The Iberian peninsula lies more than 600 m above sea level, on average, far above similar geological regions in western Europe. Even tectonically undeformed areas in the inner basins present a topography and a sedimentary infill sometimes higher than 1000 m. Why?
The elevation of continents is generally thought to be the result of the isostatic equilibrium (Archimedes balance) of the crust floating on a fluid mantle (Pratt and Airy models, late XIX century). The thicker the crust (which is less dense than the mantle), the higher topography. The denser the crust, the lower the topography.
Cartoon explaining the concept of isostatic equilibrium, according to which topography (h1) is sustained by a crustal root (b1) in the same way that the elevation of an iceberg reflects the size of its submerged part.
However, the crust of the Iberian Peninsula is about 30-33 km thick on average, similar to most of the western european platform, and nothing suggests that the Iberian crust has a lower density than other regions. Why then is the topography of Iberia higher than 600 m, in contrast with the near sea-level western Europe?
So, the underlying question is: why Iberia is 600m higher than the W European Platform, having its Moho (base of the crust) shallower?