JOINTS AND ITS MEANING… Joints are fractures along which no appreciable displacement has occurred. Most common rock structures are fractures called joints. http://nvcc.edu/home/cbentley/geoblog/uploaded_ images/columnar_layers-703634.jpg
Joints continued… Parallel group joints http://www.depauw.edu/acad/geoscienc es/fsoster/W2.jpg Although some joints occur in roughly parallel groups. http://www.geology.wisc.edu/~maher /air/122-25v.jpg
Columnar Joints Columnar joints are joints that form when igneous rocks cool and develop shrinkage fractures that produce elongated, pillar like columns. http://www.answersincreation.org/curriculum/ge ology/images/columnar_joint.jpg
How joints are produced? Most Joints are produced when rocks in the outermost crust are deformed. Tensional and shearing stresses associated with crustal movements cause the rock to fail by brittle fracture. Extensive joint patterns can also develop in response to relatively subtle and barely perceptible regional up warping and down warping of the crust. Although jointed rocks present a risk to the construction of engineering projects. For example, highways, and dams. http://www.hku.hk/yscn0007/HKNE%20- %20Landscapes%20IV%20(Hong%20Kong%27s% 20landscapes)_files/photo19sm.jpg http://www.ma.nrcs.usda.go v/news/images/Tyler_dam.jp g http://www.azdot.gov/highways/ima ges/SuperRedTan.gif
Chemical Weathering Many rocks are broken by two or even three sets of intersecting joints that slice the rock into numerous regularly shaped blocks. http://www.rbnc.org/schoolunits/sc hlphoto/terreco/weathering.jpg http://people.usd.edu/~Brennan.Jordan/Colu mnTops.jpg Chemical Weathering tends to be concentrated along joints, and in many areas groundwater movement and the resulting dissolution in soluble rocks is controlled by joint pattern.