By LiveScience Staffposted: 25 March 2009 02:03 pm ET The June 12, 1991 eruption column from Mount Pinatubo taken from the east side of Clark Air Base. Credit: USGSFull Size1 of 2The June 12, 1991 eruption column from Mount Pinatubo taken from the east side of Clark Air Base. Credit: USGS Two mechanisms for generating rotation in a volcanic plume have been shown. As the plume shoots up at an astounding 200 to 600 meters a second--winds from the environment surrounding the volcano can come into t