Say “panhole” and alot of people with automatically think “pan in a hole”. Panhole is a term unfamiliar to many not familiar with the realm of physical geography.
And thus, this geography lesson will involve fluvial geomorphology. Geomorphology is a subfield of geography. And it is fluvial geomorphology for which panholes come from.
In geography/geomorphological terms, a panhole is a depression in a stream or river bed. Very often, it’s circular in its shape, and it is often shallow as well. Very often, panholes are found in desert areas around stream beds, mainly comprised of sedimentary rock, such as sandstone. They can also be found in granite, an igneous rock.
Limestone is another type of rock panholes can be found. LImestone is a carbonate sedimentary rock. One of the minerals limestone is comprised of is calcite. Limestone is relatively soluble compared to other rocks. For this reason, many erosion landforms are sculpted out of limestone.
In the case of panholes in limestone stream beds, water is constantly weathering the limestone. Its solubility plays a role in this. Very likely, there might be rough sediments and smaller rocks carried by water grinding against the limestone, the same way potholes are formed (potholes are similar to panholes, but deeper than then are wide). Flowing water facilitates the weathering and erosion that takes place in creating panholes. Those are among the processes in fluvial geomorphology which shape stream beds. And thus, the creation of a geographic and geomorphological phenomenon known as panholes