Strange hole in garden

Strange hole in garden

Observation - Strange hole in garden - UK and Ireland. Description: These have appeared in our lawn, they are well rounded holes often with three distinct lobes about 8 cm across and up to 30 cm deep. They show no signs of digging on the surface or sub surface and we have seen no animals in them. The soil is clay rich and

These have appeared in our lawn, they are well rounded holes often with three distinct lobes about 8 cm across and up to 30 cm deep. They show no signs of digging on the surface or sub surface and we have seen no animals in them. The soil is clay rich and very dry. What are they?