Many of us picture the Arctic as largely untouched wilderness. But that has long-since ceased to be true for all of the continent. It is also home to oilfields and pipelines, mines and various other industrial activities. The corresponding facilities were built on a foundation once considered to be particularly stable and reliable: permafrost. This unique type of soil, which can be found in large expanses of the Northern Hemisphere, only thaws at the surface in summer. The remainder, extending up to hundreds of meters down, remains frozen year-round.