A naturally forming cover on rivers and oceans, ice is one of the most prevalent solids on earth. In nature it serves to insulate water sources from heat and moisture loss to the surrounding environment, while from an engineering perspective, current and wind driven ice masses threaten the integrity and safety of mechanical structures. The physical processes involved during ice-structure interaction events are governed by a multiaxial state of loading, with higher levels of confinement near the center of the contact zone and progressively lower levels of confinement towards the edges. New experiments on laboratory grown freshwater polycrystalline granular ice and columnar S2 ice loaded triaxially at T = −10° C to T = −40°C at applied strain rates [special characters omitted] = 1 × 10⁻⁵ s⁻¹ to [special characters omitted] = 2 × 10⁻¹ s⁻¹ under increasing levels of confinement have established two distinct modes of brittle-like shear faulting. One mode, termed Coulombic (C) or frictional faulting, develops under lower degrees of confinement. C-faulting is characterized by macroscopic faults, comprised of a narrow band of microcracks, oriented &thetas; ≈ 30° from the direction of maximum shortening and by pressure hardening, grain size dependent strength, localized heat production, a low degree of cohesion, an increase in relative volume and the creation of fault gouge. This mode of failure is consistent with the comb-crack mechanism. The second mode of faulting, termed plastic (P) or non-frictional faulting, develops under higher degrees of confinement, corresponding to the level of confinement required to suppress frictional sliding. P-faulting is characterized by macroscopic faults, comprised of a fine band of recrystallized grains, oriented &thetas; ≈ 45° from the direction of maximum shortening and by pressure and grain size independent strength, localized heat production, a high degree of cohesion, very little change in relative volume, and an absence of crack interaction or fault gouge. This mode of failure is consistent with the idea of adiabatic heating leading to localized instability and shear deformation. The microstructural state of the material, including the development of dynamic recrystallization and prior loading history, do not have a significant effect on the character of shear localization or the levels of deformation required to generate P-faulting. Both low-confinement and high-confinement behavior must be considered in modeling ice-structure interaction events.