Formation mechanisms for ice-stream shear margin moraines
Hindmarsh, R.C.A.; Stokes, C.R.
The lateral shear margins of palaeo-ice stream beds are occasionally marked by large curvilinear moraines, but little work has addressed how they might form. In this paper we review the characteristics of ‘lateral shear margin moraines’ and present two quantitative models for their formation: (i) differential erosion rates related to lateral variations in the stream velocity and (ii) lateral incursion from inter-stream ridges after the thinner stream retreats, where the shear margin moraine is consequently just a terminal moraine of the inter-stream ridge. Other possible mechanisms of formation are addressed qualitatively. Both of our quantitative theories are, in principle, feasible, but the incursion model is less plausible and inconsistent with observations. The differential erosion model can predict moraines tens of metres thick and several kilometres wide, which can be formed in a thousand years. The width of the moraine depends on the competition between a term that varies across the ice stream because it is dependent on ice velocity and that always causes erosion, and a term related to the local accumulation rate, which causes erosion if is positive and deposition if negative. These terms combine to create the possibility of deposition at the shear margins of ice streams in ablation areas. The width of the moraine has a tendency to increase with the width of the stream. The conditions that permit shear margin moraines to form are quite constrained: too much ablation and deposition occurs everywhere rather than just near the lateral margins of the ice streams; too little ablation and there is erosion everywhere. This is consistent with the infrequent observations of lateral shear margin moraines.
Hindmarsh, R., & Stokes, C. (2008). Formation mechanisms for ice-stream shear margin moraines. Earth Surface Processes and Landforms, 33(4), 610-626. https://doi.org/10.1002/esp.1665
|Journal Article Type||Article|
|Publication Date||Apr 15, 2008|
|Deposit Date||May 2, 2014|
|Publicly Available Date||May 2, 2014|
|Journal||Earth Surface Processes and Landforms|
|Publisher||British Society for Geomorphology|
|Peer Reviewed||Peer Reviewed|
|Keywords||Ice stream, Geomorphology, Deglaciation, Lateral shear moraine, Till.|
Accepted Journal Article
This is the peer reviewed version of the following article: Hindmarsh, R.C.A. and Stokes, C.R. (2008), Formation mechanisms for ice-stream lateral shear margin moraines. Earth Surf. Process. Landforms, 33(4): 610–626, which has been published in final form at http://dx.doi.org/10.1002/esp.1665. This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving.