Editing Erosion (section)

===Glaciers===
[[File:Pirunpesä Jalasjärvi 8.JPG|thumb|left|[[The Devil's Nest]] (''Pirunpesä''), the deepest ground erosion in [[Europe]],<ref>{{cite web| url = https://www.pizzatravel.com.ua/eng/finland/117/devils_nest| title = The Devil's Nest, the deepest ground erosion in Europe}}</ref> located in [[Jalasjärvi]], [[Kurikka]], [[Finland]]]]
[[File:MorainesLakeLouise.JPG|thumb|right|Glacial [[moraines]] above [[Lake Louise, Alberta|Lake Louise]], in [[Alberta, Canada]]]]
[[Glacier]]s erode predominantly by three different processes: abrasion/scouring, [[Plucking (glaciation)|plucking]], and ice thrusting. In an abrasion process, debris in the basal ice scrapes along the bed, polishing and gouging the underlying rocks, similar to sandpaper on wood. Scientists have shown that, in addition to the role of temperature played in valley-deepening, other glaciological processes, such as erosion also control cross-valley variations. In a homogeneous bedrock erosion pattern, curved channel cross-section beneath the ice is created. Though the glacier continues to incise vertically, the shape of the channel beneath the ice eventually remain constant, reaching a U-shaped parabolic steady-state shape as we now see in [[glaciated valley]]s. Scientists also provide a numerical estimate of the time required for the ultimate formation of a steady-shaped [[U-shaped valley]]—approximately 100,000 years. In a weak bedrock (containing material more erodible than the surrounding rocks) erosion pattern, on the contrary, the amount of over deepening is limited because ice velocities and erosion rates are reduced.<ref>{{Cite journal|last1=Harbor|first1=Jonathan M.|last2=Hallet|first2=Bernard|last3=Raymond|first3=Charles F.|date=1988-05-26|title=A numerical model of landform development by glacial erosion|journal=Nature|language=en|volume=333|issue=6171|pages=347–349|doi=10.1038/333347a0|bibcode=1988Natur.333..347H|s2cid=4273817}}</ref>

