▁also ▁have ▁been ▁a ▁sand ▁source , ▁although ▁it ▁is ▁now ▁de ple ted . ▁Other ▁d une ▁fields ▁sharing ▁the ▁same ▁formation ▁history ▁include ▁Olymp ia ▁and ▁As ple don ▁Und ae . ▁ ▁Sit on ▁Und ae ▁is ▁the ▁southern most ▁of ▁the ▁dens est ▁northern ▁circ ump olar ▁d une ▁fields ▁and ▁its ▁presence ▁indicates ▁effective ▁sand ▁transport ▁and ▁accum ulation ▁from ▁sand ▁sources ▁to ▁the ▁north ▁and ▁west . ▁Sit on ▁Und ae , ▁along ▁with ▁Ab al os , ▁and ▁Hyper b ore ae ▁Und ae , ▁is ▁also ▁a ▁trib ut ary ▁to ▁less ▁dense ▁d une ▁fields ▁that ▁continue ▁all ▁the ▁way ▁to ▁the ▁Mart ian ▁prime ▁mer id ian . ▁ ▁D une ▁characteristics ▁ ▁Spect ral ▁analysis ▁of ▁the ▁d unes ▁of ▁the ▁circ ump olar ▁er gs , ▁including ▁Sit on ▁Und ae , ▁using ▁the ▁O ME GA ▁instrument ▁on ▁board ▁the ▁European ▁Mars ▁Express ▁orb iter , ▁indicates ▁that ▁ 8 0 ▁to ▁ 9 0 ▁percent ▁of ▁these ▁s ands ▁are ▁composed ▁of ▁vol can ic ▁glass ▁produced ▁by ▁er u ptions ▁of ▁vol cano es ▁situated ▁in ▁Mart ian ▁gla ci ers . ▁These ▁r ati os ▁of ▁glass ▁and ▁cry st all ine ▁material ▁are ▁similar ▁to ▁those ▁obtained ▁in ▁I cel and ▁from ▁er u ptions ▁of ▁vol cano es ▁below ▁the ▁ice . ▁It ▁is ▁also ▁the or ised ▁that ▁significant ▁amounts ▁of ▁gran ular ▁glass ▁may ▁have ▁been ▁transferred ▁to ▁V ast itas ▁B ore