A team was able to prove that the glaciers of the penultimate ice age ('Riss' glaciation) mainly eroded the bedrock between Thun and Bern, but that during the last glaciation (' Würm'- glaciation) glacial carving resulted in a widening and not in a further deepening of the valleys. The researchers reconstructed the geometry of the bedrock using gravity measurements to reach their conclusions.

Source: The last ice age widened the Aare and Gürbe valleys