Spheroidal weathering

Spheroidal weathering

Spheroidal weathering is a type of chemical weathering that creates rounded boulders and helps to create domed monoliths. This should not be confused with stream abrasion, a physical process which also creates rounded rocks on a much smaller scale. A good example of spheroidal weathering can be found in the Alabama Hills area of eastern California.

Spheroidal weathering occurs whenever a mass of rock (most typically granitic in composition), experiences a drastic reduction in ambient heat and pressure, such as when a batholith is exposed at the surface. Rock forms at great temperatures and pressures (760 °C and 300 MPa) for granitic rock), and in granites there are three mutually perpendicular sets of joints that develop when this overburden is removed. Two things cause this in granites: the quartz crystals expand about 5%, and acidic water attacks the feldspar minerals, turning them into clay. Thus the corners become rounded, because angular edges provide more than one area of attack by exposing a greater amount of surface area. Edges and especially corners of an angular block weather faster than flatter surfaces. The ultimate result of this process is a rounded bolder or a dome monolith such as the rounded back of Half Dome in Yosemite National Park.

The process of spheroidal weathering is slower than other common types of weathering such as frost wedging, and it becomes lower still at progressively lower temperatures which slow down the chemical process of feldspar breakdown. Thus many granitic mountain peaks are jagged and craggey instead of rounded.

ee also

*Exfoliation (geology), a related form of weathering that also creates domes.
*Granite dome

References

*"Geology Underfoot in Death Valley and Owens Valley", Sharp, Glazner (Mountain Press Publishing Company, Missoula; 1997) ISBN 0-87842-362-1


Wikimedia Foundation. 2010.

Игры ⚽ Поможем сделать НИР

Look at other dictionaries:

  • spheroidal weathering —   the chemical weathering of blocks of rock so that they take on a more rounded shape …   Geography glossary

  • Weathering — This article is about weathering of rocks and minerals. For weathering of polymers, see Polymer degradation and Weather testing of polymers. Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through… …   Wikipedia

  • Granite Dells — Watson Lake in the Granite Dells Dells Granite showing s …   Wikipedia

  • Devils Marbles Conservation Reserve — IUCN Category V (Protected Landscape/Seascape) …   Wikipedia

  • tor — /tawr/, n. a rocky pinnacle; a peak of a bare or rocky mountain or hill. [bef. 900; ME; OE torr < Celtic; cf. Ir tor rocky height, Welsh twr heap, pile] * * * ▪ geology       exposed rock mass of jointed and broken blocks. Tors are seldom more… …   Universalium

  • diabase — diabasic, adj. /duy euh bays /, n. Petrol. 1. a fine grained gabbro occurring as minor intrusions. 2. Brit. a dark igneous rock consisting essentially of augite and feldspar; an altered dolerite. [1810 20; < F, equiv. to dia (error for di two) +… …   Universalium

  • Alabama Hills — are a rocky formation on the eastern slope of the Sierra Nevada mountains in the Owens Valley of California, near Lone Pine, California. Though geographically considered a range of hills, geologically they are a part of the Sierra Nevada… …   Wikipedia

  • Sphere (disambiguation) — A sphere is an object shaped like the surface of a ball, but can be used to refer to a ball shaped object, as well as a sphere like or annular region or shell. Additionally, it has several metaphorical uses.In mathematics: * Sphere, the set of… …   Wikipedia

  • Stone balls — The terms Stone balls, stone ball , stone spheres , and stone sphere have been used to designate spherical stone objects of both natural and artificial origin. Different types of stone balls include:Natural*Natural Stone Balls **megaspherulites… …   Wikipedia

  • Phallic Rock — also commonly known as Cock Rock is a precambrian granite rock formation in Carefree, Arizona, United States. The formation is caused by spheroidal weathering whereby the composition of the granite and its crystal structure facilitated the… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”