Wednesday, June 8, 2016

Glacier Activities

We made "glaciers" by freezing layers of gravel and water in bread pans. Then we had fun doing various things with them—scraping them along different surfaces, letting them melt and observing what kind of features were left behind (till, moraines, etc.), and so forth. There are several good ideas for glacier-related activities here.

Maybe the most interesting thing we did, though, was demonstrate how glaciers melt and re-freeze as they move. One book we read said to think of them less as big ice bulldozers, and more as ice conveyor belts. The thawing and freezing of successive layers of glacier ice is an important part of why they move and shape the land the way they do.

This demonstration shows how pressure can force ice to melt (as it does on the bottom of a glacier) even when the temperature itself is not cold enough to cause melting. We set up a block of ice on top of two rulers between two stacks of books, and across the ice we hung a wire tied to two heavy stones. It was a very awkward, improvised set-up—you can see a much tidier example here.
As time passed, the pressure of the wire gradually melted the ice, and the wire began to cut through the ice block. As the children saw this, they predicted that eventually the ice would be cut into two pieces.
But the surprising thing is that the ice re-freezes above the wire as the pressure lessens on a particular place, leaving the wire inside the block of ice—and eventually, allowing the wire to cut all the way through the ice and still leave an intact ice block above it! Fascinating.
We should have gotten big ice-blocks from the store and slid down steep hills atop them, as I occasionally did with youth groups or for ward activities in college. But we didn't. Maybe next time!

No comments:

Post a Comment

Related Posts Plugin for WordPress, Blogger...