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Light beams in lava tube. Mojave Desert NP, California
Viewed with the naked eye, the light in this lava tube is too dim to see the walls as more than shadowy masses. When left open for a quarter or half an hour, a photographer's lens reveals shape and texture, and even color in this underground chamber. Lava tubes are formed when magma flows from a volcano mouth, then hardens on the surface while protecting the heat under its skin. As the lava flows on out, it leaves its empty tube behind itself. Percolation and erosion sometimes leave vents on the surface that perform as spotlights for those traveling underground.