A look at the damage that could be done by three Icelandic volcanoes (Katla, Hekla and Laki) that may be ready to erupt. Each is larger than Eyjafjallajökull volcano, which caused havoc in air travel when it erupted in 2010. Scientists ponder the consequences of such an eruption not just for air travel, but for the global food supply and Earth's climate as a whole.