Hawai'i Space Grant Consortium, Hawai'i Institute of Geophysics and Planetology, University of Hawai'i, 1996

Cake Batter Lava
Teacher Page
Purpose

To understand some of the geological processes and the structures that form as lava flows across planetary landscapes by using cake batter as an analog for lava.

Background

In this activity students will use cake batter to simulate surface lava flows. The experiment demonstrates many of the key features of a'a flows, though not of whole pahoehoe flow fields, which are fed by lava tubes.

Real a'a lava flows are complicated. They are characterized by a prominent lava channel confined between levees. Shear zones, places where one portion of the flow is moving faster than an adjacent portion, usually occur. Small flows of pahoehoe lava also become channelized, but on a much smaller scale than a'a flows.

As cake batter is poured onto an inclined surface, the first and foremost thing to do is to observe the formation of distinct features in the flow. Levees form on the outer part of the flow. These are not quite the same as levees on lava flows because the latter build up levees by overflowing the banks. Inside the levees the batter moves downhill. Ridges might develop in the flowing portions, analogous to large ridges in lava flows. The thickness of the flow varies with slope, time, position in the flow, and amount of batter poured. These variables can be tested by measuring width and thickness as functions of time, as described in the procedure.

Preparation

Review and prepare materials listed on the student sheet. Begin with a standard, boxed cake mix, preferably without pudding added. Mix the dry cake mix with water only. Smooth the mixture with a wire whisk to the consistency of thick cream.

The final mixture should be fairly uniform, with only a few lumps. If the mixture is too runny, then it will pour like water. In this case, add flour to the mixture. If it is too thick, then it will mound up (though that is interesting and somewhat resembles some very viscous lava flows). In fact, at the end of the experiment, you may choose to use a very thick batter for comparison purposes.

A baking sheet is an excellent surface to use for the experiment, though any smooth, surface will do fine, such as a wooden drawing board.

Draw a grid with 10-cm spacing onto a paper taped to the baking sheet or wooden board, then cover with plastic wrap.

In Class

Using a protractor and plumb line, the baking sheet or board is propped up to an angle of 15 degrees for the procedure, then to an angle of 25 degrees for a repeat of the procedure.

Students should pour the batter slowly and at a constant rate down the inclined board. The bucket should be held about 10 cm from the high end of the board.

At each 10 cm mark, the students will:

1.
record the time the flow front passes the mark,

2.
measure the length of the flow,

3.
measure the width of the flow,

4.
measure the center depth of the flow.

"Data Tables" are provided for recording these values. Space is provided for sketches of the flow outline.

When the batter is flowing down the slope, look for areas near the edges where the flow rate is low or zero; these are the levees of the channel. The part in the middle that is moving faster is called the channel interior. You may try sprinkling red confetti onto the flow to get a better view of the relative movement between the interior and levees.

Wrap-up

1.
How do the two flows compare?

2.
Is the ratio of channel width to flow width the same? Presumably the batter volumes were the same for both slopes, but the flow areas could be determined and multiplied by the average depths as an exercise just to check.

Extensions

1.
Use a ruler with a grid to slice into the flow at each 10 cm mark to get cross sections.

2.
Can you see the levee margins in the cross sections?

3.
How do the cross sections change down the length of the flow?

4.
Add more flour to the batter to see the behavior of a thick flow.

5.
Videotape the activity.

6.
Use the batter in an "Impact Craters" activity.


Pictures  


Go to Data Tables.

Go to Cake Batter Lava Student Pages.
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