Monday, October 8, 2012

Weathering and Erosion with Found Rocks

Yoohoo?  Hello?

Hi.  It's me again.

School is back in session, the leaves are turning color and I have a huge variety of science activities rolling around in my brain that I am ready to share!  Sorry for the prolonged absence... this summer became more than a bit crazy for our family.  

In June, we were strongly considering putting our house on the market and started to do some of those little projects that have been hanging around for a little (long) while.  In July, my husband quit his job to pursue an exciting start-up company so then we really did have to put our house on the market.  (Which is not an easy feat with three young kids - thank you, thank you to my family and friends that helped us out so much!)  We got the house on the market in early August, sold it in early September, and are closing this week.  We make our official move in early November.  Oh, and did I mention this is not a small move... we are moving to California!  I think that phrase, "Life is a moving target", was invented for me this past summer!

Anyway, this activity evolved while we were in California looking for a new community in which to call home.  (We are moving to the San Diego area.)  We stayed for a week in two different locales and spent time each day exploring the area's offerings, from parks to restaurants.  And, of course we spent one day at the beach!  My little rock hunters continued their collecting ways and found a couple of rocks at the beach as well as a few at some of the more mountainous hikes that we took.  I was struck in the very clear difference due to weathering between the rocks and allowed the girls to take them home so we could do an activity with them.

Note: And, yes, I do believe in the idea of Leave Only Footprints - and got lectures by both my hubby and best friend when I let the girls take their rocks home.  I hereby promise to return the rocks to their rightful homes once we move.  (Happy, M & H?)

Materials Needed:

  • Collected rocks from "beach-type" and "mountain-type" locations
  • magnifying glasses
  • sandpaper
  • science journals

The first step is to collect your rocks.  You need two locations to collect from, one of which being a "beach" setting.  The beach does not have to be on one of the big coastal bodies of water; any reasonably-sized (not man-made!) body of water should have rocks in or near it that have been smoothed over time.  The other rocks need not be from a "mountainous" area; we are just looking for rocks that have not been weathered over time as distinctly as the "beach" rocks have been.

Once you get your rocks home, have your child make observations about the rocks.  Give them a magnifying glass and have them look closely at their rocks.  If you are using a science journal, have them trace around their rocks into their journals.

Have them sort (classify) the rocks based on their shape.  It should be very clear that the "beach" rocks have a smoother, more rounded shape in comparison to the other rocks.  Talk about how those rocks have been weathered and eroded over many, many years to cause them to have small pieces broken off the original rock until it is smoothed down.

To demonstrate that weathering takes place over a very long period of time, give them a piece of sandpaper and ask them to smooth the "mountain" rocks down so they look like the "beach" rocks.  You can play this up - I left the room and returned about 5 minutes later asking if they were done yet.  Of course, they said no, so I said that they should continue through the night and maybe when I woke up the next morning they might be done.  They got the point that weathering takes a LONG time.  (If you do this, just be careful that you don't give your child a super soft rock (like talc) which does break down very easily!)

Finally, give them a new rock and see if they can determine if it is from the "beach" or the "mountain".  Also, if your child is keeping a science journal, give them time to draw the rocks and write their observations about the two different types of rocks.

Science Talk:
The main science idea that we are exploring here is the concept of weathering, where a big rock is broken down into little rocks.  Weathering is ultimately responsible for creating all of the soil and sand that is on the surface of the earth today.  Weathering can occur via mechanical or chemical means.  Water, wind, gravity (think: rock slide), plants (think: tree roots) or ice (think: potholes) can all be the cause of mechanical weathering.  Chemical weathering can occur when water or other chemicals (like acid rain) interacts with the compounds in rocks.  In this experiment, the "beach" rocks had undergone mechanical weathering for thousands of years to create their rounded surface.

A secondary idea is that of erosion.  Erosion is the force that moves rock material from one place to another.  Erosion may also be caused by agents such as water, wind, gravity, ice and even animals.  Weathering and erosion work together over thousands of years to create major geographic features of the land such as river deltas, sand dunes, glacial lakes, sandy coastlines, etc.  The beach rocks had probably been pushed along by wave action and tumbled along the ocean floor for thousands of years.

I love the Science Works book series for young children and they have a book, "Cracking Up: A Story About Erosion", which provides a good explanation for erosion.  You could also check out "The Rock Factory", which is more about the rock cycle but does explain how sediments are formed for sedimentary rocks through the process of weathering and erosion.

For older kids, you could show them pictures of some significant geologic features caused by weathering and erosion, such as the Grand Canyon, Arches National Park, or some limestone caves.  Have them identify and research how the different features were formed.  Better yet... road trip!  I haven't been to either the Grand Canyon or Arches yet (although I devoured Desert Solitaire by Edward Abbey in one of my college English classes) but road trips to them is one of the things I'm really looking forward to when living on the west coast. 

A great example of weathering happening at warp speed is what occurs in a rock tumbler.  I think I've already written this before, but can we say "holiday gift"??  Now to figure out how to get one of the girls to put that on their holiday list...

Science Process Skills Used In This Activity:

Observing Communicating Classifying Measuring Inferring Predicting


Visit the science process skills page for more information on the different skills. 

I hope you enjoy this activity!   If you try it, please leave me a comment to let me know how it goes! Also, I'd love if you'd share any ideas for extensions for this project in the comments section below.  Thanks! :)


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