What could cause the loss of roots along with damage to the bark on a tree?

The loss of roots along with damage to the bark on a tree is most commonly associated with the activity of voles. These small rodents are known for burrowing and feeding on the roots of trees and other plants, which can lead to significant root loss. Additionally, as voles gnaw on the tree's bark, they can create wounds that expose the tree to disease and pests, further compounding the damage.

In contrast, while insects can cause bark damage, they typically do not result in significant root loss unless they specifically target the roots, which is not a primary characteristic of most common pest species. Volcanic activity is largely unrelated to tree damage in this context, as it usually affects broader ecosystems and is not a localized cause of bark and root damage on individual trees. Soil erosion, while it can expose roots and have indirect effects on tree health, does not specifically cause bark damage. Thus, voles are the most direct reason for the combination of root loss and bark damage described in the question.