Editing Scree (section)

===Physical weathering processes===
[[File:DSC 0445 Partie inférieure de la combe de Mai de la montagne d'Aurouze (Hautes-Alpes, France).jpg|thumb|Scree in the lower part of the Mai Valley on the Aurouze mountain (Hautes-Alpes, France)]]

Scree formation is commonly attributed to the formation of ice within mountain rock slopes. The presence of [[Joint (geology) |joints]], [[fracture]]s, and other heterogeneities in the rock wall can allow [[precipitation]], [[groundwater]], and [[surface runoff]] to flow through the rock. If the temperature drops below the freezing point of the fluid contained within the rock, during particularly cold evenings, for example, this water can freeze. Since water expands by 9% when it freezes, it can generate large forces that either create new cracks or wedge blocks into an unstable position. Special boundary conditions (rapid freezing and water confinement) may be required for this to happen.<ref>{{cite book|last=Whalley|first=WB|year=1984|chapter=Rockfalls|title=Slope Instability|editor1-last=Brunsden|editor1-first=D.|editor2-last=Prior|editor2-first=DB|publisher=John Wiley and Sons|location=Chichester|pages=217–256}}</ref> [[Frost weathering|Freeze-thaw]] scree production is thought to be most common during the spring and fall, when the daily temperatures fluctuate around the freezing point of water, and snow melt produces ample free water.

The efficiency of freeze-thaw processes in scree production is a subject of ongoing debate. Many researchers believe that ice formation in large open fracture systems cannot generate high enough pressures to force the fracturing apart of parent rocks, and instead suggest that the water and ice simply flow out of the fractures as pressure builds.<ref>{{cite journal|last=Hallet|first=B|year=2006|title=Why do freezing rocks break?|journal=Science|volume=314|pages=1092–1093|doi=10.1126/science.1135200|pmid=17110559|issue=5802|s2cid=140686582}}</ref> Many argue that [[frost heaving]], like that known to act in soil in [[permafrost]] areas, may play an important role in cliff degradation in cold places.<ref>{{cite journal|last1=Walder|first1=J|last2=Hallet|first2=B|year=1985|title=A theoretical model of the fracture of rock during freezing|journal=Geological Society of America Bulletin|volume=96|pages=336–346|doi=10.1130/0016-7606(1985)96<336:ATMOTF>2.0.CO;2|issue=3|bibcode = 1985GSAB...96..336W }}</ref><ref>{{cite journal|last1=Murton|first1=JB|last2=Peterson|first2=R|last3=Ozouf|first3=J-C|year=2006|title=Bedrock fracture by ice segregation in cold regions|journal=Science|volume=314|pages=1127–1129|doi=10.1126/science.1132127|pmid=17110573|issue=5802|bibcode = 2006Sci...314.1127M |s2cid=37639112}}</ref>

Eventually, a rock slope may be completely covered by its own scree, so that production of new material ceases. The slope is then said to be "mantled" with debris. However, since these deposits are still unconsolidated, there is still a possibility of the deposit slopes themselves failing. If the talus deposit pile shifts and the particles exceed the angle of repose, the scree itself may slide and fail.{{cn |date= November 2024}}