▁most ▁powerful ▁vol can ic ▁er u ptions ▁in ▁recorded ▁history ▁and ▁is ▁class ified ▁as ▁a ▁V E I ▁ 7 ▁event . ▁The ▁er u ption ▁resulted ▁in ▁a ▁brief ▁period ▁of ▁significant ▁climate ▁change ▁in ▁Man ch uria . ▁The ▁year ▁of ▁the ▁er u ption ▁has ▁not ▁been ▁precisely ▁determined , ▁but ▁a ▁possible ▁year ▁is ▁A . D . ▁ 9 4 6 . ▁ ▁The ▁er u ption ▁e ject ed ▁about ▁ ▁of ▁te ph ra ▁and ▁col lapsed ▁the ▁mountain ▁into ▁a ▁cal der a , ▁which ▁now ▁contains ▁the ▁cr ater ▁lake ▁Heaven ▁Lake . ▁ ▁The ▁er u ption ▁began ▁with ▁a ▁strong ▁Pl in ian ▁column , ▁and ▁ended ▁with ▁vol umin ous ▁py ro cl astic ▁flows . ▁An ▁average ▁of ▁ ▁of ▁Pl in ian ▁ash fall ▁and ▁co ign im br ite ▁ash fall ▁covered ▁about ▁ ▁of ▁the ▁Sea ▁of ▁Japan ▁and ▁northern ▁Japan . ▁This ▁ash ▁layer ▁has ▁been ▁named ▁the ▁" B a eg d us an - Tom ak om ai ▁ash " ( B - T m ). ▁It ▁probably ▁occurred ▁in ▁winter ▁in ▁late ▁A . D . ▁ 9 4 6 . ▁This ▁was ▁one ▁of ▁the ▁largest ▁and ▁most ▁violent ▁er u ptions ▁in ▁the ▁last ▁ 5 0 0 0 ▁years , ▁along ▁with ▁the ▁H ate pe ▁er u ption ▁of ▁Lake ▁T au po ▁( around ▁ 1 8 0 ▁AD ), ▁the ▁ 1 2 5 7