Retreat surfaces (often called glacial forefields) are areas once covered by the glacier and that were exposed as the glacier melted and retreated.  Many of Zermatt's glaciers show these retreat surfaces and what the melting glacier has left behind.  They often expose rock with polished surfaces, grooves, and striations that were carved by rocks carried by the moving glacial ice.  Also exposed are rock fragments of various sizes like sand or even boulders that were carried by the glacier.  These surfaces show the dimensions of the area of ice that has been melted. 

 

The first photograph above shows a retreat surface below the Upper Theodul Glacier.  It consists of polished rock, sediments, and a meltwater lake.  The photograph below shows glacial grooves and striations on a polished rock outcrop near the terminus of the upper part of the Gorner Glacier.  These features show the direction that the glacier moved.