This is not at all a sure sign of anything other than the normal erosion that is well known at Arches National Park. If you paid attention during your 2001 trip you would have learned that lots of features of the park have bit the dust literally over the years. There are plenty of before and after photos to show that. In fact, everyone should do their friends a favor and tell them to visit Arches soon, considering the condition of the landscape and delicate arches! I would not be surprised to hear of either of those collapsing in my lifetime.