Fig. 9. Illustration of how mantle diameter and thickness change during a jet. The lower schematic slightly exaggerates the increase in mantle wall thickness that occurs as the mantle contracts. t_i, initial (i.e. resting) mantle wall thickness; t_f, final wall thickness (i.e. at the end of contraction during the exhalant phase of the jet); r_i, initial radius of the outer edge of the mantle; r_f, the final radius of the outer edge of the mantle.