Balanced Rock in Arches National Park
September 26, 2007
The photo above shows a precariously balanced boulder in Arches National Park, Utah. Differential rates of weathering and erosion in the various sedimentary layers of this pinnacle have resulted in a more resistant cap rock, which is temporarily balanced on a much softer and thinner layer directly beneath it. In geological time, this is an exceptionally transient feature -- the balancing act will be short lived when the softer layer below it weathers away. In addition to their visual curiosity, balanced boulders are used to set upper limits on ground motion in a region, particularly in the desert southwest and in the vicinity of the San Andreas Fault. Photo taken in April of 2007.