On 14 April 2010, however, the eruption entered an explosive phase and ejected fine glass-rich ash to over into the atmosphere. The second phase was estimated to be a VEI 4 eruption, which was large, but not nearly the most powerful eruption possible by volcanic standards. By way of comparison, the Mount St. Helens eruption of 1980 was rated as 5 on the VEI, and the 1991 eruption of Mount Pinatubo was rated as a 6. This second phase erupted trachyandesite.