The posted coordinates will bring you to a spot where you can safely view the underwater arch. If you are adventurous and want to take a closer look at the arch, you can paddle a canoe or kayak up to here or even go for a swim like many visitors do. This earthcache should only be attempted during daylight hours.
In order to log your find, determine the following:
1) From your vantage point, determine the height and width of the opening that forms the arch.
2) At the time of your visit, is the opening of the arch completely under water?
3) Observe the stone that forms the arch, is it a solid arch or is it made of up smaller stones, fill or other material?
4) What nearby geological feature(s) may affect the erosion of the arch and how?
5) (Optional) Where else have you found an arch in your travels? Feel free to tell us about it in your log.
A natural arch, natural bridge, or (less commonly) rock arch is a natural rock formation where an arch has formed with an opening underneath. Natural arches commonly form where inland cliffs, coastal cliffs, fins or stacks are subject to erosion from the sea, rivers or subaerial weathering.
Most natural arches are formed from narrow fins and sea stacks composed of sandstone or limestone with steep, often vertical, cliff faces. The formations become narrower due to erosion over geologic time scales. The softer rock stratum erodes away creating rock shelters, or alcoves, on opposite sides of the formation beneath the relatively harder stratum, or caprock, above it. The alcoves erode further into the formation eventually meeting underneath the harder caprock layer, thus creating an arch. The erosional processes exploit weaknesses in the softer rock layers making cracks larger and removing material more quickly than the caprock; however, the caprock itself continues to erode after an arch has formed, which will ultimately lead to collapse.
Some other notable arches are Percé Rock, Quebec and in Bruce Peninsula National Park, Ontario where you can discover both an arch above the water (see GCG9X6) and for the adventurous an underwater opening or arch down below in the grotto that leads into Georgian Bay (see GC4WKC1).