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 000ft) is some 30 000ft 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 000km**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 the

Mauna Loa, active volcano, on Hawaii Island, one of the world's largest volcanoes. It rises from a desolate landscape of old lava flows to a high point of 4,169 m (13,677 ft) above sea level in the summit caldera (enlarged crater) of Mokuaweoweo. Lava from Mauna Loa covers about 50 per cent of Hawaii Island, including parts of Kilauea, a crater on the mountain's east flank. Since the early 19th century, Mauna Loa has exuded lava about once every four years

The largest islands, in the western region, form volcanic island arcs that rise from the broad continental shelf along the eastern edge of the Eurasian Plate. They include Japan, Taiwan, the Philippines, Indonesia, New Guinea, and New Zealand. The oceanic islands, collectively called Oceania, are the tops of mountains built up from the ocean basin by extruding molten rock. The Pacific Ocean contains more than 30,000 islands of this type; their total land area, however, amounts to only one-quarter of one per cent of the surface area of the ocean. The mountains that remain submerged are called seamounts. In many areas, particularly the South Pacific, the land features above the sea surface are accretions of coral reef. Along the eastern edge of the Pacific, the continental shelf is narrow and steep, with few island areas. The major groups are the Galapagos at the equator. Which rise from the Nazca Plate, the Aleutians in the north, which are part of the North American continental shelf. The islands of Hawaii, which rise some 5,550 m (more than 18,000 ft) from the sea floor of the central Pacific, reaching in Mauna Kea a height of 4,205 m (13,796 ft) above sea level.

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 27km 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.

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.

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.

Some common words found in the essay are:
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Approximate Word count = 2978
Approximate Pages = 12 (250 words per page double spaced)