[link to www.volcanodiscovery.com (secure)]


Excerpt:

"How many volcanoes can erupt at once?

At any given time, about 10-20 volcanoes are erupting on average, and it could be imagined that this number sometimes peaks to about 30-50 erupting volcanoes (on land). Many more than that is very unlikely.

Including submarine volcanoes, these figure probably have to be multiplied by a factor of at least two or three, but much less is know about the activity of submarine volcanoes."