Chipmunks are what commonly makes 2 inch holes in the ground and the holes that chipmunks make are usually rounded around 1 inch.
Moles will create tunnels but are always covered by conical mounts.
Pocket gophers make tunnels but their tunnels have mounds that are large, fan, bean or dune shaped and have a hole that is plugged.
The insect that makes a 1/2 hole in the ground are large wasps called Cicada killers which are commonly found outdoors around residential properties.
Cicada killers make holes which tunnel into the ground and they take preference for dry, sandy soil in places like patches of grass and dry dirt around your yard.
Sphecius speciosus, often simply referred to as the cicada killer or the cicada hawk, is a large, solitary digger wasp species in the family Crabronidae.
Female Cicada killers have significant stingers which they plunge into cicadas to inject venom that paralyzes them.
Without doubt, the stings of cicada killers are painful.
However, cicada killers are not aggressive and do not have nest-guarding instinct of honey bees and hornets.
You can walk through areas where the cicada killers are active without attracting attention.
Cicada killers are attracted to sparse lawns and bare, dry soil, so they will make nests on your property in areas that fit these criteria.
Their nests are dug into the ground in areas such as along sidewalks, on your lawn, within flower beds, and in gardens.
The cicada killer wasp is amazing, not only for being able to detect and paralyze its prey, but also because of its ability to fly carrying a cicada that is proportionally equal to or heavier than the wasp itself.
This is an amazing aeronautical feat.
Other common causes for a 1/2 hole in the ground include moles, voles, crawfish, bees, wasps, earthworms, grubs, and animals like skunks or raccoons digging for grubs.