At the confluence of Gorner- and Grenzgletscher (Valais, Switzerland) a supraglaciallake forms every spring. The annual sudden drainage of this glacier-dammed lake isimportant with respect to flood events that occurred in the past. To understand the relatedprocesses, an extensive survey on ice-dynamical and hydrological properties ofthe Gornergletscher has been carried out over the last two years. To model dischargeand therefore predict melt and drainage, ice thickness and bedrock topography are importantparameters. Ice-penetrating radar at low-frequencies in the range of 1 to 5 MHzhas been used to measure the ice-thickness distribution. In addition, selected profileshave been measured with a high-frequency radar at 40 MHz. Comparison of migratedprofiles measured at both frequencies gives insights into the accuracy of the spatiallymore extensive, but naturally less accurate low-frequency data. The comparison showsgood agreement in general but the high-frequency data could only detect the bedrockin profile sections without overlying moraine debris. A terrace in the bedrock topography,probably related to two different ice flows in Grenzgletscher, has been resolvedby the low-frequency data. Further comparison with ice thicknesses from boreholedrillingmeasurements was applied to examine the accuracy of radar-mapping results.Relative deviations are on the order of 10 percent. The high-frequency radar data hasmade visible interesting internal structures of the glacier tongue: Differences in thebackscatter made it possible to identify a core of cold ice, advected from the accumulationregion of Grenzgletscher into the tongue of Gornergletscher. The core reachesa maximum thickness of 180 m and extends laterally about 300-400 m. The coldtemperatetransition surface can be found in a maximum depth of about 300 m.