Monday, July 2, 2018

Crystal Clocks: How minerals in magmas can be used to unravel what happens before an eruption (Guest Blog by Dawn Ruth)

- Guest blogger Dawn C.S. Ruth @rockdoc11

Keeping time with volcanoes

Hi everyone. I’m neither Alison nor Janine. My name is Dawn C.S. Ruth and, like our fearless leaders, I also study volcanoes. However, where Alison uses experiments to delve deeper into volcanic processes, and Janine uses satellites to spy on volcanoes, I look at the minerals to see how magma moves and behaves before an eruption. One of the reasons I think volcanoes are so cool is because there are so many different ways to study volcanoes (and geology in general).

You want to know a little more about me, the blogging interloper? Well, a long time ago….

No really, my geologic history spans 2.54 billion years. I actually started doing research on impact ejecta from the Archean; this work formed the foundation of my undergraduate research project. When a chance to go to Antarctica and study Erebus volcano came up, I took it immediately. So I went from studying 2.54 billion year old rocks to studying the gasses coming out of Erebus. Funny story – my sister still calls me a gas sniffer. Ahhh, siblings.

Anyway, after my masters I worked for the state of New Mexico as a petrographer and then moved to the University at Buffalo to study volcanoes again. It just so happened that Llaima volcano (Chile) started erupting in January 2008, right before I began my PhD. As a result, Llaima became the focus of my doctoral research. Ok enough about me.

How does one, anyone, study volcanoes using minerals? Oh, let me count the ways. There are many blog posts I could provide, but I’ll focus on one. I use the chemistry of minerals to get at time.

Volcanoes erupt periodically, and we as volcanologists want to know when the next eruption is going to occur. By looking at the mineral chemistry we can get at the timing of processes before the eruption, which in the future we might be able to link to unrest like earthquakes and deformation.

I use element diffusion in minerals to get at the time of magmatic processes. Before I go there, let’s chat a little about diffusion.

Diffusion is a process that occurs wherever there is an unequal distribution of chemicals in a given space/volume/area. Here’s a classic analogy. Imagine you are sitting on one side of a room and some sprays perfume on the other side of the room. The chemicals that make the perfume are unevenly distributed in the room. Over time the perfume will diffuse (spread out) throughout the room, and eventually you will smell it. A similar process occurs in minerals.

In a volcano, minerals are sitting around in magmas. These minerals will have one chemical composition. We think that eruptions are triggered by injections of new magma into the shallow parts of volcanoes. When this happens the minerals that were already present start to grow new material, with a different chemistry. Now the crystal has an unequal distribution of elements (i.e. chemical gradient), which will now diffuse.

Ok, that’s a lot of background. So what do I really do?

I collect samples at volcanoes, and make thin sections, which are very thin slices of rock that allow folks, like myself, to investigate the chemistry and textures of a rock. I use a special microscope called an electron probe microanalyser (EPMA) with a backscattered detector to find minerals with the uneven element distribution. Using the EPMA, I collect a chemical profile across the chemical gradient and then use numerical models to model how long it took that chemical gradient to form. We call this a timescale. I try to analyze as many samples as possible, because nature can be messy and there will never be single timescale.
 I collected rock samples from volcanoes, and brought them back to (often very cold) labs, where I collected the images.  The different grays in the image tell me something about the chemistry and that there is an uneven distribution of chemistry in the minerals. I collected actual chemical data (see the red and yellow lines on the greyscale images) and compared them with a numerical model.  The shape of the profile gives me time.

Once I have collected these, I then try to interpret (or develop a scientific story) that explains the timing and magma movement before an eruption. By looking at data from multiple eruptions, I can get a general sense of the timing of magma movement before an eruption. At Llaima volcano, the one I studied for my PhD, I found that magma movement and injections are occurring frequently and they seem to pick up before an eruption. This makes sense because Llaima is a persistently active volcano that needs lots of magma to stay active. This accelerating behavior seems similar to that observed at other volcanoes like Etna, Mayon (another volcano I studied), and even Mount St. Helens.


We are only beginning to understand how minerals can record these events. We even have a cool name for it; we call them crystal clocks. As we move forward, we hope to take these timescales and then compare them to the seismic records and see if there is a link between was the crystals records and the seismic activity. Hopefully, we can then move toward a forecasting model to help folks plan around a pending volcanic eruption.

For more information on:

Crystal Clocks:
http://www.sciencemag.org/news/2016/11/smudged-volcanic-crystals-offer-clues-past-eruptions
 

2018    Ruth, D.C.S., Costa, F., Bouvet de Maisonneuve, C., Franco, L., Cortés, J.A., Calder, E.S. Crystal and melt inclusion timescales reveal the evolution of magma migration before eruption. Nature Communications. doi:10.1038/s41467-018-05086-8 
Open Access link: https://rdcu.be/2MVs

2016    Ruth, D.C.S., Cottrell, E., Cortés, J.A., Kelley, K., Calder, E.S. From passive degassing to violent Strombolian eruptions: Deciphering the triggering processes of the 2008 eruption of Llaima Volcano Chile. Journal of Petrology, 57(9), 1833-1864, doi: 10.1093/petrology/egw063. 
 

Cool things at Llaima: 
2014    Ruth, D.C.S. and Calder, E.S. Plate tephra: Preserved bubble walls from large slug bursts during violent Strombolian eruptions. Geology.  doi:10.1130/G34859.1. 

Gas sniffing at Erebus:
2008    Sweeney, D.C., Oppenheimer, C., and Kyle, P.R. Sulfur dioxide emissions and degassing behavior of Erebus volcano, Antarctica. Journal of Volcanology and Geothermal Research, 177, 725-733.

2005    Oppenheimer, C, Kyle, P.R., Tsanev, V.I., McGonigle, A.J.S., Mather, T.A. and Sweeney, D. Mt. Erebus, the largest point source of NO2 in Antarctica. Atmospheric Environment, 39 (32), 6000-6006.


2 comments:

  1. Hi! Interesting article. Just a correction: the name is Llaima, not Lliama as appears in the tags and references.

    ReplyDelete