Detect it: poke a stick. It stops, at a pretty consistent depth, and not because of rock. Remove it: overheat the planet. It will turn to mud. Anything built o

Detect it: poke a stick. It stops, at a pretty consistent depth, and not because of rock. Remove it: overheat the planet. It will turn to mud. Anything built on it will subside or sink. Massive amounts of trapped organic matter will turn to methane. Eventually, I presume the area would settle into a new climatic zone, with neither permafrost nor mud. Emphasis on "eventually".