Active eruptions from the south polar region of Saturn’s small (~500 km diameter) moon Enceladus are concentrated along a series of lineaments known as the ‘tiger stripes’, thought to be partially open fissures that connect to the liquid water ocean beneath the ice shell. We propose a model for the formation of the tiger stripes that explains why the tiger stripes are located only at the south pole, why there are multiple, parallel, regularly-spaced fissures, why the fissures are spaced ~35 km apart, and how the eruptions can persist over time. Secular cooling and the resulting ice shell thickening generate global tensile stresses that cause the first fracture to form at one of the poles, where the ice shell is thinnest due to tidal heating. We present new models for the evolution of stresses in a cooling ice shell and for the formation of the first cracks. After the first crack forms, the tensile stresses are partially relieved, preventing a similar failure at the opposite pole. We propose that subsequent activity then concentrates in the vicinity of the first fracture as the erupted water ice loads the flanks of the open fissure, causing bending in the surrounding elastic plate and further tensile failure in bands parallel to the first fracture, leading to a cascading sequence of parallel fissures until the conditions no longer permit through-going fractures. Open conduits can be maintained over long timescales by turbulent dissipation within the fissures.