Math Explains Why Some Volcanic Bombs Do No Explode.

When ever a certain type of volcano erupts you end up with volcanic bombs being tossed out.  Some explode on impact and others don't but it hasn't been until recently that math was used to explain why some don't. First off, a volcanic bomb is mass of cooling lava that flies through the air during an eruption.  In order to be classified as a bomb, it has to be larger than 2.5 inches. Furthermore, it is usually red or brown that weathers to a yellowish brown.

Volcanic bombs tend to occur in volcanoes near or surrounded by water and the bombs absorb a lot of water  when they are launched through the water. Then the water is turned to steam causing the bomb to explode. However, some never explode and that has confused many a scientist since no one knew why this happened. The problem is that the ones that explode mid-air are fine but its the ones that do not because they can hurt people or animals, or damage houses, cars, and other things. To help satisfy scientists curiosity, a volcanologist worked with two mathematicians to try to find the answer as to why only some bombs explode.

One of the first things they did was to create a mathematical model designed to simulate the launch of volcanic bombs because its too hard to to study the fast moving objects in real life. They used data from real life data bombs to help establish the parameters of mathematical model. In the model, they varied the temperatures and pressures to see which effected the bombs.According to the results, it appears water both causes the bombs to explode and keeps them from exploding.

They's discovered the as the magma rises towards the surface, the surrounding pressure decreases while the trapped water is turned to vapor which escapes leaving bubble holes. The object is then pushed through the water and turned into a bomb. The key to the bombs is that some bombs are not solid yet so there are ways for the water to escape so the pressure buildup is eliminated and it doesn't explode. If the bomb does not develop the bubbles and doesn't have the escape routes, so the pressure inside the bomb increases and explodes.  Fortunately most bombs allow the gases to escape. 

The scientists who created the mathematical model love that this shows how mathematics can solve a non-abstract problem. Explaining to people that you are figuring out why some volcanic bombs explode and using math to do it, impresses people and they can relate to it.  Now if you'd like to share this with students,  the American Mathematics Society has provided a couple of algebra based activities for the classroom.

The first activity looks at how the ideal gas law applies to the situation and gives students the opportunity to use it.  They also provide a link to a simulator that allows students to play with various numbers in the ideal gas law.  The second activity has students practice linear equations in reference to lava flows.  It is actually an activity provided by Science Friday.  

Check it out and let me know what you think.  I'd love to hear.  Have a great week.