▁meters . ▁ ▁When ▁p ā ho e ho e ▁la va ▁enters ▁the ▁sea ▁it ▁usually ▁forms ▁pill ow ▁bas al ts . ▁However , ▁when ▁ ʻ a ʻ ā ▁enters ▁the ▁ocean ▁it ▁forms ▁a ▁litt oral ▁cone , ▁a ▁small ▁cone - sh aped ▁accum ulation ▁of ▁t uff ace ous ▁de br is ▁formed ▁when ▁the ▁block y ▁ ʻ a ʻ ā ▁la va ▁enters ▁the ▁water ▁and ▁expl odes ▁from ▁built - up ▁steam . ▁ ▁The ▁island ▁of ▁S urt sey ▁in ▁the ▁Atlantic ▁Ocean ▁is ▁a ▁bas alt ▁vol cano ▁which ▁bre ached ▁the ▁ocean ▁surface ▁in ▁ 1 9 6 3 . ▁The ▁initial ▁phase ▁of ▁S urt sey ' s ▁er u ption ▁was ▁highly ▁explos ive , ▁as ▁the ▁mag ma ▁was ▁quite ▁fluid , ▁causing ▁the ▁rock ▁to ▁be ▁blow n ▁apart ▁by ▁the ▁bo iling ▁steam ▁to ▁form ▁a ▁t uff ▁and ▁c inder ▁cone . ▁This ▁has ▁subsequently ▁moved ▁to ▁a ▁typical ▁p ā ho e ho e - type ▁behaviour . ▁ ▁Vol can ic ▁glass ▁may ▁be ▁present , ▁particularly ▁as ▁r inds ▁on ▁rapidly ▁ch illed ▁surfaces ▁of ▁la va ▁flows , ▁and ▁is ▁commonly ▁( but ▁not ▁exclus ively ) ▁associated ▁with ▁under water ▁er u ptions . ▁ ▁P ill ow ▁bas alt ▁is ▁also ▁produced ▁by ▁some ▁sub g la cial ▁vol can ic ▁er u ptions . ▁ ▁Life ▁on ▁bas alt ic ▁rocks ▁ ▁The ▁common ▁cor ros ion ▁features