published on 5 January 2005 in earth
Tsunami in the Maldives
On the 26th December 2004, an earthquake that took place 300 km west of the Island of Sumatra generated a gigantic wave: a tsunami. In order to easily understand what we are talking about, a simple experiment can be carried out. Take a tub full of water and hit it underneath with your fist, you will immediately see a series of waves that spread out in concentric circles, starting from the point where the tub was struck. Thus we have created on a small scale, a microscopic tsunami. The earthquake that took place in Sumatra was classified as magnitude 9, therefore it was surprisingly strong, if we compare it to the earthquake in Messina in 1908 and in Irpinia in 1980 in Italy, which were approximately magnitude 7. In terms of energy however, an earthquake of magnitude 8 is 30 times greater than one of magnitude 7, while one of magnitude 9 is 900 times more powerful than one of magnitude 8. An earthquake of this intensity caused anomalous waves that in some cases reached a height of 34 metres. The victims in the countries facing the Bay of Bengal were hundreds of thousands and the economic damages provoked by the tsunami were inestimable, particularly in the countries that based their economy on tourism, such as the Republic of the Maldives.
The Maldives and tourism
The Maldives archipelago is in the middle of the Indian Ocean, approximately 700 km South-West of Sri Lanka. Together with the Laccadives in the North, and the Chagos Islands in the South, the Maldives are part of the submarine mountain range that stretches approximately 2,000 km, which was formed about sixty million years ago. On the crest of this mountain range the coral reefs developed. The Maldives archipelago is made up of approximately 1,190 coral islands (of which only about 300 are inhabited) and the distance between the island that is furthest to the North and the one that is furthest to the South is 850 km, while the distance between the island that is furthest to the East and the one that is furthest to the West is 130 km. Therefore these islands cover a surface area of 110,000 km2, however only 300 km2 are emersed land, therefore only 0.27% of the country is above sea level, while the remaining 99.73% is sea. The population is of about 270,000 inhabitants and the economy of the country is based principally on the tourism industry. The coral reef in the Maldives is one of the most beautiful in the world and it is therefore the greatest attraction of this country. Thanks to the coral reef the number of visitors in the past thirty years has increased almost exponentially, and at present “coral tourism” contributes to 30% of the Gross National Product. The flow of tourists from Italy in particular, accounts for 21.2% of the total, with approximately 130,000-140,000 tourists every year.
The coral reef in the Maldives
The sea bed in the Maldives has the richest formations of corals in the entire Indian Ocean, these are known as atolls, i.e. formations of corals that outline a central circular lagoon. These madrepore constructions usually arise in deep ocean waters near ancient submerged volcanic islands. Here there are over 66 genuses and over 100 different species of madrepores. Furthermore, almost one third of the coral fish in the entire Indian Ocean live here. The reason for such wealth depends on the variety of environments that are present in the Maldives. Near the barriers, which rise from 2,000-3,000 m deep up to the surface, there are peaceful lagoons surrounded by incredible white beaches. The reefs are continually interrupted by crevasses which transform into tunnels and canyons, providing the ideal habitat which can satisfy the requirements of each of the species and communities formed by them. Such wealth of biodiversity led to the great fear of infinite damage after the tidal wave struck this archipelago, specially as the reef was still recovering after the disastrous effect of the Niño in 1998.
Consequences of the tsunami
The impact of the tsunami in the Maldives, on the people and the structures, was more contained than in other zones that were struck even though the news in the media immediately after the tsunami was alarming, if not catastrophic. The false alarm probably derived from the particular vulnerability of the Maldive islands, due to multiple causes: the highest part of the archipelago is no more than one and a half metres above sea level, the constant erosion of the beaches of numerous islands, the difficult access to the islands, the rather modest size of most of the islands (on average, an island can be crossed on foot in ten minutes) the great economic importance of tourism and a fragile coral reef slowly recovering from the “whitening” phenomenon of 1998.On the western coasts of Indonesia, the waves reached a height of 34 metres, causing the total destruction of the infrastructures on the coast and of the vegetation, while the waves that hit the Maldive islands, were about 1 to a maximum of 3.5 metres high. The Maldives archipelago is to the West of Sumatra, thousands of kilometres away from the epicentre of the earthquake, and the tidal wave reached at low tide and therefore the damages were remarkably reduced. If the tsunami had struck the Maldives at high tide, probably the damages would have been much greater. The government declared there were 82 dead and 26 missing persons, approximately 4000 homes destroyed, while 72.5% of the tourist islands remained totally operative, (63 islands out of 87). From local evidence gathered directly in the Maldive islands, apparently the greatest damages were caused by the rapid outflow of water after the passing of the wave, which also carried with it debris of various kinds, such as boats, lumber, furniture, plants, etc. It must also be said that most of the dwellings on the fishermen’s islands had no foundations, and are simply built on the sand, so the pressure of even one metre of water against the walls that were not firmly attached to the ground, had a devastating effect. In the capital of the Maldives, Male, in fact, no buildings crumbled because these were built on solid foundations. Therefore the damages of dwellings were relatively modest, while what was more troubling was the flight of the tourists, who after the tidal wave on the 26th of December, decreased by 72.3%.
