Desiccation cracks affect all mechanical and conduction properties. Previous studies have investigated the formation of surface desiccation cracks in fine-grained sediments in relation to their compressibility and suction potential. This study explores the formation of internal desiccation cracks in saturated kaolinite specimens consolidated inside self-reactive oedometer cells to reproduce the initial effective stress in buried sediments. X-ray tomography is used to monitor internal processes during consolidation and drying. Images capture the evolution of a perimetric fracture, transverse contraction, volumetric changes in entrained gas bubbles and the development of internal desiccation cracks. Entrained gas bubbles act as nucleation sites. They shrink during loading and early stages of desiccation. Eventually, the gas-water interface penetrates the soil at the bubble surface, pushes particles away, enlarges local pores and facilitates further growth of the internal desiccation crack. While air entry is grain-displacive in soft, fine-grained sediments, it becomes pore-invasive in stiff, coarse-grained sediments and internal desiccation cracks are not expected in silts or sands.