VOLCANIC SHAPES

Some parts of the world have ancient lava (molten rock) flows that are hundreds of miles long. Flows such as these have come from fissures (cracks) in the crust, which have poured out runny lava. This lava is much thinner than the lava produced by explosive volcanoes, which is sometimes called pasty lava. Scientists use the term viscosity to talk about how easily a liquid flows. Thin, runny liquids have a low viscosity and thick liquids a high viscosity. The project shows the viscosities of two liquids, and how quickly they flow.

Heating solids to a sufficiently high temperature makes them melt and flow. Rock is no exception to this rule. Deep inside a volcano, hot rock becomes liquid and flows out on to the surface as lava. Its temperature can be as high as 2,2000F. Volcanoes grow in various shapes, depending on how runny or thick the lava is.

LAVA VISCOSITY

Two paper plates, pen, saucer, jar of liquid honey, tablespoon, stopwatch, pitcher of dishwashing detergent.

STEP 1
Mark a large circle on each plate by drawing around the edge of saucer. Pour a tablespoon of honey from the jar into the middle of one of the circles. Start the stopwatch.

STEP 2
After 30 seconds, mark with the pen how far the honey has run. After another 30 seconds mark again. Stop the watch when the honey has reached the circle.

STEP 3
Part-fill the pitcher with dish washing detergent and pour some into the middle of the other plate. Use the same amount as the honey you poured. Start the stopwatch.

After 30 seconds, note how far the liquid has run. You will probably find that it has already reached the circle. It flows faster because it has a much lower viscosity than honey.