Composite liners left exposed to solar radiation can experience large daily thermal cycles ranging from the daily low air temperature at night to upwards of 70℃ during the day. These variations in temperature can drive cyclic evaporation and hydration processes within air gaps between the geomembrane and the top surface of the geosynthetic clay liner. This paper explores the use of X-ray CT to investigate the onset of cracking and the progressive desiccation of geosynthetic clay liners under two sets of boundary conditions – a highly saturated foundation soil representative of a base liner, and an unsaturated foundation soil representative of a side slope.