Volcanic Areas

 
Tectonic theory has seven large plates, and numerous smaller microplates, floating on a mantle.

As the crustal plates nudge around the planet, on the plates ride the continents.

  


Heat rising from Earth’s core, centrifugal pull, density differences, gravitational sliding, may all be part of what causes this movement.

Plates as they collide either, push upwards, forming mountains, or are subducted into the mantle and destroyed.   Where two plates move apart, new rock is formed on the crustal surface to fill the space.

Continental crust is granite rock that has been on the surface to a time close to the creation of the planet.   Most of this older rock has been on the surface at least 1,500 million years.   Newer magma reaching Earth’s surface is basaltic crust from the mantle.   Other volcanic rock can be andesite, and rhyolite lava generated from the partial melting of continental crust.

When Antarctica separated from its ancient supercontinent and came to its polar position it was situated on two crustal plates.   65 million years ago these two plates fused into the current Antarctic plate.   The Antarctic plate is immobile, in the sense it hasn’t moved much in the last 10 million years.   It is considered to be at equilibrium, floating in the mantle.

Pressure from the abutting Pacific plate is resisted, with subduction taking place at the edge.   In the space adjoining to the two Atlantic plates, a growth of new rock occurs.   As these two plates move further apart, the Antarctic plate forms new rock islands.   Due to contour gradients of the crust, some of these islands rise in places above sea level.

On the opposite side of Antarctica the spreading seafloor is increasing the overall boundary against the Australian plate.

Antarctica is considered a stable seismic region, but on March 25, 1998 an 8.1 earthquake took place 200 kilometers west of the boundary with the Australian plate.   This earthquake is one of the largest oceanic strike-slip events ever recorded.

Dividing the west side from the east, a rift structure has produced a 3,500-kilometer long series of volcanic provinces.   Volcanic cones are well preserved along the Transantarctic Mountains and depressions in the ice surface give evidence of recent volcanism that might again become active.   Should this occur the stability of the Western sloping ice sheet might be in question.   Added water would further saturate the underlying sediment responsible for ice streaming, resulting in a much greater loss of ice.


“The Transantarctic Mountains.”
Photo by Commander John Bortniak,   NOAA


Mount Melbourne in North Victoria Land still has steam vents, fumarolic activity concentrated along the summit area.

Mount Discovery, elevation 2,681 meters was formed about five million years ago.   It has several volcanic domes on the north side of the mountain, the youngest vents being two million years old.

Mount Harcourt and three shield volcanoes make up the Hallett Peninsula that extends into the Ross Sea

Ross Island in the Ross Sea is only 72 kilometers wide but is one of the most fascinating places in Antarctica.   Situated at a latitude of 78º South, at Cape Royds, the island harbors a rookery of Adélie penguins.   Also on the western side, on the ice shelf just off Cape Crozier, there is an emperor penguin rookery.   These two colonies are the world’s southernmost penguin habitats.

The south end of the island has the world’s southernmost land accessible by ship.   There are historic buildings built and used by explorers such as Captain Robert Falcon Scott in 1902 and Ernest Shackelton in 1909.   The McMurdo Station, the center of the United States scientific research in Antarctica is close by.   As is the New Zealand Scott Base.

Two remarkable airfields are used.   One on Williams Field, built on the floating Ross Ice Shelf.   The other is a runway used in early summer on the sea ice of McMurdo Sound.

A number of crosses have been erected to commemorate people who have died, either in the seas and waters nearby, or on the treacherous ice, and steep, icy slopes of the nearby mountains.

This small island has three volcanoes.   Mount Bird, elevation 1,800 meters, forms the north part of the island.   Mount Terror on the east, elevation 3,262 meters, is mostly under snow and ice, but some rock is exposed at the summit.

Mount Erebus is on Ross Island and is the only active volcano.   3,794 meters, (12,444 feet), it is one of the few volcanoes in the world to have a lava lake in its crater.


Most volcanoes erupt, and then cool, but Erebus has a natural convection system that continually brings new 1,000º Celsius hot lava to the surface.   An older cone surrounds the newer 5-kilometer diameter caldera.

With air temperature extremely cold, the combination of cold outside air, and geothermal activity, has resulted in amazing displays of frozen fumaroles - tall cylindrical cones melted into shape by the hot gases.   The towering ice fumaroles that dot the terrain, and the labyrinth of caves carved out under the snow, make it a strange, eerie place.

Often when the volcano erupts - which it does having intermittent explosion daily - the mountain shudders.   An eruption on Erebus can be a small ejection of incandescent cinder and lapilli - magma fragments and small bombs erupting from the lava lake.   It can be a small pop, or have a sound as loud as a thunderclap.   Glass crystal bombs are regularly thrown out of the crater.

North of the Antarctic Peninsula, three chains of islands have active volcanoes.   The South Sandwich Islands in the Antarctic convergence are volcanic cones - summits that rise from a depth of 3 kilometers below sea level.

The East Scotia Sea has two north-south zones where new crust is being formed underwater.

Deception Island off the peninsula has a 7-kilometer diameter caldera now flooded by seawater.   The collapsed caldera has been breached by seawater at a point called Neptune’s Bellows and makes for a natural harbor.   A whaling and seal processing station was used on the island until 1931, when the whaling ended.

Numerous active vents are situated close to the shoreline of the natural harbor.   Thermally heated patches of water can take the surrounding seawater to near-boiling patches.

Two peaks were created by an eruption in the late 1960’s.   Today they look like snow-covered hills.   An eruption in the late 1970’s destroyed a Chilean Base.   The most recent eruption was in 1991.   There are several small bases sporadically occupied on the western shore of the island - governments seeking to maintain a presence in the Antarctic.

Another volcanic island, Paulet Island, is home to more than 100,000 breeding pairs of Adélie penguins.



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Mount Erebus            (Give it time to load.     See the image gallery.     Click on live shot.)



Scientific Information on Work in the Dry Valleys and southern Victoria Land



 
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Photograph top of page: Transantarctic Mountains - NSF