GeoLog

GeoLog

Top ten tourist beaches threatened by tsunamis

Top ten tourist beaches threatened by tsunamis

December 2004 saw one of the deadliest natural disasters in recorded history. 228,000 people were killed when an earthquake off the coast of the Indonesian island of Sumatra triggered tsunami waves up to 30 m high. The destruction was extreme as the waves hit 14 different countries around the Indian Ocean. Economic losses totalled over 10 billion US dollars. The tourism industry in particular suffered a significant blow. In Phuket, a province of Thailand, a quarter of the island’s hotels had closed six months after the tsumani.

“The 2004 Sumatra tsunami and some of the recent Pacific Island tsunamis have shown their devastating impact on beaches and beach-related tourism,” says Andreas Schaefer, a researcher from the Karlsruhe Institute of Technology (KIT). But where is disaster likely to strike next? And can we be prepared for it?

Schaefer and his colleagues are trying to find out. “We asked the question: can we quantify potential tsunami losses to tourism industries along beaches?” he says. The number of tourists visiting the most exotic locations in the world, places such as Thailand, Indonesia, Colombia and Costa Rica, are rising twice as fast as the global average. In some cases, visitor numbers are growing by as much as 11 percent each year.

This rise in tourism in tsunami-prone locations is potentially a cause for real concern. “We compiled the first ever global loss index for the tourism industry [associated with beaches],” continues Schaefer. His findings were presented last month at the European Geosciences Union General Assembly in Vienna .

Beaches can be affected by tsunamis in a variety of ways. As well as the immediate threat to human life, a tsunami wave can leave behind piles of debris or offshore sand that can damage a beach environment. Alternatively, large swathes of beach sand might be removed by erosion. And in cases where an earthquake is very close to the shore, the beach itself may be down-thrust or uplifted during the event, leaving it either permanently submerged underwater or high and dry.

To quantify the locations in the world that are most at risk, Schaefer and his colleagues used two large datasets: tourist information and earthquake statistics.

Tourism-derived GDP per capita across the world. (Image credit: Andreas Schaefer)

To calculate the human exposure, “we compiled a global tourism destination database,” he explains. This database includes over 200 countries, at least 10,000 tourist destinations, more than 24,000 beaches, and almost a million hotels from all around the globe.

“It was important to get the latest and best tourism and hotel information,” says James Daniell, another member of the KIT research team. “Tourism contributes over 6 trillion [US] dollars directly and indirectly to the global economy every year.”

The research team then calculated tsunami probabilities all around the world using earthquake statistics and tectonic modelling. Chile, central America, Indonesia and Japan are the main countries that frequently experience large tsunamis.

Over longer time periods, the Caribbean and Mediterranean are also likely to be affected by rarer events. To put the numbers in perspective, if you spend a day on the coast of Mexico you have a one in 60,000 chance of seeing a tsunami; in Crete, this decreases to one in 600,000.

To model the tsunamis, it is also important to have a good understanding of the shape of the seafloor in the vicinity of the tourist sites. In the deep ocean, big tsunamis can have gaps between waves of as much as 200 km and wave heights as small as 1 m; ships are often unable to feel them passing. But as they approach the shore, the water shallows, causing the waves to slow down and pile up. The wave spacing decreases to less than 20 km, whilst the wave heights can grow to tens of metres. Hence, what looks like an innocuous fluctuation at sea can cause major damage when it reaches land. The depth of the adjacent seafloor plays a major role in this.

Simulated tsunamis across the world showing maximum potential wave heights. (Image credit: Andreas Schaefer)

Given the large number of variables at play, tsunami modelling involves many calculations and typically requires the use of a supercomputer. But in a paper published last year, Schaefer helped to develop a new simulation framework called TsuPy, which allows for quick modelling of tsunamis on personal computers. With this in place, he could rapidly simulate more than 10,000 tsunamis all around the world, calculate the expected wave heights at the tourist sites in his database, and estimate the likely economic losses.

The researchers estimate 250 million US dollars in global annual loss to the tourism industry from tsunami waves. Furthermore, every 10 years they expect a single $1 billion event.

Of all the tourist destinations, “Hawaii is the number one,” says Schaefer. This is “because of all the potential tsunamis that come from around the Pacific Ring of Fire,” he explains. “There are so many [tsunami] sources all around, that, even though they are far away, they have an effect.”

The last major tsunami to strike Hawaii was as a result of the biggest earthquake ever recorded: the 1960 magnitude 9.6 Valdivia earthquake on the coast of Chile. 60 people on Hawaii were killed and the damage amounted to 500 million US dollars in today’s terms.

Top ten locations on the global risk index for beach tourist destinations threatened by tsunamis. (Image credit: Andreas Schaefer)

Other notable locations on the top ten list include Valparaiso (Chile), Bali (Indonesia), and Phuket (Thailand). “Locations that are known for their tourism are at the top of the list because there is a lot [of existing infrastructure] that could be damaged,” explains Schaefer.

