▁Ma ars ▁range ▁in ▁size ▁from ▁ ▁across ▁and ▁from ▁ ▁deep ; ▁most ▁ma ars ▁commonly ▁fill ▁with ▁water ▁to ▁form ▁natural ▁la kes . ▁Most ▁ma ars ▁have ▁low ▁r ims ▁composed ▁of ▁a ▁mixture ▁of ▁loose ▁fragments ▁of ▁vol can ic ▁rocks ▁and ▁rocks ▁torn ▁from ▁the ▁walls ▁of ▁the ▁di atre me . ▁ ▁Ma ar ▁la kes ▁and ▁dry ▁ma ars ▁ ▁Ma ar ▁la kes , ▁also ▁referred ▁to ▁simply ▁as ▁ma ars , ▁occur ▁when ▁ground water ▁or ▁precip itation ▁fills ▁the ▁fun nel - sh aped ▁and ▁usually ▁round ▁h ollow ▁of ▁the ▁maar ▁de pression ▁formed ▁by ▁vol can ic ▁explos ions . ▁Ex amples ▁of ▁these ▁types ▁of ▁maar ▁are ▁the ▁three ▁ma ars ▁at ▁Da un ▁in ▁the ▁E if el ▁mountains ▁of ▁Germany . ▁ ▁A ▁dry ▁maar ▁results ▁when ▁a ▁maar ▁lake ▁d ries ▁out , ▁becomes ▁ag grad ed ▁or ▁s ilt ed ▁up . ▁An ▁example ▁of ▁the ▁latter ▁is ▁the ▁E ck fel der ▁Ma ar . ▁Near ▁Ste ff eln ▁is ▁the ▁E ich hol z ma ar ▁( also ▁called ▁the ▁G uss wei her ) ▁which ▁has ▁d ried ▁out ▁during ▁the ▁last ▁century ▁and ▁is ▁being ▁ren atural ised ▁into ▁a ▁maar . ▁In ▁some ▁cases ▁the ▁underlying ▁rock ▁is ▁so ▁por ous ▁that ▁maar ▁la kes ▁are ▁unable ▁to ▁form . ▁After ▁winter s ▁of ▁heavy ▁snow ▁and ▁ra inf all ▁many ▁dry ▁ma ars ▁fill ▁partially ▁and ▁tempor arily ▁with ▁water