How freezing groundwater creates massive, dome-shaped hills in the Arctic

Gardening · Published 18 October 2026 Swipe more like this →

In short: In the frozen reaches of the north, the ground doesn't just sit still. Under specific conditions, the pressure of freezing water can heave the earth upward, creating massive mounds called pingos. These periglacial landforms are a testament to the hidden mechanical power of ice and hydrostatic pressure.

The formation of a pingo is a mechanical process driven by the pressure of freezing groundwater. In regions of continuous permafrost, an impermeable ground layer can trap water. When this water freezes, it expands, creating hydrostatic pressure that pushes a layer of frozen ground upward to form a dome-shaped hill. These structures are typically circular or oval-shaped and can reach heights of up to 90 metres (300 feet) and diameters exceeding 800 metres (0.5 mile).

These features, specifically known as hydrostatic or closed-system pingos, often occur in flat, poorly drained areas like river deltas or shallow lakes that have been infilled with sediment. The sediment acts as an insulator, allowing liquid water to collect beneath it. During winter, this sediment freezes and expands, confining the water and forcing the soil upward. Conversely, during the summer months, the ice core of the pingo can begin to melt, which may cause the mound to cave in and leave a depression in the landscape.

The existence of pingos is inextricably linked to permafrost—ground that remains colder than 0 °C (32 °F) for at least two consecutive years. While permafrost underlies about 24 percent of the Northern Hemisphere's land surface, pingos are specific landforms that require these frozen conditions to persist. They serve as geological markers; even when a pingo collapses, the resulting inverse depression provides evidence that permafrost was once present in that location.

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