how are the eruptions of volcanoes predicted and what scale are they measured on?

Question

help please my friend thinks they are measured by tons of pumice erupted. also how do they predict the eruptions

Answer 1

The size of volcanic eruptions is given using the volcanic explosivity index (VEI). This is a logartihmic scale, much like the Richter scale used for quantifying earthquakes.
For more info see
http://en.wikipedia.org/wiki/Volcanic_explosivity_index

It is based on the total volume of all erupted products.
This is a pretty misleading way of measuring the scale of an eruption since pumice-dominated eruptions will give unusually high values (pumice is low density, its full of air). More recent studies (see sources) have tried to convert these volumes into masses, which gives a better indication of the amount of erupted magma.

Volcanoes are predicted based on observations such as an increase in minor earthquake activity, surface uplift/bulging, that kind of thing. Its still a very imprecise science and some would argue a total waste of time. All it takes is one large random earthquake to trigger a major eruption and it may come without any warning signs.
The biggest volcanic eruptions (VEI=8, such as Yellowstone) have simply never been observed in action and so we don't know if the warning sings would be the same, since their eruption styles would probably be unlike anything we've ever seen before.

Answer 2

There are earthquakes of a particular type called Harmonic that indicate magma moving toward the surface which usually means an eruption is coming. The usual rating of the scale of an eruption applies to the volume of material ejected, including but not just limited to pumice. The usual figure is in cubic miles of "ejecta".

Answer 3

As long as everyone ignores the geothermal effect upon the climate nothing can be judged to be good science reguarding GW. The fact that the iceage cycle and hurricanes come and go is effected by the heat that flows from the interior of Earth into the ocean. The people saying the climate is not being effected by the geothermal flux are not being truthful about GW even though they may just be mislead by all the BS being vented at this time.

Answer 4

They're measured on the Rictor Scale. It's when abnormal "burps" in the read out apear, a specialist is called in to determine the severity of the situation. Other things such as temperature, gas expulsion, etc. can be factors in determining the activity of a volcano.