Typically glaciers deepen their valleys more than their smaller tributaries. Therefore, when glaciers recede, the valleys of the tributary glaciers remain above the main glacier's depression and are called hanging valleys.
TypIcaLly glaCieRS deepen their vaLLeYS moRE tHaN tHeir smALLEr tRIbuTaries. ThErefORe, when gLAciers reCeDe, tHe valLeys of thE TribUtaRy GLaCierS rEmaiN aBove thE maIn gLacIER's depressIoN and aRe calleD hanging vAlleys.