s . ▁An ▁estimated ▁ ▁length ▁of ▁Atlantic ▁sh elf ▁is ▁only ▁ ▁wide . ▁At ▁the ▁ ▁is ob ath , ▁on ▁the ▁edge , ▁the ▁sh elf ▁dro ps ▁off ▁to ▁. ▁ ▁The ▁sub marine ▁top ography ▁of ▁the ▁coast al ▁waters ▁of ▁the ▁I ber ian ▁Pen ins ula ▁has ▁been ▁studied ▁extens ively ▁in ▁the ▁process ▁of ▁dr illing ▁for ▁oil . ▁Ult imately , ▁the ▁sh elf ▁dro ps ▁into ▁the ▁Bay ▁of ▁B isc ay ▁on ▁the ▁north ▁( an ▁aby ss ), ▁the ▁I ber ian ▁aby ss al ▁plain ▁at ▁ ▁on ▁the ▁west , ▁and ▁Tag us ▁aby ss al ▁plain ▁to ▁the ▁south . ▁In ▁the ▁north , ▁between ▁the ▁contin ental ▁sh elf ▁and ▁the ▁aby ss , ▁is ▁an ▁extension ▁called ▁the ▁Gal icia ▁Bank , ▁a ▁plate au ▁that ▁also ▁contains ▁the ▁Porto , ▁V igo , ▁and ▁Vas co ▁da ▁G ama ▁se amount s , ▁which ▁form ▁the ▁Gal icia ▁interior ▁bas in . ▁The ▁southern ▁border ▁of ▁these ▁features ▁is ▁marked ▁by ▁Naz ar é ▁C any on , ▁which ▁spl its ▁the ▁contin ental ▁sh elf ▁and ▁leads ▁directly ▁into ▁the ▁aby ss . ▁ ▁R ivers ▁ ▁The ▁major ▁rivers ▁flow ▁through ▁the ▁wide ▁valle ys ▁between ▁the ▁mountain ▁systems . ▁These ▁are ▁the ▁E bro , ▁Dou ro , ▁Tag us , ▁Gu ad iana ▁and ▁Gu adal qu iv ir . ▁All ▁rivers ▁in ▁the ▁I ber ian ▁Pen ins ula ▁are