Bridges are either spans of lava tube roofs left after
collapses, or roofed-over segments of lava trenches. They may form between
two closely spaced skylights, or may be found in isolation spanning
trenches. There is no formal definition that distinguishes between a
bridge and a short passage segment, which it most often represents. |
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Created: December 11, 2008 Author: Dave Bunnell |