THE TRACKING of VOLCANIC SULFUR DIOXIDE and ASH CLOUDS

                               Mt St. Helens, Washington, USA............May 1980
                                        Alaid, Kuril Islands, Russia.....................Apr  1981
                                        Nyamuragira, Zaire..................................Dec 1981
                                        El Chichon, Mexico..................................Apr 1982
                                        Mauna Loa, Hawaii, USA.......................Mar 1984
                                        Ruiz, Colombia.........................................Nov 1985
                                         Mt Pinatubo, Phillipines...........................Jun  1991
                                         Mt Pinatubo, Phillipines (ash).................Jun  1991
                                         Cerro Hudson, Chile................................Aug 1991
                                         Cerro Hudson, Chile (ash).......................Aug 1991
                                         Mt Spurr, Alaska, USA............................Aug 1992
                                         Mt Spurr, Alaska, USA (ash)..................Aug 1992
                                         Lascar, Chile.............................................Apr 1993
                                         Nyamuragira, Zaire...................................Jul  1994
                                         Rabaul, Papua New Guinea....................Sep 1994
                                        Rabaul, Papua New Guinea (ash)..........Sep 1994
                                         Kliuchevskoi, Kamchatka, Russia...........Oct 1994

                            Hypothetical Ash Cloud Of Ann Arbor, MI........December 16, 1998