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Imaggeo on Mondays: Indonesian mangroves and tsunamis

Imaggeo on Mondays: Indonesian mangroves and tsunamis

Pictured here is a solitary mangrove tree, rooted off the northern coast of the Indonesian island Flores. While this tree has the shallow sandy reef to itself, mangroves are often found clumped together in large forests covering tropical and subtropical coastlines. The propped-up roots of mangrove trees often tangle together, creating a dense natural barrier that can weaken the coastal impact of ocean tides, currents and storms. As a consequence, islands with mangrove forests on their coastlines experience less erosion and less damage from storm surges compared to barer shorelines.

Mangroves are also often said to provide protection against tsunami destruction. Indeed, there have been several cases in which mangroves trees were believed to have curtailed the devastating effect of tsunami waves. Recent research suggests that extensive mangrove forests hundreds of metres wide have been able to reduce tsunami wave heights by 5-30 percent.

Unfortunately, over the past decades, these environmental benefits are now under threat due to deforestation. About half of the global mangrove population (32 million hectares) has been wiped out, often to make way for fish farming operations. In Indonesia, mangrove ecosystem decline has been largely attributed to developing shrimp ponds and logging activities. There are now a number of places where mangrove plantations are supported by local individuals and governments.

Jörn Behrens, a professor of numerical methods in Earth sciences at the University of Hamburg in Germany, captured this shot while on a field trip in Indonesia. He and his colleagues were looking for traces of the powerful 1992 tsunami that struck the coast of the Indonesia island of Flores and other nearby smaller islands.

The tsunami, triggered by a magnitude 7.9 earthquake, sent waves reaching 4 to 27-metres high on the island’s northeastern coast, even destroying a whole village situated on the nearby island Babi. About 2,500 residents and tourists died from the event, with hundreds more injured, and thousands more homeless.

The 1992 Flores tsunami was also one of the first such events documented by an international survey that adhered to internationally accepted post-tsunami assessment standards.  On their field trip Behrens and his colleagues revisited some of sites assessed by the 1992 post-tsunami survey, spoke to eye witnesses, learned about the region’s current mitigation measures, and exchanged latest results from modeling and experimental tsunami research.

While on this field trip, Behrens came across this solitary mangrove, surrounded by what appears to be young mangrove propagules growing out from the water.

By Olivia Trani, EGU Communications Officer

References

Spalding M, McIvor A, Tonneijck FH, Tol S and van Eijk P (2014) Mangroves for coastal defence. Guidelines for coastal managers & policy makers. Wetlands International and The Nature Conservancy.

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/.

September GeoRoundUp: the best of the Earth sciences from around the web

September GeoRoundUp: the best of the Earth sciences from around the web

Drawing inspiration from popular stories on our social media channels, major geoscience headlines, as well as unique and quirky research, this monthly column aims to bring you the latest Earth and planetary science news from around the web.

Major stories

This month has been a whirlwind of Earth and space science news; the majority focusing on natural hazards. Powerful cyclones, earthquakes, and tsunamis have received significant coverage from the geoscience media. Quickly recap on an action-packed month with our overview:

On 14 September, Hurricane Florence, made landfall in the mid-Atlantic region of the United States, making first contact near Wrightsville Beach in North Carolina then traveling up the East Coast. By the time Florence had reached the US coastline, the cyclone’s sustained wind speed had dropped considerably, downgrading the hurricane from a category 4 to category 1 storm on the Saffir–Simpson scale.

This designation may sound mild, but as many scientists and journalists have pointed out, sluggish hurricanes are especially dangerous, since they are more likely to dump heavy rainfall over a relatively small surface area compared to faster storms that distribute their rainfall over more territory. This proved to be true for Hurricane Harvey, which dumped more than 150 centimetres of rain onto some areas of Houston, Texas.

Hurricane Florence’s record-breaking rainfall forced more than a million people to evacuate their homes, and experts estimate that the storm inflicted damages worth more than $38 billion (USD). The hurricane also produced very concerning environmental damages. In Wilmington, North Carolina, for instance, the the rainfall flooded a pit of coal ash at a power plant, releasing more than 1,530 cubic metres of ash, with much of it likely ending up in a nearby lake.

Across the planet, just one day following Hurricane Florence’s landfall, Super Typhoon Mangkhut wreaked havoc on southeast Asia, pounding the Mariana Islands, the Philippines, China, Taiwan, and Vietnam with strong wind and rain. Reaching wind speed over 240 kilometres per hour, Mangkhut is the most intense storm of the year so far. The New York Times created an interesting three-dimensional visual of the storm’s intensity, using NASA satellite data.

In addition to unleashing incredibly strong winds, the typhoon’s rainfall also triggered deadly landslides. Just outside of the city Baguio, which recorded more than 75 centimetres of rain, more than 40 gold miners were buried under a landslide that hit their bunkhouse.

Big storms like Hurricane Florence and Typhoon Mangkhut are expected to be more frequent in the future as our climate changes. And this stems from many factors; a recent article from the New York Times explains that, due to climate change, the world’s oceans are warming (fueling more hurricane formation), the atmosphere is holding more moisture (leading to wetter storms), hurricane wind speeds are slowing down (causing more concentrated rainfall), and Earth’s sea levels are rising (increasing the risk of flooding).

