The freeze-thaw cycle is what happens when water soaked into rock, soil, pavement, or concrete freezes and then melts, again and again, as temperatures swing around 0 °C (32 °F). Each round does only a little damage, but over many winters it can crack mountains, crumble roads, and shove plants out of the ground. Ice expanding in a crack is only part of the story, because freezing ground also pulls in more water and builds the ice up from the inside.
Why Freezing Water Pushes Things Apart
Water expands by about 9% when it freezes, which is unusual, since most substances shrink as they solidify. Ice needs more room than the water it came from. If that water is in a space it can’t escape from, it presses outward on the walls around it.1Communications Physics. Freezing water at constant volume and under confinement A crack full of water becomes a crack being forced wider once it freezes.
A glass bottle filled to the brim and left in the freezer shows this well. It cracks because the ice has nowhere to go. A half-full bottle usually survives, because the ice can grow into the empty space. Cracks and pores in rock and concrete behave like the full bottle when they are packed with water. That’s why saturation, not just cold, decides how much damage a freeze does. A driveway slab that dried out before winter faces much less risk than one that stayed soaked, and a crack that is open at the surface and draining can let some water or ice move out and ease the pressure.
The pressure can be large. In mountain rock walls, ice expanding in cracks can push with up to 10 MPa, about 100 times normal air pressure, within hours.2Geophysical Research Letters. The Efficacy of Frost Weathering Processes in Alpine Rockwalls That strongest push mostly happens in particular conditions, such as autumn freezes on water-filled cracks, and only now and then reaches the level that snaps rock in one go.3Geophysical Research Letters. The Efficacy of Frost Weathering Processes in Alpine Rockwalls Most freeze-thaw damage comes from many small pushes instead.
The thaw matters as much as the freeze. Melting lets water seep deeper into the crack the ice just widened, so the next freeze works on a bigger, wetter crack. Damage grows with each round. That is why a steady deep freeze all winter does less harm than swings above and below freezing.
Damage concentrates in pores and cracks that already hold water, since dry spaces have nothing to freeze. Medium-sized pores tend to be where freezing water expands and enlarges the space most.4Case Studies in Thermal Engineering. Mechanism of pore water phase change, freezing expansion, and pore enlargement of coal samples under low-temperature liquid nitrogen action Even dense, tightly packed materials aren’t automatically safe, because a few fine pores or hairline cracks that stay wet can be enough for ice to start working.
How Ice Keeps Growing by Pulling in Water
As soil freezes, liquid water moves from the unfrozen ground toward the frozen zone.5Water. Numerical Study of Pore Water Pressure in Frozen Soils during Moisture Migration In soil, this forms flat bands of pure ice separated by frozen soil, and those bands lift the ground.6Frontiers in Earth Science. Water Migration and Segregated Ice Formation in Frozen Ground: Current Advances and Future Perspectives
Water in very thin films stays liquid slightly below 0 °C (32 °F) when it is held tightly against soil grains or rock surfaces. So some liquid remains near the ice instead of everything freezing at once. As the ice layer grows, it pulls water along those films from the wetter, unfrozen ground below. It can keep lifting the soil above it as long as the water supply holds and the freezing front stays roughly in one place. The result can be much more ice than the soil held as water at the start, which is why heaved ground can rise far more than the 9% expansion alone would explain.
The same pull works inside rock. Cracks in porous rock can grow as water migrates to ice inside them, much as it does in freezing soil.7GSA Bulletin. A theoretical model of the fracture of rock during freezing This slow growth pushes with about 1 MPa over days, roughly a tenth of the quick expansion push.8Geophysical Research Letters. The Efficacy of Frost Weathering Processes in Alpine Rockwalls But steady force over days keeps nudging cracks longer, and this slow growth is thought to set up most rockfalls.9Geophysical Research Letters. The Efficacy of Frost Weathering Processes in Alpine Rockwalls
Soil type matters a great deal. Silty and clay-rich soils hold water and let it creep toward the frost. Coarse gravel and sand drain fast, so there is little water to feed ice. A water table close to the surface keeps supplying the growing ice. That’s why some yards heave every winter while nearby ones don’t.
The pace of the cold matters too. A slow, steady freeze gives water time to travel and build thick ice layers, while a sudden hard freeze locks water in place before much can move. A long stretch hovering just below freezing can therefore do more lifting than one bitter night.
