Continental rifting is a key facet of plate tectonics that can evolve into ocean basins. The dynamics of continental break-up has been studied for decades, yet questions remain about the origin of rifts. In this work we investigate the onset of continental two regions: the Natron Rift in Tanzania and the broadly deforming island of Madagascar. We first quantify surface motions with high precision Global Navigation Satellite System / Global Positioning System (GNSS/GPS) data. We find slip along the Natron Rift coincident with volcanic activity at a nearby volcano that appears to be localized along the major border fault. In Madagascar surface observations indicate differential extensional and transform movements between northern and southern Madagascar. We then employ analytical and numerical models to assess the relative roles of long-term tectonic forces and short-term magmatic processes on our examples of narrow and broad continental rifting. Our work suggests that in regions of broad deformation coupling to upwelling and diverging asthenospheric flow is consistent with surface observations, and in narrow continental rifts volcanism is key in promoting rifting processes.