August 12, 2024 – Yosemite National Park officials show example of what a weathering pan is and where they are in the park.

This weathering pan at the summit of North Dome offers an interesting insight into the history of glaciation on the North Rim of Yosemite Valley.

Weathering pans form when water collects in small natural depressions. Chemical interactions between the rock and water then cause the rock to break down into grus, a sandy material that is often swept away by the wind. While the specific mechanics of weathering pan formation are still debated, they are intriguing since the entire pan weathers downward at the same rate and keeps a relatively flat bottom. Chemical decomposition likely occurs at a faster rate at pan margins, where the rock is periodically wet and dry, causing pits to widen and gradually deepen.

These features tell us that the granite has been exposed for a long time— broken down by elements like wind and water rather than large volumes of ice. Weathering pans indicate that the top of North Dome has not been glaciated or has escaped recent glaciations (within the last 10,000 years.)

Source & photo: NPS