What is Considered an Arch?
With such a simple question, one would expect a simple answer. I can assure you that is not the case, however.
You see, just what is considered an arch is a bit of a contested topic. In fact, different groups and regions all seem to have their own definition of what’s considered an arch. If you ask the Natural Arch and Bridge Society, NABS, you’ll find the following:
A natural arch is a rock exposure that has a hole completely through it formed by the natural, selective removal of rock, leaving a relatively intact frame.
Reading further, you’ll come across the following paragraph:
Finally, note that size is not a factor in the definition. Some features not normally considered natural arches, because of their size, still qualify as such.
By this logic, any hole in a rock formation would qualify as being a natural arch. Indeed, this seems to be the metric that many areas go by. Personally, I, and many others, disagree with this metric for measuring an arch.
How I Classify Something as an Arch
If I don’t go by the definition set forth by NABS, then what definition do I use?
Well, it’s quite simple. In order for an opening to be considered a natural arch, the opening must be at least 3 feet in any direction. Anything that does not meet this threshold is not an arch.
Wait, Why 3 Feet?
This may bring about the logical question of why I use3 feet as the cutoff. The reason, ironically enough, comes from NABS. On a page detailing the classification of natural arches, they make the following definitions:
Miniature Arch – Any opening less than 1 meter in the largest dimension
Minor Arch – Any opening whose largest dimension is at least 1 meter
Significant Arch – Any opening whose dimensions are at least 10 square meters
Major Arch – Any arch that has a span of at least 50 meters
Three feet is a close approximation to the NABS definition of a minor arch, which is why we choose to use three feet as the cutoff for what we consider an arch. Anything smaller than this, we often refer to simply as a window.
I’m Not the Only One
It’s worth mentioning that I’m far from being the only one that classifies arches in this way. This is the metric used by both Arches National Park and the Kentucky Arch Database.
Honestly, at this point, I think it’s fair to say that the vast majority of arch hunters use the three-foot definition of an arch and that the Natural Arch and Bridge Society simply need to update their definition of what constitutes an arch.
Not having a cutoff for what qualifies as an arch simply leads to muddied datasets that one could not possibly hope to make sense of.
