IN GEOLOGY, UNLIKE business, nothing is too big to fail. Mountains offer the most spectacular example. Pushed up by the crumpling of Earth’s crust following the collision of tectonic plates, they could in theory keep rising almost indefinitely. In practice, they do not. A suite of geological processes—including the grinding of glaciers, the gentle impact of rain, and forcible cracking by freezing and thawing of water—erode them down to size.