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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?

Topographic map of Europe Topographic map of Europe

Depth to the base of the crust in Europe (from Tesauro et al., 2008) Depth to the base of the crust in Europe (in km; from Tesauro et al., 2008)

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3 Answers 3

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I don't know for sure, but my guess is that at least a part of the high Iberian elevation is due to NNE-SSW compression in northeast Spain, caused by rotation of the Iberian block. That is,the same rotation that opened up the Bay of Biscay deep basin, whilst compressing the Pyrennean mountains. The gentle dip of most of Iberia towards the southwest would fit well with such an explanation. But then you may ask: 'Why is there a low elevation sedimentary basin just southwest of the Pyrenees?' Check the age of sediments in this trough. I would bet they are pretty recent, and I suspect that there may well be some late-stage counter-rotation caused by the relative east-west displacement along the Rif-Betic arc.

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  • $\begingroup$ the problem is that if compression and crustal thickening would explain the elevation then you would expect the moho to be substantially below the normal depth in the neighbouring European platform $\endgroup$
    – DrGC
    Jan 13, 2017 at 15:00
  • $\begingroup$ ..which it probably will be in due course, but it takes a very long time for the Moho to adjust to major tectonic events. $\endgroup$
    – Gordon Stanger
    Jan 15, 2017 at 3:13
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A combination of the Opening Atlantic and push of Africa...my guess is failure of the ocean-continent contact of western Iberia in a couple of million years leading to subduction...

If no hints for differences in density, the elevation must be sustained by external forces. In this sw corner of Eurasia the only continent-continent collision between Africa and Eurasia occurs, west of Arabian plate. And the Ridge Push from Atlantic opening is significant large as well.

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    $\begingroup$ Could you provide some information (references) that support your answer? $\endgroup$
    – arkaia
    Jan 16, 2016 at 17:25
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    $\begingroup$ ehmm.. my thesis (www.geo.vu.nl/~andb/iberia $\endgroup$
    – bernd andeweg
    Jan 16, 2016 at 18:14
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    $\begingroup$ Wow! That is great! Maybe you could include some of the relevant points of your thesis in the response! $\endgroup$
    – arkaia
    Jan 16, 2016 at 20:07
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A more localised, and not applicable to the whole of Iberia, but perhaps worth a mention might be the proposed crustal delamination of southern Spain.

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