VIOLENTLY erupting volcanoes are well-known triggers of climate change. But
strangely enough, climate change may also induce volcanic activity. A team of US
researchers studying the history of volcanic eruptions in the northern
hemisphere has found that rapid changes in the climate鈥攂oth cooling and
warming鈥攎ay be linked with an increase in the rate of volcanic
eruptions.
Gregory Zielinski and colleagues at the University of New Hampshire in Durham
discovered the correlation after studying an ice core from Greenland. The core,
obtained by a US drilling project completed in 1993, contains a record of
environmental conditions in the northern hemisphere dating back 110 000
years.
Zielinski鈥檚 team measured the amounts of volcanic sulphates present in the
core to get a picture of past rates of volcanic eruptions (Quaternary
Research, vol 45, p 109). Violent eruptions, such as that of Mount Pinatubo
in the Philippines in 1991, often send huge plumes of sulphuric acid into the
atmosphere. These can block sunlight and cool the climate.
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As expected, the researchers found that the global cooling that led into the
last glacial period, between 35 000 and 22 000 years ago, coincided with more
active volcanism. But to their surprise, there were also high rates of eruptions
during periods of climate warming. The longest period of enhanced volcanism
recorded in the ice core, between 13 000 years ago and 7000 years ago,
corresponded to the end of the last ice age, when the glaciers were melting.
Zielinski says the correlation between volcanism and both warming and cooling
is probably due to the build-up and melting of ice during the cycles of
glaciation. During glaciation, the Earth鈥檚 crust is pushed down by about
one-third the thickness of the ice that accumulates on the surface. When the ice
later melts, the crust rebounds. This movement would cause changes in the amount
of pressure on the magma chambers that power volcanoes. The chambers would then
erupt violently鈥攋ust like an uncorked champagne bottle.
The idea that rapid climate change could increase the rate of eruptions was
first suggested about two decades ago by Michael Rampino, a glaciologist at New
York University, and his colleagues. Rampino says that Zielinski鈥檚 records
provide the first convincing evidence for the idea. 鈥淭his is the best dated
record of climate and volcanism together,鈥� says Rampino.
He says that the new results hint that the interaction between the solid
Earth and the climate is much more significant than any one realises. 鈥淓verybody
talks about the ocean and atmosphere being linked,鈥� he says. 鈥淏ut why not the
ocean, the atmosphere and the solid Earth as well? It is, after all, a single
蝉测蝉迟别尘.鈥