The transformation of fixed dunes into shifting dunes and the diverse feedback loop that drives the transformation process has been observed in various dune systems around the world. However, the precise details of how environmental controls influence the dune transformation and stabilisation remain poorly understood. Comprehensive understanding of processes and mechanisms behind newly formed shifting dunes is essential to identify niche targeting measures for desert expansion control. On the basis of measured soil minerals from expanded desert land in northern Shaanxi province, China, desert expansion mechanisms identified were associated with dune sand migration, loess decline, and stabilized dune reactivation. The dune sand migration-associated desertification occurred when a horizon of shifting sand dunes was deposited on top of the loess soil of degraded farmland due to the prevailing windy conditions in this region, and it can be identified by the significant difference in soil minerals (SiO₂, Al₂O₃, Fe₂O₃, CaO, MgO, TiO₂, MnO, K₂O, and P₂O₅) between the sand dune and the loess soil. Loess decline-associated desertification mainly occurred in farmlands in the southern part of the desert area by wind erosion, and it can be identified by the nonsignificant difference in soil minerals between the sand dune and the loess soil. Stabilized dune reactivation-associated desertification occurred due to damage to the soil biological crusts by human activities, and it can be identified by the nonsignificant difference in soil minerals between the sand dune and the stabilized dune. The dominant causes of desert expansion identified were heavy winds and intensive human activities.