Please use this identifier to cite or link to this item: http://hdl.handle.net/1893/25503
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dc.contributor.authorKrabbendam, Maartenen_UK
dc.contributor.authorBradwell, Tomen_UK
dc.contributor.authorEverest, Jeremy Den_UK
dc.contributor.authorEyles, Nicken_UK
dc.date.accessioned2017-08-08T02:11:31Z-
dc.date.available2017-08-08T02:11:31Z-
dc.date.issued2017-08-01en_UK
dc.identifier.urihttp://hdl.handle.net/1893/25503-
dc.description.abstractGlaciers and ice sheets are important agents of bedrock erosion, yet the precise processes of bedrock failure beneath glacier ice are incompletely known. Subglacially formed erosional crescentic markings (crescentic gouges, lunate fractures) on bedrock surfaces occur locally in glaciated areas and comprise a conchoidal fracture dipping down-ice and a steep fracture that faces up-ice. Here we report morphologically distinct crescentic scars that are closely associated with preexisting joints, termed here joint-bounded crescentic scars. These hitherto unreported features are ca. 50–200mm deep and involve considerably more rock removal than previously described crescentic markings. The joint-bounded crescentic scars were found on abraded rhyolite surfaces recently exposed (<20years) beneath a retreating glacier in Iceland, as well as on glacially sculpted Precambrian gneisses in NW Scotland and various Precambrian rocks in Ontario, glaciated during the Late Pleistocene. We suggest a common formation mechanism for these contemporary and relict features, whereby a boulder embedded in basal ice produces a continuously migrating clast-bed contact force as it is dragged over the hard (bedrock) bed. As the ice-embedded boulder approaches a preexisting joint in the bedrock, stress concentrations build up in the bed that exceed the intact rock strength, resulting in conchoidal fracturing and detachment of a crescentic wedge-shaped rock fragment. Subsequent removal of the rock fragment probably involves further fracturing or crushing (comminution) under high contact forces. Formation of joint-bounded crescentic scars is favoured by large boulders at the base of the ice, high basal melting rates, and the presence of preexisting subvertical joints in the bedrock bed. We infer that the relative scarcity of crescentic markings in general on deglaciated surfaces shows that fracturing of intact bedrock below ice is difficult, but that preexisting weaknesses such as joints greatly facilitate rock failure. This implies that models of glacial erosion need to take fracture patterns of bedrock into account.en_UK
dc.language.isoenen_UK
dc.publisherElsevieren_UK
dc.relationKrabbendam M, Bradwell T, Everest JD & Eyles N (2017) Joint-bounded crescentic scars formed by subglacial clast-bed contact forces: Implications for bedrock failure beneath glaciers. <i>Geomorphology</i>, 290, pp. 114-127. https://doi.org/10.1016/j.geomorph.2017.03.021en_UK
dc.rightsThis item has been embargoed for a period. During the embargo please use the Request a Copy feature at the foot of the Repository record to request a copy directly from the author. You can only request a copy if you wish to use this work for your own research or private study. Accepted refereed manuscript of: Krabbendam M, Bradwell T, Everest JD & Eyles N (2017) Joint-bounded crescentic scars formed by subglacial clast-bed contact forces: Implications for bedrock failure beneath glaciers, Geomorphology, 290, pp. 114-127. DOI: 10.1016/j.geomorph.2017.03.021 © 2017, Elsevier. Licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International http://creativecommons.org/licenses/by-nc-nd/4.0/en_UK
dc.rights.urihttp://creativecommons.org/licenses/by-nc-nd/4.0/en_UK
dc.subjectConchoidal fractureen_UK
dc.subjectSubglacial erosionen_UK
dc.subjectJointen_UK
dc.subjectRock strengthen_UK
dc.titleJoint-bounded crescentic scars formed by subglacial clast-bed contact forces: Implications for bedrock failure beneath glaciersen_UK
dc.typeJournal Articleen_UK
dc.rights.embargodate2018-04-05en_UK
dc.rights.embargoreason[Crescentic_Scars_FINAL_AAM_withFigs_tables.pdf] Publisher requires embargo of 12 months after online publication.en_UK
dc.identifier.doi10.1016/j.geomorph.2017.03.021en_UK
dc.citation.jtitleGeomorphologyen_UK
dc.citation.issn0169-555Xen_UK
dc.citation.volume290en_UK
dc.citation.spage114en_UK
dc.citation.epage127en_UK
dc.citation.publicationstatusPublisheden_UK
dc.citation.peerreviewedRefereeden_UK
dc.type.statusAM - Accepted Manuscripten_UK
dc.author.emailtom.bradwell@stir.ac.uken_UK
dc.citation.date04/04/2017en_UK
dc.contributor.affiliationBritish Geological Surveyen_UK
dc.contributor.affiliationBiological and Environmental Sciencesen_UK
dc.contributor.affiliationBritish Geological Surveyen_UK
dc.contributor.affiliationUniversity of Torontoen_UK
dc.identifier.isiWOS:000405056100009en_UK
dc.identifier.scopusid2-s2.0-85017577546en_UK
dc.identifier.wtid529849en_UK
dc.contributor.orcid0000-0003-0947-3309en_UK
dc.date.accepted2017-03-22en_UK
dcterms.dateAccepted2017-03-22en_UK
dc.date.filedepositdate2017-06-15en_UK
rioxxterms.apcnot requireden_UK
rioxxterms.typeJournal Article/Reviewen_UK
rioxxterms.versionAMen_UK
local.rioxx.authorKrabbendam, Maarten|en_UK
local.rioxx.authorBradwell, Tom|0000-0003-0947-3309en_UK
local.rioxx.authorEverest, Jeremy D|en_UK
local.rioxx.authorEyles, Nick|en_UK
local.rioxx.projectInternal Project|University of Stirling|https://isni.org/isni/0000000122484331en_UK
local.rioxx.freetoreaddate2018-04-05en_UK
local.rioxx.licencehttp://www.rioxx.net/licenses/under-embargo-all-rights-reserved||2018-04-04en_UK
local.rioxx.licencehttp://creativecommons.org/licenses/by-nc-nd/4.0/|2018-04-05|en_UK
local.rioxx.filenameCrescentic_Scars_FINAL_AAM_withFigs_tables.pdfen_UK
local.rioxx.filecount1en_UK
local.rioxx.source0169-555Xen_UK
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