Friday I gave the kids a slide show on craters and explained how they come in different sizes, but they’re almost always nice and circular because when the object hits the surface it blows out material (ejecta) in ALL directions, no matter the shape of the object. We also discussed how you can tell some are older than others, and what might be under the surface – the ejecta blanket around the crater looks like mud flows, rather than the nice rays you get from an impact on a dry surface. Then the kids went out and dropped rocks into trays filled with flour to make craters of their own. I used disposable foil trays, put a few inches of cheap flour in the bottom and then sprinkle cornmeal or chocolate drink mix powder on top so when the eject is blown out of the crater its easy to see with the contrasting colors. The kids dropped rocks from different heights (giving the rock a different impact velocity) and compared the size of the craters. They also looked at how crater size depended on the size of the rock. Then it quickly became a free for all with rocks and flour everywhere, which is why this activity is done OUTSIDE! I couldn’t believe I forgot to take movies of the impacts because that’s kind of coolest part, so here’s a slow motion movie of this lab that we took a few years ago.
The second activity we did involved making a volcano with baking soda and vinegar, but instead of starting with clay all around the cup before the first ‘eruption’, we built up the clay as we went. Every time we had an eruption we put down a different layer of clay where the vinegar and baking soda mixture flowed over the cup (I cut down a medicine cup). In this way we slowly built up a nice shield volcano. Here’s a picture showing the first two layers, black and red.
And after many eruptions, and lots of playdoh we ended up with the following. The blue straw bits were used for taking core samples of the volcano and was a bit hit with the kids. I explained how scientists trying to studying a volcano can’t sit there for hundreds of years and watch where the lava flows but they can take core samples to look at the different layers that built up over time… of course they won’t be brightly colored like ours.
I had done the crater activity many times before but the Universe at Your Fingertips DVD has it laid out for you in their Activity C-16, What Craters Can Tell Us About a Planet. And the volcano activity is C-15, Making and Mapping a Volcano.