Modeling Lava Viscosity

Some liquids tend to flow easily, while others tend to flow more slowly. A liquid's resistance to flow is called viscosity. Milk and maple syrup have two different viscosities. Milk is less viscous, so it flows easily across a surface compared to maple syrup. Similarly, different types of lava can have different viscosities. This chart shows the three types of lava and their relative viscosities:

Type of Lava	Viscosity	Estimated Rate of Flow
basaltic	lowest	30 km/hr
andesitic	medium	10 km/hr
rhyolitic	highest	1 km/hr

In this activity, you will model viscosities of lava using several different liquids.

Estimated time to complete: 1 hour You will need these materials:

• a teaspoon or graduated cylinder
• 15 milliliters (three teaspoons) each of water, cooking oil, and light corn syrup
• a small block about 4 centimeters (1.5 inches) in height, or a stack of books
• a nonstick cookie sheet, at least 25 centimeters (10 inches) long
• paper towels
• a stopwatch or timer
• a metric ruler
• a calculator

Follow these steps to complete the model:

1. Build an inclined ramp. Use the cookie sheet as the ramp by placing one of its ends on top of the block or stack of books. Use the metric ruler to ensure that the height is 4 centimeters.
2. Use a stopwatch to measure the time it takes for each of the three liquids to travel down the inclined ramp in seconds. Use 5 mL (one teaspoon) per trial. Clean the surface with paper towels between trials. Complete three trials for each liquid and record your data in part A.

Part A

After completing three time trials for each liquid, enter the results in the table.

1. Calculate the average time separately for each liquid. To calculate average time, add the three times and divide by the number of trials.
2. Calculate the average flow rate for each liquid: distance traveled (cm) average time (sec). The distance traveled is approximately the length of your cookie sheet in centimeters. One inch is about the same as 2.5 centimeters.
3. Give each liquid a relative viscosity rating: low, medium, or high.

Based on their viscosity, explain how each of the liquids compared with the three types of lava.

One way to test viscosity is to drop an object into a cup of the liquid and see how long it takes for the object to sink to the bottom. Which liquid would cause the object to sink the fastest? Why is it important for scientists to know the viscosity and flow rate of lava when a volcano erupts? Which type of lava from the experiment is most likely to cause the most widespread damage?