Slightly surprisingly, southwest Turkey is also high on the list. Furthermore, places like Tonga and Vanuatu are particularly at risk. They have rapidly developing tourist industries and large projected losses per dollar of tourism-related business, so they feature highly on Schaefer’s list. “They are mostly small island nations with a significant need for tourist dollars,” explains Daniell.

For many parts of the world, the results are not necessarily good news. But they are a first step inasmuch as they highlight the locations that are currently thought to be at greatest risk. “We hope, with these results, to raise awareness among tourists. But they do not need to be afraid,” says Schaefer. With adequate preparation and evacuation planning, it is hoped that future disaster on the scale of the 2004 event might be averted.

By Tim Middleton, EGU 2018 General Assembly Press Assistant

References

Schaefer, A., Daniell, J., and Wenzel, F. Beach Tsunami Risk Modelling – A probabilistic assessment of tsunami risk for the world’s most prominent beaches. Geophysical Research Abstracts, Vol. 20, EGU2018-11955, 2018, EGU General Assembly 2018 (conference abstract)

Schaefer, A. and Wenzel, F. TsuPy: Computational robustness in Tsunami hazard modelling. Computers & Geosciences, 102, 148-157, 2017

Imaggeo on Mondays: A volcanic point of view

Imaggeo on Mondays: A volcanic point of view

It’s not every day that you can peer into a volcano, much less gaze out at the sky from the inside of one. The Algar do Carvão, or “the Cavern of Coal,” is one of the few places on Earth where you can explore the underground reaches of a volcanic site.

The volcanic pit is found on the island of Terceira, part of the Azores archipelago. This collection of islands is an autonomous region of Portugal, located in the Atlantic Ocean about 1800 kilometres west from the Portuguese mainland. The archipelago is an especially volcanic hotspot, situated on the border of three major tectonic plates: the North American, Eurasian and African Plates.

The Algar do Carvão is essentially an ancient lava tube, made up of a volcanic chimney, about 80-90 metres deep, which then opens up into secondary magma chambers. The chimney formed first roughly 3,200 years ago, in the wake of a volcanic eruption. Then a second eruption, occurring in the same spot 1,200 years later, created many of the magma chambers seen today.

A profile of the Algar do Carvão, based on a similar cutaway produced by “Os Montanheiros,” (Credit: Ruben JC Furtado / Wikimedia Commons)

Despite what the cavern’s title suggests, the volcanic site is not a source of coal, but rather named for the walls’ dark black, ‘sooty’ colour. The volcanic pit is actually better known by geologists and cave enthusiasts for its source of silica-rich stalagmites and stalactites, a feature not commonly found in this region. Scientists have hypothesized that the structures’ silicate composition could have come in part from the volcano’s past hydrothermal activity or its population of diatoms, microorganisms which contain silica in their cell walls.

As you can see from the lush flora featured in today’s photo, the Algar do Carvão is teeming with life. Vegetation blankets the mouth of the cone structure and many animal populations thrive in the cavern environment. The volcanic pit is also home to several species found only on the Azores islands, like the troglobian spider Turinyphia cavernicola and the Terceira Island scarab Trechus terceiranus.

References

Daza, D. et al.: Isotopic composition (δ¹⁸ O y δD) of silica speleothems of the Algar do Carvão and Branca Opala volcanic caves (Terceira Island, Azores, Portugal), Estudios Geológicos, 70, 2, 2014.

Borges, P. A. V., Carlos Crespo, L., Cardoso, P.: Species conservation profile of the cave spider Turinyphia cavernicola (Araneae, Linyphiidae) from Terceira Island, Azores, Portugal, Biodiversity Data Journal 4: e10274, 2016.

Nunes, J.C., J.P. Constância, M.P. Costa, P. Barcelos, P.A.V. Borges & F. Pereira: Route of Azores Islands Volcanic Caves. Associação Os Montanheiros & GESPEA (Ed.). 16, 2011.

Algar do Carvão, Associação Os Montanheiros

Natural Monument of Algar do Carvão, 2011 Regional Secretariat for Agriculture and Environment, Governo dos Açores

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Plate Tectonics and Ocean Drilling – Fifty Years On

Plate Tectonics and Ocean Drilling – Fifty Years On

What does it take to get a scientific theory accepted? Hard facts? A strong personality? Grit and determination? For many Earth Scientists today it can be hard to imagine the academic landscape before the advent of plate tectonics. But it was only fifty years ago that the theory really became cemented as scientific consensus. And the clinching evidence was found in the oceans.

Alfred Wegener had proposed the theory of continental drift back in 1912. The jigsaw-fit of the African and South American continents led him to suppose that they must once have been joined together. But in the middle of the century, the idea fell out of favour; some even referred to it as a “fairy-tale”.

