Natural stone arches are geological formations that occur when rock is exposed to significant amounts of erosion, which, over time, forces the rock to take the shape of an arch. Stone arches are among the most diverse rock formations, not only because of the vast area where they are known, but also because of their complex formation patterns. Although many factors contribute to making natural stone arches so captivating, one key role maintains and sharpens our constant attention: every stone arch formed, no matter what it is, will fall. Despite everything we know about stone arches, they continually change and teach us new things about themselves and the world around us. All naturally occurring stone arches are formed by the selective erosion of rock, but the terms by which this can occur are massive. Among the most common types of formation are wave action and lava flows. Under wave action, water constantly crashes into rock, effectively accelerating erosion while the sediment carried by the water is extremely abrasive, removing chunks of rock. When the lava flow occurs, the outermost...