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.