Bourdon et al. reply.

Replying to: D. L. Anderson & J. H. Natland 450, doi: 10.1038/nature06376 (2007)Anderson and Natland’scomment does not question our results regarding the velocity structure of mantle upwellings based on uranium-series. We stated clearly that our results do not provide direct measurements of the depth from which hotspot volcanism starts; we have not made unjustified claims by saying we have identified deep mantle plumes. However, our results do shed light on the still incompletely understood causes of hotspot volcanism. [ABSTRACT FROM AUTHOR]