Fracture of Antarctic shelf ice

Abstract

[1] We have investigated the fracture of Antarctic shelf ice core using two fracture mechanics test methods: the chevron-notched short-rod specimen loaded in tension and the chevron-notched round-bar specimen loaded in three-point bending. These tests have been used to measure the fracture initiation toughness, K init , at which crack growth starts, on samples taken through the entire thickness of the Ronne Ice Shelf, from low-density firn through consolidated meteoric ice to basal marine ice. The fracture data are presented together with depth profiles of relevant physical and mechanical properties derived from the test specimens: temperature, density, elastic modulus, and grain size. It is found that the trend in measured fracture toughness closely reflects changes in ice density and elastic modulus. We augment the experimental study by presenting a fracture mechanics analysis of ice shelf surface and basal crevassing which directly incorporates our measurements. For the examined ice shelf profiles, basal crevasses are found to be inherently unstable unless an external restraining force is imposed, which has important implications for overall ice shelf stability. On the other hand, surface crevassing is shown to be innately stable at depth. Our fracture mechanics model is used to predict local ice shelf back stresses in the vicinity of basal crevassing and is validated directly against field observations of crevasse penetration on the Ronne Ice Shelf.

Upper and lower limits on the stability of calving glaciers from the yield strength envelope of ice

“…Previous attempts to model the failure of glacier ice have focused on tensile fractures (crevasses), assuming that an iceberg will detach when either a surface crevasse or a bottom crevasse penetrates the entire ice thickness or some critical fraction thereof (Weertman 1980;Rist et al 2002;Benn et al 2007;Nick et al 2010). The depth to which crevasses penetrate can be estimated using the Nye zero-stress model in which surface (d s ) and bottom (d b ) crevasses penetrate to the depth where the net horizontal stress vanishes (Nye 1957;Jezek 1984;Nick et al 2010),…”

Evaluation of the criticality of cracks in ice shelves using finite element simulations

“…Valid BCs and a satisfying numerical model are identified in Sects. 2.4 and 2.5 followed by the validation using the well known model of Rist et al (2002) …”

“…Rist et al (2002) performed three-pointbending and short-rod fracture tests on samples taken from a core of the Ronne Ice Shelf that contained meteoric as well as marine ice. The measured K Ic show a strong dependence on density or porosity, respectively.…”

“…He simplified the crack geometry and boundary conditions (BCs) to facilitate the use of tabulated values gained from semianalytical methods by Tada et al (1973) and Sih (1973). The method of Smith (1976) was adapted and extended by Van der Veen (1997), who discussed the importance of depth dependent density profiles and Rist et al (2002) who additionally analysed depth dependent tensile stresses. The model by Rist et al (2002) has been repeatedly used for the analysis of bottom and surface crevasses, e.g.…”

“…The method of Smith (1976) was adapted and extended by Van der Veen (1997), who discussed the importance of depth dependent density profiles and Rist et al (2002) who additionally analysed depth dependent tensile stresses. The model by Rist et al (2002) has been repeatedly used for the analysis of bottom and surface crevasses, e.g. by Nath and Vaughan (2003) and Luckman et al (2011), and will be used here as a benchmark for our finite element simulations.…”