Walnut Tree Bark disease

[rich.wolcott]

Mature (~3ft diameter) Eastern Black Walnut Tree bark dead around Base dirt line as attached. southern New Jersey. Some Upper limbs dead . Looking to ID the Disease. Tremendous walnut production last fall from this tree. Any help
Appreciated. Thanks

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[ATH]

Looks like the trunk may have been buried???

In picture 2...it also looks like there is a bit of a bulge right at the soil line. If you did down a little, is there a root against the trunk?

 

[TroutBrookTree]

Basal rot from girdling roots