Iceland is having some interesting activity (ht NC). I really don’t know how predictable the size of an eruption is. My guess is that it is somewhat accurate until it is not. In other words, there is a lot of outliers.
BBC News Europe, 21 May, 2011
Iceland's most active volcano, Grimsvotn, has started erupting, scientists say.
The volcano, which lies under the Vatnajokull glacier in south-east Iceland, last erupted in 2004.
In 2010, plumes of ash from Iceland's Eyjafjallajokull volcano caused weeks of air travel chaos across Europe.
Officials say the latest eruption is unlikely to cause similar problems, although a flight ban has been imposed around the area.
Volcanic eruptions are common in Iceland, which lies along the Mid-Atlantic Ridge that divides the Eurasian and North American continental plates.