We have seen that alternate heat and cold can cause rocks to break. What are some other ways nature has of breaking rocks?

Fill two small jars to the brim with water. Cap one jar tightly; leave the other jar uncapped. (Pretend that the jars are rocks and that the water has filled any cracks in
them.) Place the jars in plastic bags, and seal them tightly. Set the bags, with the jars standing upright so that no water spills, in a freezer overnight. (Be especially careful to see that the open jar does not spill.)

Examine the results the next day. The capped jar may have broken, and the water in the open jar may have expanded above the rim without breaking the jar. What does this tell us? It tells us that water expands when it freezes. Well what does that have to do with breaking rocks?

Now soak several pieces of porous rock (e.g., sandstone, limestone, pumice; maybe even some aa lava) in water for an hour. Place the pieces in a plastic bag, and set the bag in a freezer overnight. Hypothesize about what will happen to the rocks.

The next day remove the rocks from the freezer, and examine them. Some will have broken.

By analogy, you will realize that water from rain and melting snow flows into cracks and pockets in rocks in the daytime, then at night, it freezes, expands, and sometimes causes rocks to crack.