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eruptions of the past. Lavas, pyroclastic flows and tephras can be preserved for
millions of years. Stratigraphy, geological dating, isotope analysis and magne-
tostratigraphy have become some of the main tools for unravelling the long-
term history of volcanic eruptions. The evidence can also occur much further
afield than close to the erupting source. Fine-grained ash layers are evident in
ice layers in Antarctica and the Arctic and these markers represent truly large
eruptions where ash has been projected into the stratosphere and encircled the
globe. Pollen studies of the demise of vegetation communities due to volcanic
eruptions also offer an interesting form of proxy evidence as do the desktop
studies of the size of volcanic maars as a guide to the magnitude of prehistoric
eruptions.
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