Sump (cave)

Two sectional diagrams illustrating the concept of a sump. Diagram "A" illustrates a U-shaped passage with water filling the rounded bottom section, blocking the dry passage either side. Diagram "B" shows a passage blocked similarly by a sump, but on one side the water level is being held back by a natural dam, with dry passage continuing beyond, below the water level of the sump.
Sumps often block access to "dry" passage beyond them. Diagram B shows a "perched" sump, which could be siphoned to lower the water level.

A sump, or siphon, is a passage in a cave that is submerged under water.[1] A sump may be static, with no inward or outward flow, or active, with continuous through-flow. Static sumps may also be connected underwater to active stream passage. When short in length, a sump may be called a duck, however this can also refer to a section or passage with some (minimal) airspace above the water.

Depending on hydrological factors specific to a cave – such as the sea tide, changes in river flow, or the relationship with the local water table – sumps and ducks may fluctuate in water level and depth (and sometimes in length, due to the shape of adjacent passage).

  1. ^ Culver, David C.; Pipan, Tanja; White, William B., eds. (10 May 2019). Encyclopedia of Caves. Elsevier Science. ISBN 9780128141250. Retrieved 18 April 2023.