Frost Heave in Yards, Fields, and Gardens
Frost heave is the upward push of soil when ice layers grow underneath it.10Water. Numerical Study of Pore Water Pressure in Frozen Soils during Moisture Migration Heaving can lift alfalfa crowns above the soil surface and break the roots.11Ohio State University Extension. Managing Frost Heave in Alfalfa Those plants often green up normally in spring and then die once the top two inches of soil dry out, because alfalfa usually survives only a few weeks with a broken taproot.12Ohio State University Extension. Managing Frost Heave in Alfalfa Plants that stay anchored may still lose their smaller side roots and stop growing.13Penn State Extension. Frost Heaving and Herbicides Heaving damage is worst on poorly drained clay soils after a wet autumn and early winter followed by mild winter temperatures.14Agronomy Journal. Frost Heaving of Soil and Plants. I. Incidence of Frost Heaving of Forage Plants and Meteorological Relationships
In early spring, look for perennials and bulbs sitting higher than they did in fall, with roots or crowns exposed. Newly planted shrubs may tilt or feel loose when you push them, and fence posts and stakes can creep upward over winter. If you pull a heaved plant, you may find a cleanly snapped root deep down.
A few habits help. Mulch after the ground freezes, so it stays frozen instead of thawing and refreezing. Plant late-fall perennials early enough for roots to anchor before winter. Once the soil thaws, gently press heaved plants back down and cover exposed roots. And improve drainage in soggy beds, since wet clay heaves most.
Why Freeze-Thaw Causes Potholes
Water seeps into cracks in the pavement and the ground beneath it.15beadedstream. Potholes and the Freeze-Thaw Cycle: How Smart Temperature Monitoring Can Help Prevent Road Damage It freezes, expands, and pushes the cracks apart. When it melts, it leaves gaps where solid support used to be. Then cars and trucks pressing on the weakened spot break pieces of asphalt loose.16beadedstream. Potholes and the Freeze-Thaw Cycle: How Smart Temperature Monitoring Can Help Prevent Road Damage Road agencies list moisture, freeze-thaw, traffic, and poor support underneath as the usual causes, often together.17Federal Highway Administration. Materials and Procedures for Repair of Potholes in Asphalt-Surfaced Pavements — Manual of Practice Repeated cycles wear asphalt faster, since freeze-thaw speeds up how quickly it loses stiffness under repeated traffic loads.18Frontiers in Materials. Effect of recycled aggregate and freeze-thaw cycles on fatigue performance of asphalt concrete
That timing is why potholes bloom in late winter and early spring. Temperatures cross freezing many times a week instead of staying cold, and snowmelt and rain supply plenty of water to fill cracks. The ground underneath is still thawing and soft, so pavement has little support, while plows and heavy traffic add stress at the same time.
For a home driveway, seal small cracks in fall before water gets in. Keep downspouts and snowmelt draining away from the edge, and fix low spots where water pools, since standing water feeds the damage. Shovel snow off rather than letting it melt and refreeze on the surface.
What Freeze-Thaw Does to Concrete and Brick
Concrete pavement usually fails in two ways, surface scaling and internal cracking.19PubMed Central. Impact of Freeze–Thaw Cycles on the Long-Term Performance of Concrete Pavement and Related Improvement Measures: A Review Scaling is the flaking or peeling of the top surface, which looks rough and pitted. Internal cracking weakens the slab’s strength and can eventually ruin the whole structure.20PubMed Central. Impact of Freeze–Thaw Cycles on the Long-Term Performance of Concrete Pavement and Related Improvement Measures: A Review Wet freeze-thaw makes concrete soak up water faster, a pumping effect that worsens damage.21Frost Resistance of Concrete. Scaling and internal cracking in wet freeze/thaw testing In lab tests, slower cooling made surface scaling from frost and salt worse, while faster cooling made internal cracking worse.22Frost Resistance of Concrete. Scaling and internal cracking in wet freeze/thaw testing
Air-entrained concrete is made with an additive that fills it with billions of microscopic air bubbles.23PubMed Central. Freeze-Thaw Durability of Air-Entrained Concrete These bubbles give freezing water room to expand, relieving the pressure inside. As a result, it breaks down more slowly than plain concrete over the same number of freeze-thaw cycles.24PubMed Central. Freeze-Thaw Durability of Air-Entrained Concrete The bubbles only work if they are the right size and spacing.25Federal Highway Administration. Air Entrainment and Concrete Durability
Brick and older masonry hold up well for a while. Lime-mortar brick walls withstood 50 freeze-thaw cycles with no loss of strength.26Elsevier / Construction and Building Materials. Influence of freeze–thaw cycles on mechanical properties of historical brick masonry After 150 cycles the brick surfaces and mortar joints showed visible damage, though the walls kept their strength to bear weight.27Elsevier / Construction and Building Materials. Influence of freeze–thaw cycles on mechanical properties of historical brick masonry
On steps, patios, and walkways, watch for thin flakes peeling off the top layer, often worst where water and salt sit. Exposed stones or gravel showing through the surface, and hairline cracks running across or near edges, are other signs. On brick, look for spalled faces and crumbling mortar, especially on north-facing walls that stay damp.
