I have always wondered what is the origin of Montmartre mountain in Paris. What surprises me is that the whole area seems quite flat, and yet there's a very steep hill in the middle. How has that happen? Is it an instance of some common geological phenomenon?
$\begingroup$ Might be uplifted due to evaporite-diapirism; water reacting with anhydrite to form gypsum (volume expansion). Only thing I could find is: earth.esa.int/workshops/salzburg04/papers_posters/… $\endgroup$– tobias47n9eApr 16, 2014 at 15:12
A clue is in the full name of the hill: 'Butte Montmartre'. A butte is an erosional feature in which a block of resistant rock overlies a less resistant layer. Erosion of the soft layer below causes the more resistant rock to erode as well by undercutting. This can lead to an isolated hill in a relatively flat surrounding.
The Montmartre hill itself consists of relatively resistant sedimentary rocks (can't find what exactly, although Deffontaines (2005) and De Wever (2002) hint at sandstones and shales) overlying soft marls and gypsum, which was mined until 1860, also contributing to instability of the butte (Deffontaines, 2005). Evaporite-diapirism, as mentioned by Spießbürger, might therefore have played a role as well.
Deffontaines, B., B. Fruneau, A. Prunier-Leparmentier, A. Arnaud, R. Cojean, E. Pajot, J. Rudant (2005) Urban instability revealed by DINSAR and SPN Interferometry: The Montmartre "Funiculaire" case example (Paris, France). Géoline 2005
De Wever, P., F. Guillocheau, J. Reynaud, E. Vennin, C. Robin, A. Cornée, D. Rouby (2002) Deux siècles de stratigraphie dans le bassin de Paris. Comptes Rendus Palevol
$\begingroup$ It would be good to to link the sources from the actual statements in your answer, or at least indicate what they are - "(source)" doesn't give any information. $\endgroup$ Apr 17, 2014 at 2:31
2$\begingroup$ @naught101 I expanded one reference and replaced the other with a more credible source. $\endgroup$ Apr 17, 2014 at 5:55
$\begingroup$ And "martre" means "martyr". $\endgroup$– QuidamNov 17, 2019 at 17:58