I've been doing some street tree inventory work near where I live. I see a lot of older Norway and red maples with raised ridges on the trunk. The ridges are more or less vertical, sometimes they spiral. They may be a foot or two long, sometimes longer, and an inch or two high. Do you know what causes them and do they constitute some sort of structural weakness or defect? I am not referring to the natural ridges in the bark, but the underlying wood seems to be raised.

Thanks,

--Bob