Rock bridge; natural bridge; natural tunnel
A natural (rock) arch is a rock exposure with a hole completely through it, created by the natural removal of some of the rock to leave an intact rock frame around the hole (Natural Arch and Bridge Society n.d.).
A natural bridge is a natural arch that crosses a valley of erosion.
A natural tunnel is a natural arch which has a width greater than three times its span (Synder 2011).
- Kolb K (2010) Small winding channel in Tartarus Colles. http://hirise.lpl.arizona.edu/PSP_001420_2045
- Natural Arch and Bridge Society (n.d.) Frequently asked questions. http://www.naturalarches.org/archinfo/faq.htm
- Synder TA (2011) Ohio’s natural arches. Educational leaflet 18. http://www.dnr.state.oh.us/Portals/10/pdf/EL/el18.pdf