Radio-echo sounding (RES) of polar ice sheets reveals extensive internal layering. The degree of continuity of internal layering holds critical information about the ice-flow field, but previous analyses of this parameter have been limited to qualitative classifications. Here we present a new quantitative method for analyzing internal layer continuity—named the continuity-index. When applied to data from Pine Island Glacier, West Antarctica, the new method clearly identifies a continuum of discontinuity of internal layers that corresponds with the current ice-velocity field. The analysis provides further support that the main trunk and tributaries are unlikely to have undergone substantial migration since the deposition of the internal layering. Significantly, our new method for analyzing internal layers is readily transferable across RES datasets, offering promise for data-led assessments of past and present flow dynamics across large areas of Antarctica and Greenland.