Over mulching your trees is a great way to give them an early death. Piling the mulch up too high can lead to surface roots that can ultimately end up strangling and killing your tree - who wants that? So save a little money and buy a little less mulch this year. Make sure not to pile it up against the trunk of your trees. See the images and link below for information on proper mulching technique.
If you have been volcano mulching for years you may want to consider having Good Nature look at the health of your root system by performing a Root Collar Excavation. See the video and pictures below for more information.
The pictures below show Harmful Stem Girdling Roots and Decay due to improper mulching and planting techniques.
Links below on girdling roots and proper tree planting: