Protection against earthquakes — mangroves

Recently French researchers found that wildlife can much more efficiently than the human race, to confront the destructive force of earthquakes. She has the reliable protection from the disaster — mangroves. These communities, otmiraya form the interesting underground pillows can put out the most powerful vibrations the land.

Let me remind you that the mangrove forests or natural community called developing on periodically flooded areas of sea coasts and estuaries, protected from waves and storms coral reef offshore islands. These communities may dominate woody vegetation (and then they are called forests) or shrubs (then talk about mangrove swamps). "Pioneer" of the ecosystem are plants, settling in areas protected from wave energy, where fine sediments accumulate, often with high organic content. That is what the plants and necessary — for marine organic matter, as it is known — an excellent fertilizer.

All mangroves are concentrated in the inter-tidal zone, so twice a day to flood the sea water (which sometimes extends almost to the tops of trees). However, when the tide is out, exposing the intricate roots of trees and shrubs. These roots are sort of stilts that help the plant to gain a foothold in the muddy sediments and do not fall under the blows of the waves. And some of them have a negative geotropism (ie do not grow down, and up), and their plants are used for breathing — exactly as divers tube.

Among the bizarre and diverse roots swarming with various animals. And who is to not only meet: and crabs, and clams, and fish, more walk by the Authority for their fins, rather than floating, and even crocodiles. The trees also affect the abundance and diversity of the population — birds, lizards, snakes, monkeys and many other wood animals. No wonder bush mango is considered one of the most diverse biocenosis on our planet (second only to coral reefs and humid tropical forests in the number of species).

But the floristic composition of mangrove relatively uniform. Most frequencies are plants belonging to the genera Rhizophora, Bruguiera, Avicennia, Sonneratia.
And often the trees shrubs belong to one or two species. Sometimes, the top tier of the mangrove forest is formed by palm trees, for example,
Nypa fruticans in the eastern tropics, Manicaria succifera in the north-eastern part of South America, or some species of the genus Pandanus — on the west coast of Africa, Asia and Oceania. Only in Indonesia are multispecies mangrove community.

All the plants that grow in this amazing ecosystem, a remarkable ability to survive and develop in saline environments on soils devoid of oxygen. In addition, because the soil under them is poor in nutrients, they have adapted by changing their roots, to receive many gaseous substances (such as nitrogen) directly from the atmosphere, and some metal salts they need — straight from the sea water.

Interesting way to mangrove plants provide an extension of its kind — the seeds are able to germinate, not yet separated from the tree. After germination, a small seedling growing for some time, either within the fruit, or the fruit through to the outside. When, in the end, the real "biooranzhereya" falls into the water, a tiny sapling can long swim in the waves, and in this situation the seedling as it becomes dormant and leaves it only when it washes up in a favorable position to take root .

Circulated mangroves mainly in the humid tropics — on the shores of East Africa, South Asia, Australia and Oceania. However, sometimes they are found in the subtropical zone in the Red Sea (Gulf of Aqaba) and the south of Japan, as well as in the temperate (south of New Zealand).

By the way, there is growing mangroves can tolerate short-lived even freeze. But in most cases they require a frost-free climate.

Scientists have already found out that mangroves play an important role in the so-called holding the coastline or, as geologists, to prevent coastal erosion. Still, after a strong root system of mangrove plants is quite effective at maturity of wave energy. The same root system also prevents erosion of the coast, since the passage of the tidal water through the root system acts as the last sieve, strain off the various particles of the soil. When the low-tide water goes back to the roots of the slow movement of her and she can not take away the soil delivered back into the ocean. It turns out that mangroves as it was constantly reinforced the shore, which are growing.

Recently, scientists have discovered that the mangrove forests can also very effectively cope with the effects of earthquakes. They oppose dilution of soil — one of the main hazards associated with the disaster. This phenomenon comes from the fact that as a result of vibrations caused by earthquakes, large surface areas are losing their mechanical strength and behave like a liquid. That is why often when shake the earth, and even after the large houses, roads and other large objects just "sink" in the ground, which has just been solid, but suddenly turned into a "mess." In particular, this phenomenon has further deepened the destruction caused by a seismic wave in the earthquake in Japan on March 11, 2011.

Geologist Philip Hugo from the University of Fourier in Grenoble (France) and colleagues, exploring mangrove soils and underlying rocks on the island of Guadeloupe, faced with an unexpected effect. They put accelerometers in different places Bellepleyn area, where at that time there was a small earthquake, and began to collect data on tremors. They are interested in one caveat — the place where the mangroves were located, tremors were felt much weaker than in the surrounding area. Scientists have suggested that this is clearly no accident.

In order to solve this problem, scientists have drilled several wells in Bellepeyne. And it turned out that the weaker tremors were felt in areas where sedimentary rocks have been found, is not nothing but a petrified multimeter (absorbed the calcium salt) the remains of millions of prehistoric mangrove plants. It turns out that even after the death of the trees continued to defend his favorite beach from destruction, creating a kind of "stone pillow", which is just extinguished tremors. She was able to do this because inside this education were air pockets that make the whole structure becomes elasticity and flexibility.

"Flexible mangrove layer reduces the strain and stress in the upper sand layer and, therefore, reduces the potential for liquefaction of soils in this area" — commented on the results of the study, Dr. Hugo. He also said that apparently, these deposits defended this place for hundreds of thousands of years. Scientists made this conclusion after carefully studied the shore, which, being in a very seismically active place, however, almost did not reveal traces of past earthquakes. At the same time around they were pretty well marked.

So, those who live in areas of growing mangroves, can not be afraid of the soil liquefaction during earthquakes. And what do those who dwell far away. Dr. Hugo believes that engineers should consider the structure of the stone mangrove "cushion" and use it to create a design that would be to enclose the ground in communities of seismic zones. That is, a man, apparently, it should again learn from nature …

Anton Evseev


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