How many volcanic eruptions occurred since 1956?
There is a recent book called Volcanoes of the World, by Tom Simkin and Lee Seibert. It has a chronology section listing all volcanic eruptions up to the end of 1993. I did not count them all. There are about 200 eruptions listed on each page, and I estimate that there have been about 2600 since 1956, including eruptions that are continuous from year to year.
2004-1956=48 years
2600 eruptions in 48 years.
15,750 eruptions in 6000 years
We can compare the eruptions with recent and see
Current Volcanic Activity since June 6, 1995:
http://volcano.und.nodak.edu/vwdocs/cur ... rrent.html
Roughly that's about 150 eruptions in 9 years.
So let's round it and say 150 eruptions every 10 years.
That's 90,000+ volcanic eruptions in just 6000 thousand years.
Largest Explosive Eruptions Since 1400 AD to 1981 AD
VEI Greater Than or Equal to 5
There has been about 35 since 1400 AD
1981-1400=581
581/35 = 16.6 years between each one
http://volcano.und.nodak.edu/vwdocs/vw_ ... erups.html
What does a VEI of 5 mean?
Plume Height >25 km
Volume 1 km3
Example St. Helens, 1981
http://volcano.und.nodak.edu/vwdocs/eruption_scale.html
So we can conclude that for ever 500 years 35 volcanic eruptions occurs.
In 6000 thousand years that would be 420 volcanic eruptions VEI Greater Than or Equal to 5.
A VEI of 4 is considered cataclysmic!
Here's all the Volcanoes active in the entire world
http://volcano.und.nodak.edu/vwdocs/vol ... egion.html
Fossilization rates???
http://www.asa3.org/archive/asa/200001/0216.html
Redwood trees up to 8 feet in diameter and 100s of feet high
were blown down like matchsticks in the direction of flow of
awave of ash and glass from a major volcano to the north and
east. They were subsequently deeply buried by ash and
preserved by replacement of organic material by fine-grained
silicon and oxygen (chalcedony).
http://www.sonoma.edu/Geology/Wright/PFguide.html