How Does Freeze-Thaw Break Rock Apart? Ice in Cracks Explained

As an Amazon Associate we earn from qualifying purchases.

How does freeze-thaw break rock apart? The short answer is that water collects in cracks, freezes, and the ice that forms there can widen the crack. One research paper states the core point directly: “The formation and growth of ice layers in fractured rock masses is one of the main causes of frost weathering in bedrock in cold regions.” This article explains the mechanism described in two sources, shows how repeated freeze-thaw cycles weaken rock, and lists what the sources do not settle.

Quick answer

Ice that forms and grows in cracks can break rock. One source says that “the formation and growth of ice layers during freezing leads to cracking of bedrock or expansion of existing fissures.”
Cracks are where the water is held. The same source notes that “fractures are often the main water storage and transport channels.”
Repeated freezing and thawing weakens rock further. The anhydrite study reports that properties “decrease exponentially” as freeze-thaw processes increase.
The sources do not give a rule for when a specific rock will split.

Why water in cracks matters

Most rock is not uniform, and the first study targets a gap in earlier work. It says: “Most of the existing bedrock frost weathering studies discussed above only consider the solid rock matrix.” The authors argue that real bedrock also contains fractures, and their test model reflects that. The model is described as a simulated rock mass with a vertical through fracture, “fabricated by splicing two cement blocks.”

The reason fractures matter is that the study states “fractures are often the main water storage and transport channels.” Water held in a crack is in contact with the crack walls, and the study’s cracking claim depends on ice forming in exactly that space. This is why the first study focuses on the layers that form inside the fracture rather than on the solid rock alone. The sources treat the crack as the place where the process happens, not as a side detail.

Two ways ice forms in rock

The study distinguishes two ideas about how ice layers form in rock. It says: “Two mechanisms have been proposed, in literature, for the formation of an ice layer in rock.” The first is the one the study calls “One mechanism is in situ volumetric expansion.” In that model, the water sits in place and freezes there, and the paper describes the condition as “if water completely fills the spaces in rock and freezes in situ.”

The study gives a pressure figure for this model. It says that ice growth “can, in principle, generate pressures up to 207 MPa inside cracks in rock,” and that this is “strong enough to fracture any rock.” The reason it gives is “because the maximum tensile strength of rock is one to two orders of magnitude lower than 207 MPa.” In other words, the stress from ice is far higher than the rock can hold in tension, according to the study’s own numbers.

The study does not treat that model as complete. It states: “As such, it is difficult to directly explain the relevant ice formation and growth process by the existing in situ volumetric expansion or ice segregation mechanism.” The authors then propose what they call “the initial crack-frost effect,” which links ice formation to moisture that moves into the crack. The sources do not present this as settled for all rock types.

Ice segregation: water drawn toward the cold

The second mechanism in the study is ice segregation. The paper defines it this way: “Ice segregation occurs when temperature gradient-induced suction in freezing or frozen ground (or rock) drives unfrozen water through a porous media towards a freezing site, where lenses or layers of ice grow.” The key difference from in situ expansion is that the water is moved to the ice rather than frozen where it sits.

The study notes that the topic is not new. It says: “Some typical ice segregation experiments and phenomenon is listed in Table 1.” That table is a summary of earlier experiments, and the sources provided here do not repeat its contents. For the purpose of this article, the useful point is that the study separates the two processes and treats them as candidate explanations for the same kind of damage.

Repeated freezing and thawing in the laboratory

The second source is a laboratory study of anhydrite rock. The authors describe where their sample came from: “The anhydrite rock studied in this paper was taken from Donghuishe Town, Pingshan County, Hebei Province, where the annual extreme low temperature is −16.4 °C.” This detail matters because the study is about a real rock under real winter conditions, not an artificial block.

The freeze-thaw test is described as a repeated cycle. The study explains: “One freeze–thaw cycle process is as follows: the water-saturated rock is frozen for 4 h in a freezing environment at −20 °C and then thawed for 4 h in distilled water at 20 °C.” The samples were arranged in groups. The paper states that the test scheme was “to divide the samples into five groups and conduct 0, 30, 60, 90, and 120 freeze–thaw cycles on each group.”

