or
Very Cold with a slight chance of trans-Atlantic Tsunami
Matthew Tarling
Introduction
The assessment of the severity of a natural hazard, tectonic or otherwise, is directly related to the population density in the affected regions. Loss of human life, damage to property and infrastructure and disruption of regional economics are all considered when weighing the risk and possible toll of a tectonic hazard. However, ignoring the tectonic hazard potential for a region simply due to a lack of significant settlement and population may prove to be a fatal error when evaluating global tectonic related risks.
The Antarctic region has a human population of approximately 4490 (in the summer) to 1100 (in the winter) (C.I.A. 2008) . Although the Antarctic is relatively uninhabited, it has localities of high tectonic activity with the potential for generating tsunami (Okal & Hartnady 2009) that can affect populations thousands of kilometers away.
The Antarctic region has a human population of approximately 4490 (in the summer) to 1100 (in the winter) (C.I.A. 2008) . Although the Antarctic is relatively uninhabited, it has localities of high tectonic activity with the potential for generating tsunami (Okal & Hartnady 2009) that can affect populations thousands of kilometers away.
Seismicity of the Antarctic Tectonic Region
Large earthquakes have occurred in the region in recent past , such as the Mw=7.3 earthquake that occurred along the strike slip fault between South America and Antarctica plate south of Bristol island in July 2013, (USGS Earthquake Report). Studies of earlier seismological records show that the largest recorded event in the region consists of a Mw=8.3 earthquake in June 1929 due to normal faulting in the South American plate subducting under the South Sandwich plate (Okal & Hartnady 2009) .
Such events could lead to far-field phenomena such as trans-oceanic tsunami. Within the region's highly tectonically active zones, there is a large number of submarine volcanoes (Leat et al. 2004). Submarine volcanoes eruptions have the potential to displace large volumes of water, possibly generating tsunamis (Latter 1981). Submarine landslides of critically unstable slopes, such as collapsing ancient volcanoes also hold potential for generating tsunamis (Ward 2001).
Such events could lead to far-field phenomena such as trans-oceanic tsunami. Within the region's highly tectonically active zones, there is a large number of submarine volcanoes (Leat et al. 2004). Submarine volcanoes eruptions have the potential to displace large volumes of water, possibly generating tsunamis (Latter 1981). Submarine landslides of critically unstable slopes, such as collapsing ancient volcanoes also hold potential for generating tsunamis (Ward 2001).
Earthquake Generated Far-field Tsunamis
Recent modeling and simulation work done by Okal and Hartnady demonstrated the potential for tsunami generation by earthquakes from normal faulting of the South American plate subducting under the South Sandwich plate (Okal & Hartnady 2009). Using the Mw=8.3 June 1927 earthquake as a trigger, simulations showed that the tsunami generated showed strong wave amplitudes along the coastline of Brazil as well as on the other side of the Atlantic along the shoreline from Guinea to Cameroon.
Volcano and Landslide Generated Tsunamis
Over 41 volcanoes are recorded in the Antarctic region, not including a possibly larger number of submarine volcanoes. In 2011, a group from the British Antarctic Survey discovered 12 previously unknown submarine volcanoes on the seafloor around the South Sandwich Islands with relief as great as 3 km as well as a number craters of collapsed volcanoes as wide as 5 km (British Antarctic Survey 2011). It is likely that other volcanoes lie in the unmapped regions of the arctic. Submarine volcanic eruption have the potential to produce tsunami by rapidly displacing large volumes of water (Latter 1981).
In addition, landslides from these collapsing ancient volcanoes can also displace large volumes of water with the potential to generate tsunami (Ward 2001) (See AV Animation 1). While landslide tsunami and small scale volcanic tsunami tend to be a more local hazard (Bardet et al. 2003), there are ways in which relatively small tsunami can be amplified and focused to cause significant damage to distant regions. |
AV Animation 1: Simulation of submarine landslide resulting in a tsunami (Edanya 2011).
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Amplification of far-field tsunami
AV Animation 2 : Principle of water refraction. (Meldahl 2011)
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Refraction of a tsunami generated in the Scotia Basin (Okal & Hartnady 2009) by the shallow water of the South Atlantic Mid-Oceanic Ridge, could lead to a 'focusing' effect for certain portions of the South-African Coastline as well as parts of Southern Mozambique (Okal & Hartnady 2009) intensifying the effect of even small amplitude tsunami. The phase velocity of a surface water wave is dependent on the depth of the basin through which it travels. When shallow water is encountered, the wave slows and turns towards the region of shallow water as shown in Audio-visual Animation 2. |
Wave interference can be combined with refraction to turn a small amplitude tsunami into a more devastating wave. This results when a wave collides with another wave, meets a refracted portion of itself or is split by an island. The two waves will superimpose and constructively interfere. Where two crests meet to create a wave twice as high and cancel each other where a crest meets a trough as demontrated in AV animation 3.
