Mulch volcanoes are a terrible practice.

Drive down nearly any suburban street, and we’ll see mulch mayhem. That is to say, mulch 8-12 inches deep in some areas, and piled in a volcano-like fashion against the base of trees. This is a terrible practice that can result in so many tree and shrub issues. Take a moment to Google, “Mulch volcano,” and you will find a prolific amount of information on the topic, even entire non-profit organizations dedicated to stopping the madness.
 

So, why does this practice continue?

Simple; cause and effect are so far separated in many arboreal plants (especially trees) that it can be difficult to see the associations. Trees are resilient, fighters to the end, they have excellent survival systems designed to keep them going for, in some cases, thousands of years. It could take years for some problems to manifest. When they do occur, symptoms may not allude to the actual cause of the trouble. Your trees and shrubs could simply become high-maintenance, requiring routine sprays, pruning, treatments, and watering right up until their ultimate demise. Some trees will not display any symptoms whatsoever. Instead, they can just fall over, for seemingly no reason (like the one in the pictures shown).

Mulch is highly beneficial.

Mulch can be a great and precious resource for our trees, shrubs, and gardens. I encourage, advocate even, the use of mulch in landscapes. Mulch can hold five times its weight in water, aiding trees and shrubs through difficult times. It acts as an insulating blanket during winter months, preventing frost-injury to fine roots near the surface of soil. As mulch is broken-down by microorganisms, it returns natural fertility to the soil and enhances soil structure, as well as the soil-food web.

The Solution! Spread the word (and the mulch)!

• Spread organic mulch within the root-zones of trees and shrubs, creating wider beds.
• Although depths may vary, a good rule of thumb would be no greater than 3-4 inches.
• Remove piles of mulch from the bases of trees and shrubs. Doing so now can save you a lot of heartache and money later. You should excavate until you see the root-flare (wide part of the trunk, where it meets the ground).
• Create a “dish-like” ring around individual trees and shrubs. Mulch should be deeper at the outermost portion of the dish, and become shallower toward the center (where a 2-3 inch air-gap between the root-flare and the mulch should be maintained).
• Finally, tell someone what you learned. By all of us doing our small part, we can stop this poor and costly practice.

For more on mulching, Morton Arboretum has this great guide:

Mulching Trees and Shrubs