While it may sound gentle, frost heaving is a relentless process that can lift boulders, buckle roads, fracture foundations, and sculpt entire landscapes into bizarre and beautiful patterns. It is a defining feature of cold regions, a constant battle for engineers, and a fascinating window into the physics of water and soil.

The Science of the Lift: More Than Just Ice Cubes

The common assumption is that frost heave happens simply because water expands by about 9% when it freezes. While this expansion plays a role, it’s not the main driver of the significant upward movement we see. The real power comes from a phenomenon known as ice lens formation.

For significant frost heaving to occur, three ingredients are necessary:

• Freezing Temperatures: The ground temperature must drop below 0°C (32°F) for a sustained period.
• A Supply of Water: There needs to be a source of groundwater below the freezing zone.
• Frost-Susceptible Soil: This is the key ingredient. Soils with fine particles, like silts and loams, are perfect. Their small pores create a strong capillary action, essentially acting like a wick.

Here’s how it works: As the cold penetrates from the surface, a “freezing front” moves down into the soil. When this front encounters a pocket of water in frost-susceptible soil, it freezes. But the process doesn’t stop there. The strong capillary action of the fine-grained soil begins to draw more water up from the unfrozen ground below, pulling it towards the initial sliver of ice. This new water freezes onto the bottom of the existing ice, causing it to grow thicker. This growing sheet of ice is called an ice lens. As it thickens, it pushes the overlying soil and anything on top of it—rocks, pavement, fence posts—upwards with immense force.

Coarse soils like sand and gravel are not frost-susceptible because the large spaces between particles prevent strong capillary action. Clay, while fine-grained, has such low permeability that water can’t move through it fast enough to form large ice lenses.

A Landscape Sculptor: The Art of Periglacial Environments

Nowhere is the power of frost heaving more evident than in periglacial landscapes. These are cold, non-glaciated regions, often at high latitudes or high altitudes, where the ground experiences intense freeze-thaw cycles. In places like Siberia, Alaska, Northern Canada, and Scandinavia, frost heaving is a dominant geomorphic process, creating landforms that look like they belong on another planet.

Patterned Ground and Stone Circles

One of the most striking creations of frost heaving is patterned ground. Over many cycles of freezing and thawing, the ground can sort itself into stunningly geometric shapes like circles, polygons, and stripes made of stones. The process, known as frost sorting, begins when the heave pushes rocks and finer sediment upwards. During the spring thaw, the ground contracts, and the finer particles (silt and sand) fall back into the cracks and crevices first. The larger stones can’t fit back in, so they are left stranded on the surface. Repeated cycles slowly and progressively nudge these stones outwards from the center of the heave, concentrating them into well-defined borders.

Pingos: Ice-Cored Hills

Imagine a hill, up to 90 meters high and hundreds of meters across, that grew from the ground up. This is a pingo, an ice-cored mound pushed up by the immense pressure of freezing groundwater. Found in permafrost regions like the Mackenzie River Delta in Canada, pingos form where a lake drains, exposing the unfrozen, saturated soil beneath to the intense cold. As this ground freezes from all sides, it squeezes the trapped water, forcing it to move towards the center and upwards, where it freezes into a massive core of ice that heaves the overlying earth into a dome.

Human Geography: The Battle Against the Heave

While fascinating to geographers, frost heaving is a costly and persistent nightmare for anyone trying to build and maintain infrastructure in cold climates. The battle is ongoing in cities from Fairbanks, Alaska, to Yakutsk, Russia—the coldest large city on Earth.

• Roads, Railways, and Runways: Pavement is the most common victim. Ice lenses forming under a road can create bumps and undulations, leading to dangerous driving conditions. When the ground thaws in the spring, the water-saturated soil loses its strength, creating soft spots called “frost boils” that can cause the pavement to collapse.

– Foundations and Buildings: Uneven frost heave can lift one part of a building’s foundation while leaving another stationary, leading to cracked walls, warped floors, and structural failure. This is why building codes in cold climates mandate that foundations be placed below the “frost line”—the maximum depth to which the ground freezes in winter.

– Utilities and Pipelines: Buried pipes for water and sewer can be bent and broken by the force. The famous Trans-Alaska Pipeline System had to be engineered to account for this. Much of its length is elevated on vertical supports with special heat pipes to prevent the permafrost below from thawing and shifting.

– Agriculture: Farmers in cold regions often talk about their fields “growing rocks.” Each winter, frost heave lifts new stones to the surface, which must be cleared before planting. It can also uproot seedlings and damage the roots of perennial plants like fruit trees and grapevines.

Living with the Lift

We can’t stop the seasons, but we can adapt. Engineers have developed several strategies to mitigate the effects of frost heave:

1. Replace the Soil: The most common method is to excavate frost-susceptible soil from under roads and foundations and replace it with non-frost-susceptible material like coarse sand and gravel.
2. Improve Drainage: Since water is a key ingredient, installing proper drainage systems to carry water away from infrastructure can drastically reduce the problem.
3. Insulate the Ground: Placing rigid foam insulation boards below ground can prevent the freezing front from penetrating deep enough to cause damage.

From the subtle crack in a driveway to the monumental rise of a pingo, frost heaving is a testament to the quiet, irresistible power of water and ice. It is a constant reminder that the ground beneath our feet is not always as solid and stable as it seems, and that in the planet’s cold corners, the earth itself is alive and moving.