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The volcano-like appearance is certainly reminiscent of a funnel-ant nest. But there was just this one mound. And the opening was relatively small.
Might this be the home owner (a species of Camponotus I believe)?
These small, shiny black ants were purposefull moving in and out of the nest. So either they are indeed the rightful homeowners, or they are moving in. Another puzzle I didn't have time to solve. Perhaps an accurate species ID will help. Later.