Oceanic basin an active - and growing - oceanic basin include an elevated mid-ocean ridge, flanking abyssal hills leading down to abyssal plains. The elements of an active oceanic basin often include the oceanic trench associated with a subduction zone. The Atlantic ocean and the Arctic ocean are good examples of active, growing oceanic basins, whereas the Mediterranean Sea is shrinking. The Pacific Ocean is also an active, shrinking oceanic basin, even though it has both spreading ridge and oceanic trenches. Perhaps the best example of an inactive oceanic basin is the Gulf of Mexico, which formed in Jurassic times and has
Sistan Basin Mount Khajeh, rises beside the lakes and marshes of the basin. The lowest part of the Sistan Basin contains a series of shallow lakes, known as "hamuns". It appears that in the past there was a single Hamun Lake, but there are now three separate lakes. From north to south the lakes are: The Hamun-e Puzak lies mostly in Afghanistan. It receives water from the Shelah Charkh channel of the Helmand River, and also from the Khash River and other small rivers. The Hamun-e Sabari is split between Iran and Afghanistan. It receives water from the Parian branch of Helmand