melbourne and Edmonson Point area.
The Pleiades volcano is a small trachytic stratovolcano, Mount Pleiones, and several lava domes and nested cinder cones. They appear to be among the youngest volcanic centers in Antarctica dated as recently as 3,000 years ago. Other dating efforts go back between 12,000 – 40,000 years. Volcanic products include trachyandesites, evolved basalt, trachyte, and phonolites. There is a confirmed eruption around 1050 BC, though the uncertainty on this eruption can go back as long as 14,000 years.
An eruption identified in ice core samples from Talos Dome some 250 km to the east document what may have been the largest volcanic eruption in this part of Antarctica in the last eight centuries. The fall took place in 1254. Chemically, the tephras and ash are consistent with trachyites from The Pleiades or Mount Rittmann of the Melbourne Volcanic Province.
Mount Rittman is an 8 x 5 km caldera under the Aviator Glacier. It has been dated between 4 – 0.07 Ma and still has active fumaroles and heated ground.
Mount Melbourne is a young, large stratovolcano on the coast of the Ross Sea. It is 2,732 m high and clad in glaciers. It is at the center of a volcanic field that includes subglacial vents along a N-S axis. There are a large number of scoria cones, lava domes, lava flows, and lava fields exposed on the summit and the upper flanks. Some of them look very young. There are tephra layers between the ice layers. The most recent eruption likely took place between 1862 – 1922. The volcano has active fumaroles along a generally N-S line cutting through the summit and along a line of phreatomagmatic craters on the southern rim. Active fumaroles build ice towers. Primary eruption products include trachyte, various evolved basalts. There is even some rhyolite. This is an interpolate volcano.
Hallett Volcanic Province
Next group to the north is the Hallett Volcanic Province. It consists of four massive near offshore piles of volcanic rock. One, Coulman, is an island. The other three, Daniell, Hallett, and Adare, are peninsulas connected to the shore by ice-filled troughs. Each volcano is a broad, elongated mountain, as eruptions progressed northward along underlying fissure zones. They generally top out at 2,000 m and have large calderas on top. The volcanoes are distributed along the Hallett Fracture Zone.
The volcanoes date from Miocene to Holocene and are constructed from basalt and trachyte magmas. The base of the volcanoes are primarily breccias, and pillow-breccias, indicating initial growth was subglacial. The volcanoes are topped with lavas and scoria cones which are no subaerial. Small masses of upper Cenozoic volcanic rocks occur on the mainland, west and SW of the volcanoes.
Coulman island is the southernmost of the volcanoes. It is 33 km long, and ranges from 5 – 14 km wide. It is topped with a caldera. The island is surrounded with cliffs some 700 – 1,000 m above the ocean. The cliffs are steep, with angles approaching 80 degrees in several places. The caldera is 6 km in diameter and tops out at 1,900 – 2,200 m. The caldera has a depth of at least 700 m and is breached in several places by glaciers. There is a semicircular bay in the SW coast of Coulman island that is 7 km in diameter that may be another caldera.
The Daniell (sometimes called Danielle) Peninsula is some 70 km long and as much as 20 km wide. The northern two thirds is a broad symmetrical dome. The island is surrounded by steep cliffs some 100 – 900 m high. Although the entire peninsula can properly be called a single volcano, it is also described as a massive shield consisting of more than one volcanic center. The northern two thirds of the peninsula was formed by overlapping shield volcanoes along a fissure zone. The largest in this section (Mount Tucker?) rises some 2,000 m. Next to the south is Mount Brewster, also 2,000 m high, and a young volcano. South of Brewster is an eroded ice-filled caldera. The southern part of the peninsula looks to be formed by overlapping volcanoes broken by two large, breached calderas. Mount Lubbock is the most prominent volcanic center on this part of the island at 1500 m high. There are Holocene cinder cones through ice covering the northern volcano.
