Recent research has discovered that the inner gorges and valleys cut into the Swiss Alps were most likely created by huge glaciers and rivers. Until now this had been a highly speculative area, and nobody was really certain what had caused them. But now it seems that as the glaciers moved down the mountains, they followed the paths of old rivers, which had been frozen over. Then, during periods of warming, the rivers would return and wash out the debris and further erode the gorges. Eventually the glaciers would return and start the process all over again.