Cattle grazing with ash fall from Grimsvotn Volcanic Eruption in the Vatnajokull Glacier, Iceland May 21, 2011 eruption began spewing tons of ash, initially the plume was over 20 kilometers high Volcanic ash is an extreme danger to jet engines closing a. Cattle grazing with ash fall from Grimsvotn Volcanic Eruption in the Vatnajokull Glacier, Iceland May 21, 2011 eruption began spewing tons of ash, initially the plume was over 20 kilometers high Volcanic ash is an extreme danger to jet engin