“Dear Scouter Atom,
Did you hear about what happened at Hopewell Rocks?! One of the rocks collapsed. How could such a big rock, that has been around for so long, fall over?
Yours in Scouting,
Dear Tic Tac,
Rocks are worn down (weathered) and moved (eroded) over time whenever they come into contact with moving water or air. Riverbanks are eroded as the river flows by, cliff faces shrink because of strong ocean tides and sand dunes change size and shape as the wind lifts the sand.
Water has the greatest impact on Earth’s geology. It can get into small cracks in seemingly solid rocks. From there, water will move down towards the earth, flowing under the force of gravity. As the water flows through these small cracks, the cracks become bigger and bigger as the rock is eroded away.
Water is the only material we know of that gets bigger (less dense) when it freezes. Ice expands as it freezes, changing the shape of its surroundings. Next time you put a plastic bottle filled with water in the freezer, take note of how your bottle has expanded and warped to fit the ice inside. The same thing happens when water freezes in those cracks in the rock – the rock has to expand to make room for the ice. If the water inside melts and freezes a few times in a short period of time, this can put a lot of stress on the rocks and make small cracks even bigger. Once the pressure and stress becomes too much, a piece of the rock will break off.
Try it out at home:
- Grab a piece of sidewalk chalk and soak it in water overnight. Make sure to give the chalk a lot of water – at least twice its volume. You can also use another type of porous rock, such as shale or siltstone.
- Take the chalk out of the water and put it in a bowl.
- Put the chalk in the freezer and wait.
- Come back later, after the water has frozen. Take the chalk out of the freezer. What do you notice?
- Let the chalk thaw out, then put it back in the freezer.
- Repeat the freeze-thaw cycle a few times. What do you notice each time you bring the chalk out of the freezer?
After a winter of fluctuating temperatures, you can expect more potholes than usual. That’s because there have been more cycles of freezing and thawing, and more stress has been put on the asphalt
Until next time,
Scouter Atom is a Colony Scouter with a passion for STEM adventures. There is no question too small, no question too large – if you have a question, Scouter Atom has an answer. Send your questions to firstname.lastname@example.org.