The topography features flat to rolling sandy desert with dunes to the Caspian Sea, which lies in the west. The Kara Kum desert occupies over 80% of Turkmenistan's total area. The desert is bounded by oases in the north that are watered by the Amu Dar'ya, and by the Murgab, Tejen, and Atrek rivers in the south. The highest point in Turkmenistan is the Gora Ayribaba (3,139 m/10,299 ft), located along the eastern border near Uzbekistan. Only 4% of Turkmenistan's land is arable with approximately2.5% under irrigation.