Lava domes form when highly viscous magma erupts on the surface. Several types of lava dome morphology can be distinguished depending on the flow rate and the rheology of magma: obelisks, lava extrusions and endogenic structures. The viscosity of magma is nonlinear depending on the volume fraction of crystals and temperature. Here we present an approach to magma viscosity estimation based on a comparison of observed and simulated morphological forms of lava domes. We consider a two-dimensional axisymmetric model of magma extrusion on the surface and lava dome evolution, and assume that the lava viscosity depends only on the volume fraction of crystals. The crystallization is associated with a growth of the liquidus temperature due to the volatile loss from the magma, and it is determined by the characteristic time of crystal content growth (CCGT) and the discharge rate. Lava domes are modeled using a finite-volume method implemented in Ansys Fluent software for various CCGTs, and volcanic vent sizes. For the selected period of time a set of morphological forms of domes (forms of interface between lava dome and air) is developed. The lava dome forms modeled in this way are compared with the “observed” form of lava dome obtained by random modification of one of the calculated forms. To estimate magma viscosity, the deviation between the observed dome shape and the simulated dome shapes is assessed by three functionals: the symmetric difference, the peak signal-to-noise ratio, and the structural similarity index measure. These functionals are often used in the computer vision and in image processing. Although each functional allows for determining the best fit between the mo-deled and observed shapes of lava dome, the functional based on the structural similarity index measure performs it better. This approach can be extended to three-dimensional case studies to restore the conditions of natural lava dome growth.