Glaciers can also cause pieces of bedrock to crack off in the process of plucking. In ice thrusting, the glacier freezes to its bed, then as it surges forward, it moves large sheets of frozen sediment at the base along with the glacier. This method produced some of the many thousands of lake basins that dot the edge of the [[Canadian Shield]]. Differences in the height of mountain ranges are not only being the result tectonic forces, such as rock uplift, but also local climate variations. Scientists use global analysis of topography to show that glacial erosion controls the maximum height of mountains, as the relief between mountain peaks and the snow line are generally confined to altitudes less than 1500&nbsp;m.<ref>{{Cite journal|last1=Egholm|first1=D. L.|last2=Nielsen|first2=S. B.|last3=Pedersen|first3=V.K.|last4=Lesemann|first4=J.-E.|title=Glacial effects limiting mountain height|journal=Nature|volume=460|issue=7257|pages=884–887|doi=10.1038/nature08263|pmid=19675651|bibcode=2009Natur.460..884E|year=2009|s2cid=205217746}}</ref> The erosion caused by glaciers worldwide erodes mountains so effectively that the term ''[[glacial buzzsaw]]'' has become widely used, which describes the limiting effect of glaciers on the height of mountain ranges.<ref name="reference">{{cite journal | last1 = Thomson | first1 = Stuart N. | last2 = Brandon | first2 = Mark T. | last3 = Tomkin | first3 = Jonathan H. | last4 = Reiners | first4 = Peter W. | last5 = Vásquez | first5 = Cristián | last6 = Wilson | first6 = Nathaniel J. | year = 2010 | title = Glaciation as a destructive and constructive control on mountain building | journal = Nature | volume = 467 | issue = 7313| pages = 313–317 | doi = 10.1038/nature09365 | pmid = 20844534 |bibcode = 2010Natur.467..313T | s2cid = 205222252 | hdl = 10533/144849 | hdl-access = free }}</ref> As mountains grow higher, they generally allow for more glacial activity (especially in the [[accumulation zone]] above the glacial equilibrium line altitude),<ref>{{cite journal | last1 = Tomkin | first1 = J.H. | last2 = Roe | first2 = G.H. | year = 2007 | title = Climate and tectonic controls on glaciated critical-taper orogens | url = http://earthweb.ess.washington.edu/roe/Publications/TomkinRoe_Glaciers_EPSL07.pdf | journal = Earth Planet. Sci. Lett. | volume = 262 | issue = 3–4 | pages = 385–397 | doi = 10.1016/j.epsl.2007.07.040 | bibcode = 2007E&PSL.262..385T | citeseerx = 10.1.1.477.3927 | access-date = 2017-10-24 | archive-url = https://web.archive.org/web/20170809121522/http://earthweb.ess.washington.edu/roe/Publications/TomkinRoe_Glaciers_EPSL07.pdf | archive-date = 2017-08-09 | url-status=live }}</ref> which causes increased rates of erosion of the mountain, decreasing mass faster than [[isostatic rebound]] can add to the mountain.<ref>Mitchell, S.G. & Montgomery, D.R. "Influence of a glacial buzzsaw on the height and morphology of the Cascade Range in central Washington State". ''Quat. Res''. 65, 96–107 (2006)</ref> This provides a good example of a [[negative feedback loop]]. Ongoing research is showing that while glaciers tend to decrease mountain size, in some areas, glaciers can actually reduce the rate of erosion, acting as a ''glacial armor''.<ref name="reference"/> Ice can not only erode mountains but also protect them from erosion. Depending on glacier regime, even steep alpine lands can be preserved through time with the help of ice. Scientists have proved this theory by sampling eight summits of northwestern Svalbard using Be10 and Al26, showing that northwestern Svalbard transformed from a glacier-erosion state under relatively mild glacial maxima temperature, to a glacier-armor state occupied by cold-based, protective ice during much colder glacial maxima temperatures as the Quaternary ice age progressed.<ref>{{Cite journal|last1=Gjermundsen|first1=Endre F.|last2=Briner|first2=Jason P.|last3=Akçar|first3=Naki|last4=Foros|first4=Jørn|last5=Kubik|first5=Peter W.|last6=Salvigsen|first6=Otto|last7=Hormes|first7=Anne|title=Minimal erosion of Arctic alpine topography during late Quaternary glaciation|journal=Nature Geoscience|volume=8|issue=10|pages=789|doi=10.1038/ngeo2524|bibcode=2015NatGe...8..789G|year=2015}}</ref>

These processes, combined with erosion and transport by the water network beneath the glacier, leave behind [[glacial landform]]s such as [[moraine]]s, [[drumlin]]s, ground moraine (till), [[glaciokarst]], kames, kame deltas, moulins, and [[glacial erratic]]s in their wake, typically at the terminus or during [[Retreat of glaciers since 1850|glacier retreat]].<ref>Harvey, A.M. "Local-Scale geomorphology – process systems and landforms". ''Introducing Geomorphology: A Guide to Landforms and Processes''. Dunedin Academic Press, 2012, pp. 87–88. EBSCO''host''.</ref>

The best-developed glacial valley morphology appears to be restricted to landscapes with low rock uplift rates (less than or equal to 2mm per year) and high relief, leading to long-turnover times. Where rock uplift rates exceed 2mm per year, glacial valley morphology has generally been significantly modified in postglacial time. Interplay of glacial erosion and tectonic forcing governs the morphologic impact of glaciations on active orogens, by both influencing their height, and by altering the patterns of erosion during subsequent glacial periods via a link between rock uplift and valley cross-sectional shape.<ref>{{Cite journal|last1=Prasicek|first1=Günther|last2=Larsen|first2=Isaac J.|last3=Montgomery|first3=David R.|date=2015-08-14|title=Tectonic control on the persistence of glacially sculpted topography|journal=Nature Communications|language=en|volume=6|doi=10.1038/ncomms9028|issn=2041-1723| pmc=4557346 |pmid=26271245|page=8028|bibcode=2015NatCo...6.8028P |bibcode-access=free |doi-access=free }}</ref>