When pouring new concrete in a cold climate, request air-entrained concrete for anything outdoors that will freeze. Make sure the surface slopes so water runs off instead of pooling. Let it cure before its first winter, avoid deicing salts that first season, and apply a penetrating sealer to slow water uptake.
How Freeze-Thaw Shapes Mountains and Landscapes
Repeated freeze-thaw makes rock develop cracks and lose strength.28PubMed Central. Evaluating shear strength and acoustic emission in rock-like materials with non-persistent joint geometries under freeze-thaw conditions Chunks fall from cliffs and pile up at the base as scree, also called talus.29Wikipedia. Scree Freeze-thaw keeps moving scree, with small pieces working downward many times faster than big ones, leaving large rocks on top.30Engineering Geology. Freeze-thaw migration behavior of scree deposits in the cold regions: Insight from physical model test Cliffs shed rock steadily in these climates rather than all at once, mostly when meltwater seeps into cracks, refreezes, and wedges slabs apart. The fallen fragments stay angular and sharp-edged because they break along cracks and aren’t rolled smooth by water. In Arctic tundra, uneven frost heave sorts the ground into circles, stripes, and polygons.31Journal of Geophysical Research: Biogeosciences. Cryogenesis and soil formation along a bioclimate gradient in Arctic North America
On gentle slopes, freeze-thaw makes soil creep downhill faster as the slope gets steeper, though very steep, dry slopes moved less.32PubMed Central. Solifluction rates and environmental controls at local and regional scales in central Austria Growing ice lifts frozen soil straight out from the surface, and it settles back more downhill when it thaws, so each cycle shifts the soil a small step downslope. This drift is too gradual to see but can tilt fence posts, walls, and tree trunks over years.
On a hike, fan-shaped piles of angular broken rock at the foot of cliffs are scree,. Lumpy hummocks or stone circles on high ground hint at frost-sorted soil. In spring, listen for rockfall on cliffs as thawing loosens frozen-in rock.
How Climate Change Is Shifting Freeze-Thaw
Warming winters bring more frequent freeze-thaw cycles, more rain-on-snow, and more black ice.33Climatic Change. Long-term trends of freeze-thaw cycles in the Northern Hemisphere Under a high-emissions path, freeze-thaw days in southern Canada and the northern US could become much more frequent in winter by 2070 to 2100.34Journal of Applied Meteorology and Climatology. The Impact of Climate Change on the Annual Cycle of Freeze–Thaw Events in Eastern North America The same areas would see them start about 2 weeks later in fall and end about 2 weeks earlier in spring.35Journal of Applied Meteorology and Climatology. The Impact of Climate Change on the Annual Cycle of Freeze–Thaw Events in Eastern North America
Freeze-thaw needs temperatures to cross 0 °C (32 °F) back and forth, so a place that used to stay frozen all winter can end up with more cycles once mid-winter warm spells begin. A place that already hovers near freezing may eventually see fewer winter cycles as freezing becomes rare. Rain-on-snow adds water at the moment it can do the most harm, soaking cracks and soil that can then freeze again. In permafrost areas, the top layer heaves when it freezes and sinks when it thaws each year.36Remote Sensing. Seasonal InSAR Displacements Documenting the Active Layer Freeze and Thaw Progression in Central-Western Spitsbergen, Svalbard
How Living Things Survive Freezing
Ice crystals are the real danger to cells. Growing crystals pierce and tear cell walls much as ice cracks rock, so surviving the cold comes down to controlling where and how fast ice forms. It’s the same logic as air bubbles in concrete: give ice room, or stop it spreading.
Antarctic fish carry proteins in their blood that lower its freezing point and stick to tiny ice crystals so they can’t grow.37AskNature. Anti-Ice Coating Inspired by Antarctic Fish Blood — Innovation The proteins attach to the crystal’s surface and block more water molecules from joining, so it stays too small to hurt tissue. Similar proteins exist in insects, microbes, and plants.38UCLA Samueli School of Engineering. UCLA Scientists Develop All-in-One Coating to Prevent Ice Formation Scientists have made an ice-prevention coating modeled on the fish proteins.39UCLA Samueli School of Engineering. UCLA Scientists Develop All-in-One Coating to Prevent Ice Formation
The wood frog takes the opposite approach, with blood proteins that start ice forming in a controlled way so it can survive freezing.40PubMed. Biochemical modification of plasma ice nucleating activity in a freeze-tolerant frog Ice forms in the spaces around its cells instead of inside them, which spares the cells from being punctured.