▁between ▁No ct is ▁Lab yr inth us ▁and ▁the ▁Clar itas ▁F oss ae ▁at ▁the ▁approach ▁of ▁Sy ria ▁Plan um ▁to ▁Pav on is ▁M ons . ▁At ▁this ▁location , ▁the ▁relief ▁of ▁the ▁Th aum asia ▁Pl ate au ▁reaches ▁up ▁to ▁ 8   km ▁relative ▁to ▁the ▁surrounding ▁high lands ▁terrain . ▁The ▁top ography ▁dimin ishes ▁to ▁the ▁sout heast ▁towards ▁Ar gy re ▁Plan it ia . ▁ ▁Ge ology ▁ ▁Some ▁authors ▁have ▁suggested ▁that ▁the ▁Th aum asia ▁Pl ate au ▁was ▁once ▁a ▁large , ▁ancient ▁d rain age ▁bas in ▁pre - dating ▁the ▁extensive ▁vol can ic ▁formation ▁of ▁the ▁Th ars is ▁R ise . ▁At ▁this ▁time , ▁it ▁was ▁likely ▁bounded ▁by ▁the ▁same ▁structures ▁( the ▁Clar itas ▁R ise ▁to ▁the ▁west , ▁the ▁Th aum asia ▁high lands ▁to ▁the ▁south , ▁and ▁the ▁Cop r ates ▁R ise ▁to ▁the ▁east ). ▁During ▁Th ars is ' ▁Stage ▁ 2 ▁( center ed ▁over ▁the ▁central ▁section ▁of ▁the ▁Vall es ▁Mar iner is ) ▁and ▁Stage ▁ 3 ▁vol can ot ect onic ▁activity ▁( in ▁which ▁t ect onic ▁activity ▁became ▁radial ly ▁centered ▁over ▁the ▁north western ▁portion ▁of ▁Sy ria ▁Plan um ), ▁significant ▁vol can ic ▁activity ▁is ▁understood ▁to ▁have ▁in filled ▁this ▁bas in , ▁forming ▁the ▁modern ▁pla ins ▁terra ins ▁observed ▁in ▁the ▁modern ▁period . ▁The ▁bur ial ▁of ▁this ▁put ative