ase ▁( 2 8 ▁December ▁ 1 9 4 3 ▁– ▁ 2 2 ▁June ▁ 1 9 4 4 ) ▁On ▁ 2 8 ▁December ▁ 1 9 4 3 , ▁earth qu akes ▁starting ▁to ▁occur ▁frequently ▁around ▁Mount ▁U su , ▁with ▁occurr ences ▁of ▁more ▁than ▁ 2 0 0 ▁times ▁per ▁day ▁on ▁some ▁days . ▁The ▁hyp oc enter ▁in ▁the ▁early ▁days ▁was ▁located ▁in ▁the ▁vic inity ▁of ▁Lake ▁T ō ya . ▁As ▁the ▁year ▁entered ▁ 1 9 4 4 , ▁the ▁hyp oc enter ▁started ▁to ▁move ▁toward ▁the ▁eastern ▁part ▁of ▁the ▁base ▁of ▁Mount ▁U su ▁and ▁this ▁resulted ▁in ▁the ▁prot uber ance ▁of ▁the ▁over lying ▁ground . ▁ ▁Event ually ▁the ▁prot uber ance ▁started ▁to ▁spread ▁to ▁the ▁north , ▁reaching ▁up ▁to ▁height s ▁of ▁ 5 0 ▁meters ▁in ▁some ▁areas . ▁The ▁S ō b ets u ▁river bed ▁also ▁started ▁to ▁rise , ▁and ▁many ▁f iss ures ▁started ▁to ▁appear ▁in ▁the ▁surrounding ▁far ml ands . ▁The ▁longest ▁f iss ure ▁recorded ▁was ▁about ▁ 6 0 0 ▁meters ▁long . ▁On ▁ 2 2 ▁June ▁ 1 9 4 4 , ▁there ▁were ▁about ▁ 2 5 0 ▁earth qu akes ▁in ▁one ▁day , ▁and ▁accordingly ▁the ▁prot uber ance ▁of ▁the ▁ground ▁rose ▁by ▁ 1 5 0 ▁cent im eters ▁in ▁one ▁day . ▁ ▁Ph ase ▁ 2 , ▁E ruption ▁Ph ase ▁( 2