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Geo-#giroditalia2023 - Stage 12. The peloton is leaving the Apennines, will race over Adria again, and then enters the Alps today. The difference between these mountain belts is not just geographical: geologically, they're entirely different beasts! But it's a complex geometry! 
As we saw last week, the Apennines formed because Adria, the continent that underlies the Adriatic Sea and that is part of the African Plate, subducted below Europe and its sediments were offscraped. In the Alps, however, it's the opposite: Europe subducted below Adria.
So for most of the day, the peloton races over the African Plate again, which in in the morning is a downgoing plate and in the afternoon an overriding plate. Sounds like an ancient Roman riddle, right? The transition is a geological mess called the 'Ligurian Knot'
At depth, the geometry is (a little) simpler: the European plate in the western Alps is diving eastwards, the African plate in the Apennines westwards. A similar geometry is also known from the SW Pacific region! Let's hope it's only the geology that is messed up today...
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