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“The frequency of Icelandic eruptions seems to rise and fall in a cycle lasting around 140 years,” he said. “In the latter part of the 20th century we were in a low period, but now there is evidence that we could be approaching a peak.” The three other volcanoes cited by Thordarson as being potentially close to a large eruption are Grimsvotn, Hekla and Askja — all of which are bigger than Eyjafjallajokull. In the past, they have proved devastating. Hekla alone has erupted about 20 times since AD874, pouring out a total of two cubic miles of lava. Geologists report that snow is once again melting on Hekla’s summit, suggesting that magma is rising. Grimsvotn, another highly active volcano, is linked to the massive Laki fissure volcano whose 1783 eruption ejected so much ash into the atmosphere that it cooled the entire northern hemisphere for nearly three years. The resulting low temperatures caused crop failures and famines that killed 2m people and helped trigger the French Revolution. Some scientists suggest that historic clusters of eruptions could well have occurred by chance. A recent report suggested that Katla - 15 miles to the east of Eyjafjallajokull - is “close to failure [eruption]”.
See entire article, entitled “Scientists forecast decades of ash
clouds”
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