Editing Karlu Karlu / Devils Marbles Conservation Reserve (section)

==Formation==
[[File:Karlu Karlu 2.jpg|thumb|left|upright=0.7|Suspended boulder]]
The Devils Marbles constitute a [[erosion|degraded]] [[nubbin (landform)|nubbin]].<ref name=Twidale1995>{{cite journal |last=Twidale |first=C.R.|author-link=Charles Rowland Twidale |date=1995 |title=Bornhardts, Boulders and Inselbergs |journal=Cadernos do Laboratorio Xeolóxico de Laxe |volume=20 |pages=347–380 }}</ref> The formation is made of [[granite]] and are part of the top layer of a formation which penetrates the ground from below, like little geological islands in the [[desert]], surrounded by large amounts of [[sandstone]]. The granite was formed millions of years ago as a result of the hardening of [[magma]] within the Earth's crust. Thick layers of sandstone on top of the granite exerted extreme downward pressure on the granite. After some time, [[Tectonics|tectonic]] forces caused folding of the Earth's crust in the area, which lifted the granite and fractured the sandstone, allowing the granite to come closer to the surface. As the pressure diminished, the granite expanded causing cracks to form, and then the larger formations began to separate into big, square blocks.<ref name=form>{{cite web|title=Weathering: Types of Weathering|url=http://facstaff.gpc.edu/~pgore/geology/geo101/weather.htm|publisher=Georgia Perimeter College/Pamela J. W. Gore|date=5 Feb 2002|access-date=29 Jan 2014|url-status=dead|archive-url=https://web.archive.org/web/20130510224332/http://facstaff.gpc.edu/~pgore/geology/geo101/weather.htm|archive-date=2013-05-10}}</ref>

The next phase of the formation of the Marbles started when the blocks were exposed to [[water]].<ref name=form /> The surface of the blocks began to decay under the influence of the water and a layer of loose material surrounded the individual blocks. When the blocks came to the surface completely, the loose material was [[erosion|eroded]] away by water and wind.

The rounding of the granite blocks is a result of [[Weathering#Biogeochemical weathering|chemical]] and [[Weathering#Physical weathering|physical (also called mechanical) weathering]].<ref name=form /> Chemical processes cause the surface of the blocks to expand and contract, resulting in thin layers of rock coming off the boulder in a process called [[exfoliation joint|exfoliation]]. This process rounds the granite block because the chemical processes have more effect on areas with edges. The rock begins to look like it is made of layers like an [[onion]]. Only the outer few centimetres are affected by chemical weathering in a process called [[spheroidal weathering]].

The boulders are affected more deeply by the extreme temperature differences between day and night in the arid desert region where the reserve is located. During daylight hours the rocks expand slightly and after nightfall they contract slightly, repeating the process every 24 hours. These repeated cycles of expansion and contraction, called [[Weathering#Thermal stress|thermal stress weathering]], create cracks which sometimes go so deep that the boulder is completely split in half.<ref>{{cite book|author=Paradise, T. R.|doi=10.1130/0-8137-2390-6.39|title=Petra revisited: An examination of sandstone weathering research in Petra, Jordan in Special Paper 390: Stone Decay in the Architectural Environment|year=2005|isbn=0-8137-2390-6|volume=390|pages=39}}</ref>

[[Image:Devils Marbles 4 Steps.PNG|thumb|center|800px]]