On Day 1, students explored the impact of viscosity on bubbles by using straws to blow bubbles in milk, ketchup, and peanut butter. It takes some serious lungs to get a bubble going in JIF! For the lower viscosity fluids, bubbles were able to rise up and even form a foam. In low viscosity magmas, the bubbles will be able to rise independently of the melt, which creates opportunities for passive degassing. In a high viscosity fluid (chunky JIF moves a bit like molten rhyolite), bubbles that form are much more likely to be trapped in place; as the magma depressurizes, the bubbles will grow next to each other like bubbles in rising bread dough. If the bubbles grow too quickly for the magma to stretch around it, the bubble walls will rupture like popped balloons -- but with much greater force.
Day 2 witnessed much larger bubbles than any of us could manage with a straw: it was time for trashcano eruptions! In a trashcano, the eruptive energy comes from the expansion of liquid nitrogen as it transitions to the gas phase. The liquid nitrogen, in a sealed pop bottle held underwater in the trash can by an anchoring brick, expands until it creates too much pressure inside of the bottle and then explodes. All of that expanding gas has to go somewhere as it escapes the now-useless bottle, so it pushes the water from the trash can up and out of the way in a glorious eruption. Our middle schoolers were real troopers, despite the freezing conditions! We set off a couple of eruptions, then worked together to map the maximum trajectories of the ejecta (packing peanuts) that were thrown out along with the water during the eruption. The highlight for the students? Professor Mike M sacrificing himself and one of the (unwitting) graduate students to the freezing spray in the name of showmanship!
On the third day, we used 'Eject!' software to figure out our vent velocities during the eruption based on ejecta distances and ambient conditions. The program, written by Larry Mastin of the USGS, lets students model trajectories for various conditions using a simple GUI. The students worked in teams of 3-4 to see who could come up with the best fit conditions to describe the eruption from the day before. One group, determined to test the limits of the program, nearly sent their packing peanut into orbit!
It was a fantastic opportunity to share our science with a local school, get dirty, and practice our outreach skills. The students were absolutely fantastic! Thank you so much to Mrs. Casselman and Grace Lutheran School for inviting us over to play. We hope to see some of the students in our 101 classes in a few years!
