View source for Earth:Holocene glacial retreat

{{short description|Global deglaciation starting about 19,000 years ago and accelerating about 15,000 years ago}}
The '''[[Earth:Holocene|Holocene]] glacial retreat''' is a geographical phenomenon that involved the global retreat of glaciers ([[Earth:Deglaciation|deglaciation]]) that previously had advanced during the [[Earth:Last Glacial Maximum|Last Glacial Maximum]]. Ice sheet retreat initiated ca. 19,000 years ago and accelerated after ca. 15,000 years ago.  The [[Earth:Holocene|Holocene]], starting with abrupt warming 11,700 years ago, resulted in rapid melting of the remaining ice sheets of North America and Europe.

==Geographical alterations==
=== Antarctica ===
[[File:Fragments_of_Larsen_B_Ice_Shelf_Lingered_Until_2005.gif|thumb|227x227px|Fragments of Larsen B ice shelf lingered until 2005.]]
Radiocarbon dating has been used to date the start of glacial retreat on Alexander island 18,000 years ago.<ref name=":1" /> The outermost locations like Marguerite Bay were fully deglaciated 12,000 years ago and the further inland locations continued deglaciating for an additional 3,000 years.<ref name=":1">{{Cite journal|last1=Roberts|first1=S. J.|last2=Hodgson|first2=D. A.|last3=Bentley|first3=M. J.|last4=Sanderson|first4=D. C. W.|last5=Milne|first5=G.|last6=Smith|first6=J. A.|last7=Verleyen|first7=E.|last8=Balbo|first8=A.|date=2009-11-01|title=Holocene relative sea-level change and deglaciation on Alexander Island, Antarctic Peninsula, from elevated lake deltas|journal=Geomorphology|volume=112|issue=1–2|pages=122–134|doi=10.1016/j.geomorph.2009.05.011|bibcode=2009Geomo.112..122R}}</ref> The [[Earth:Larsen Ice Shelf|Larsen ice shelf]] was formed in the early Holocene at a latest estimation of 10,700 years ago.<ref name=":3">{{Cite journal|last1=Curry|first1=Philip|last2=Pudsey|first2=Carol J.|date=2007|title=New Quaternary sedimentary records from near the Larsen C and former Larsen B ice shelves; evidence for Holocene stability|journal=Antarctic Science|volume=19|issue=3|pages=355–364|doi=10.1017/S0954102007000442|issn=1365-2079|bibcode=2007AntSc..19..355C|s2cid=129610602 |doi-access=free}}</ref> Certain segments of the ice shelf have collapsed as recently as 1995 for Larsen A and a large segment of Larsen B collapsed in 2002.<ref name=":3" />

=== Europe ===
The many valleys of the Cairngorms, a mountainous region in the Eastern [[Place:Scottish Highlands|Scottish Highlands]] are littered with deposits from this period.

In northwestern Iceland, the Icelandic ice sheet began its non-uniform retreat about 15,000 years ago.<ref name=":0" /> [[Earth:Surface exposure dating|Surface exposure dating]] using the [[Physics:Isotope|isotope]] [[Physics:Chlorine-36|<sup>36</sup>Cl]] was the primary means of dating boulders and [[Earth:Terminal moraine|terminal moraine]]s in the Drangajökull area in Iceland.<ref name=":0" /> Ages of erratic boulders found near the Leirufjörður valley and moraine range from 7-12 thousand years old.<ref name=":0" /> The average ages for the groupings of boulders in the Leirufjörður area is 9.3 thousand years ago.<ref name=":0" /> Directly south of Leirufjörður in the Kaldalon Valley the average age of the boulders is 15,000 years old.<ref name=":0" /> The two different average ages are a result of different rates of glacial activity in Iceland.<ref name=":0">{{Cite journal|last1=Brynjólfsson|first1=Skafti|last2=Schomacker|first2=Anders|last3=Ingólfsson|first3=Ólafur|last4=Keiding|first4=Jakob K.|date=2015-10-15|title=Cosmogenic 36Cl exposure ages reveal a 9.3 ka BP glacier advance and the Late Weichselian-Early Holocene glacial history of the Drangajökull region, northwest Iceland|journal=Quaternary Science Reviews|volume=126|pages=140–157|doi=10.1016/j.quascirev.2015.09.001|bibcode=2015QSRv..126..140B}}</ref>[[File:Glacier Mass Balance Map.png|thumb|278x278px|Modern glacial activity. Antarctica is not pictured.]]

