First, some definitions: In general, permafrost is soil that has been frozen for at least two years—common in regions that are cold year-round, such as the Arctic. The part of the soil that freezes in winter but thaws in summer is not permafrost, but is known by scientists as the “active layer” of soil.

So, how far do you have to dig to get past this “active layer” and hit real permafrost? In parts of Alaska from Anchorage to the North Slope, the surface layer of healthy permafrost might be found anywhere from 1 to 5 feet underground.

Whether your particular hole would have to be deep or shallow depends on a number of factors. For example, the farther south you are, the deeper you might expect to dig. But that’s only a general rule.

The most important factor is really what’s on the surface. If the soil surface is covered with moss and organic material, these organic materials will serve as insulation, protecting the soil from summer thawing - and you could expect the active layer, and the permafrost beneath, to be close to the surface.