Tributary glaciers that once joined a valley glacier (like streams joining a river) have retreated and, as a result, have become disconnected from the valley glacier.  In this way the glacier is fragmenting into pieces.  The amount of separation from the valley glacier gives a general idea of how much length, width, and thickness they have lost since they were connected.  Once disconnected, tributary glaciers no longer are able to supply ice from higher elevations to the valley glacier below. 

The lower part of the photograph above shows tributary glaciers that have been disconnected from the Gorner Glacier.  The photograph shown in the section on scientific studies of the Findel Glacier shows a tributary glacier above the left side of the valley part of the glacier that disconnected in the early 1990s.