active layer

American  

noun

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

---

Example Sentences

The active layer holds large quantities of organic material that have been frozen for thousands of years.

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

Built in the early 1960s, Arecibo was initially designed to study the Earths ionosphere, the chemically active layer in the upper atmosphere that is ionized by solar radiation.

From Slate • Nov. 23, 2020

Increased phase separation and crystallization have a profound effect on the photophysical and transport properties 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