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BIG ENCYCLOPEDIA FOR CHILDREN AND ADULTS
Why are volcanoes located in certain places? Detailed answer
Directory / Big encyclopedia. Questions for quiz and self-education Did you know? Why are volcanoes located in certain places? In the area of cities such as New York, London or Paris, there are no volcanoes, and they are unlikely to appear there in the future. However, in some areas of the globe, several volcanoes are located in one place at once. The Pacific coast of Central America is one of the most active places of volcanic activity in the world. And in fact, more than two-thirds of the active volcanoes are located in this place, as well as many of those that have ceased their activity relatively recently. And the reason is this: in these places the earth's crust is very weak compared to other regions of the globe. Where there is a weak section of the earth's crust, a volcano appears there. Here is how it is formed. As we already know, the Earth's core is very hot. As the depth increases, so does the temperature. At a depth of 25 km, the temperature is so high that all rocks (here the temperature reaches 1000-1100 ° C) are in a molten state. When rock melts, it increases in volume - it needs more space. In some regions of the Earth, new mountain systems were formed not so long ago (that means several thousand years ago). Below them, the pressure in this area is lower than in other areas. This is a kind of weak spot in the earth's crust. Molten rock, called "magma", infiltrates these areas, creating reservoirs of molten rock. Magma rises through cracks formed by the uplift of the earth's rocks. When the pressure in such a reservoir exceeds the forces that hold the magma underground, the molten rock breaks out, forming a volcano. The eruption stops with the end of the release of associated gas. During the eruption, gaseous substances are mainly released, as well as a large amount of molten rock "lava", solid particles in the form of ash. An eruption is an explosion of gases, but part of the lava turns into dust, and during the eruption we observe a cloud of black smoke. Author: Likum A.
Why do trees need bark? The outer shell of a tree trunk or root is called the bark. However, it is wrong to call it a shell; rather, it is the outer part of the trunk or root. It is sometimes quite difficult to determine its thickness, because in trees such as palm trees, for example, there is no clear boundary between bark and wood at all. Why do trees need bark? One of its main functions is that it protects the inner, more delicate part of the tree. The bark not only prevents it from drying out, but also protects it from all kinds of external damage. The bark of some trees is even capable of resisting flames. There are cases when mammoth trees were found in America with traces of a fire on a thick, fibrous bark, while the reliably protected wood turned out to be intact. The process of bark formation can take years. For example, on a very young shoot of a maple, there is no hard bark as such, and small branches have an absolutely smooth surface. Therefore, when the woody layer of such a shoot begins to grow, the soft outer skin may burst in one place or another. However, damage of this kind, as a rule, is not terrible for a tree and heals itself from the inside. Gradually, one by one, sections of the outer shell of the young plant dry up and these dead scales die off and give the bark such a rough look. Some of them are constantly broken off or shed by the tree itself as it grows and matures. People have learned to use the bark of many trees for their practical needs. For example, almost all wood corks are made from cork oak bark. The bark of the hemlock is used for tanning leather. The spice used in cooking, known to us as "cinnamon", is nothing more than the powdered bark of a tree growing in Southeast Asia. Quinine - a wonderful medicine against malaria - is obtained from the bark of the cinchona tree. In medicine, in general, many extracts from the bark of branches and roots of various tree species are used.
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