Volcanoes erupt on Earth billions of years, but unfortunately or fortunately I was not always present to record the intensity of these phenomena. Unfortunately only a relatively recent eruption, which took place thousands of years ago, can be denoted by the degree of intensity is right with less accuracy than those from the twentieth century. American scientists use a scale called the Volcano Explosivity Index (VEI) to measure the magnitude of volcanic eruptions. It is a scale of 1-8, where a rash of magnitude involves throwing an air of 10,000 cubic meters of volcanic material, and the most dangerous, of magnitude 8, requires the release of at least 1,000 cubic kilometers of material volcanic. For example, the recent eruption of Merapi or Eyjafjallajokull in Iceland, were both of magnitude 4, according to Life's Little Mysteries. The 1980 eruption of St. Helens volcano in the U.S., had a magnitude of 5. Studying samples of rock, etc. layers of ash., Scientists were able to realize the intensity of some of the distant past eruptions, some now even a few hundred million years. It seems that the most powerful occurred after 27 million years in the San Juan Mountains in southwestern Colorado. An estimated 5,000 cubic kilometers of lava were thrown in the air long enough that the whole California is covered by a considerable layer of lava, a few feet tall. It seems that it is the most powerful eruption in the last 504 million years. It was so severe in the Bulletin of Volcanology, 2004, scientists have recommended adding yet another level VEI scale, because it is estimated that this eruption had a magnitude of 9, being the only one of this magnitude ever known.

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