Very curious.  In wet areas crayfish can create mounds in lawns.  See https://content.ces.ncsu.edu/crayfish-in-turf. Is your lawn wet?

Voles can’t make tunnels, and moles make tunnels, not kicking out so much soil in a single location.  And it’s not like an ant mound. 

I’ll send in on to NCSU's PDIC for their advice.  This may take a few days. 

Here’s what NCSU team wrote:

Mounds like this can be difficult to identify as several larger digging arthropods and vertebrates (moles and voles as you said) can cause them. If they see something going in and out that may help, but otherwise the soil would need to be removed from the surface and activity be monitored to see if a culprit can be found. Some likely culprits other than what's been mentioned are mole crickets, Earth-boring dung beetles (Geotrupidae), and some digging wasps (though there would likely be external holes for them).Please let me know if they find some other evidence.Matt

Looks like you’ll have to do more investigating

Thanks for the info.