; ▁others ▁contain ▁small ▁b ogs ▁or ▁often ▁artificial ▁p onds ▁that , ▁however , ▁only ▁occup y ▁part ▁of ▁the ▁h ollow . ▁ ▁Ex amples ▁ ▁The ▁largest ▁known ▁ma ars ▁are ▁found ▁at ▁Esp enberg ▁on ▁the ▁S ew ard ▁Pen ins ula ▁in ▁north west ▁Al aska . ▁These ▁ma ars ▁range ▁in ▁size ▁from ▁ ▁in ▁diameter ▁and ▁a ▁depth ▁up ▁to ▁. ▁These ▁er u ptions ▁occurred ▁in ▁a ▁period ▁of ▁about ▁ 1 0 0 , 0 0 0 ▁years , ▁with ▁the ▁young est ▁( the ▁Dev il ▁Mountain ▁Ma ar ) ▁occurr ing ▁about ▁ 1 7 , 5 0 0 ▁years ▁ago . ▁Their ▁large ▁size ▁is ▁due ▁to ▁the ▁explos ive ▁reaction ▁that ▁occurs ▁when ▁mag ma ▁comes ▁into ▁contact ▁with ▁per ma f rost . ▁H yd rom ag m atic ▁er u ptions ▁are ▁increasing ly ▁explos ive ▁when ▁the ▁ratio ▁of ▁water ▁to ▁mag ma ▁is ▁low . ▁Since ▁per ma f rost ▁mel ts ▁slowly , ▁it ▁provides ▁a ▁steady ▁source ▁of ▁water ▁to ▁the ▁er u ption ▁while ▁keeping ▁the ▁water ▁to ▁mag ma ▁ratio ▁low . ▁This ▁produces ▁the ▁prolong ed , ▁explos ive ▁er u ptions ▁that ▁created ▁these ▁large ▁ma ars . ▁Ex amples ▁of ▁the ▁S ew ard ▁Pen ins ula ▁ma ars ▁include ▁North ▁K ille ak ▁Ma ar , ▁South ▁K ille ak ▁Ma ar , ▁Dev il ▁Mountain ▁Ma ar ▁and ▁White fish ▁Ma ar . ▁ ▁Ma ars ▁occur