The Hallett Peninsula is roughly triangular, with sides of 22 km, 33 km, and 33km. Most of the surface is buried under an ice cap, but has spectacular tock exposures along the eastern cliffs, and good along the southern cliffs. The cliffs rise directly from the sea to 1,500 – 1,700 m with a 60 degree slope. Most of the volcanoes are part of what is called the eastern belt. The northern volcano is a large dome 1 km west of the cliffs which are composed of breccias and basaltic pillow lavas, capped by layers of scoria and lavas. To the south, there are a number of volcanoes, though they are not circular, indicating eruptions took place from fissures along the belt. There is a southeastern volcano that appears to be somewhat older than the rift volcanoes just mentioned. The eastern belt is joined to the mainland by another mass of volcanic rocks, 15 km on a side. The highest and most recent portion of this is Mount Harcourt, an eroded volcano some 1,600 m high. There are remains of what appear to be a vanished volcano south to SE of Harcourt. Cliffs here expose palagonite and pillow breccias below 300 m above current sea level.
The Adare Peninsula is also a complex of overlapping shield volcanoes that date from 6 – 13 Ma. There are uneroded cinder cones thought to be as recent as the Holocene, though similar Antarctica cones have dated back to the Tertiary. Samples have dated at 1.1 and 2.3 Ma. It is the longest exposed volcanic pile of the Hallett at 77 km long. The southern two thirds of the peninsula is an ice-capped dome cresting at 2,000 m. Its southern slope is smooth with a gentle descent into the sea. The northern slope is much steeper, with outcrops and cinder cones. The high part of the dome contains at least four volcanoes, one capped with a 6 km caldera.
Volcanic remnants form the Possession Island east of southern Adare Peninsula. These are four islands and four stacks of basaltic rocks 10 km long and 3 km wide.
The palagonite breccias in the Hallett Volcanic Province look much like those produced in Iceland by eruptions beneath recent ice caps. The breccias in Iceland form about an eighth of the surface. Additionally, steep-sided tuyas in Iceland look much like the volcanoes of Hallett, with much of the construction being subglacial. The steep sides are considered to be an artifact of sub-glacial eruptions, which means that much of the construction of the Hallett volcanoes took place at times when there was at least a kilometer more ice on the ice cap surrounding them.
Balleny Island Volcanic Province
The Balleny Islands are a 200 km-long linear chain of elongated islands in the Southern Ocean off eastern Wilkes Land (northern Victoria Land). There is a long chain of seamounts that traverse the Tasman Sea floor portion of the Australian Plate. This chain may represent the track of the Balleny Plume. Magmas have erupted through oceanic crust 10 – 20 Ma old.
The magmas are primitive lavas and pyroclastics of basalt. There is little highly fractionated phonolites or trachytes present, meaning the source either had a shorter residence time in the mantle or a lower chemical ration than other sources. One of the signatures supports a plume origin for the Balleny magmas.
Argon dating of the magmas indicate the islands date from 2.6 Ma to less than 10,000 years ago. Volcanic activity on each island indicates a progression from south to north around 7 cm / year, which introduces yet another oddity, as the plate is essentially motionless. Alternative explanations are leaky transform or propagating fracture. A series of fractures that open first to the south and last to the north will explain the island shapes. Indeed we have seen this sort of propagation in other Hallett volcanoes. The problem is that this does not easily explain the line of seamounts to the north.
There are three primary islands – Young Island (255 km2), Buckle Island (124 km2), and Sturge Island (438 km2) – and a number of satellite islands. Large stratovolcanoes make up the majority of the main islands. They are also heavily glaciated and home to penguins. They are distributed along the Balleny Fracture Zone.
Young Island has active fumaroles and produced a VEI 7 eruption some 1.7 Ma. There was a report by its discoverer of “smoke” from Freeman Peak in Feb. 1839.
Buckle Island is 21 km long with an icecap. It has two relatively recent VEI 2 eruptions, 1839 and 1899.
Sturge Island is the largest of the Balleny Islands. It is 44 kmm long with a prominent summit, Russel Peak. While volcanic activity has been reported on a US Navy chart, there are no indications of present or past activity. There have not been any detailed geologic studies done on the islands.
Ross Sea Seamounts
While there are seamounts near the Ross Sea, they are well offshore and to the north of the continental shelf and slope. These seamounts generally follow lines of fracture on the surface of the Southern Ocean. I have not found subglacial volcanoes or seamounts under the Ross Ice Shelf as of this writing. While I would expect them to exist based on the subglacial volcanoes discovered under the WAIS, none have yet been reported.