It was not until the discovery of magnetic reversals on the seafloor in the early 1960s that the theory began to sound plausible again. If brand new ocean crust was being formed at the mid-ocean ridges, then the rocks either side of the ridge should show symmetrical patterns of magnetism. Fred Vine and Drummond Matthews, geologists at the University of Cambridge in the UK, were the first to publish on the idea of seafloor spreading in 1963.

But plate tectonics was still not the only theory on the market. The expanding Earth hypothesis held that the positions of the continents could be explained by an overall expansion in the volume of the Earth. Numerous twentieth-century physicists subscribed to such a view. Or, similarly, the shrinking Earth theory proposed that the whole planet had once been molten. Mountain ranges would then be formed as the Earth cooled and the crust crumpled.

Helmut Weissert, President of the EGU Stratigraphy, Sedimentology and Palaeontology Division, remembers the difficult exchanges that took place whilst he was a student at ETH Zürich in the late 1960s. “Earth-science-wise it was a hot time,” he recalls. “In Bern University they did not teach plate tectonics. We did not have a course on plate tectonics either. I probably first heard about plate tectonics in [my] second or third year.”

Weissert especially remembers Rudolf Trümpy, professor of Alpine geology at ETH at the time, saying that plate tectonics sounds interesting, but it does not work for the Alps. Meanwhile, younger voices at ETH, postdocs and lecturers, were becoming increasingly convinced by plate tectonic theory.

Weissert soon found himself in the midst of the controversy as his own research had a direct bearing on the debate. “I had an interesting diploma topic,” says Weissert. “I worked on continental margin successions and associated serpentinites.” Serpentinites are green-coloured rocks that are full of the water-rich mineral serpentine, and therefore must have formed on the ocean floor. The fact that Weissert was finding them in Davos, at the top of the Alps, was a good indication that modern-day Switzerland had once been part of the oceans. As Weissert succinctly puts it, “green rocks were ocean”.

The observed and calculated magnetic profile for the seafloor across the East Pacific Rise, showing symmetrical patterns of magnetism. (Image Credit: U.S. Geological Survey. Distributed via Wikimedia Commons)

By 1967, interest in the theory of plate tectonics had snowballed. When the Deep Sea Drilling Project (DSDP) was launched the following year, it had its sights firmly set on finding evidence that would definitively either confirm or reject the hypothesis of seafloor spreading.

The DSDP research vessel, the Glomar Challenger, set sail from Texas in March 1968. By its third leg it had drilled 17 holes at 10 sites along the mid-Atlantic ocean ridge and was already producing results that looked like they would confirm Wegener’s theory of continental drift. “After a few legs it was clear that the seafloor spreading hypothesis was tested and proven,” remembers Weissert.

There were only eight scientists on board, but two or three of them were working on the stratigraphy of the seafloor sediments. “The stratigraphy was superb,” explains Weissert. “You have the very young [sediments near the ridge] and then at the edges of the ocean the Jurassic sediments. If you have aging crust then you have aging sediment, so the hypothesis was very clear.” If the sediments got progressively older on moving away from the ridge, then so must the crust, a sure sign that new ocean floor was being created at the ridge.

Karen Heywood, EGU Division President in Ocean Sciences, remembers how her own fascination with the theory of plate tectonics ended up sparking her career in physical oceanography. Heywood began as a physics student at the University of Bristol in the 1980s. “They said we had to write an essay on the historical development of an idea in physics,” she recalls. “I did the development of the theory of plate tectonics and seafloor spreading. I wrote this essay all about Alfred Wegener.”

“This essay inspired me to think about earth sciences,” she says. “The idea that you could apply physics to the real world was amazing. It got me into oceanography.”

Heywood went on to establish her career at the University of East Anglia (UEA), where she became the first female professor of Physical Oceanography in the UK. “I went to the UEA and Fred Vine was there. It brought me back full circle. I could not believe that this was Fred Vine, who had discovered the magnetic stripes. This was the real person and that was amazing… it was the same person that I had read about and written about in my essay as an undergraduate in the 80s.”

There were clearly strong personalities on both sides of the debate about plate tectonics, but Weissert is pragmatic about the progress of science. “You have to accept that you are part of a scientific development. Everybody makes hypotheses… We all make mistakes. We all learn. We all improve.”

Indeed, many years later, in 2001, Trümpy wrote what Weissert calls “a beautiful small article” entitled Why plate tectonics was not invented in the Alps. Trümpy magnanimously writes, “Shamefacedly, I must admit that I was not among the first Alpine geologists to grasp the promise of the new tectonics.”  And yet, he continues, “to the Alps, plate tectonics brought a better understanding”. The humans and the science move on together.

By Tim Middleton, EGU 2018 General Assembly Press Assistant

References

DSDP Phase: Glomar Challenger, International Ocean Discovery Program

Trümpy, R., Why plate tectonics was not invented in the Alps, International Journal of Earth Sciences, Volume 90, Issue 3, pp 477–483, 2001.