active layer

American  

noun

1. (in Arctic or subarctic regions) the layer of soil, above the permafrost, that thaws during the summer.

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Example Sentences

This model estimates key processes such as snow accumulation, melt, and changes in the active layer to better represent real conditions.

From Science Daily • Apr. 4, 2026

Writing in the paper, the researchers noted: "Expansion of vegetation and especially in wetland areas indicates but also exacerbates permafrost thaw, active layer thickening and thus emissions of greenhouse gasespreviously stored in these Arctic soils."

From Science Daily • Feb. 13, 2024

Permafrost still covers 85 percent of the state, but “almost everywhere, the depth of the active layer is increasing over the last few decades,” said Thoman.

From Slate • Mar. 11, 2015

This sequence of steps is affected by the morphology of the active layer.

From Nature • Aug. 15, 2012

Because the frozen permafrost was just a half meter beneath the active layer of soil, all the water on the tundra stayed near the surface.

From "Two Degrees" by Alan Gratz