Re: What is longest eruption by a volcano?

Well, it depends on what is your concept about a volcano...
The largest volcanoes we have are underwater, separating
the continents, in a region that we call "mid oceanic ridges".
In North Atlantic, for example, in the middle of the ocean,
between USA and Europe, the mid oceanic ridge goes from near
the north pole to the equator. Iceland is formed by the lava
of this volcanic system, and is a special case, where the
volume of magmatic material was so big that it formed an
island. Hawaii is another example, although it is not in
the mid oceanic ridge, but over a hotspot.

In these regions, the magma is continuously being erupted
between rock fractures, and, in contact with the sea water,
it becomes a solid rock, joining the adjacent ones and 
forming big structures. In South Atlantic, this mid oceanic
ridge has about 135 million years of continuous activity.

Best regards

Eder C. Molina
eder@iag.usp.br
Dept. of Geophysics
IAG-USP
Brazil