Observations and results
How did your stream change over time? What influenced its path, size and shape?

The study of water is called hydrology. Scientists study the ways in which different types of materials (such as dirt, sand and rock) affect the formation and shapes of streams and rivers. Some researchers have even found structures that look like riverbeds and canyons on Mars, which they say is evidence that Mars once had liquid water.

But water is not the only substance that changes the surface of Earth. Can you think of other forces that change Earth's surface? Big blocks of frozen water in the form of glaciers—such as those that covered much of North America during previous ice ages—can slowly scrape surfaces clear or push dirt and rock to make hills as they advance and recede. Even wind can blow lighter material, such as sand, around, shifting the position of sand dunes. The study of these different processes is called geomorphology.

Share your stream erosion observations and results! Leave a comment below or share your photos and feedback on Scientific American's Facebook page.

Cleanup
Recycle the water bottle and be careful when cleaning up the flour and water mixture.

More to explore
 "Data Deluge: Texas Flood Canyon Offers Test of Hydrology Theories for Earth and Mars" from Scientific American
 "Planting Trees Can Shift Water Flow" from Scientific American
 "Investigate and Report on Erosion" from Dirtmeister's Science Reporters
"Erosion" overview from BrainPOP
 Erosion: Changing Earth's Surface by Robin Koontz and Matthew Harrad, ages 4–8
 Janice VanCleave's Earth Science for Every Kid: 101 Easy Experiments that Really Work by Janice VanCleave, ages 9–12

Up next…
Big Space: The Scale of the Solar System

What you'll need
•    Nine small, round objects about the size of a peppercorn (0.1 inch, or 2.5 millimeters, across)
•    Measuring tape
•    Nine small pieces of paper labeled for the sun and planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune)
•    A clear, 21.5-foot- (6.6-meter-) long path on the floor inside or ground outdoors
•    A grapefruit (optional)
•    Two grains of table salt (optional)
•    Two grains of sea salt (optional)
•    35 feet (10.7 meters) of space in at least one direction (optional)

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