Why do Arctic lowlands become boggy during the summer thaw?

Arctic lowlands become boggy during the summer thaw primarily because the presence of permafrost acts as an impermeable barrier that retards the downward movement of water through the soil.1

Because this frozen layer prevents water from draining into the ground, the upper layer of soil—known as the active layer—becomes saturated and waterlogged when it thaws during the summer months. This poor drainage is a defining characteristic of Arctic terrain, often leading to the formation of shallow lakes and widespread boggy conditions across the landscape. In areas with fine-grained sediments, this saturation is particularly pronounced, sometimes resulting in solifluction, where the waterlogged soil flows slowly downhill over the underlying frozen ground.123