As a result of its equatorial location, the DRC experiences high precipitation and has the highest frequency of thunderstorms in the world. The annual rainfall can total upwards of  in some places, and the area sustains the Congo Rainforest, the second-largest rain forest in the world after 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 (Rwenzori Mountains) are found in the extreme eastern region. 