ote . ▁It ▁has ▁the ▁classic ▁hum mock y ▁top ography ▁of ▁land sl ides ▁and ▁covers ▁a ▁length ▁of ▁ ▁and ▁a ▁surface ▁area ▁of ▁, ▁roughly ▁half ▁of ▁the ▁surface ▁area ▁of ▁the ▁Mount ▁St ▁Hel ens ▁a val anche ▁of ▁ 1 9 8 0 ▁and ▁one - third ▁of ▁the ▁surface ▁area ▁of ▁the ▁O ll ag ü e ▁a val anche . ▁A ▁volume ▁of ▁ ▁is ▁assumed ▁based ▁on ▁a ▁probable ▁thick ness ▁of ▁. ▁ ▁Pet ro graph ically , ▁the ▁composition ▁of ▁the ▁cluster ▁ranges ▁from ▁and es ite ▁to ▁d ac ite ▁with ▁Si O 2 ▁r anging ▁from ▁ 6 2 . 8 % ▁to ▁ 6 5 . 7 %. ▁And es ites ▁appear ▁as ▁la va ▁flows ▁while ▁d ac ites ▁form ▁la va ▁dom es ▁and ▁d ome ▁complex es . ▁The ▁rocks ▁from ▁the ▁main ▁A uc an qu il cha ▁vol cano ▁are ▁uniformly ▁d ac it ic ▁and ▁show ▁little ▁evidence ▁of ▁temporal ▁variation ▁in ▁their ▁composition . ▁Pot ass ium ▁content ▁ranges ▁from ▁ 1 . 5 ▁to ▁ 4 %. ▁Pl agi oc l ase ▁is ▁the ▁dominant ▁component ▁of ▁the ▁mag ma . ▁C lin opy ro x ene + orth opy ro x ene + am ph ib ole ▁( horn bl ende ▁and ▁par gas ite ) ▁or ▁am ph ib ole + bi ot ite + min or ▁amounts ▁of ▁py ro x ene ▁are ▁sub ordinate ▁components . ▁A pat