Why do some cave passages have elliptical tube shapes?

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cave Stalactites and stalagmites in the Queen's Chamber, Carlsbad Caverns National Park, southeastern New Mexico.

Cave passages develop elliptical tube shapes when they are formed under conditions of complete flooding. In this state, the water fills the entire passage, allowing it to dissolve the surrounding limestone bedrock equally across the walls, ceilings, and floors.1

This process differs from passages formed by flowing streams with a free air surface, which can only dissolve the rock in the stream bed, resulting in canyon-shaped passages.1