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AV Animation 3 : Animation of Water wave interference (AllRealityVideo 2013)
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AV Animation 4: Refraction and constructive interference of the 2011 Tohoku-Oki earthquake Tsunami (Djxatlanta 2012)
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These phenomena occurred during the tsunami that resulted from the 2011 Tohoku-Oki earthquake (Tony Song et al.) as shown in AV Animation 4. It is reasonable to assume that given the proximity to shallow water zones such as the South American continental shelf as well as the South Atlantic Mid-Oceanic Ridge that even small tsunamis originating from the Antarctic tectonic region, in particular the region surrounding the East Scotia ridge and the South Sandwich trench, have the potential to amplify, creating significant hazard for the coastal region of South American and southern Africa.
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Conclusion
Despite the low population density of the area, the Antarctic tectonic region should be carefully monitored. Tectonic events in the region hold the potential to create far-field tsunami with devastating consequences for coastal populations in South America and Africa.
References
[AllRealityVideo(2013)] Double Slit Experiment - Water Wave Interference Pattern [Video file]. (2013, June 10). Retrieved 29 January 2014 from http://www.youtube.com/watch?v=Jqm4f55soJQ
[C.I.A. (2008)] Central Intelligence Agency, (2004). The CIA World Factbook 2004 . No. bk. 2004 in CIA World Factbook. Skyhorse Publishing.
Bardet, J.- P., Synolakis, C. E., Davies, H. L., Imamura, F., Okal, E., 2003. Landslide tsunamis: Recent findings and research directions. Springer.
landslide_tsunamis_recent_findings_and_research_directions.pdf | |
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[Djxatlanta (2013)] Seafloor Focuses and Merges Tsunami Waves [Video file]. (2012, March 12). Retrieved 28 January 2014 from http://www.youtube.com/watch?v=IfpIQeeM-_A
[Edanya (2011)] Landslide generated tsunami in Alboran Sea (Mediterranean) [Video file]. (2013, December 15). Retrieved 29 January 2014 from http://www.youtube.com/watch?v=IhpOglN9y0Q&list=PL73CD6050461DFA7F
Latter, J., 1981. Tsunamis of volcanic origin: Summary of causes, with particular reference to krakatoa, 1883. Bulletin volcanologique, 44 (3), 467-490.
tsunamis_of_volcanic_origin_summary_of_causes_with_particular_reference_to_krakatoa_1883.pdf | |
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Leat, P. T., Day, S. J., Tate, A. J., Martin, T. J., Owen, M. J., Tappin, D. R., 2013. Volcanic evolution of the south sandwich volcanic arc, south atlantic, from multibeam bathymetry. Journal of Volcanology and Geothermal Research, 265 , 60-77.
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Leat, P., Pearce, J., Barker, P., Millar, I., Barry, T., Larter, R., 2004. Magma genesis and mantle flow at a subducting slab edge: the south sandwich arc-basin system. Earth and Planetary Science Letters, 227 (1), 17–35.
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Meldahl K. Wave Refraction [Video file]. (2011, December 17). Retrieved 28 January 2014 from http://www.youtube.com/watch?v=G1FIBuybN78
Okal, E., Hartnady, C., 2009. The south sandwich islands earthquake of 27 June 1929: Seismological study and inference on tsunami risk for the south atlantic. South African Journal of Geology, 112 (3-4), 359-370.
the_south_sandwich_islands_earthquake.pdf | |
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[Siebert L, Simkin T (2002-)]. Volcanoes of the World: an Illustrated Catalog of Holocene Volcanoes and their Eruptions. Smithsonian Institution, Global Volcanism Program Digital Information Series, GVP-3, (http://www.volcano.si.edu).
Tony Song, Y., Fukumori, I., Shum, C., Yuchan, Y., 2012. Merging tsunamis of the 2011 tohoku-oki earthquake detected over the open ocean. Geophysical Research Letters, 39 (5).
merging_tsunamis_of_the_2011_tohoku-oki_earthquake_detected.pdf | |
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[United States Geological Survey]. "M7.3 - 218km SSE of Bristol Island, South Sandwich Islands". 2013-07-15. Retrieved 25 January 2014 from http://comcat.cr.usgs.gov/earthquakes/eventpage/usb000ief9#summary
Ward, S. N., 2001. Landslide tsunami. Journal of Geophysical Research: Solid Earth (1978-2012), 106 (B6), 11201-11215.
landslide_tsunami.pdf | |
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