It’s much more wet on one side of a mountain than the other because of a process known as orographic precipitation. Orographic precipitation causes air to rise up the side of a mountain range and cool, creating precipitation and storms. The storms deposit a great deal of precipitation on that side of the mountain and create a rain shadow effect on the opposite side of the range. The Sierra Nevada mountains are an excellent example of orographic precipitation because the mountains of the western Sierras receive considerable rainfall (far more than California’s Central Valley), while the eastern Sierras of Nevada are quite dry.
A satellite image of Greenland shows a large island almost entirely covered by a thick sheet of ice. (NASA)