Editing Mountain (section)

===Block mountains===
{{Main|Block mountains}}
[[File:Vihren Pirin IMG 8898.jpg|thumb|alt=the highest summit of Pirin|[[Pirin|Pirin Mountain]], Bulgaria, part of the fault-block [[Rila]]-[[Rhodope Mountains|Rhodope]] massif]]
Block mountains are caused by [[fault (geology)|faults]] in the crust: a plane where rocks have moved past each other. When rocks on one side of a fault rise relative to the other, it can form a mountain.<ref name="Ryan">{{Cite book |last=Ryan |first=Scott |url=https://archive.org/details/cliffsquickrevie0000ryan |title=CliffsQuickReview Earth Science |publisher=Wiley |year=2006 |isbn=0-471-78937-2 |chapter=Figure 13-1 |chapter-url=https://books.google.com/books?id=PV_BabxTTkcC&pg=PA94 |url-access=registration}}</ref> The uplifted blocks are block mountains or [[Horst (geology)|horsts]]. The intervening dropped blocks are termed [[graben]]: these can be small or form extensive [[rift valley]] systems. This kind of landscape can be seen in [[East Africa]],<ref>{{Cite journal |last=Chorowicz |first=Jean |date=October 2005 |title=The East African rift system |journal=Journal of African Earth Sciences |volume=43 |issue=1–3 |pages=379–410 |bibcode=2005JAfES..43..379C |doi=10.1016/j.jafrearsci.2005.07.019}}</ref> the [[Vosges]] and [[Rhine graben|Rhine]] valley,<ref>{{Cite journal |last=Ziegler |first=P. A. |last2=Dèzes |first2=P. |date=July 2007 |title=Cenozoic uplift of Variscan Massifs in the Alpine foreland: Timing and controlling mechanisms |journal=Global and Planetary Change |volume=58 |issue=1–4 |pages=237–269 |bibcode=2007GPC....58..237Z |doi=10.1016/j.gloplacha.2006.12.004}}</ref> and the [[Basin and Range Province]] of Western North America.{{sfn|Levin|2010|pp=474-478}} These areas often occur when the regional stress is extensional and the [[crust (geology)|crust]] is thinned.{{sfn|Levin|2010|pp=474-478}}