Freeze Thaw Weathering

This demonstration models freeze–thaw (ice wedging) weathering using water-saturated chalk or sandstone that is repeatedly frozen and warmed. Expansion of freezing water inside the porous chalk weakens it until it cracks and breaks, simulating how rocks fracture in nature.

1. Snap a piece of pavement chalk in half to create fresh surfaces.
2. Submerge the chalk in cold water and keep it there until no more air bubbles escape (gently move it to release trapped air); the pores should be filled with water.
3. Remove the saturated chalk, place it in a plastic bag (to contain fragments), and put it in a freezer for at least 6 hours or until fully frozen.
4. Prepare a bowl of hot water. Using tongs, transfer the frozen chalk into the hot water and observe any cracking or flaking.
5. Re-soak the chalk in cold water to refill pores, then repeat the freeze (bag → freezer) and warm steps.
6. Continue cycling freeze → warm → re-soak until the chalk fractures; record how many cycles are needed and what type of breakage occurs (cracks, flakes, shattering).

Physical Weathering: Freezing - AusEarthEd:

📄 Freeze-Thaw Weathering - Fizzics Education: https://www.fizzicseducation.com.au/150-science-experiments/geology-rocks/freeze-thaw-weathering/?srsltid=AfmBOoo-PtjZqntUEKxvsQ8vZko50QmE0KVJtrGj9Zu9PRgDL-ozv1zp

• Compare small chalk pieces versus larger chalk blocks and note cycle counts to failure.
• Test different warming methods (room temperature vs hot water) to see how thermal change affects cracking.
• Try partially saturated chalk (short soak) versus fully saturated chalk (long soak) to assess the role of pore water.
• Place chalk on a rough surface while warming to mimic abrasion from moving fragments.
• Advanced: Use dry ice for the cooling step and boiling water for warming to increase thermal stress (only with strict supervision and added safety precautions).

• Use tongs when handling hot water and frozen chalk to avoid burns and cold injury.
• If using an oven or very hot water, heat-resistant gloves are required; keep water below boiling unless specifically testing that variable.
• Contain the sample in a plastic bag during freezing to prevent loose shards; open the bag away from the face when removing chalk.
• Keep work area dry to prevent slips; wipe up spills promptly.
• Advanced variation with dry ice: adult supervision only; wear insulated gloves; work in a well-ventilated area; never seal dry ice in an airtight container.

• Why is the chalk soaked before freezing? (Filling pores with water allows expansion upon freezing to generate stress.)
• What causes the chalk to crack during freezing? (Water expands about 9% when it freezes and ice crystal growth exerts pressure on pore walls.)
• How does repeating the freeze–thaw cycle change the result? (Microcracks accumulate and link up, weakening the material until it fails.)
• Which rocks in nature are most susceptible to freeze–thaw weathering? (Porous or fractured rocks such as sandstone and limestone; fine cracks in granite can also widen.)
• Where on Earth would this process be most active? (Mountainous or temperate regions that cross 0°C frequently, where water can infiltrate and freeze.)
• How does this model differ from real-world rockfalls and pothole formation? (Real rocks experience additional stresses like pressure release, salt crystallization, and abrasion, but freeze–thaw is a major contributor.)