Another area that has experienced deglaciation during the Holocene is Spitsbergen island within the [[Place:Svalbard|Svalbard]] archipelago in Norway.<ref name=":4">{{Cite journal|last=André|first=Marie-Françoise|date=1997-05-01|title=Holocene Rockwall Retreat in Svalbard: A Triple-Rate Evolution|url=http://onlinelibrary.wiley.com/doi/10.1002/(SICI)1096-9837(199705)22:53.0.CO;2-6/abstract|journal=[[Earth:Earth Surface Processes and Landforms|Earth Surface Processes and Landforms]]|language=en|volume=22|issue=5|pages=423–440|doi=10.1002/(SICI)1096-9837(199705)22:5<423::AID-ESP706>3.3.CO;2-Y|issn=1096-9837|bibcode=1997ESPL...22..423A}}</ref> For the last 12,000 years exposed rockwalls have been eroding due to a mixture of biogenic flaking, frost shattering, and stress relaxation that results when glaciers retreat.<ref name=":4" /> One way the rate of rockwall retreat is measured is by examining the diameters of local lichen to establish an age of growth.<ref name=":4" />

=== North America ===
The retreat of the [[Earth:Laurentide Ice Sheet|Laurentide Ice Sheet]] in Canada led to the formation of moraines and up to 26 proglacial lakes scattered throughout central Canada. The deglaciation occurred from the last glacial maximum (21,000 years ago) until about 7000 years ago. Some of the lakes in the southern Ungava Bay area were fully deglaciated c. 6,000 years ago.<ref>{{Cite journal|last=Jansson|first=Krister N|date=2003-05-01|title=Early Holocene glacial lakes and ice marginal retreat pattern in Labrador/Ungava, Canada|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|volume=193|issue=3|pages=473–501|doi=10.1016/s0031-0182(03)00262-1|bibcode=2003PPP...193..473J}}</ref> Meltwater from the glacial prehistoric [[Earth:Lake Agassiz|Lake Agassiz]] contributed to the [[Earth:Neoglaciation|neoglaciation]] during the Holocene, which resulted in an uptick of glacial activity at least as far away as Iceland.<ref name=":0" />

The Nuup Kangerlua and Sermilik regions, in southwestern and southeastern [[Place:Greenland|Greenland]] respectively, are two localities that experienced deglaciation after the Holocene warming period started.<ref name=":2">{{Cite journal|last1=Larsen|first1=Nicolaj K.|last2=Funder|first2=Svend|last3=Kjær|first3=Kurt H.|last4=Kjeldsen|first4=Kristian K.|last5=Knudsen|first5=Mads F.|last6=Linge|first6=Henriette|date=2014-05-15|title=Rapid early Holocene ice retreat in West Greenland|journal=Quaternary Science Reviews|series=APEX II: Arctic Palaeoclimate and its Extremes|volume=92|pages=310–323|doi=10.1016/j.quascirev.2013.05.027}}</ref> Warming atmospheric temperatures as well as warming waters in the [[Earth:Labrador Sea|Labrador Sea]] accelerated the speed of deglaciation which started on the coasts of Greenland before heading inland.<ref name=":2" /> Moraines located in the interior of the Nuup Kangerlua area have been dated to 8.1 to 8.3 thousand years ago; they mark a local cooling that caused glaciers to re-advance and leave moraines behind.<ref name=":2" />

The modern Ohio River was formed when the river was temporarily dammed just southwest of Louisville, Kentucky, creating a large lake until the dam burst. The Ohio River largely supplanted the former Teays River drainage system, which was disrupted by the glaciers.

Ancient [[Earth:Lake Chicago|Lake Chicago]], on the southern margin of the Wisconsin Glacier, found successive lower outlets as the glacier retreated, until the Saint Lawrence River route was uncovered. Corresponding to each level, remnant lake shore features may be found in many areas. One prehistoric shoreline is delineated by Bluff Avenue, a north–south street on the La Grange, Illinois, east side. [[Image:Holocene Sea Level.png|right|thumb|280px|Changes in sea level during the Holocene.]]

