Earth Science, Science at the South Pole

Science at the South Pole: Fire and Ice

“Antarctica is a huge continent, nearly double the size of Australia, and more or less untouched by humanity (at least until we started polluting the globe with plastic and greenhouse gases). It’s almost entirely covered by ice sheets averaging over a mile thick (but can be triple that in East Antarctica), which meet the sea and float above it, forming huge ice shelves that can break off into icebergs. Under that ice are teeming communities of sea life unlike anywhere else, and back on land ice conceals towering mountains, volcanoes, and rift valleys offering vital clues to Antarctica’s geological history.”

The above is an extract from my *winning* (omg!!) entry to the annual A Short Scientist blog competition. It is an overview of some of the cool science that is happening at the South Pole, and why scientists fight for funding to go there despite the freezing temperatures. You can read it here 🙂 I went down many a rabbit hole while researching that post, particularly when investigating the tectonic processes occurring beneath the ice, so I thought I would dedicate a blog post to it! 

Antarctica is often disregarded as the strip of land at the bottom of the world map, or, that one freezing, uninhabited continent. So it’s plate boundaries are missed off many maps, for 2 reasons: a) they would be weirdly distorted and not make sense, and b) we don’t know much about it, and it isn’t technically classed as a plate boundary!

But if we flip the view, and centre our map on Antarctica (the one below is a distorted globe view), we can see that Antarctica is a very interesting place.

Tectonic Features of Antarctica, by me!
As you can see there are very few subduction zones (marked by red lines with shading behind eg. along S America) so the volcanoes must be fuelled by another source.

Only discovered in the 1800s, Antarctica doesn’t make it easy for scientists to study its geology- it’s incredibly cold, which makes work outdoors (and just living there in general) a huge logistical challenge, particularly difficult. Oh, and 98% of the rock is covered by ice averaging over a mile thick, but up to 4,800m in parts of East Antarctica! 

Despite these difficulties, we’ve managed to discover quite a bit about what features the ice covers. What you have to remember is that Antarctica is a continent just like any other- if it was positioned away from the south pole (and it has been in the past- over 100 million years in the past- when it was part of supercontinent gondwana, and throughout the cretaceous era when temperatures soared) the ice sheets would melt, exposing the terrain of mountains and valleys, lakes and rivers. Some of these lakes actually remain today, far under the ice, like Lake Vostok (but that’s a story for another day- or check out my article on A Short Scientist for a taste!)

Vostok: Lake Under Antarctic Ice | Live Science

Antarctica can be split into two regions, creatively named East Antarctica and West Antarctica, and are divided by the Transatlantic mountain range, which despite reaching over 4km tall, are almost entirely covered by ice! 

East Antarctica covers the largest area, including the geographic south pole. It’s an ancient continental plate, known as a craton, formed earlier than 1.6 billion years ago! It’s 40km thick, and is covered by over 4km of ice, with its main feature the Antarctic Plateau: a barren plain 1000km across, 3000m above sea level, which helps make Antarctica the highest continent in elevation. The ice sheet hides the only other major geological feature I could find- the Gamburtsev Mountain Range, which is roughly the same size as the european alps, and were probably formed at the same time as the supercontinent Rodinia. But east Antarctica isn’t boring- it’s home to the South Pole Telescope, Lake Vostok and breeding grounds for many antarctic species like seals… but that’s not the focus of this post!

West Antarctica couldn’t be more different. Instead of one ancient continental plate, West Antarctica is a mishmash of microplates, with tall volcanoes and deep basins causing much of it to be below sea level! So if the ice disappeared off of Antarctica, this region or at least the Bentley Subglacial trench, which is deeper than the grand canyon, would fill with water- even after the land undergoes decompression (isostatic readjustment for all my fellow A-Level geographers!) and rises due to the release of the pressure that the ice had created. 

West Antarctica without ice

But West Antarctica also has areas of high elevation in the form of mountains and volcanoes! The stark elevation differences are because most of West Antarctica is on top of a huge rift valley system (also creatively named the West Antarctic Rift System, often shortened to WARS). The volcanoes that form here- particularly those in Marie Byrd Land are remarkably similar to those found in the East African Rift Valley, suggesting that the volcanic activity in Antarctica may also be powered by a mantle plume- a column of superheated rock in the mantle which rises quickly from the core to the surface, heating the crust and forming volcanoes.

The volcanoes seem to form in lines, but unlike other hotspots (eg. Hawaii, where the island chain is a result of plate movement) these apparent chains have probably just formed along lines of weakness in the rift system, as Antarctica doesn’t actually move very much, because only a small part of its plate boundaries are subduction zones where the weight of the subducted slab would pull the plate down. Instead, most of Antarctica’s boundaries with other major plates are transform faults (where plates move side by side) or constructive boundaries (where plates move apart). It’s possible that the WARS is where a new constructive plate boundary is forming.

