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Which are the biggest (tallest and largest volume) and smallest volcanoes on Earth? The island of Hawaii is probably the largest volcano on earth. From its base (on the floor of the Pacific Ocean) to the summit of Mauna Kea (about 13 000 ft) is some 30 000 ft i. e. higher than Everest.
The island comprises several coalescing volcanoes including Mauna Loa, Mauna Kea and Kilauea. Mauna Loa alone has an estimated volume of 40 000 km 3. It is impossible to say which is the smallest volcano since there are thousands of small eruptions on the ocean floor and around already established volcanoes only a few yards across. Volcanoes are caused when molten rock from within the mantle breaks through the crust and flows out over the surface.
But volcanoes don't occur everywhere. There are none in Britain at the moment, although in the past (300 - 400 million years ago) there were plenty in Wales and Scotland. Volcanoes form in two places on the Earth. The Earth's crust is made up of a series of plates. When these plates collide, one can be forced below the other. As this happens it is pushed into the hotter mantle and starts to melt.
The melting rocks rise back up through the mantle and start working their way into the crust. Some will get trapped and cool slowly. Others will reach the surface forming volcanoes. There are other places on Earth where the crust is being heated strongly from the mantle below. This can be thought of like a bunsen burner heating a pan. As the Earth's crustal plates move over these "Hot Spots" a series of volcanoes will form.
This combination of moving the crust over a single hot spot will create a string of volcanoes like those in Hawaii and Indonesia. The line of volcanoes shows the direction the plate has moved in. Once a volcanic cone has built up, it might block itself up if the molten rock solidifies inside it. But when the pressure of more rising molten rocks beneath is great enough, it blows the solidified rocks off the top and erupts again. Just before this happens there are sometimes a lot of earthquakes in the area. This can be a warning to people who live on the volcano that it is about to erupt.
The problem is that volcanic eruptions are not predictable and many people die each year when eruptions happen suddenly. So why do people want to live near volcanoes? The answer is that volcanic rocks form very fertile soils that are good for growing crops. In crowded countries like Indonesia where there is not much space to grow crops, farming on volcanic soils is vital to keep the population alive.
If the molten rock comes out under water then it will cool very quickly. This is happening along the middle of the Atlantic Ocean where lavas are erupting out along huge cracks that run from Iceland in the north down to the Falkland Islands in the south. This is the longest volcanic mountain chain on Earth but not a lot of people know it is there because it is hidden beneath the sea. There are also other planets in the solar system with volcanoes on them. Mars has one of the biggest volcanoes - a mountain called Olympus Mons. Scientists believe that all the volcanoes on Mars are inactive now.
Venus is almost completely covered in volcanoes. 80 % of the planet is peppered with them. But scientists are yet to find a smoking one. One theory suggests that Venus burps out its heat from the mantle every 500 million years in a catastrophic volcanic event which covers the whole planet. The rest of the time it stays dormant. 1. In volcanic areas - water which is contained within rocks can be heated by the molten rocks which give rise volcanoes. The hot water can be 'tapped' and used for power - this power is called hydrothermal energy (hydro = water and thermal = heat or energy).
In Iceland, hydrothermal energy is used in greenhouses to grow tomatoes and bananas! It can also be used to generate steam which in turn can power turbines and produce electricity. 2. Soils produced from the ash and weathered rocks of volcanic eruptions are extremely fertile and flanks of large volcanoes are often used for agriculture. 3. On the island of Lanzarote, to the west of Africa, the locals use volcanic rocks for building stone; its readily available, cheap and there are very few other building materials. It is also light so easy to transport but not very strong so buildings can't be very tall - which is great if you don't want to ruin your skyline with skyscrapers! 4. Volcanic eruptions themselves have been important in geological history by introducing gases into the Earth's atmosphere, in particular water vapour, sulphur, carbon dioxide and carbon monoxide.
These gases have played an important role in the development of our atmosphere. 5. Tourism - many volcanic areas are exploited for tourism e. g. trips to Vesuvius and Mt Etna in Italy. The volcanoes and hydrothermal areas of New Zealand and Hawaii also attract many tourists. 6. Finally, volcanic activity produces fluids in rocks which are rich in minerals.
When these fluids cool, the minerals crystalline out and are deposited. Many of these minerals are of considerable economic wealth. Do other planets other than Earth have volcanoes? There are many signs of volcanic eruptions on the other Earth-like planets - especially Venus and Mars, but it all seems to have happened in the distant past, and they show all the signs of being quiet and inactive now.
Both Mars and Venus have volcanoes much larger than any on Earth, and they have erupted huge amounts of lava onto their surfaces in the past (Olympus Mons on Mars is over 27 km high! ). Mars even has an enormous bulge on one side of the planet, where the molten lava rising up to the volcanoes from inside the planet has pushed the solid crust 6 kilometres above the surrounding land. The other worlds in the Solar System which do have active volcanoes are both moons of the outer gas giant planets. This is strange, because in general, the further from the Sun a planet is, the colder and less active it should be.
Io, one of Jupiter's satellites, about the same size as our own Moon, actually has more erupting volcanoes than the Earth. This is because it orbits very close to Jupiter, and is constantly being pulled around by the gravity of Jupiter and its other moons. This keeps the rocks beneath the surface hot enough to be molten lava, and it keeps bursting out through vents in the surface. The other volcanic moon is even stranger.
Triton is slightly bigger than Io and our Moon, but. orbiting Neptune, lies even further away from the Sun's heat. On Triton, all the rocks are frozen solid, yet even here geological activity can be found in the form of geysers. Every summer, on this distant moon, the faint light of the Sun is sufficient to raise the surface temperature. The moon erupts in one of the most arresting displays in our solar system: jets of pure nitrogen escape like the steam from a pressure cooker to rise several kilometres into space before taking a right angle in Triton's high altitude winds. Where does the gas that comes out of volcanoes come from?
The most common volcanic gases are carbon dioxide, water, sulphur dioxide and hydrogen sulphide - these giving the distinctive odour associated with volcanic activity. Small quantities of other volatile elements and compounds are also present such as hydrogen, helium, nitrogen, hydrogen chloride, hydrogen fluoride and mercury. These gases come from the magma - basically any molten rock beneath the surface - and exactly which gases are released depends on temperature, pressure and what other volatile elements are present. Some volcanic gases are less soluble in magma than others and will separate out at higher pressure. As magma ascends from deep inside the earth, the pressure acting on it decreases and allows the various gases to 'bubble' out. Studies at Kilauea Volcano in Hawaii suggest that carbon dioxide begins to separate from its parent magma at depths of about 40 kilometres, whereas most of the sulphur gases and water are not released until the magma has reached nearly to the surface.
Carbon dioxide is the least soluble and so is the first to separate. It is the expansion and joining up of these gas bubbles which tears the magma up into lumps or clots which form the pumice and ejected material in explosive eruptions. So how do these gases get into the magma? This depends on where the magma was formed in the earth. The magma in basalt volcanoes, such as those in Iceland or Hawaii, has its source in the mantle, the layer directly beneath the surface 'crust' of the earth, and so any gas here comes mainly from gas...
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