▁the ▁ma ars , ▁apart ▁from ▁the ▁dry ▁maar , ▁R ande cker ▁Ma ar ▁and ▁the ▁Mol ach , ▁are ▁only ▁detect able ▁ge olog ically . ▁In ▁the ▁O re ▁Mountains ▁near ▁Ham mer unter w ies ent hal , ▁the ▁Ham mer unter w ies ent hal ▁Ma ar ▁formed ▁about ▁ 3 0   mill ion ▁years ▁ago ▁during ▁the ▁O lig oc ene ; ▁the ▁maar ▁measures ▁ 2 ▁kilometres ▁from ▁east ▁to ▁west ▁and ▁ 1 . 4 ▁kilometres ▁from ▁north ▁to ▁south . ▁ ▁Rest ▁of ▁Europe ▁ ▁The ▁Cha îne ▁des ▁Pu ys ▁in ▁France ▁contains ▁numerous ▁ma ars ; ▁Lake ▁Alb ano ▁in ▁the ▁Alban ▁Mountains ▁is ▁a ▁complex ▁maar , ▁and ▁there ▁is ▁also ▁a ▁maar ▁( Col om bo ) ▁near ▁Sant or ini ▁in ▁Greece . ▁The ▁Cam po ▁de ▁Cal atra va ▁Vol can ic ▁Field ▁in ▁Spain ▁contains ▁numerous ▁ma ars ; ▁a ▁typical ▁example ▁being ▁the ▁maar ▁of ▁Ho ya ▁del ▁Mor tero ▁at ▁Po ble te ▁in ▁the ▁Province ▁of ▁Ciudad ▁Real . ▁Active ▁ma ars ▁were ▁common place ▁in ▁F ife ▁and ▁L oth ian , ▁Scotland ▁during ▁the ▁Car bon ifer ous ▁era . ▁ ▁Amer icas ▁Active ▁maar ▁vol cano es ▁are ▁mainly ▁known ▁outside ▁Europe . ▁ ▁In ▁the ▁USA ▁there ▁are ▁numerous ▁maar ▁areas , ▁such ▁as ▁Al aska ▁( U kin rek ▁Ma ars , ▁N un iv ak ▁in ▁the ▁Ber ing ▁Sea ), ▁in ▁Washington ▁( B attle ▁Gr