Following the confused information which had no scientific foundations, of the very first news bulletins, now the first studies are being carried out on the damages caused by the tsunami on the environment. It is an Italian organization that has been the first to verify the situation of the delicate coral reef in the Maldives archipelago, the Department of Evolutionary Biology of the University of Bologna, on invitation of the Government Authorities of the Republic of the Maldives. With the help of videofilms, the Organization is studying 18 underwater stations, situated in the North Male and South Male atolls, distributed on: ocean slopes (exposed reef outside the atoll that is therefore subjected to the impact of the ocean waves), internal reef (reef inside an atoll and therefore that does not directly feel the influence of the ocean wave), passes (the channels that connect the ocean outside and the sea inside an atoll) and the sandbanks (underwater reefs).
No permanent damage
The results obtained from this preliminary study indicate that there was no considerable damage in the coral reefs in the atoll of North Male, while in the atoll of South Male, particularly near the pass, numerous coral branches (particularly of the Tubastrea genus) were partly broken or destroyed and some parts of the reef crumbled as a result of a recent violent event such as the particularly powerful anomalous wave. According to the Department of Evolutionary Biology of the University of Bologna, the coral reef in the North Male atoll was hit less violently by the wave, probably because of the island of Sri Lanka, which could have slowed the speed of the tsunami in the northern part of the Maldives archipelago. Instead, the South Male atoll is much more exposed and therefore had a much more violent impact, particularly in the areas of the pass, as the acceleration of the sea in these channels that connect the external ocean with the inner sea of the atoll was so strong that it caused the breaking and crumbling of part of the reef. The passes are the only apertures towards the ocean and it is there that most of the mass of water flows in and out of the atolls during the tides. It is therefore easy to understand how violent the currents flowing through the passes must have been, but nothing compared to the current caused by the tsunami that was passing, which could be defined as an exceptionally high tide. The corals living in these particular areas are adapted to resist against the strong currents, but not to resist a current that is so exceptionally strong. Fortunately the pass areas represent a very low percentage compared to the entire ecosystem of the coral reef and the percentage of the reef that was damaged did not exceed 5.7%. Therefore these damages are only a very small fraction that can be recovered in about ten years time. In other words the tourists will not note any consequences due to the passage of the anomalous wave and the coral larvae that will arrive from the areas of the reef that remained intact will repopulate the areas that were struck by the tsunami in a short amount of time.
Only feared damages
At first it was thought that in addition to the mechanical damages incurred by the coral reef due to the impact of the tidal wave, there could be drastic consequences due to the enormous mass of sand that was swept away from the islands during the tsunami. Coral polyps, in fact, live in symbiosis with particular algae, which use photosynthesis to enable their growth. In fact, if the sand had deposited on the coral, removing its source of light, this would have caused the death of entire colonies, and all the sea life would have suffered irreparably as a consequence. Fortunately it seems that in the Maldives the currents have already washed away the sand, and the situation is rapidly returning to normal.
Underwater morphology: what luck!
In the Maldives, even the morphology of the coral reefs helped prevent the catastrophe. The waves generated by a tsunami are different from those generated by the wind. In fact, a normal wave only involves the surface of the sea, and its width does not exceed a hundred metres; the waves of a tsunami, instead, involve the water in its entire depth and are dozens of kilometres wide, with a truly enormous mass. When a wave generated by a tsunami reaches the beach, even though its speed is not great, but is equal, for example, to a man running, it does not stop, because behind it are millions of tons of water that continue unrelentingly. For this reason the parts of the coast characterized by plains were completely devastated by the tidal wave. If we consider a vertical cliff that rises from the surrounding deep sea, instead, when the tsunami hits the area, the surface of the sea will simply rise and fall again not much later (from a few minutes to a maximum of one hour), with a wave height of only few metres. In this case there should not be any consequences because the morphology of the cliff prevents the enormous potential energy of the wave from being transformed into kinetic energy or, more simply, an enormous mass of water rises and falls, remaining in its place. This is the case of the Maldives archipelago, made up of coral atolls, which as already mentioned, formed on the tips of ancient submarine volcanoes and as a consequence are surrounded by very deep slopes and seas that rapidly become deep. Because of this morphology of the sea beds the tsunami waves did not cause particular deformations or overturning, but almost only phenomena of remarkable flooding, with consequences that were much less disastrous than the other areas struck by the tidal wave. Furthermore the external oriental coral reef absorbed the impact of the anomalous wave, protecting the more internal islands.
Paradise cannot wait
Initially the destruction of the coral reef was estimated to be around 20%, and erroneously it had been stated that the fish were in great danger, in particular the Caribbean parrotfish that would not have found the algae that grow on the corals to eat, or the lobsters that would not have been able to hide from their predators as a consequence of the effects of the tsunami. Fortunately, as stated above, all this did not occur, and as a consequence of the first Italian research work, the conclusions have been surprisingly optimistic. Therefore no fear for the fish inhabiting the coral reef in the Maldives, (vedi immagine Pesci Tropicali) and for all the other organisms that are directly connected to the same. The Maldives will continue to be a paradise for all the tourists who wish to visit them, and by doing so, tourists will also contribute to support the country’s economy.
Written by Tiziana Bosco