For a sense of scale, the WARS mostly sits under Marie Byrd Land, which is roughly the same size as Greenland! Marie Byrd Land is also where New Zealand rifted from during the final stage of the breakup of the supercontinent Gondwana, so this has been the location of rifting for many millions of years!

Map centred on West Antarctica during the break up of supercontinent Gondwana. MBL = Marie Byrd Land, CR (Chatham Rise), CP (Campbell Plateau), SNZ (South NZ) and NNZ (North NZ) are all part of the continent of Zealandia, which is mostly submerged except for New Zealand itself. Image from Fitzgerald, 2002, a very interesting paper I only found when finding images for this, but would have been very useful while writing, so I will attempt to read it and do a summary on my instagram stories at some point!

Many of these volcanoes sit under the West Antarctic Ice Sheet and Ross Ice Shelf, some of the fastest melting regions of Antarctica. Although this will be without a doubt partly due to climate change, the reason this particular region is melting so quickly could be due to the volcanic and geothermal activity. In turn, as the ice sheet melts, it decreases the pressure on the plate, which can melt the underlying magma and increase volcanic activity, potentially resulting in a cycle in which more and more ice melts. (Don’t you just love finding more ways sea level can rise!? *cries in climate change*) As expected at a hotspot, the volcanoes here are shield volcanoes- there are probably over 100 small ones beneath the ice, some of which may be active, but they can only be indirectly detected through earthquakes and radar. Of the few at the surface, at least 2 (Mt. Berlin and Mt. Siple), are currently active but there could be more. The tallest volcano here is Mount Sidley, but this is assumed to be dormant. 

Some volcanoes in Marie Byrd Land

The West Antarctic Rift System is also responsible for the formation of the Transantarctic Mountains, the largest mountain range not formed by subduction or folding, but instead from periods of extension (when the plates are pulled apart and thinned) and uplift (mechanism unknown, potentially due to heat from the mantle plume?). There is some discussion as to whether it could be formed by subduction, as where else would the new crust created on the east of the rift go? (this isn’t a rhetorical question, I actually don’t know- any geologists/geographers/volcanologists with the answer please let me know!) But if it was formed by subduction, you would expect to see violent tectonic hazards (big earthquakes and composite volcanoes) here, which you don’t.

image017

Moving away from Marie Byrd Land and the main rifting zone, we come to one of the most studied volcanoes in Antarctica- Mount Erebus! Mount Erebus is found amongst another cluster of volcanoes, on the other side of the ross ice shelf to Marie Byrd Land.

It’s possible that this is a different hot spot (called the Erebus Plume) though fuelled by the same mantle plume. The volcanoes in this area are more complex than the ones in Marie Byrd Land- they may be linked to the WARS, but although they began as shield volcanoes, they have actually developed into stratovolcanoes with strombolian eruptions.

Mt Erebus diagram | Ross island, Ice sheet, Island

This is interesting because Strombolian eruptions are named after those linked to Mount Stromboli in Italy, which has a similar structure to those found here in the McMurdo Volcanic Group. The Mediterranean is another complex tectonic zone, where the processes of rifting related to the East African mantle plume and subduction of remaining oceanic crust as the African plate collides with the Eurasian plate, intermix, suggesting that antarctic plate tectonics is even more complicated! Mount Erebus is the most active volcano on Antarctica: it has been continuously erupting to fill a permanent lava lake (one of only 5 in the world!) ever since it was discovered. 

Other volcanoes can be found on the Antarctic peninsula (mostly dormant here, probably linked to WARS), the South Shetland Islands (some active) and South Sandwich Islands (very active). The latter 2 clusters are more well understood than those on mainland Antarctica, as they are a typical volcanic arc caused by subduction of 2 small plates. 

Did you know Antarctica had volcanoes? Would you want to go to Antarctica? I think this sort of stuff is so fascinating- let me know if you want to learn more about earth science/plate tectonics/volcanoes, or if I should stick to space! And to be totally transparent, I felt quite out of depth researching this (but that’s just sparked my curiosity and inspired me to keep reading!), so if there are any inaccuracies, please tell me so I can address them!

Sources

For an incredibly thorough crash course in Antarctic volcanology, I suggest reading this 5 part series from the blog volcano hotspot, which I found really useful while researching this post, and goes into much more detail than I am able to with my current geographical knowledge and in just one post!

Other

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s