ions ▁were ▁explos ive , ▁and ▁possibly ▁even ▁ph re atom ag m atic ▁( water ▁ice / mag ma ▁interaction - dri ven ). ▁These ▁vol cano es ▁are ▁observed ▁to ▁approximate ▁features ▁observed ▁elsewhere ▁on ▁Mars , ▁including ▁H ec ates ▁Th ol us ▁on ▁the ▁E ly si um ▁R ise ; ▁T yr rh ena ▁P ater a ; ▁Had ri aca ▁P ater a ; ▁and ▁Apol lin aris ▁P ater a . ▁ ▁Later ▁vol can ic ▁activity ▁on ▁the ▁Th aum asia ▁Pl ate au ▁occurred ▁in ▁the ▁H esper ian ▁in ▁association ▁with ▁a ▁prof usion ▁of ▁sheet ▁la vas ▁covering ▁Sy ria ▁Plan um , ▁Sol is ▁Plan um , ▁S ina i ▁Plan um , ▁and ▁Th aum asia ▁Plan um , ▁em an ating ▁from ▁the ▁eastern ▁fl anks ▁of ▁the ▁Ar s ia ▁M ons ▁region . ▁In ▁Th aum asia ▁Plan um ▁and ▁against ▁the ▁Cop r ates ▁R ise , ▁these ▁sheet ▁la vas ▁were ▁observed ▁to ▁on lap ▁underlying ▁pla ins ▁materials ▁and ▁their ▁associated ▁rid ged ▁morph ologies . ▁Further ▁vol can ism ▁occurred ▁to ▁the ▁south ▁of ▁the ▁Th aum asia ▁high lands ▁in ▁Da ed alia ▁Plan um . ▁ ▁Some ▁authors ▁have ▁analog ized ▁the ▁Th aum asia ▁Pl ate au ▁to ▁instances ▁of ▁int ra plate ▁regional - scale ▁plate au ▁u pl ifts , ▁including ▁the ▁Colorado ▁Pl ate au ▁( s outh western ▁United ▁States ), ▁the ▁R hen ish ▁shield