Found this for the curious.
<< They have a very high metabolism and must eat a lot, often an amount of food equal to their body weight each day. To eat that much they have to find a lot of food and that means a lot of digging. In average garden or lawn soil a mole can dig at the rate of 12 to 15 feet per hour. The tunnels moles dig in search of food are just below the surface and the digging of these tunnels severs plant roots and causes grass and other plants to decline. In addition to their surface feeding tunnels moles also dig deeper tunnels, called runways, in which they make their nests and travel throughout their territory. The soil excavated from these runways are deposited on the surface in the form of mounds of loose soil called mole hills. >>
When Mole Hills Become Mountains