During extremely severe winter, frost depth penetration is how many times deeper than average?

• A. 4 times
• B. 3 times
• C. 1.5 times
• D. 2 times

Answer: (D)

When winter is extremely severe, the freezing front can penetrate deeper because the ground experiences longer and colder subfreezing periods. The depth of frost responds to the accumulated freezing, and in practice, that tends to push the frost depth about twice as deep as the average. The soil’s thermal inertia and any insulating effects (like snow cover) keep it from increasing far beyond that, so increases to three or four times are not typical. A 1.5 times increase would be a smaller deviation than what’s usually observed in a truly severe season, making two times the most reasonable and commonly used estimate.