International audienceAims. In this paper we focus on the possible observational signatures of the processes which have been put forward for explaining eruptive prominences. We also try to understand the variations in the physical conditions of eruptive prominences and estimate the masses leaving the Sun versus the masses returning to the Sun during eruptive prominences. Methods. As far as velocities are concerned, we combined an optical flow method on the Atmospheric Imaging Assembly (AIA) 304 Å and Interface Region Imaging Spectrograph (IRIS). Mg ii h&k observations in order to derive the plane-of-sky velocities in the prominence, and a Doppler technique on the IRIS Mg ii h&k profiles to compute the line-of-sight velocities. As far as densities are concerned, we compared the absolute observed intensities with values derived from non-local thermodynamic equilibrium radiative transfer computations to derive the total (hydrogen) density and consequently compute the mass flows. Results. The derived electron densities range from 1.3 × 10 9 to 6.0 × 10 10 cm −3 and the derived total hydrogen densities range from 1.5 × 10 9 to 2.4 × 10 11 cm −3 in different regions of the prominence. The mean temperature is around 1.1 × 10 4 K, which is higher than in quiescent prominences. The ionization degree is in the range of 0.1-10. The total (hydrogen) mass is in the range of 1.3 × 10 14-3.2 × 10 14 g. The total mass drainage from the prominence to the solar surface during the whole observation time of IRIS is about one order of magnitude smaller than the total mass of the prominence
