A natural eruption on the desert surface of Arrakis that exposes a pre-spice mass to the air and sunlight, triggering its transformation into melange. A spice blow was preceded by a characteristic hissing sound and the release of cinnamon-scented gases. Spice harvesting operations on Arrakis centred on detecting and reaching these blows before the inevitable arrival of sandworms, which were attracted to the vibrations of harvesting equipment. The danger of sandworm attack made spice harvesting one of the most perilous occupations in the Imperium.