It is formed by a kind of drilling action when pebbles are caught in eddy currents and whisked around within a small natural crack or hollow.
Near Nuannuan, the Keelung River is narrow with faster flowing water and turbulence.
The formation phenomena provokes wide research interests in fluid dynamics, landscape, geology, climate, hydrological and rock studies.
The people of the Guo-Gang community play an important part in the protection of the potholes in Nuannuan.
The highways are due for service in 2012 and the Guo-Gang community has been active raising government's awareness of how valuable these potholes are in the hope to reduce the overall damage.