permafrost

American  

[pur-muh-frawst, -frost] / ˈpɜr məˌfrɔst, -ˌfrɒst /

noun

1. (in Arctic or subarctic regions) perennially frozen subsoil.

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permafrost British  

/ ˈpɜːməˌfrɒst /

noun

1. ground that is permanently frozen, often to great depths, the surface sometimes thawing in the summer

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permafrost Scientific  

/ pûr′mə-frôst′ /

1. A layer of soil or bedrock that has been continuously frozen for at least two years and as long as tens of thousands of years. Permafrost can reach depths of up to 1,524 m (4,999 ft). It is found throughout most of the polar regions and underlies about one fifth of the Earth's land surface.

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Etymology

Origin of permafrost

First recorded in 1943; perma(nent) + frost

Explanation

Permafrost is ground that is frozen permanently. As you can imagine, permafrost is extremely cold. If you know that frost has many cold-related meanings and permanent means "always," then you should be able to figure out what permafrost is: ground that is permanently frozen. You won't be able to plant a garden in permafrost — or do much with it — since it’s so hard and cold. You won't find permafrost in warm climates or places that have distinct seasons. Permafrost only exists in areas where it's cold all the time, so the ground never thaws out.

Example Sentences

Shortly afterward, lawmakers amended the country's glacier protection law to relax restrictions on mining in areas of permafrost, despite fears the new law could endanger crucial water supplies.

From Barron's • May 23, 2026

Managing heat from a data center built on permafrost requires specialized engineering.

From The Wall Street Journal • Feb. 12, 2026

"We gained access to exceptionally well-preserved mammoth tissues unearthed from the Siberian permafrost, which we hoped would still contain RNA molecules frozen in time," adds Emilio Mármol.

From Science Daily • Nov. 15, 2025

Canada and Russia, where large amounts of ice and permafrost are melting, are losing the most fresh water.

From Los Angeles Times • Sep. 3, 2025

The big tires helped protect the fragile permafrost below, and kept the tourists up high, out of the reach of curious polar bears.

From "Two Degrees" by Alan Gratz