Dramatically lower sea levels during ice ages allow rivers to carve deeper valleys.
Notes on verification
Well-established geomorphological principle confirmed by multiple independent academic sources (Penn State, Britannica, University of Maryland), consistent with standard base-level control theory of fluvial incision.
Sources
- Ice Age - Definition & Timeline (history.com)
- https://courses.ems.psu.edu/earth107/node/970 (courses.ems.psu.edu)
- https://www.geol.umd.edu/~tholtz/G102/102ceno3.htm (geol.umd.edu)