Long term burnout shape of the anode bottom is believed to reflect the quasi-stationary liquid metal interface dome-shaped deformation. The shape profiles and their interplay affect the MHD stability, the velocity fields, set up of new anodes and electrical efficiency of the cell. Spent prebake anode bottom profiles were systematically measured at Rusal 309 kA cell to obtain the overall view of the liquid metal deformation. The magnetic field distribution and velocities of liquid metal flow were measured in order to obtain a more complete characterization of the cell. The results are compared to the modelling results using the specialised MHD-VALDIS software giving the insight to the cell dynamics.