A pingo is a dome-shaped hill with a core of solid ice, found in permafrost regions. These mounds form when freezing groundwater builds up pressure underground and pushes the surface upward, creating hills that can reach up to 50 meters tall. More than 11,000 pingos exist across the Northern Hemisphere, with the highest concentrations in Arctic coastal lowlands.
How a Pingo Forms
Pingos grow from the inside out. Beneath the surface in permafrost regions, pockets of unfrozen water can become trapped between layers of frozen ground. As that water freezes, it expands, and the pressure forces the ground above it upward like a slow-motion blister. Over centuries, the freezing process builds a massive ice core that can be nearly as large as the hill itself. The soil, sediment, and vegetation on top get carried along for the ride.
There are two types, and they form through different mechanisms.
Closed-system pingos are the more common variety. They typically form in drained lake basins. When a shallow Arctic lake loses its water, the unfrozen sediment beneath the former lakebed is exposed to cold air. Freezing closes in from all sides, trapping a pocket of waterlogged soil. As that residual water freezes, the pressure squeezes the remaining liquid upward, where it also freezes, gradually building the ice core. About 90% of the pingos mapped in the Tuktoyaktuk Peninsula of Canada’s western Arctic sit on the sites of former lakes.
Open-system pingos are fed by groundwater flowing from deeper sources. In this case, water moves upward through cracks or gaps in the permafrost, driven by pressure from below. One model suggests that as permafrost slowly thickens at its base over thousands of years, the expansion of freezing water generates enough hydraulic pressure to push groundwater to the surface. Where that water reaches the surface and freezes beneath the active layer of soil, a pingo begins to grow. These pingos maintain an open connection to the groundwater system below, which is what distinguishes them from the closed-system type.
Size, Shape, and Lifespan
Pingos range widely in size. Diameters span from 30 to 600 meters, and heights range from barely noticeable bumps of a few tens of centimeters to towering hills. The most famous example is Ibyuk Pingo in Canada’s western Arctic, which stands 49 meters tall with a base 300 meters across. Radiocarbon dating and heat conduction analysis suggest Ibyuk is roughly 1,300 years old, give or take 200 years. It is the second tallest known closed-system pingo in the world.
Pingos are not permanent. They grow slowly, but they also eventually collapse. When the ice core melts, whether from climate shifts, changes in local drainage, or simply reaching a size where the overlying soil can no longer insulate the ice, the mound caves in on itself. What remains is a distinctive scar: a circular or oval depression surrounded by a low ridge of sediment, called a rampart, that was originally pushed up and outward by the growing ice core. These remnant scars range from 20 to 400 meters in diameter, with ramparts 1 to 10 meters high. They often appear in clusters, sometimes overlapping, with smaller scars superimposed on larger ones.
Pingo scars are useful to geologists because they indicate that permafrost once existed in a location, even if it no longer does. Identifying these features in landscapes far south of today’s permafrost boundary helps reconstruct past climate conditions.
Where Pingos Are Found
The western Canadian Arctic holds the densest known concentration of pingos on Earth. A recent survey identified over 2,300 pingos in the region, nearly 1,000 more than earlier estimates. Of those, 95% are clustered within the Tuktoyaktuk Lowlands, where underlying sandy deposits from ancient river systems provide the right conditions for lake drainage and closed-system pingo formation. By contrast, the modern Mackenzie Delta, where low-lying terrain doesn’t drain lakes as effectively, contains only about 5% of the regional population, and those pingos tend to be smaller.
Pingos also occur across northern Alaska, Siberia, Svalbard, and Greenland. Western Canadian Arctic pingos are roughly 10% larger in radius than those in northern Alaska, though both populations have comparable slopes. Outside the Arctic, pingo scars have been identified in places like Montana’s Mission Valley, evidence of permafrost conditions during past ice ages.
Pingos vs. Palsas
Palsas are another type of frost mound found in cold regions, and they’re sometimes confused with pingos. The two form through fundamentally different processes. A pingo grows when a trapped mass of water freezes under pressure, creating a large ice core. A palsa forms when groundwater migrates slowly toward a freezing zone through a process called cryosuction, building up layers of segregation ice within the soil.
The differences show up clearly in size and setting. Palsas rarely exceed 10 meters in height and are almost always associated with peat bogs in areas of discontinuous permafrost, where average annual temperatures hover between negative 1 and negative 5 degrees Celsius. Permafrost exists only beneath the palsa itself, not in the surrounding landscape. Pingos, on the other hand, form well within continuous permafrost zones and can reach five times the height of a typical palsa. In most cases, the distinction between the two is obvious at a glance.
Cultural Uses in the Arctic
For Inuvialuit communities in the western Arctic, pingos have practical value that goes well beyond geology. In a landscape that is overwhelmingly flat, a large pingo is often the highest point for kilometers in every direction. Travelers on the ocean or inland use them as landmarks to orient themselves. They also serve as lookout points, known as “nasisaqturvik,” where people scan for caribou, check sea ice conditions, or watch for other travelers.
Pingos have also been used as natural cold storage. At Tuktoyaktuk, tunnels carved into pingos functioned as meat freezers, keeping caribou carcasses preserved in the ice core. The two largest pingos in the area were traditionally known as Ibyuk, and the surrounding landscape is now protected as the Pingo Canadian Landmark, a national historic site managed by Parks Canada.