oded ▁ones ▁to ▁possibly ▁post g la cial ▁la va ▁flows ▁that ▁may ▁be ▁tens ▁of ▁thousands ▁of ▁years ▁old . ▁ ▁A uc an qu il cha ▁cluster ▁▁ ▁The ▁A uc an qu il cha ▁cluster ▁formed ▁in ▁four ▁stages , ▁each ▁corresponding ▁to ▁a ▁group . ▁The ▁Al con cha ▁group , ▁with ▁seven ▁vol cano es , ▁is ▁constructed ▁from ▁py ro x ene , ▁and es ite ▁and ▁d ac ite ▁and ▁formed ▁ 1 1 – 8 ▁my a . ▁It ▁is ▁constructed ▁from ▁two ▁northern ▁composite ▁con es , ▁Al con cha ▁and ▁Vol can ▁Tu co ▁( also ▁known ▁as ▁Cer ro ▁Gar age , ▁dated ▁ 1 0 . 9 6 – 1 0 . 5 1 ▁my a ), ▁and ▁five ▁la va ▁dom es ▁on ▁the ▁n ort he astern ▁side ▁of ▁the ▁cluster . ▁Al con cha ▁has ▁a ▁large ▁bre ach ▁on ▁the ▁southern ▁side ▁of ▁its ▁cr ater ▁that ▁is ▁likely ▁the ▁product ▁of ▁a ▁fl ank ▁collapse ▁but ▁the ▁a val anche ▁depos it ▁may ▁be ▁buried ▁beneath ▁younger ▁material . ▁L avas ▁within ▁the ▁bre ach ▁are ▁dated ▁ 1 0 . 7 8 – 1 0 . 4 3 ▁my a . ▁The ▁cent res ▁of ▁Vol can ▁Tu co ▁and ▁Al con cha ▁are ▁heavily ▁er oded , ▁and ▁Al con cha ' s ▁la vas ▁and ▁sc oria ▁lie ▁on ▁top ▁of ▁Tu co . ▁The ▁U j ina ▁ign im br ite ▁was