Deformation of debris-ice mixtures

Abstract

Mixtures of rock debris and ice are common in high-latitude and high-altitude environments and are thought to be widespread elsewhere in our solar system. In the form of permafrost soils, glaciers, and rock glaciers, these debris-ice mixtures are often not static but slide and creep, generating many of the landforms and landscapes associated with the cryosphere. In this review, a broad range of field observations, theory, and experimental work relevant to the mechanical interactions between ice and rock debris are evaluated, with emphasis on the temperature and stress regimes common in terrestrial surface and near-surface environments. The first-order variables governing the deformation of debris-ice mixtures in these environments are debris concentration, particle size, temperature, solute concentration (salinity), and stress. A key observation from prior studies, consistent with expectations, is that debris-ice mixtures are usually more resistant to deformation at low temperatures than their pure end-member components. However, at temperatures closer to melting, the growth of unfrozen water films at ice-particle interfaces begins to reduce the strengthening effect and can even lead to profound weakening. Using existing quantitative relationships from theoretical and experimental work in permafrost engineering, ice mechanics, and glaciology combined with theory adapted from metallurgy and materials science, a simple constitutive framework is assembled that is capable of capturing most of the observed dynamics. This framework highlights the competition between the role of debris in impeding ice creep and the mitigating effects of unfrozen water at debris-ice interfaces.

Thermal Conductivity and the Unfrozen Water Contents of Volcanic Ash Deposits in Cold Climate Conditions: A Review

“…Similar films of unfrozen water may play an important role in surface weathering of Martian rocks (Anderson et al, 1967). The presence of unfrozen water films is an important factor in weakening rock/ice mixtures for a subtle climate sensitivity (Moore, 2014).…”

“…Unfrozen water exists naturally in silts and clays, but is absent in sands and granular soils (Ershov et al, 1978;Andersland and Ladanyi, 2004;Yershov and Williams, 2004). In glacier interlayers, the unfrozen water between ice and mineral particles can act as a lubricant to modify the stress transfer between ice-particle and particleparticle contacts by relaxing the interactions between the particles and the ice (Moore, 2014). In permafrost areas, unfrozen water controls ice segregation processes at freezing temperatures, which are responsible for frost heaving in soils and rock disintegration mechanisms (Ershov et al, 1978;Andersland and Ladanyi, 2004;Yershov and Williams, 2004;French, 2013).…”

The Impact of Rheology on the Transition From Stick‐Slip to Creep in a Semibrittle Analog

“…The overall idea is that an abundant viscous fluid phase would lead to a creep signal, whereas an abundant brittle phase would lead to a stick‐slip signal. The impact of a semibrittle rheology on the transition between creep and stick‐slip has been investigated in a number of physical experiments (Burton et al, ; Moore, ; Reber et al, ) as well as theoretical (Lavier et al, ) and numerical (Jammes et al, ; Webber et al, ) studies.…”

Modelling debris transport within glaciers by advection in a full-Stokes ice flow model

“…The simulations highlight that for spatially restricted debris deposition events, distinct debris bands form within the glacier that will lead to initially delimited areas of debris cover on the surface. Hence, an assumption of a uniform englacial debris distribution of constant englacial debris concentration (Naito et al, 2000) that would result in a continuously debriscovered glacier surface where surface ablation is occurring might not reflect reality adequately in order to capture the geometrical response of the glacier to the developing debris cover. The model presented here allows us to simulate the advection of debris concentration through a glacier in great detail.…”

“…Although dynamics of debris-ice mixtures can differ from clean-ice dynamics depending on several parameters such as concentration of debris, particle size and temperature (Moore, 2014), in this work we assume that sediment inclusions within the glacier do not affect ice rheology due to the small total amount of transported material in comparison to overall ice volume. The model is coded in python and relies on the FEniCS framework, an open-source software for automated solution of partial differential equations (PDEs) (Alnaes et al, 2015;Logg et al, 2012a).…”