We have studied the impact of morphological changes of the source material during physical vapor transport growth of silicon carbide (SiC). Digital X-ray imaging (P.J. Wellmann et al., Mat. Res. Sec. Symp. Proc. 572 (1999) 259) was carried out to visualize the ongoing processes inside the SIC source material and numerical modeling was performed in order to study the impact on the crystal growth process. According to numerical modeling there is a large impact of the SiC powder compression and morphology on the global heat transfer and mass transfer inside the growth cell. Two different SiC sources containing microscopic SiC powder and macroscopic SIC pieces, respectively, were investigated. Although the SIC source material undergoes fundamental transitions during growth (i.e. evolution from powder to compressed SiC block) it was found that self-stabilizing of the growth process occurred by formation of a disk-like structure on the top of the source material, independent of the initial source morphology. The experimental results were confirmed by the numerical simulation of the global growth process.