Current river delta positioning and sediment composition in northern Michigan were created by a glacial lake. The lake resulted from retreating glaciers.<ref>{{Cite journal|last1=Schaetzl|first1=Randall J.|last2=Lepper|first2=Kenneth|last3=Thomas|first3=Sarah E.|last4=Grove|first4=Leslie|last5=Treiber|first5=Emma|last6=Farmer|first6=Alison|last7=Fillmore|first7=Austin|last8=Lee|first8=Jordan|last9=Dickerson|first9=Bethany|date=2017-03-01|title=Kame deltas provide evidence for a new glacial lake and suggest early glacial retreat from central Lower Michigan, USA|journal=Geomorphology|volume=280|pages=167–178|doi=10.1016/j.geomorph.2016.11.013|bibcode=2017Geomo.280..167S}}</ref>

=== South America ===
The [[Earth:Northern Patagonian Ice Field|Northern Patagonian Icefield]] is one of the locations that experienced a surge in glacial activity during the neoglaciation period. Terminal moraines formed 5.7 thousand years ago in the San Rafael Glacier and around 4.96 thousand years ago they formed in the nearby Colonia glacier.<ref>{{Cite journal|last1=Nimick|first1=David A.|last2=McGrath|first2=Daniel|last3=Mahan|first3=Shannon A.|last4=Friesen|first4=Beverly A.|last5=Leidich|first5=Jonathan|date=2016-08-01|title=Latest Pleistocene and Holocene glacial events in the Colonia valley, Northern Patagonia Icefield, southern Chile|journal=Journal of Quaternary Science|language=en|volume=31|issue=6|pages=551–564|doi=10.1002/jqs.2847|issn=1099-1417|url=https://zenodo.org/record/1229257|bibcode=2016JQS....31..551N|s2cid=132303469 }}</ref> In the [[Earth:Southern Patagonian Ice Field|Southern Patagonian Icefield]] located in Argentina and Chile, some glaciers have actually been advancing to their peak extents as recently as the 19th century as evidenced by moraines.<ref>{{Cite journal|last1=Strelin|first1=Jorge A.|last2=Kaplan|first2=Michael R.|last3=Vandergoes|first3=Marcus J.|last4=Denton|first4=George H.|last5=Schaefer|first5=Joerg M.|date=2014-10-01|title=Holocene glacier history of the Lago Argentino basin, Southern Patagonian Icefield|journal=Quaternary Science Reviews|volume=101|pages=124–145|doi=10.1016/j.quascirev.2014.06.026|bibcode=2014QSRv..101..124S}}</ref> Another remnant of glacial activity in the southern Patagonian icefield is the creation of meltwater channels within the El Canal spillway found near the Lago del Toro in Chile. The different layers of stratification have been used to date different occurrences of glacial lakes in the region.<ref>{{Cite journal|last1=García|first1=Juan-Luis|last2=Strelin|first2=Jorge A.|last3=Vega|first3=Rodrigo M.|last4=Hall|first4=Brenda L.|last5=Stern|first5=Charles R.|date=2015-05-13|title=Deglacial ice-marginal glaciolacustrine environments and structural moraine building in Torres del Paine, Chilean southern Patagonia|url=http://www.andeangeology.cl/index.php/revista1/article/view/V42n2-a03|journal=Andean Geology|language=en|volume=42|issue=2|pages=190–212|doi=10.5027/andgeov42n2-a03|issn=0718-7106|doi-access=free}}</ref>

=== New Zealand ===
Within the last 30 years while most locations have experienced continue glacial retreat, glaciers located in the Southern Alps of New Zealand have advanced in position. Glaciers located near coasts such as those in New Zealand are especially responsive to climate change and serve as an indicator of local climate change. The anticipated warming waters near New Zealand in the Tasman Sea will lead to a reduction in glacial mass balance.<ref>{{Cite journal|last1=Mackintosh|first1=Andrew N.|last2=Anderson|first2=Brian M.|last3=Lorrey|first3=Andrew M.|last4=Renwick|first4=James A.|last5=Frei|first5=Prisco|last6=Dean|first6=Sam M.|date=2017-02-14|title=Regional cooling caused recent New Zealand glacier advances in a period of global warming|journal=Nature Communications|language=en|volume=8|pages=ncomms14202|doi=10.1038/ncomms14202|pmc=5316876|pmid=28195582|bibcode=2017NatCo...814202M}}</ref>[[Image:Holocene Temperature Variations.png|right|thumb|261x261px|Eight records of local temperature variability on multi-centennial scales throughout the course of the Holocene, and an average of these (thick dark line).]]

==See also==
*{{annotated link|Earth:Deglaciation}}
*{{annotated link|Biology:Postglacial vegetation}}
*{{annotated link|Earth:Meltwater pulse 1B}}
*{{annotated link|Earth:Early Holocene sea level rise}}

==References==
{{Reflist|33em}}

==External links==
*[https://web.archive.org/web/20060218161132/http://www.jamestown-ri.info/holocene.htm The Post-Glacial Period Holocene Epoch]

[[Category:Glaciology]]

{{Sourceattribution|Holocene glacial retreat}}