The small footprint (~70 m) and ~172 m along-track spacing of the Geoscience Laser Altimeter System (GLAS) on the Ice, Cloud and land Elevation Satellite (ICESat) provides unprecedented horizontal resolution for a satellite altimeter. This enables ICESat to map many previously unresolved features on ice shelves, such as crevasses, rifts, grounding zones and ice fronts. We present examples of ICESat-derived elevation data showing topography over rifts on the Amery and Ross ice shelves, widths of rifts and as estimates of the thickness of m¿lange (a collection of ice and snow trapped inside the rifts). We show that m¿lange thickness remains constant over the ICESat data period and tends to be thicker in older rifts. We validate the ICESat-derived m¿lange depth estimate with an in situ measurement on the Ross Ice Shelf.