Posts Tagged ‘viscosity’

(this submission to the Accretionary Wedge #30 Bake Sale is late due to a missing camera.   Luckily, someone found my camera and now I can show off my baking “mistake”)

My original goal was to bake a metamorphic rock cake that had a bimodal distribution of porphyroblasts.   I was going to use green & blue sprinkles to defining the schistose layering (micas) and two different sizes of chocolate chips (the normal & minis) to represent a bimodal garnet distribution.   Instead of going the “easy” route, I decided to crack open my copy of Fannie Farmer and make the cake from scratch.   This is what came out of the oven:

my non-metamorphic cake

Well, that’s not a schist.   So what happened?

I had assumed that the viscosity of the cake batter would prevent the chocolate chips & sprinkles from moving very far within their original location in the pan.   However, as the cake went into the oven, the viscosity of the batter went down and the “garnets” started to settle at the bottom of the pan.   Which, had I had a way to capture the movement, would have been a great example of crystal settling within a magma chamber:

The blue & green sprinkles were not as heavy as the chocolate chips, so they simply homogenized within the “magma chamber” and gave the cake its green look.   My oven also has issues, so even though the middle of the cake had originally swelled and was a good bit higher than the edges, during cooling the center “caldera” of the cake subsided.   A similar process occurs with volcanoes when you remove the magma from the chamber either quickly (a massive eruption like Pinatubo in 1991) or slowly draining it (Mauna Loa from 1983-2001):

So, ironically enough, I didn’t produce a schist, but I managed to accidentally make a fairly decent mafic volcano similar to what might be found in Iceland 🙂   I’ll have to try again for the schist sometime this spring.

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(I’m still catching up with some of activities we did over the past few weeks.   This one was done during the first week of class while we were discussing magma / lava properties.)

I went searching at the SERC site for a viscosity experiment demonstration and found one by Ben Edwards written for a petrology class.   Since my class didn’t have that kind of background, I changed the assignment some to make it more simplistic (removing the math & compositional links).   I wasn’t really sure how well this was going to go, but it turned out to be one of the best assignments I’ve ever downloaded from the SERC site.

I’ve posted my notes, handouts, and logic over on my Google site.   But I’d like to post pictures here.

Basic setup:

  • use a tilted large wooden board covered with wax paper as our flow surface; whole set-up on top of an old plastic shower curtain for easy clean-up
  • have 9 different corn syrup preps to pour down the board to record things like: how long does it take to get to the bottom; shape of the flow; width of the flow
  • before pouring them down the board, we blew bubbles in the corn syrup with straws to determine how easy / hard it was to do, what the bubbles looked like, and how quickly they moved to the surface

All in all?   Great set of experiments that the students got into & maybe more importantly, still remembered which ones and gone faster / slower and easier / harder for the bubbles to move several weeks later.   High recommendation for this activity if you want to teach about viscosity.

Amy blows bubbles in the "cold" experiment while Todd looks on

Emily pours the mix with lots of couscous (ie crystals) down the board

run with lots of water got the bottom before any of us were really ready :)

the cold one took forever to get to the bottom

we had plenty of time to sketch & take pictures with the cold one

the cold one also had the most interesting morphology at the bottom

beginning to wonder if it was ever going to get to the bottom line...

part of it finally crossed the line... this one was no issue to get into the trash before it ran off the wax paper onto the shower curtain 🙂

the warm one got to the bottom before Emily had even stopped pouring!

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