By Eleanor

This post begins with a crying stress-ball and ends with a video of me pouring lava. Curious? Read on!

On my desk, underneath my computer screen, I have a collection of bits and pieces. These include rocks found or given to me, a pocket English-German dictionary, and a smiley-face stress ball.

This is the stress ball soon after it was given to me. It had a habit of falling on its face so I propped it up with a rock.

original-stress-ball

I went away for three months this year, and when I came back, I noticed my stress-ball was crying.

tear

Huh? I thought it was a practical joke at first, but when I looked closer, I realised that the clear stuff was coming out of the top of its eye. The rest of the stress ball had become brittle. This was not a joke: the fluid inside (I hadn’t even realised there was fluid inside!) had slowly begun to drip out its eye.

The drip continued to grow over the next few months until eventually it dripped off my computer stand and onto the desk below

drip-pile

So apart from this being kind of weird and fascinating, the reason I mention it is because this is a viscous fluid. There is something mesmerising about watching viscous fluids flow. And it’s not just me: after all, the longest-running laboratory experiment in the world involves watching drips of an even more viscous fluid, pitch.

What else is a viscous fluid? Honey, tomato sauce, molten chocolate… and lava.

Lava varies in its viscosity quite a bit. It varies depending on its temperature for one thing, but also what it is made of. Lava is molten rock, but not all rocks are the same. If you melt granite, you’ll get really thick lava that’s very viscous and doesn’t flow very much. If you melt a basalt, you’ll get a much more runny lava. And some lavas (called komatiites), which were erupted billions of years ago when the Earth was much hotter, are thought to have had the viscosity of olive oil.

If you want some more detailed information about why different lavas have different viscosities, check out this nifty website.

For my PhD, I make lava. I mainly use one particular composition of lava, something more like a granite than a basalt. So I thought it would be quite viscous, but I didn’t really know how viscous. Recently I did some experiments where I took my lava out of a furnace and poured it into water – and I’ve got a video to show you! In this experiment, my lava is sitting in a small bowl made of graphite, and I take this bowl out of the furnace with tongs and tip it upside down into a large beaker of water. So, now I have a kind of ‘mental picture’ of the viscosity of my lava: it’s kind of like honey on a cold day… except that it’s at 1300 °C!

Video credits
Pete: Filming and commentary
Michael: Fellow lab user