River Runs Under It

Drive along California Highway One and you'll observe scenic landscapes of our nation's western shores. But what you don't see is even more impressive.

By Michael DiSpezio|Friday, April 15, 2005

Just offshore, the ocean's bottom forms an incredible system of underwater canyons. Unlike the nation's Eastern Seaboard, the California coast lacks the shallow ledge of the Continental Shelf. Instead, the offshore bottom plunges steeply to over a mile in depth! Underwater mudslides race through these canyons, cutting paths into this unseen seascape. Within these waters, all sorts of bizarre deep-ocean animals and communities can be observed. 

Making models
Minor earthquakes can set in motion unstable mud. This moving mud produces a mudslide that flows along the natural cut of the submarine canyon. Within this turbid flow, a variety of coast pollutants and sediments can be carried miles offshore into the deeper cuts of the canyon. In this activity, you’ll get the opportunity to model this event.

Waterproof clay
Small bowl
Food coloring

1. Examine the illustration on page 88. Note how the color depth key can be used to interpret the topography of the sea bottom. Identify the canyons, plains and hill-like features of this underwater scene.

2. In a small bowl, construct a model of this underwater landscape. Make sure to sculpt out the major cuts illustrated in this diagram. Use a different color clay to represent the dry land of the California coast.

3. Add water to the bowl to submerge the underwater topography.

4. Fill a cup half full of water. Add several teaspoons of salt. Stir to dissolve the salt. Add several drops of food coloring. Mix well.

5. Slowly pour the dyed saltwater solution into the bowl. This thin stream should enter the bowl just above the mouth of the sculpted major canyon. Observe its movement. What do you see? Does the poured water mix with the water already in the bowl? Explain.

1. How many major channels can you observe? (One.) Where does it begin? (In the bay located between the cities of Santa Cruz and Monterey.)

2. Why did you add salt to the solution? (To increase its density.) Why did you add food coloring to the water? (To make it more easily visible.)

3. What happened when the dyed salt-water was added to the model? (It sank, flowing mostly within the channel. As it moved, it flowed down the sculpted slope.)

Topographic too
Examine topographic maps in both print and online resources. Note how areas of equal depth are connected by a single line. Divide the illustration on page 88 into four equal rectangular quadrants. Select the top right quadrant. Use what you’ve learned about topographic maps to construct a topographic map of this underwater seascape.Many of the telescopes on the top of Kitt Peak use mirrored lenses that collect, magnify and reflect the image to an electronic sensor. These sensors have taken the place of the optical eyepie

The slope effect
Does the slope of a channel affect the speed at which particles travel down it? Make a prediction. Then, design a method of inquiry that can answer this question. Share your experimental strategy with your instructor. With his or her permission, proceed with your research. Display your results in a manner that would be acceptable for a school science fair.

A different view
Turn page 88 so that the illustration appears upside down. Check out the submarine channels. Do they still appear to be cuts in the surface? Explain. Why do you think the appearance flip-flops when viewed upside down? Explain how the direction of overhead light helps you interpret what you see.

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