Glossary of Karst and Cave Terms
half tube; half-tube
1. An inverted channel with semi-circular cross section seen in cave-passage ceilings, most clearly where the ceiling is an uneroded bedding surface. The half tube originates as part of a phreatic tube guided by the bedding plane, and the lower half is subsequently removed by vadose enlargement. The presence of half tubes provides important evidence of early phreatic-cave development . 2. Trace of a tube remaining in the roof or wall of a cave . See also tube.