Introduction

Ice fractures under tension in a number of engineering and geophysical situations. Examples include ice breaking by ships (Michel, 1978), the bending of floating ice sheets against offshore structures (Riska and Tuhkuri, 1995), the formation of thermal cracks (Evans and Untersteiner, 1971) and the building of pressure ridges (Hopkins et al., 1999) within the sea ice cover on the Arctic Ocean. Other examples include the fracture of pancake ice within the southern Atlantic Ocean (Dai et al., 2004), the calving of icebergs (Nye, 1957; Nath and Vaughan, 2003) and the crevassing of ice shelves (Rist et al., 1999, 2002; Weiss, 2004). Extra-terrestrial tensile failures include the initiation of polygonal features within the ground ice on Mars (Mellon, 1997; Mangold, 2005) and the formation of long lineaments within the icy crust of Europa (e.g., Greenberg et al., 1998; Greeley et al., 2000). In many cases, fast crack propagation is at play, which is to say that crack growth occurs so rapidly that the dissipation of mechanical energy through creep deformation is not a major consideration. Linear elastic fracture mechanics is then a valid method of analysis. In other cases, such as the formation of crevasses and the slow propagation of cracks within ice shelves, analysis based upon non-linear processes and/or sub-critical crack growth may be more useful (Weiss, 2004). In still other cases, more in the laboratory than in the field, tensile strength is limited by crack nucleation, as will become apparent.