The sea floor around and to the north of the Balleny, Amare, Admiralty, and Scott Islands is littered with volcanic seamounts. Analysis of rocks building these seamounts show they are alkali basalts similar to the basaltic rocks of the Balleny Islands. Scott Islands are intermediate in type between volcanics of the coastal Hallett provinces and Balleny.
Volcanic activity on the Balleny Islands and seamounts increased some 10 Ma. Admiralty seamounts started some 25 Ma. Both lines of islands and seamounts appear to be structurally connected to major transform faults. The close association suggests that the fracture zone may be a “leaky” transform fault, a fault system that allows intraplate magmas to pass to the surface.
The alignment of the Balleny Fracture Zone and the Adare Peninsula suggests a structural relationship as the West Antarctica Rift System leaves the continent and proceeds into the thinner portions of the plate underlying the Southern Ocean.
Volcanic activity in the Ross Sea / Victoria Land part of Antarctica is driven by the same tectonic forces that built the Transantarctic Mountains and opened the West Antarctic Rift System (WARS). Compared with what we saw in Marie Byrd Land, the volcanoes close to the shoreline are no longer subglacial or subaerial.
Volcanic activity in this region tends to follow lines of crustal weakness – fault lines, deep crust discontinuities where the crust thickness changes abruptly, and locations where transverse fault lines cross fault lines caused by extension.
In Marie Byrd Land we say significant volcanic activity tied to the formation of the WARS and buried under the WAIS. There were a number of relatively recent, massive stratovolcanoes on one side of the WARS. A logical question would be what happens to the WARS as it travels northward under the Ross Sea, along the coast and out into the Southern Ocean toward Tasmania.
If the lines of seamounts between the Ross Sea and Tasmania are any indication, something has been happening between the Ross Sea and Tasmania. Question is: What?
Normally, our experience with lines of seamounts is generally an indication of plate movement over a stationary hot spot. Problems with this in Antarctica is that the plate has moved very little over the last 80 Ma. Another option is that the hot spot itself is somehow mobile or fragmented into many active hot spots – one under Ross Island fueling Erebus and Terror. One (or several) moving northward along the lines of seamounts. The elongated nature of the volcanoes in the Hallett and Balleny volcanic provinces would tend to argue for this sort of movement. But we don’t normally see moving hot spots.
Two other explanations would be propagating fissure systems and leaky transform. Both would explain the linear nature of the two provinces. The problem is that the island and volcano orientations are not parallel, which takes us to the third possible explanation – a leaky transform.
If we consider a leaky transform, where does the magma come from in such quantities? To generate the magma, we need to look at the cycles of extension this part of Antarctica underwent.
Initial crust thickness before the breakup of Gondwanaland was between 40 – 50 km. The first event took place after 105 Ma and was complete by 85 Ma. At the end of the first event, crust thickness was 20 – 25 km. A second extension event took place around 30 Ma, following the initial uplift of the Transantarctic Mountains some 55 Ma. This second major extension is going on today, and has thinned portions of the plate to oceanic thicknesses – 10 – 15 km. It is through these thin, weak portions of the plate that magmas formed by decompression melt have found their way to the surface through the myriad fault system parallel to the Transantarctic Mountains and part of the WARS. Total extension in the region is in the neighborhood of 80 – 100 km.
The Decesari et al paper suggests that the Ross Sea covers foundered continental crust from the collapse of thick, elevated lithosphere since the Cretaceous. West Antarctica structure and geologic history may be due to a high plateau collapse, extension, and subsidence lithosphere in two phases creating its three basins.
The Luyendyk et al paper compares physiographic similarities between basement topographies of the eastern Ross Sea and the extension in the Sonoran extensional province of southern Arizona and northern Mexico. Extension in the Sonora peaked some 25 Ma. Erosion and thermal subsidence will lead to widespread ocean inundation of Sonora some 20 – 30 Ma in the future.
The four volcanic provinces of Victoria Land are all driven by crustal extension, with magmas likely being produced by decompression melt. Volcanoes in the region appear to have begun their active lives below the ice and are built on bases of breccias and pillow lavas.
There is no small amount of current and relatively recent volcanic activity with Erebus, The Pleiades, Mount Rittman, Mount Melbourne and the Balleny Islands being the most recent (and current) active.
The region is complex and at least to me surprisingly active. There is no reason this activity will cease any time soon. The region is very, very remote and could use significant scientific study to better characterize what has happened and more importantly, why.