Mount st helens eruption false dating

07-Sep-2015 04:01

The May 18 eruption ejected about 0.3 cubic mile of uncompacted ash, not counting an unknown but probably much smaller amount that was deposited in the atmosphere or too diffuse to form measurable deposits.This volume of ash is less than those of several earlier eruptions of Mount St.Helens and considerably less than the ejecta volumes of some historic eruptions elsewhere.The 1815 eruption of Tambora (Sumbawa, Indonesia) ejected about 30 to 80 times more ash than did Mount St. The 1815 Tambora eruption ranks as the largest known explosive eruption in historic times.All these factors relate directly or indirectly to the total amount of energy released during the eruption.

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Helens was exceeded in "size" by many other eruptions, both in historic times and in the recent geologic past.For the study of earthquakes, two standard measures of the "size" of the seismic event are commonly used: the Richter Magnitude Scale (based on energy released as measured by seismometers) and the Modified Mercalli Intensity Scale (based on damage caused as assessed by people).But even the Tambora eruption pales by comparison with the gigantic pyroclastic eruptions from volcanic systems such as Long Valley Caldera (California), Valles Caldera (New Mexico), and Yellowstone Caldera (Wyoming)--which, within about the last million years, produced ejecta volumes as much as 100 times greater.Ejecta volume, in cubic miles Some scientists recently proposed the Volcanic Explosivity Index (VEI) to attempt to standardize the assignment of the size of an explosive eruption, using ejecta volume as well as the other criteria mentioned earlier. A VEI of 0 denotes a nonexplosive eruption, regardless of volume of erupted products.

Although some attempts have been made to develop a scale to compare the relative sizes of volcanic eruptions, none has yet been adopted for general use.

Volcanologists have proposed and used various schemes to rank eruptions, and these generally included one or more of the following factors - height of eruption column, volume of material erupted, distance and height of hurled blocks and fragments, amount of aerosols injected into the upper atmosphere, and duration of eruption.