Rock pillars shaped by columnar joints in granite at Mt. Mizugaki, Central Japan

Abstract

AbstractRock pillars of granite form a special type of characteristic topography in granite, but their origin is not well understood, partly because their 3D morphology has never been well characterized. Rock pillars were investigated at Mt. Mizugaki, which is underlain by Neogene granite that intruded into the Cretaceous accretionary complex in central Japan. Three rock pillars and their surrounding areas were investigated in detail using unmanned aerial vehicle (UAV) images and structure from motion (SfM). The rock pillars were up to 70 m high and were shaped by columnar joints, which has hardly been reported before in granitic rocks. Columnar joints in granite are much larger than columnar joints in volcanic rocks. The columnar joints curved vertically, and some of them showed dipyramid shapes. The large size and curved morphology of the columnar joints may be the result of the slow cooling of the granite, compared to that of volcanic rocks. Thus, the columnar joints at Mt. Mizugaki made large, high rock pillars, which are not common in volcanic rocks.