Largest Holocene volcanic eruption in Antarctica identified, dated and tracked right across the continent

Posted by lcb14 at Dec 04, 2018 12:15 PM |
Leicester Geology volcanologist, Professor John Smellie reports on his research on Deception Island, one of a handful of active volcanoes in the Antarctic.
Largest Holocene volcanic eruption in Antarctica identified, dated and tracked right across the continent

Map showing the location of Deception Island and the sediment & ice cores containing signs of the 4000 year caldera-forming eruption.

In the minds of most people, Antarctica is not usually associated with volcanoes, let alone active volcanoes. Yet the world’s most isolated continent has many, of which a few are still active (dormant). One of those is called Deception Island, situated at the northern end of the Antarctic Peninsula. Although known to be the largest volcano in Antarctica and still active, Deception Island previously supported three scientific stations (by UK, Chile & Argentina). However, in 1967 the volcano awoke with a snarl and erupted three times in successive years (1967, 1969 and 1970). The eruption destroyed two of the stations on the island and the third was abandoned. The eruptions were relatively small in volume but were highly explosive due to the magma, with a temperature of > 1000°C, interacting violently with groundwater and surface water. Ash was distributed hundreds of kilometres to the north-east and formed a thin drape on the adjacent ice-covered South Shetland Islands. Since then, despite several seismic crises, the volcano has lapsed once more into sleepy somnolence and two scientific stations (by Argentina & Spain) have been re-established, but are occupied for 1 or 2 months only in the summer, for safety reasons. Deception volcano has also become the most popular destination for Antarctic wilderness tourists. Currently more than 25 000 regularly arrive by ship each year during the short Antarctic summer, where they take advantage of the unique combination of hot rock, steam and warm water in which they can take a (brief!) swim. Try googling ‘Deception Island caldera’ if you want to see some of the brave souls. [Note: The author tried this, only once. One leg was burning hot, the other was freezing cold. Not recommended.]

Aerial view of Deception Island. The large central bay, 9 km in diameter, was formed by flooding by the sea following the caldera collapse.
Aerial view of Deception Island. The large central bay, 9 km in diameter, was formed by flooding by the sea following the caldera collapse.

The innocent appearance of the volcano is highly deceptive. Although historical eruptions were relatively minor, we know from geological investigations that Deception has experienced at least one major paroxysmal event in Holocene time (< 12 000 years), that probably had devastating environmental effects. The huge volume of magma ejected - 30-60 km3 - makes it one of the largest eruptions on Earth over the last several millennia. Indeed, the eruption evacuated so much material that it covered the entire island to a depth of 70-90 m and extended the island’s limits by several kilometres. The eruption also destabilised the upper half of the volcano, which then collapsed, forming a huge sunken bowl known as a caldera. The caldera was flooded by the sea and gives the island its distinctive horseshoe shape.

Volcanic steamfield inside Deception caldera. The stark remains of a scientific station can be seen in the background. The building was buried by ash in 1967 and then burned down by hot volcanic lapilli in 1969.
Volcanic steamfield inside Deception caldera. The stark remains of a scientific station can be seen in the background. The building was buried by ash in 1967 and then burned down by hot volcanic lapilli in 1969.

Despite the magnitude of the caldera-forming eruption, and its potential for far-reaching environmental impacts, its age has never been established. Studies by the author showed that the eruption was probably triggered by the influx of fresh magma into the pre-existing magma chamber. Mingling between the two different magmas led to the combined product being compositionally very distinctive. Subsequently, Spanish geologists working on lake sediments on Livingston Island, 40 km away, unexpectedly discovered interbedded tephra layers that compositionally matched with the caldera eruption on Deception. Moreover, the sediments closely associated with the tephras were deposited rapidly en masse, probably due to destabilisation caused by massive seismic shocks associated with the caldera collapse. There was probably also a large tsunami but its deposits have not yet been identified.

The author measuring the temperature of gases inside Deception caldera in 1987. Although 20 years after the most recent eruptions and far from the eruptive sites, the fumarolic gases were still slightly superheated (107°C), indicating that molten rock is
The author measuring the temperature of gases inside Deception caldera in 1987. Although 20 years after the most recent eruptions and far from the eruptive sites, the fumarolic gases were still slightly superheated (107°C), indicating that molten rock is still present close to the surface.

It is very hard to date Holocene volcanic rocks directly, which is why the age of the caldera-forming eruption was unknown. By contrast, lake sediments can be dated precisely by the 14C method using organic matter found in sediments. Using that method, we now know the eruption took place 3980 ± 125 years ago. Furthermore, now that its age is known, it is possible to look elsewhere for other evidence of its presence, as ash layers or sulphate signals in ice cores, and in marine sediments. Signs of the eruption were found all across Antarctica, indicating that it had a pan-Antarctic distribution, the widest of any known Antarctic eruption. The associated environmental impact is currently unknown but it was potentially considerable. For example, it has been surmised that a prolonged but smaller-volume eruption of another Antarctic volcano 17 000 years ago might have helped push Antarctica out of the last glacial and thus accelerated the world’s migration into the current warm interglacial. Studies such as these, with their serendipidous results, are helping scientists to re-examine prevailing ideas about environmental change and how the Earth is affected by climate-modulating and tipping events. They reveal a more complicated Earth system than is often envisaged and which still has the capacity to surprise.

The author overlooking the flooded interior of Deception volcano. The bay formed over an enormous volcanic subsidence structure known as a caldera, caused by a catastrophic collapse of the top of the volcano 4000 years ago during or immediately following
The author overlooking the flooded interior of Deception volcano. The bay formed over an enormous volcanic subsidence structure known as a caldera, caused by a catastrophic collapse of the top of the volcano 4000 years ago during or immediately following a major eruption.

The author’s field camp on Deception Island during a rare sunny day.
The author’s field camp on Deception Island during a rare sunny day.
‘It may be a warm volcano but it’s also cold’. One of the author’s campsites during one of the frequent snow storms.
‘It may be a warm volcano but it’s also cold’. One of the author’s campsites during one of the frequent snow storms.

Thick yellow-coloured deposits of pyroclastic flows formed during the climactic phase of the caldera-forming eruption. These deposits covered the entire island and originally extended its margins by several kilometres.
Thick yellow-coloured deposits of pyroclastic flows formed during the climactic phase of the caldera-forming eruption. These deposits covered the entire island and originally extended its margins by several kilometres.

The results of the study on Deception Island were published in Nature Scientific Reports
[Antoniades, D., Giralt, S., Geyer, A., Álvarez-Valero, A.M., Pla-Rabes, S., Granados, I., Liu, E.J., Toro, M., Smellie, J.L. and Oliva, M. 2018. The timing and widespread effects of the largest Holocene volcanic eruption in Antarctica. Nature Scientific Reports, 8: 17279; doi:10.1038/s41598-018-35460-x.]

For a popular account of the results and their importance, see the article published by Forbes Media.

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