Erosion, Mountains, Rivers, Canyons

It's hard when posting about this subject, as it was when teaching it, to sort things into discrete subjects. Erosion and weathering are inextricably linked with canyon formation, and mountains and plate tectonics go together, but erosion goes with mountains too, and you can't separate rivers and water erosion. I'll do my best to place related topics in the same post, but if you need more ideas, you can check the tags at the bottom of the post too.

We did several small activities to demonstrate water erosion and weathering. We poured a small stream of water into a pan filled with sediment, then inclined the pan and watched how the water moved. We could see the gradual wearing of a channel, as well as the spreading out of the water into as it slowed or the slope decreased. We talked about deltas and alluvial fans (here is a page with related activities), as well as meanders and oxbow lakes.

Next we observed the effects of wave erosion on coastlines. We buried several cylinders of clay (representing layers of harder rock) in a pile of sand (the softer rock). Then we filled the rest of the pan with water and gently rocked the pan back and forth to make waves:

As you can see, the waves gradually picked up the sediment on the coastline and deposited it farther out, leaving a smoothed-out coastline and exposing the rock stacks. Some of the stacks were even left standing alone in the water. We've seen lots of examples of these types of stacks when we go to the beach (Haystack Rock in Oregon, for example). Some even form arches.

We watched the carving action of water as it runs down a channel. We formed several "canyons" in the yard, and saw that the river deposits sediments downstream in deltas as well. This is an even better way to observe meanders, as a slope evens out.

And of course we made play-doh mountains of various sorts: fold mountains, fault-block mountains, volcanic mountains, etc.

You can find several other erosion and weathering activities at the bottom of this post.

Here are some illustrations of anticlines and synclines.

You can also see examples of mountains in the Plate Tectonics post.

Here's a cute landforms flipbook to make.

Sediments and Erosion

Somehow in all my years of studying geology, I never understood that clay and silt and sand are simply names for materials composed of different sizes of sediment! We collected samples of each type and sorted them onto a plate, and then looked at them under the microscope.

Here's what sand looked like. Cool, huh? Like teeny pebbles. Which, of course, it is!

We also looked at how weathering and erosion affects different sediments. 

You can see, as we dropped water on our "mountain," the water wore away at the slopes, and formed river channels where it "preferred" to flow. You can also see the deposition of sediment at the bottom of the "mountain."

Wind plays a part in weathering and erosion as well.

Eventually, the mountain is all worn away and the sediment has been deposited throughout the flood plain.

We looked at different sizes of sediment too. The water, obviously, had less of an effect on large "boulders" than it did on smaller sediments.

After flooding the sediments, they mixed and settled. Then we allowed the water to evaporate for a few days, and when it was gone, we had a "sedimentary rock" composed of the old sediment.

We also repeated an activity we've done before, where you put different sizes of soil/sediment into a bottle, add water, and shake it up. The sediments mix and then settle to the bottom in layers sorted roughly by size. It's cool to see it work.

More sedimentary rock activities—here.