voles make runs just under the surface, or when you move something that was resting on the surface the runs will be exposed and open. mole tunnels are deeper and a bit larger.
voles love our no dig mulch 
and they’re supposed to be very destructive, particularly eating roots. in our patch some things are thriving despite them, while other things are disappearing and we’re not sure yet whether this is voles, slugs, the grubs that come when you are converting pasture into garden, or a team effort.
i’ve been advised that a bottle sunk into the soil, neck upwards, can cause vibrations (from wind blowing across the top) that voles and moles don’t like, but we haven’t got round to trying this yet