 Activity continued for approximately 150 @,@ 000 years in the form of quiet andesitic eruptions , as glaciation took place . About 0 @.@ 15 mya ( 150 @,@ 000 years ago ) , a third and final ash flow was erupted . With a volume of 175 cubic kilometers ( 42 cu mi ) to 250 cubic kilometres ( 60 cu mi ) , it was smaller than the second eruption , but acted similarly , and had much more densely welded tuff . The ash was thickest at 300 metres ( 984 ft ) , at Loma Seca , and the top of the deposit has undergone erosion . It is densely welded in crevasses , but not at thin 50 metres ( 164 ft ) layers , where much of the material is barely welded or not welded at all . 
