Ice Wedging
Ice wedging is when water seeps into cracks in rock, freezes, and expands until the rock splits apart.
Think of it this way
Water seeps into a small crack in a frozen ice cube tray. As the water freezes, it expands and pushes the walls apart. Over time, the plastic cracks and splits at the weak spots. Rock breaks the same way when ice grows inside its cracks.
Explaining ice wedging by grade level
Water can get into small cracks in rocks. When that water freezes, it gets bigger. The ice pushes on the rock from the inside. Over time, the pushing breaks the rock into pieces.