The knowledge of the composition and dynamics of eruption columns is very important because tephra dispersal strongly depends on it. Few measurements on the vertical distribution of volcanic particles within the eruption column are available. In this work, we analyze data from the X-band radar that were located 75 km far from the crater of Grímsvötn (Iceland) during the eruption in 2011 and propose a first attempt to characterize how the mass eruption rate and the particle size are distributed within the eruption column. We find that both quantities are not uniformly distributed along it. In particular, a greater percentage of particle size and mass eruption rate is confined in the convective region with respect to the umbrella region. We think that this work can make new advancements in the characterization and dispersal of explosive eruptions.