Experiments have established that cracks form within compressed ice du
ring rapid unloading, provided that the initial compressive loading is
sufficient to generate cracks. Cracks do not form when the ice is unl
oaded slowly. The unloading cracks are transverse to those formed whil
e loading and appear as transgranular spurs to the loading cracks. The
y are attributed to the development of tensile stresses during the unl
oading.