The Indian Ocean is dominated by as system of 3 mid-ocean ridges converging at the Rodriguez Triple Junction located near 25 degree 30'S and 70 degree E. Numerous studies carried out on these 3 ridges provided the basic information on spreading rates and spreading directions. In 1984 the R/V Jean Charcot conducted a detailed survey over the Rodriguez Triple Junction and over an axial ridge segment located on each of the 3 associated ridges. The ridge axes are cut by distinct rift valleys; the depth of these rift valleys is a function of spreading rates. The rift valleys are not in isostatic equilibrium, but show clear density and mass deficits (0.4 to 0.8 g.cm super(-3) for spreading rate of 1 cm/a and 0.1 to 0.3 g.cm super(-3) for spreading rates of 3 cm/a). The Rodriguez Triple Junction is unstable. The axis of the Central Indian Ridge is offset from the axis of the Southeast Indian Ridge at a velocity of 0.14 cm/a.