Last week, a 7.5-magnitude earthquake struck the Indonesian island of Sulawesi, sending a massive tsunami, with waves up to 6 metres high, into Palu Bay, causing massive devastation in the regional capital Palu and surrounding areas. Officials report that nearly 1,350 people have died from the earthquake and tsunami, and the death toll is expected to rise as rescue workers make their way towards more remote places. Scientists told BBC that “a combination of geography, timing and inadequate warnings meant that what happened in Palu was a worst case scenario.”

Map of the September 28, 2018 Palu, Indonesia Earthquake. Credit: USGS.

Indonesian aid workers and humanitarian relief envoys are currently working to provide supplies and assistance to the affected communities. At the same time, scientists are still puzzling over the tsunami’s strength, which caught many experts by surprise. This is because the earthquake’s behavior isn’t known for generating catastrophic tsunamis.

Powerful tsunamis are typically caused by earthquakes with vertical motion, where part of the seafloor juts forward, disturbing the water column and consequently sending massive waves to the coast. The 2004 Indian Ocean tsunami, for example, was caused by a 9.1 magnitude megathrust earthquake. On the other hand, last week’s quake is known as a ‘strike-slip earthquake,’ where the ground shifts horizontally. This kind of movement doesn’t move ocean water as dramatically.

“Some early calculations suggest a floor displacement of perhaps half a metre. Significant but generally insufficient to produce the waves that were recorded,” reported the BBC.

While it is too early to tell what exactly happened, scientists suspect that a number of factors could have played part in helping the tsunami gather strength. For example, underwater landslides have been known to trigger tsunamis of similar strength. Additionally Palu Bay’s narrow geometry could have amplified the waves’ height.

The underlying factors that contributed to the event will hopefully become more clear as scientists analyse the series of events in more detail.

What you might have missed

This month, the Japanase spacecraft Hayabusa 2 has sent three robots to the rocky surface of an asteroid near Earth, known as Ryugu. The spacecraft had successfully reached the asteroid this June, after travelling for more than three years. The craft first released two small devices, no bigger than frying pans, which tumbled around the rock’s surface and even sent digital postcards and a short video back home. A few days ago, Hayabusa 2 released a third rover, which will use a suite of different scientific instruments to collect data on the asteroid. “Hayabusa2 itself is likely to make the first of three touchdowns on the asteroid to collect samples later this month,” said Science Magazine.

Links we liked

  • StarTrek creators once said that Spock’s fictional home planet Vulcan orbited the 40 Eridani A star. Now scientists have found an exoplanet that fits the description.
  • Rediscovered: the 19th century geological drawings of Orra White Hitchcock, a pioneering female scientific illustrator
  • Researchers discover that kidney stones grow and dissolve much like geological crystals
  • We all know about lava volcanoes, but have you heard of ice volcanoes? New study suggests that cryovolcanoes have likely been erupting for billions of years on Ceres.
  • This new map of Antarctica is like ‘putting on glasses for the first time and seeing 20/20’

The EGU story

Last week, the EGU hosted its first science-policy dinner debate in Brussels. The event, ‘Horizon Geoscience: overcoming societal challenges, creating change’, was organised in collaboration with the European Federation of Geologists (EFG) and brought together geoscientists, policymakers and industry representatives. On the EGU website, we report on the outcome of the discussion and publish the key findings from the Horizon 2020 Geoscience Survey conducted earlier this year.

Panel members during the Horizon Geoscience dinner debate. From Left to right: Jonathan Bamber, John Ludden Lieve Weirinck, Jean-Eric Paquet and Vitor Correia

In the past few weeks, we have also issued three press releases highlighting research published in some of EGU’s open access journals. Follow the links to find out how bombing raids in the Second World War impacted the ionosphere, how glacial geoengineering could help limit sea-level rise, and what the point of no return for climate action might be.

And don’t forget! To stay abreast of all the EGU’s events and activities, from highlighting papers published in our open access journals to providing news relating to EGU’s scientific divisions and meetings, including the General Assembly, subscribe to receive our monthly newsletter.

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: Aoraki & a round-up of the latest New Zealand earthquake news

Imaggeo on Mondays: Aoraki & a round-up of the latest New Zealand earthquake news

On Sunday the 13th November, New Zealand’s South Island was struck by a powerful 7.8 M earthquake. Initial analysis by the United States Geological Survey (USGS) indicates that the source of the tremor was faulting on or near the boundary between the Pacific and Australia plates. A tsunami alert (no longer active) was triggered following the earthquake, with risk of tsunami waves along coastal areas. The maximum wave high recorded by a gauge at Kaikoura, 181 km north of Christchurch, was 2.5m, according to Weatherwatch.co.nz.

The collision of the two plates is also responsible for the formation of the Alpine Fault, which runs along the western flank of the Southern Alps, (Kā Tiritiri o te Moana). The mountain range runs 500km along the South Island, explains Katrina Sauer on our open access image repository, Imaggeo.  In addition, the Alpine Fault is responsible for the uplift of this impressive mountain range. Sunkissed by a setting sun (pictured above), Aoraki/Mt. Cook is the highest mountain in New Zealand (3,724 m). Katrina took the beautiful picture from Mueller Hut.

For more information about yesterday’s earthquake, as well as photographs which depict the staggering aftermath of the tremors see the list of links below (by no means exhaustive):

For some of the latest news about the earthquake, you might also follow the #eqnz  and  #nzearthquake on Twitter. For details about New Zealand geology and why and how it’s tremors are triggered, you can follow Chris Rowan  (@Allochthonous), Jascha Polet (@CPPGeophysics), @IRIS_EPO (particularly good for teaching resources for kids), and Anthony Lomax (@ALomaxNet) (among many other  great scientists!).

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/.