Panhole

In fluvial geomorphology, the term pothole is typically used for a smooth, bowl-shaped or cylindrical hollow, generally deeper than wide, found developed in the rocky bed of a stream.

[5] Panholes are erosional or destructional features that are developed in a variety of climatic environments and in a wide range of rock types.

[4] In the Sierra Nevada, California these features were termed weathering pits[9] by François E. Matthes, where they are thought to indicate rock surfaces that are unglaciated or escaped more recent glaciations.

In Sierra Nevada granitic rocks, these features have a characteristic shape such that they expand more rapidly in width than they grow in depth.

[10] One explanation for their conformation is because the most active environment for weathering is the zone of alternate wetting and drying along the margins of the pools that collect in the pits, the margins tend to deepen and enlarge until all points of the bottom are equally wet or dry at the same time, thus producing their characteristic shape.

Gnamma is an anglicization of a Nyoongar language word, used by that Aboriginal people of Western Australia to describe a naturally formed rock hole as well as its retained rainwater.