The country straddles the Equator, with one-third to the North and two-thirds to the South. As a result of this equatorial location, the Congo experiences large amounts of precipitation and has the highest frequency of thunderstorms in the world. The annual rainfall can total upwards of 80 inches 2,032 mm in some places, and the area sustains the second largest rain forest in the world after that of the Amazon. This massive expanse of lush jungle covers most of the vast, low-lying central basin of the river, which slopes toward the Atlantic Ocean in the West. This area is surrounded by plateaus merging into savannas in the south and southwest, by mountainous terraces in the west, and dense grasslands extending beyond the Congo River in the north. High, glaciated mountains are found in the extreme eastern region.