Tsunami and coral reef.. (by  Marco Angelozzi)
 

The day December 23 year 2004, in the north of the Macquarie Islands (near Australia) it happen one of the strongest earthquakes that can be remembered in the history of that angle of the planet. The magnitudo is 8,5 of the Richter scale, a very high value and in the following hours there are many arrangement shakes.
The Geology teaches that generally a strong earthquake doesn't cause others of it and also for this motive nobody could imagine that later as soon as three days there would be recorded, to around 3000km of distance, the most violent earthquake of the last 40 years.. 

On December 26 in fact it happen an earthquake with epicentre in northwestern of the island of Sumatra, in the backdrops of the Indian ocean, it frees an energy equal to that that would be had with the explosion of 20000 atomic bombs..
This event causes the move of the Earth of 3 cms in comparison to its axle of rotation, a shortening of the day of 3 second milionesimis, a move of the island of Sumatra of 30 mt toward southwest and above all one of the more powerful tsunami ever observed to man memory.. 

The tsunami, from the Japanese “wave of the port”, can be caused, as in this situation, from a strong submarine earthquake that upsets and it moves upward very violently the column of impending water from the lower part.
This move produces a series of so that anomalous waves that can spread for thousand kilometres with very high speed, up to reach the dry land.
In opened sea the waves have a least height, as soon as 50 cms or less, but when they reach lower backdrops the masses of water, because of the attrition, decrease the speed of their run and they also raise him up to 10 meters, as on December 26 happened, flooding the dry land..
Before the waves get depressed on the coast there is a strong backwash, the sea withdraws it for about ten meters and this is the signal that water is about to invade the dry land. 

The areas struck by the tsunami of December 26 have been Thailand, India, the Sri Lanka, Indonesia, the Malesia, the Maldives and the waves have also arrived in Africa, on the coasts of Somalia, Kenya and Tanzania.

(Zones struck by the tsunami. The red zone points out the probable point of departure
of the anomalous waves) 

(Zones struck by the tsunami. The red zone points out the probable point of departure
of the anomalous waves) 
 

All the coral formations of these zones, the richest of the globe as biodiversity (with around 1700 different kinds of fishes and 400 of madrepore) have harshly been stricken from the destroying strength of the waves and on them there are poured great quantities of mud, sand and refusals. 

The waves of return that have invaded the dry land have in fact dragged in water deposits, refusals, poisons and hydrocarbons torn from the industries and from the man residences.  They are still few, to two months from the event, the underwater surveys effected to know the state of the flora and fauna, but they immediately result evident the great quantities of sand that have covered the coral reefs.. 

This coverage can put to risk the survival of the same coral, in fact it doesn't allow the algas zooxantelle that live inside of it to receive the light of the sun and to effect the chlorophyllose photosynthesis.

(Images drawn from the Italian giornal “Il corriere della sera”: the anomalous wave reaches the coast) 

If this situation persisted different months the algas they would risk to die, putting also in serious difficulty the coral that he/she lives in symbiosis with them, receiving important organic substances for the development and for the construction of the barrier. 

A solution could be that to organize a plan of “cleaning” of the corals that involves numerous and willing scuba divers making to literally return to the light these wonder of the nature. We hope that the strong tides that are present in a lot of of these zones can naturally polish up the barrier and to contribute to the return of a situation of normalcy. 

The strength of the waves has caused besides the breakup of many branched corals, landslides of portions of reef (even stop of 1-2 ms cubes eradicated by the walls) with the accumulation of them on the backdrops, inclusive those of the passes, that have decreased their depth of 2-3 meters in some zones!
(the passes are of the small interruptions of the coral barrier that connect the ocean with the inside sea to the atoll, through which strong tides generally flow). 

(Images of the coral barrier struck by the tsunami, with fans and corals branched broken) 
 

The numerous destroyed areas could have left besides the abundant tropical fauna of which this area is rich without shelter, as for example the parrot fish that is usual to use the hollow among the corals as mend for the night. This fish nourishes him of algas that it tears from the barrier with its horny beak and the zones where usual feed could have been destroyed. 

The lobster as other kinds of shellfishes and tropical molluscs that hide him in the ravines of the madrepores, could be found again without habitat and forced to adapt again and to colonize other zones. The "barracuda", great raider that can reach 2 meters length that it stirs at night in flock during the day and hunting, needs to live in clear waters and the movements caused by the tsunami could now create difficulty.   

Which zones has been mostly struck by the violence of the tsunami ? 

The Asian area and particularly the coral barriers of the islands Andamene and Nicobare have mostly been reached by the violence of the anomalous waves. Here numerous bushes of corals have been observed branched broken, heaps of fragments, deposits in the backdrops and portions of collapsed reef and partially covered of sand.. 

In the most distant areas, reached by a smaller violence of the waters, the coral barriers seem to have brought damages of smaller entity. 

To the Maldives for instance, in base to the preliminary study effected by the Marine Science Group of the university in Bologna, the damages would be more contained and they would represent only the 6% of the whole coral system, recoverable in brief times. 

In this case a function of protection of the island of Sri Lanka is hypothesized. The island would have braked the run of the anomalous waves and also the particular conformation of the depths backdrops of the Maldive. 

These are the effects that the impact of the anomalous waves has directly produced and indirectly on the natural environment of the coral barrier of the Asian area. Which have been the direct effects of the arrival of the tsunami on the sea fauna and earthling instead? 

The results of the first searches seem amazing. All the animals that had the possibility to get further in hurry would have done it just before the arrival of the anomalous waves reducing their losses to very low levels. As it surely regards the sea fauna some fishes, molluscs and shellfishes of small dimensions will have surely been beaten with deadly result on the barrier but the majority of them will have perceived with good advance the arrival of the masses of water. This thanks to their acute senses, above all the ability to gain tall or low frequencies that would have alerted them with good advance giving them the permission to shelter in sure depht waters. 

(Obviously the underwater surveys have noticed that in some zones there is no more abundance of fishes but this situation it is probably connected to the alteration of the habitat, with the destruction of shelters and dens in the barriers, referable situation to normalcy in brief times). 

These “information” about the arrival of so that anomalous situation have also been perceived by the terrestrial animals, making them get further in territories distant from the coasts and to greater heights on the level of the sea. 

In the Yala National Park of the Sri Lanka in fact, house of hundreds of buffalos, elephants, crocodiles, leopards, monkeys and other numerous mammals there has not been found anybody trace of carcasses even if the tsunami in that territories of the park has arrived with great violence flooding it almost entirely!   

Bibliographer: 

- “Tsunami Survey Expedition, Maldivian Coral Reefs, 2 weekses after” Marina Science Group. 

- “The risk tsunami” of L. Bignami. 

- Articles: “Tsunami, thing has favorite the Maldives” and “You truth on the Maldives.” 

- Article: “The sixth sense has saved all the animals.”