Lava Natural Arch

(Genetic type)

Examples: Indian Tunnel, unnamed arch, unnamed arch, possible Mars arch

This type of natural arch results when portions of the roof of a lava tube collapse. The remaining roof segments become lintels. Lava natural arches have the same observable attributes as the subterranean variety of waterfall natural bridge, except that flowing lava rather than water created the underground passageway. Thus, a geologic attribute, the type of rock, is used to discriminate a lava natural arch from a waterfall natural bridge. A lava natural arch always has a rock frame made of basalt or lava. Like the waterfall natural bridge, they frequently occur in series and clusters, but can also be isolated. A maturity attribute should be based on the ratio of lintel area to the area of collapsed roof rather than on the age of the lava flow.