The study reports how properties change across those groups. Its summary is that “The results show that with the increase in freeze–thaw processes” the properties fall, and it uses the term “decrease exponentially.” This is the basis for the claim that repeated cycles weaken rock. The sources do not give a fixed number of cycles that will split a given stone.

What the internal tests show

The anhydrite study looked at more than overall strength. It says that “the micropores and cracks induced by freeze–thaw cycles can also be detected through nondestructive tests such as Nuclear Magnetic Resonance (NMR) and Scanning Electron Microscope (SEM).” It also states that “The microstructure of rocks directly impacts the mechanical characteristics.” Taken together, these two statements explain why the authors measured pores and cracks alongside strength.

The paper also points to a gap in prior work. It says: “Few studies have involved the multi-scale deterioration mechanisms of anhydrite rock under a freeze–thaw environment.” The study responds to that gap with laboratory tests at more than one scale. The sources do not claim that the same results would hold for granite, sandstone or other rock types.

Putting the two sources together

Read together, the two sources describe a sequence. Water sits in cracks. Ice forms and grows, either where the water is or by drawing water toward a cold site. The ice layer then cracks the rock or widens the fissure. The anhydrite study adds that repeated cycles weaken rock, measured through strength and pore structure rather than through a visible break.

The two studies agree on one point: ice formation inside a rock’s pores or cracks is the driver. They differ in scope. The first is a controlled model with a single fracture, and the second is a laboratory series on anhydrite rock. Neither produces a single formula that predicts when every stone will break.

How we chose

Both sources are research articles hosted on PubMed Central. The first is an experimental study of ice layers in fractured rock. The second is a laboratory study of freeze-thaw effects on anhydrite rock. Each source was opened and read for a direct description of the freezing mechanism. No retail page was used, and every factual sentence in this article is tied to a quote from one of the two sources listed at the end.

What we could not verify

Several parts of the question remain open. Both sources cover narrow cases, and neither addresses garden stone or outdoor paving directly.

What the sources do not say

The first study’s test rock is a laboratory construct: the simulated rock mass was “fabricated by splicing two cement blocks.” It is not natural bedrock, and it is not garden stone. The second study is devoted to one material, and the paper’s own framing is “The anhydrite rock studied in this paper.” The sources do not give a time for a given rock to split in the field. They also do not give a temperature threshold that always causes damage. Those gaps are not filled here.

Frequently asked questions

What is frost weathering?

The first study describes it in one sentence: “Frost weathering consists of two physical processes, freezing and melting, in which the formation and growth of ice layers during freezing leads to cracking of bedrock or expansion of existing fissures.” The study uses the term for both the freezing and the melting stages of this process.

Does ice always break rock?

The sources do not say that. The first study states that “it is difficult to directly explain the relevant ice formation and growth process” with the existing models, which means the explanation is not settled. The study proposes a different idea, which it calls “the initial crack-frost effect,” but it does not present that idea as universal.

Why does rock crack in cold weather?

The sources point to ice in cracks. The study’s central claim is that “the formation and growth of ice layers during freezing leads to cracking of bedrock or expansion of existing fissures.” Because the study also says “fractures are often the main water storage and transport channels,” the cracks are where the water and the ice are most likely to meet.

Does one freeze matter, or only repeated cycles?

The anhydrite study tests repeated cycles, with groups receiving “0, 30, 60, 90, and 120” cycles. It reports that properties decline with more cycles and uses the term “decrease exponentially.” The sources do not describe the effect of one freeze on its own, so the answer for a single freeze is not given here.

Can these results be applied to stone in a garden?

Not directly. The first study uses a laboratory model, and the second uses anhydrite rock from a single site. The sources explain mechanisms rather than giving advice for a particular stone. For a related question about how soil holds water, see How Does Clay Hold Water in Soil? For how soil particles bind together, see How Does Soil Aggregation Form? Glue, Roots and Fungi Explained.

Sources

Experimental study on the mechanism of ice layer formation in fractured rock masses in cold regions. https://pmc.ncbi.nlm.nih.gov/articles/PMC9605980/
Investigation of the Multi-Scale Deterioration Mechanisms of Anhydrite Rock Exposed to Freeze–Thaw Environments. https://pmc.ncbi.nlm.nih.gov/articles/PMC10856804/