TY - JOUR
T1 - Glaciotectonic disintegration of roches moutonnées during glacial ripping in east Sweden
AU - Krabbendam, M.
AU - Hall, A. M.
AU - Palamakumbura, R. M.
AU - Finlayson, A.
N1 - Funding Information:
This work was supported by the Svensk Kärnbränslehantering AB, as part of a SKB-funded project on glacial ripping. Sam Roberson is thanked for comments on an earlier version of the manuscript. The authors thank three anonymous reviewers for constructive reviews. Use of SGU mapping data, and elevation data and aerial photographs aerial photos from Lantmäteriet is gratefully acknowledged. MK, AF and RNP publish with the permission of the Executive Director of BGS.
Publisher Copyright:
© 2022 Crown Copyright. Reproduced with the permission of the Controller of Queen's Printer for Scotland and British Geological Survey. Published by Informa UK Limited, trading as Taylor & Francis Group.
PY - 2022/1/27
Y1 - 2022/1/27
N2 - Roches moutonnées are typical landforms of glacial erosion developed in hard rocks, with an asymmetric profile caused by abrasion and lee-side plucking. In eastern Sweden, some roches moutonnées show extensive damage, including open fractures, disintegration into blocks, fracture caves and short boulder trains. Disintegration increases along ice-flow directions during deglaciation of the last Weichselian Fennoscandian Ice Sheet, indicating a subglacial origin: limited edge rounding can be explained by a combination of hard rock, slow abrasion rates and disintegration just prior to deglaciation. The roches moutonnées initially developed in kernels of gneissic rocks with a wide fracture spacing (large block size) and interlocking fracture pattern, and hence high overall rock mass strength. Dilated fractures and ‘fracture caves’ occur up to 15 m below the ice-bed interface. It is proposed that hydraulic jacking by overpressured water opened up the rock mass along pre-existing fractures. Jacking reduced rock mass strength, allowing glaciotectonic deformation of the roches moutonnées. Uneven hydraulic jacking led to uplift of individual fracture-bound blocks above the pre-existing smooth, abraded surface of the roches moutonnées, creating blunt, step-like edges. These edges allowed high ice pushing forces to act on large blocks: where blocks extend into the deeper rock mass, they further aided the disintegration of the rock mass. The disintegrated roches moutonnées can be regarded as transient features between intact bedrock and complete disintegration into boulders. The jacking-disintegration-transport sequence is characteristic of glacial ripping and very different from classic lee-side plucking.
AB - Roches moutonnées are typical landforms of glacial erosion developed in hard rocks, with an asymmetric profile caused by abrasion and lee-side plucking. In eastern Sweden, some roches moutonnées show extensive damage, including open fractures, disintegration into blocks, fracture caves and short boulder trains. Disintegration increases along ice-flow directions during deglaciation of the last Weichselian Fennoscandian Ice Sheet, indicating a subglacial origin: limited edge rounding can be explained by a combination of hard rock, slow abrasion rates and disintegration just prior to deglaciation. The roches moutonnées initially developed in kernels of gneissic rocks with a wide fracture spacing (large block size) and interlocking fracture pattern, and hence high overall rock mass strength. Dilated fractures and ‘fracture caves’ occur up to 15 m below the ice-bed interface. It is proposed that hydraulic jacking by overpressured water opened up the rock mass along pre-existing fractures. Jacking reduced rock mass strength, allowing glaciotectonic deformation of the roches moutonnées. Uneven hydraulic jacking led to uplift of individual fracture-bound blocks above the pre-existing smooth, abraded surface of the roches moutonnées, creating blunt, step-like edges. These edges allowed high ice pushing forces to act on large blocks: where blocks extend into the deeper rock mass, they further aided the disintegration of the rock mass. The disintegrated roches moutonnées can be regarded as transient features between intact bedrock and complete disintegration into boulders. The jacking-disintegration-transport sequence is characteristic of glacial ripping and very different from classic lee-side plucking.
KW - Fennoscandian Ice Sheet
KW - glacial erosion
KW - glaciotectonicsm
KW - hydraulic jacking
U2 - 10.1080/04353676.2021.2022356
DO - 10.1080/04353676.2021.2022356
M3 - Article
AN - SCOPUS:85124078577
VL - 104
SP - 35
EP - 56
JO - Geografiska Annaler: Series A, Physical Geography
JF - Geografiska Annaler: Series A, Physical Geography
SN - 0435-3676
IS - 1
ER -