iding ▁of ▁the ▁Ind o - Austral ian ▁Pl ate ▁north ▁relative ▁to ▁the ▁Pacific ▁Pl ate . ▁The ▁plate ▁boundary ▁forms ▁the ▁nearly ▁ ▁long ▁Al pine ▁F ault . ▁This ▁fault ▁has ▁an ▁estimated ▁ru pt ure ▁re occ urrence ▁interval ▁of ▁~ 3 3 0 ▁years , ▁and ▁last ▁ru pt ured ▁in ▁ 1 7 1 7 ▁along ▁ ▁of ▁its ▁length . ▁It ▁passes ▁directly ▁under ▁many ▁settlement s ▁on ▁the ▁West ▁Coast ▁of ▁the ▁South ▁Island ▁and ▁sh aking ▁from ▁a ▁ru pt ure ▁would ▁likely ▁affect ▁many ▁cities ▁and ▁towns ▁throughout ▁the ▁country . ▁ ▁The ▁rapid ▁u pl ift ▁and ▁high ▁er os ion ▁rates ▁within ▁the ▁Southern ▁Al ps ▁combine ▁to ▁expose ▁high ▁grade ▁gre ensch ist ▁to ▁am ph ib ol ite ▁fa cies ▁rocks , ▁including ▁the ▁gem stone ▁p oun am u ▁( ja de ). ▁Ge olog ists ▁visit ing ▁the ▁West ▁Coast ▁can ▁easily ▁access ▁high - grade ▁met am orph ic ▁rocks ▁and ▁my lon ites ▁associated ▁with ▁the ▁Al pine ▁F ault , ▁and ▁in ▁certain ▁places ▁can ▁stand ▁ast ride ▁the ▁fault ▁trace ▁of ▁an ▁active ▁plate ▁boundary . ▁ ▁To ▁the ▁south ▁of ▁New ▁Zealand ▁the ▁Ind o - Austral ian ▁Pl ate ▁is ▁sub duct ing ▁under ▁the ▁Pacific ▁Pl ate , ▁and ▁this ▁is ▁beginning ▁to ▁result ▁in ▁back - arc ▁vol can ism . ▁The ▁young est ▁( ge olog ically ▁speaking ) ▁vol can ism ▁in ▁the ▁South ▁Island ▁occurred ▁in