Sapping

Sapping is a type of erosion where the ground seems to have collapsed into wide valleys. Steep-sided U-shaped valleys of fairly uniform width with box-like, "theater-shaped" headwalls are characteristic of sapping. ^[1] Sapping is caused by water in the ground moving laterally until it eventually seeps out and creates its ampitheater-like shape. Cite error: Invalid <ref> tag; invalid names, e.g. too many

The two canyons at center-left in this photo from Canyonlands National Park in Utah have the theater-shaped heads typical of valley features shaped by groundwater sapping.

Many channels have been seen on Mars that look like ones created by groundwater sapping here on Earth.^[2]

References

↑ Kocher, R. and J. Piper. 1986. Morphology of Large Valleys on Hawaii: Evidence for Groundwater Sapping and Comparisons with Martian Valleys. Journal of Geophysical Research. volume = 91. Issue = B13|pages = 175–192.
↑ Gulick, V. 2001. Origin of the Valley Networks on Mars: a Hydrological Perspective. Geomorphology. volume = 37. issue = 3–4. pages = 241–268