What causes mountains to have rounded tops?

Good question! It depends on the age of the mountain, and on the processes that shape it. For most mountains, the answer is that soil surfaces like to be smooth. Given time, soil diffuses into smooth, round parabolas. read more

First, not all mountains have rounded tops; many mountains have very jagged and irregular tops (see the Tetons in the US, or the Alps or the Himalayas). However, rounding of the exposed tops of high places occurs over time due to erosion and weathering, which soften exposed rock surfaces and cause fragments to fall or be dissolved away. read more

In nature, points are unstable for the most part (takes extra energy to keep a thing pointed), so pointed parts get physically or chemically attacked preferentially. Mountain tops tend to be rounded because they have been exposed to erosion for a long time. However, oddly I suppose, pointiness in mountains is often a result of glacial erosion. read more

When it stops growing, rain, winds and frost take over and in a hundred million years or so the jagged peaks have become rounded hills. The Laurentians of Canada are old old mountains. Their ancient peaks are worn down to round hills, The young Coastals of California are young rounded hills. read more