First, I want you to know that I admire what you do very much and thank you, in advance, for any help you can give me in answering the following question: > > I am trying to find out if there is an upward or downward trend in volcanic activity when comparing the 19th century to the 20th century. I realize that our ability to monitor has improved and more attention has probably been given to volcanoes over the past 100 years or so. I guess the only way to answer my question would be to pick, let's say, 1500 volcanoes which were known about in BOTH centuries and compare the number of major eruptions. For example, did 500 volcanoes erupt violently in the 19th century and 800 in the 20th? Thank you, again, for your help.

Christopher

That's a question that lots of folks like to ask. I think that the best discussion of whether or not there has been an increase (or decrease) in volcanism is found in the book "Volcanoes of the World" by Tom Simkin and Lee Seibert. Basically, they found that if you plot the number of reported eruptions vs. time, you get what looks like an almost exponential increase. This, as you have observed, is attributable to our ability to know what is going on just about everywhere in the world now days. They also find that there is a decrease in the number of reported eruptions during WWI and WWII, and increases after the Krakatau and Mt. Pelee eruptions. These are not natural. During the wars folks were paying attention to things other than volcanoes, and after the big eruptions people paid more attention to eruptions. What they did to test these observations was to look at the number of large eruptions through time - those that didn't really require someone looking at the volcano to notice. They found that there was no change in the frequency of large eruptions. The increase in total eruptions through time is due to a larger number of observed small eruptions. Thus their answer (which I personally think is correct) is that there has not been any increase in activity.

Sincerely,
Scott Rowland

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