Abstract Ground-penetrating radar (GPR) is used to image the sub-surface architecture of the 1993 pumice flow deposits at Lascar volcano, northeastern Chile. This non-invasive geophysical technique allowed the determination of the three-dimensional, stratigraphic and facies variations of a deposit that is morphologically pristine but problematic to view internally. The geometry, sedimentological characteristics and compositional nature of the deposit make it ideal for investigation by GPR, which has been successfully used to map deposit-scale variations as well as detailed outcrop-scale features. This work both compliments and extends the interpretation of flow emplacement dynamics postulated for these flows by previous studies. Deposit shape, erosional and non-erosional contacts, buried units and stacked lobes are all informative deposit characteristics that can be readily ascertained from sub-surface imaging. Without such techniques, we are commonly unable to visualize these important features. In a broader context, we present this work in an attempt to demonstrate the suitability of GPR as a tool for studying the emplacement dynamics of pyroclastic currents and to encourage the diversification of applied field techniques in volcanology.