How does the active layer change between winter and summer in permafrost regions?

In permafrost regions, the active layer is the surface portion of the ground that undergoes seasonal changes in response to temperature variations.1

During the winter, this layer freezes, becoming seasonally frozen ground. In contrast, during the summer, the active layer thaws. Because the underlying permafrost remains impermeable to water, the thawed active layer often becomes saturated and boggy.12

The thickness of this layer is dynamic and depends on factors such as moisture content and soil type, typically ranging from less than 0.3 metres (1 foot) in wet, organic sediments to as much as 3 metres (10 feet) in well-drained gravels. This alternating freeze-thaw cycle is a defining characteristic of these environments, driving geological processes like solifluction and the formation of patterned ground. Most biological activity, including root growth and the decomposition of organic matter, is restricted to this active layer.21