tubular passage

   ; tube; tube passage

   1. Cave passage formed by approximately equal dissolution all round when full of flowing water within the phreas. Relict tubes, abandoned as the water table was lowered, are common in old caves, and may be partially filled by sediment, breakdown or stalagmite, or entrenched to form keyhole passages. Tube sizes range to over 15m in diameter, but the larger ones are rarely of uniform section. Peak Cavern in Derbyshire is well known for its fine circular phreatic tubes. Some of the trunk passages of Mammoth Cave, Kentucky, are spectacular tubes of elliptical section, formed by dissolution rates that were higher along the bedding than across [9].

   2. These are nearly horizontal cave passages (tunnels) with round or elliptical cross sections and are either straight or winding. At Mammoth Cave they vary in size up to 30 feet high and nearly 100 feet wide. They are formed while completely filled with flowing water. Whereas they are typically wider than high as a result of dissolution along horizontal cracks and beddingplane partings, they may also form as high, narrow, straight fissures along major vertical or near vertical fractures [15].

   See also canyon passage; keyhole passage; passage; vertical shaft.