▁is ▁followed ▁by ▁later ▁lower - volume ▁activity ▁( , ▁followed ▁by ▁). ▁Un zen ▁in ▁Japan ▁and ▁Mount ▁D uff ▁and ▁L assen ▁Pe ak ▁in ▁California ▁have ▁similar ▁er u ption ▁histor ies . ▁Such ▁decre ases ▁may ▁occur ▁because ▁of ▁the ▁l ith ost atic ▁load ▁im posed ▁by ▁the ▁edific es ▁on ▁the ▁mag ma ▁ch amb ers ▁and ▁the ▁increased ▁travel ▁distance ▁of ▁the ▁mag ma ▁through ▁the ▁ed ifice . ▁ ▁Local ▁setting ▁▁ ▁A uc an qu il cha ▁is ▁part ▁of ▁a ▁cluster ▁of ▁vol cano es ▁located ▁between ▁the ▁Rio ▁Lo a ▁and ▁the ▁Chile – B ol iv ia ▁border . ▁A uc an qu il cha ▁s its ▁on ▁top ▁of ▁a ▁ 2 . 7 – 3 . 3 ▁my a ▁and es ite ▁platform ▁and ▁r ises ▁more ▁than ▁ ▁over ▁it . ▁The ▁main ▁vol cano ▁is ▁composed ▁of ▁an ▁east - west ▁ ▁long ▁chain ▁of ▁strat ov ol cano es ▁and ▁has ▁an ▁estimated ▁volume ▁of ▁. ▁The ▁maximum ▁slope ▁of ▁the ▁sum mit ▁area ▁is ▁ 2 5 ° . ▁During ▁the ▁C um bre ▁Neg ra ▁stage , ▁a ▁py ro cl astic ▁flow ▁occurred ▁on ▁the ▁north western ▁side ▁of ▁the ▁vol cano . ▁It ▁covered ▁ ▁on ▁a ▁run ▁of ▁ ▁and ▁now ▁has ▁a ▁volume ▁of ▁. ▁It ▁was ▁at ▁first ▁identified ▁as ▁a ▁de br is ▁a val anche , ▁but ▁the ▁lack ▁of ▁hum mock y ▁top ography ▁and ▁the