Why did the second head of mount Rushmore start to cumble?

The second head of Mount Rushmore, representing Thomas Jefferson, began to crumble primarily due to natural weathering processes and the effects of erosion. Factors such as freeze-thaw cycles, rain, and wind contributed to the deterioration of the granite over time. Additionally, flaws in the rock and the original carving techniques may have made certain areas more susceptible to damage. Preservation efforts are ongoing to address these issues and protect the monument.