commit 2155b2767f7cc48c73887962b690c097dba5b7a2
parent 215521adeec48458e93e0effcb3f4076ddf3bcfb
Author: Anders Damsgaard <anders@adamsgaard.dk>
Date: Mon, 7 Oct 2019 11:32:09 +0200
Work on intro
Diffstat:
1 file changed, 13 insertions(+), 16 deletions(-)
diff --git a/continuum-granular-manuscript1.tex b/continuum-granular-manuscript1.tex
@@ -50,29 +50,26 @@ We show that past pulses in water pressure can transfer shear away from the ice-
\section{Introduction}%
\label{sec:introduction}
Subglacial sediment deformation is in many settings of primary importance to glacier flow \citep[e.g.][]{Boulton1974, Engelhardt1990, Fischer1994, Truffer2006}.
-The rheology of the sediment is long debated \citep[e.g.][]{Alley1986, Boulton1987, Kamb1991, Iverson1995, Hindmarsh1997, Hooke1997, Fowler2003, Kavanaugh2006, Iverson2010, Hart2011}.
-There are several reasons for the long-standing debate.
-For considerations of till erosion, transport, and deposition, it is necessary to be able to quantify the strain distribution inside the sediment as the glacier flow shears it from above.
+Sediment mechanics influence glacier stability, sediment transport, and bedform genesis, which is why till rheology is long debated \citep[e.g.][]{Alley1986, Boulton1987, Kamb1991, Iverson1995, Hindmarsh1997, Hooke1997, Fowler2003, Kavanaugh2006, Iverson2010, Hart2011}.
+Modeling of till erosion, transport, and deposition requires quantification of strain distribution in the sediment.
+With analytical models or numerical continuum models
-If subglacial sediment movement is modeled analytical and numerical modeling, it requires unique links between stress and strain rate.
-
-Till continuity (Alley and Cuffey).
-Landform development (Hindmarsh, Fowler, Schoof).
-
-
-Early on, till was assumed to be viscous \citep{Boulton1987} which allowed the formulation of analytical solutions to the coupled ice-till problem \citep[e.g.][]{Walder1994, Hindmarsh1999, Fowler2000}.
-Viscous materials loose all strength if deformation rates approach zero, and strength is without an upper bound as rates increase.
-Resultant glacier sliding laws are similar to hard-bed sliding laws without cavitation \citep[e.g.][]{Budd1979}.
+Early on, till was assumed to be viscous \citep{Boulton1987} which allowed the formulation of analytical solutions to the coupled ice-till problem \citep[e.g.][]{Alley1987, Walder1994, Hindmarsh1999, Fowler2000}.
+The viscous rheology implies that the till looses all strength if deformation rates approach zero, and the till strength is without an upper bound as strain rate increases.
+Resultant glacier sliding laws are similar to hard-bed sliding laws without cavitation \citep[e.g.][]{Budd1979}, acting as a negative feedback on perturbations in glacier flow rate.
However, laboratory experiments on tills \citep[e.g.][]{Kamb1991, Iverson1998, Tulaczyk2000, Rathbun2008, Iverson2010, Iverson2015} and field observations \citep[e.g.][]{Iverson1995, Hooke1997, Tulaczyk2006} have concluded that till strength is nearly independent of deformation rate, and behaves according to Mohr-Coulomb plasticity.
-Beneath the Mohr-Coulomb yield strength there can be slight creep with a highly-nonlinear rate dependence \citep[e.g.][]{Kamb1991, Damsgaard2016, Hart2019}.
-The presence of water can add a transient rate dependence due to volumetric adjustmend during early shear \citep[e.g.][]{Iverson1997, Moore2002, Damsgaard2015}, but the rate dependence is generally shortlived.
+
+In some cases, it has been observed that till strength slightly decreases at faster shear rates \citep{Iverson1998, Iverson2015}, which could potentially amplify changes in glacier velocities.
+The presence of water can add a transient rate dependence due to volumetric adjustmend during early shear \citep[e.g.][]{Iverson1997, Moore2002, Damsgaard2015}, but this rate dependence is generally shortlived.
+Furthermore, pre-failure creep can be contributed by adjustment of sediment-internal stresses, giving a highly-nonlinear rate dependence \citep[e.g.][]{Kamb1991, Damsgaard2016, Hart2019}.
Besides smaller scale laboratory and field investigations, the basal sliding problem is investigated by inverting observations of glacier-surface flow velocities to subglacial sliding physics.
-At Whillans Ice Plain the velocities vary three orders of magnitude during a tidal cycle, and are contributed by basal deformation \citep[e.g.][]{Bindschadler2003, Tulaczyk2006}.
-The inferred nonlinearity manifests itself in stress exponent values from 2 to over 10 \citep[e.g.][]{Tulaczyk2006, Gudmundsson2006, King2011, Gudmundsson2011, Walker2012, Rosier2014, Goldberg2014, Thompson2014, Rosier2015, Gillet-Chaulet2016, Minchew2016}.
+Ice streams primarily move by sliding and subglacial sediment deformation, and velocities can vary by three orders of magnitude during a tidal cycle \citep[e.g.][]{Bindschadler2003, Tulaczyk2006}.
+The nonlinearity manifests itself in stress exponent values from 2 to over 10 \citep[e.g.][]{Tulaczyk2006, Gudmundsson2006, King2011, Gudmundsson2011, Walker2012, Rosier2014, Goldberg2014, Thompson2014, Rosier2015, Gillet-Chaulet2016, Minchew2016}.
The degree of non-linearity may pose drastically different contributions to global mean sea-level rise in future scenarios \citep[e.g.][]{Parizek2013, Ritz2015}.
+% Till continuity (Alley and Cuffey).
% Damsgaard2013
