Editing Soil erosion (section)

===Mass movement===
[[File:NegevWadi2009.JPG|thumb|Wadi in Makhtesh Ramon, Israel, showing gravity collapse erosion on its banks]]
''[[Mass wasting|Mass movement]]'' is the downward and outward movement of rock and sediments on a sloped surface, mainly due to the force of [[gravity]].<ref>{{cite book|author=Van Beek, Rens|chapter=Hillside processes: mass wasting, slope stability, and erosion|editor=Norris, Joanne E.|display-editors=etal|title=Slope Stability and Erosion Control: Ecotechnological Solutions|publisher=Springer|year=2008|isbn=978-1-4020-6675-7|chapter-url=https://books.google.com/books?id=YWPcffxM_A0C&pg=PA17}}</ref><ref>{{cite book|author=Gray, Donald H.|author2=Sotir, Robbin B.|name-list-style=amp|chapter=Surficial erosion and mass movement|title=Biotechnical and Soil Bioengineering Slope Stabilization: A Practical Guide for Erosion Control|publisher=John Wiley & Sons|year=1996|isbn=978-0-471-04978-4|page=20|chapter-url=https://books.google.com/books?id=kCbp6IvFHrAC&pg=20}}</ref>

Mass movement is an important part of the erosional process, and is often the first stage in the breakdown and transport of weathered materials in mountainous areas.<ref>{{cite book|author=Nichols, Gary|title=Sedimentology and Stratigraphy|publisher=John Wiley & Sons|year=2009|isbn=978-1-4051-9379-5|page=93|url=https://books.google.com/books?id=zl4L7WqXvogC&pg=PA93}}</ref> It moves material from higher elevations to lower elevations where other eroding agents such as streams and [[glacier]]s can then pick up the material and move it to even lower elevations. Mass-movement processes are always occurring continuously on all slopes; some mass-movement processes act very slowly; others occur very suddenly, often with disastrous results. Any perceptible down-slope movement of rock or sediment is often referred to in general terms as a [[landslide]]. However, landslides can be classified in a much more detailed way that reflects the mechanisms responsible for the movement and the velocity at which the movement occurs. One of the visible topographical manifestations of a very slow form of such activity is a [[scree]] slope.<ref>{{Cite journal|last1=Sun|first1=Wenyi|last2=Shao|first2=Quanqin|last3=Liu|first3=Jiyuan|last4=Zhai|first4=Jun|date=2014-10-01|title=Assessing the effects of land use and topography on soil erosion on the Loess Plateau in China|url=http://www.sciencedirect.com/science/article/pii/S0341816214001362|journal=CATENA|language=en|volume=121|pages=151–163|doi=10.1016/j.catena.2014.05.009|bibcode=2014Caten.121..151S |issn=0341-8162}}</ref>

''[[Slump (geology)|Slumping]]'' happens on steep hillsides, occurring along distinct fracture zones, often within materials like [[clay]] that, once released, may move quite rapidly downhill. They will often show a spoon-shaped [[isostatic depression]], in which the material has begun to slide downhill. In some cases, the slump is caused by water beneath the slope weakening it. In many cases it is simply the result of poor engineering along [[highway]]s where it is a regular occurrence.<ref>{{Cite journal|last1=van den Berg|first1=J.|last2=van de Wal|first2=R. S. W.|last3=Milne|first3=G. A.|last4=Oerlemans|first4=J.|date=2008-05-31|title=Effect of isostasy on dynamical ice sheet modeling: A case study for Eurasia|journal=Journal of Geophysical Research|language=en|volume=113|issue=B5|pages=B05412|doi=10.1029/2007JB004994|bibcode=2008JGRB..113.5412V|issn=0148-0227|doi-access=free}}</ref>

''Surface creep'' is the slow movement of soil and rock debris by gravity which is usually not perceptible except through extended observation. However, the term can also describe the rolling of dislodged soil particles {{convert|0.5|to|1.0|mm|abbr=on|2}} in diameter by wind along the soil surface.<ref>{{Cite book|title=Soils and Their Environment|last=Hassett|first=John|publisher=Prentice Hall|year=1992|isbn=9780134840499|pages=377|url=https://books.google.com/books?id=RbkdAQAAMAAJ}}</ref>