At http://sciencenews.org/view/generic/id/59172 April 11th … it is thought ash particles generated lightning storms when Mount Rinjani in Indonesia erupted in 1995. Now, this idea is being expanded in a Nature Physics paper to suggest colliding dust grains charge each other to create electricity. Physicists have been puzzled over why sand grains and other small particles can hold an electrical charge after colliding with earch other, sometimes to the point of discharging lightning in dust and sand storms or in plumes of volcanic ash. This is now explained by positive charges moving downwards and inter-actiing with negative charges moving upwards (in clouds). The researcher became interested in the phenomenon after watching lightning in swirling sands over dune fields at night.