We present a new criteria to detect thermal plumes from the velocity field in a horizontal plane that pass from the local boundary layer to the plume close to the hot plate in turbulent Rayleigh Benard convection. Based on the characteristics of deformation of fluid elements, we propose that the negative dominant eigenvalues of the 2D strain rate picks up the thermal plume regions. We also show that the areas identified by this criteria match the areas identified by the horizontal divergence criteria ¯H.¯u < 0 proposed by Vipin and Puthenveettil [4]