▁to ▁ ▁of ▁mag ma , ▁total ing ▁ ▁of ▁total ▁depos its . ▁The ▁er u ption ▁is ▁divided ▁into ▁ 1 0 ▁different ▁phases ▁on ▁the ▁basis ▁of ▁nine ▁ma pp able ▁fall ▁units ▁and ▁a ▁t enth , ▁poor ly ▁preserved ▁but ▁vol um etr ically ▁dominant ▁fall ▁unit . ▁ ▁Modern - day ▁Lake ▁T au po ▁( ▁in ▁area ▁and ▁ ▁deep ) ▁partly ▁fills ▁the ▁cal der a ▁generated ▁during ▁this ▁er u ption . ▁A ▁ ▁struct ural ▁collapse ▁is ▁conce aled ▁beneath ▁Lake ▁T au po , ▁while ▁the ▁lake ▁outline ▁at ▁least ▁partly ▁reflect s ▁vol cano - te ct onic ▁collapse . ▁Early ▁er u ption ▁phases ▁saw ▁sh ifting ▁vent ▁positions ; ▁development ▁of ▁the ▁cal der a ▁to ▁its ▁maximum ▁extent ▁( ind ic ated ▁by ▁l ith ic ▁lag ▁bre c cias ) ▁occurred ▁during ▁phase ▁ 1 0 . ▁ ▁The ▁O ru an ui ▁er u ption ▁shows ▁many ▁unusual ▁features : ▁its ▁epis od ic ▁nature , ▁wide ▁range ▁of ▁mag ma - water ▁interaction , ▁and ▁complex ▁inter play ▁of ▁py ro cl astic ▁fall ▁and ▁flow ▁depos its . ▁As ▁the ▁er u ption ▁occurred ▁through ▁a ▁lake ▁system ▁over lying ▁the ▁vent , ▁many ▁of ▁the ▁depos its ▁contain ▁vol can ic ▁ash ▁aggreg ates . ▁▁▁ ▁Te ph ra ▁from ▁the ▁er u ption ▁covered ▁much ▁of ▁the ▁central ▁North ▁Island , ▁with ▁ign im br ite ▁up ▁to ▁ ▁deep . ▁Ash