▁stages : ▁Ba eg du ▁Pl in ian ▁p um ice ▁fall , ▁Ch ang b ai ▁py ro cl astic ▁flow , ▁Y uan chi ▁te ph ra ▁falls , ▁and ▁Ba ish an ▁py ro cl astic ▁flow . ▁But ▁Ba ish an ▁py ro cl astic ▁flow ▁may ▁related ▁to ▁post - cal der a ▁activity ▁(? A . D . 1 6 6 8 ▁er u ption ? ). ▁More ▁recent ▁study ▁indicate ▁that ▁er u ption ▁include ▁ 2 ▁stages : ▁Pl in ian ▁p um ice ▁fall ▁and ▁unw eld ed ▁ign im br ite . ▁ ▁Pl in ian ▁stage ▁ ▁This ▁stage ▁formed ▁a ▁large ▁area ▁of ▁white ▁com end it ic ▁p um ice ▁and ▁ash . ▁The ▁Pl in ian ▁er u ption ▁column ▁reached ▁about ▁ 3 6   km ▁in ▁height . ▁B - T m ▁ash ▁and ▁" white ▁ash ▁rain " ▁may ▁related ▁to ▁this ▁stage . ▁Based ▁on ▁variations ▁of ▁gra in - size ▁and ▁thick ness ▁of ▁p um ice , ▁the ▁Pl in ian ▁stage ▁can ▁divided ▁into ▁ 3 ▁parts : ▁early ▁period , ▁clim ax , ▁and ▁later ▁period . ▁ ▁Early ▁period ▁ ▁In ▁a ▁Pl in ian ▁p um ice - fall ▁section , ▁the ▁gra in - size ▁of ▁p um ice ▁is ▁revers ely ▁grad ed ▁( co arse ▁p um ice ▁on ▁bottom ▁and ▁fine ▁p um ice ▁on ▁top ). ▁The ▁variation ▁of ▁p um ice ▁size ▁shows