The “Puff-Volcanic Ash Tracking Model” is a system of Google Maps and Google Earth KML files that help predict the ash patterns for volcanoes around the world. As explained in their user manual:
Puff simulates the transport, dispersion and sedimentation of volcanic ash. It requires horizontal wind field data as a function of height on a regular grid covering the area of interest. Puff output includes the location (in 3 dimensions), size, and age-since-eruption of representative ash particles. It can also produce gridded data of relative and absolute ash concentration in the air and on the ground. Puff is a fast and efficient research and operational tool for predicting the trajectories of ash particles, which is essential for hazard assessment.
When you visit their site, you can click on any volcano icon to view information about their predicted ash trajectory, as seen here:
In many cases, you can click on the “3D” icon to view the ash cloud as a 3D tour in Google Earth, as seen here:
It’s quite a sophisticated system, and could be quite useful in the event of a major eruption. You can see it all for yourself on the Puff website.