Orogenic collapse

Orogenic collapse is the phase transition within a mountain belt from compressional thickening to extensional thinning, driven by the gravitational instability of over-thickened crust. When orogenic construction pushes crustal thickness beyond a critical value — typically 50–70 kilometers — the gravitational potential energy of the elevated topography exceeds the strength of the underlying lithosphere, and the system collapses under its own weight. This produces a paradoxical landscape where the highest mountains coexist with extensional basins and normal faulting, as seen in the Tibetan Plateau and the Aegean. Orogenic collapse is not a failure of mountain building but its inevitable next phase: the same post-orogenic extension that destroys the range also exhumes deep crustal rocks to the surface, preserving the metamorphic record for geologists to read.