This arch has been sitting around for half a million years or so without falling. Of course the long term cause is gradual erosion, but I suspect the immediate cause was weather and tide related: drier than normal, coupled with shear stresses caused by a temperature gradient. Problem is, August 1 had a 40 degree differential compared to a 25 degree drop Monday night, and the new moon occurred 2 days earlier as well. The winds were stronger Friday than Monday night. Did it fall two days after it cracked? I doubt it, but there must have been some reason it fell when it did. We're a month past aphelion, with its weaker tides, but the arch has gone through the worst of a summer full of expansion and contraction. Winter freezing and thawing does the long term damage, but summer probably provides more triggering mechanisms. Ice ages may set the arches up to tumble during interstadials. I think natural global warming could be the culprit. --AGF