How do you know where volcanic ash will end up?

Volcanic plume associated with the April-May 2010 eruption of Eyjafjallajökull volcano (Iceland) and Scanning Electron Microscope image of a typical ash cluster made of micrometric volcanic particles collected on an adhesive paper during fallout. UNIGE, Costanza Bonadonna - A team from the University of Geneva studied the ash from volcanic eruptions and discovered two effects of ash sedimentation that will improve our ability to predict the danger posed by volcanic ash clouds. When the Eyjafjallajökull volcano in Iceland erupted in April 2010, air traffic was interrupted for six days and then disrupted until May. Until then, models from the nine Volcanic Ash Advisory Centres (VAACs) around the world, which aimed at predicting when the ash cloud interfered with aircraft routes, were based on the tracking of the clouds in the atmosphere. In the wake of this economic disaster for airlines, ash concentration thresholds were introduced in Europe which are used by the airline industry when making decisions on flight restrictions. However, a team of researchers, led by the University of Geneva , Switzerland, discovered that even the smallest volcanic ash did not behave as expected. Its results, to be read , will help to refine the way that volcanic ash is represented in forecasting models used by the VAACs, which must react in real-time to provide useful advice during a volcanic eruption.