Thierry Alboussiere, senior researcher CNRS, Laboratoire de Geologie de Lyon,

Tel : (33) 4 72 43 27 41

September 17, 2018

Letter of recommendation for Nelly Pons, to whomit may concern

Nelly Pons was a third year student at the university Polytech in Clermont-Ferrand, when she contacted our laboratory for a practice project in geophysics.I gave her a two-months project on crystallization experiments (June and July2017). The objective was to study phenomena occuring in magmatic chambers, inthe Earth’s core or in the deep mantle, in experiments at room temperature andpressure conditions. Such phenomena are not restricted to the Earth and may alsoconcern other planets: in a cooling melt, crystals can nucleate and grow to form aporous zone, a so-called mushy layer. In the same time, the liquid is depleted insome chemical elements. The time evolution of this system is important to under-stand the future state of the deep interior of the planets. In the laboratory, theexperiments consist in cooling down a mixture of water and ammonium chloridesalt, for 50 to 10 degrees Celsius. Ammonium chloride crystals form a layer of’frost’ while the residual water is more and more depleted in ammonium chloridesalt.

The phenomena generated by this situation are rather complex: the liquid(salted water) convects because of the temperature difference (a wall is cooled down)and because of the change in salt concentration (like sea water, a mixture rich inammonium chloride is denser than fresh water). Convection occurs also whithin themushy layer and takes the form of chimneys where the depleted liquid leaves themush (after it has lost new ammonium chloride crystals). This chimneys contributeto the cooling of the system and the growth of the mushy layer. The other aspectof the coupling is that crystallization has an impact on melt composition and con-vection.

During this practice period, Nelly learned how to run these experiments. Shechanged the inclination of the cooling plate and the initial composition of the melt.She also became familiar with the temperature measurement using platinum probes,to obtain a vertical temperature profile. Moreover, she set up a synthetic Schlierenmethod (close to PIV) to visualize the convective plumes from the chimneys andthe stratification of the fluid.

In a short time, Nelly could use Labview (an acquisition software) and could useand develop Matlab programs to extract information from the image correlation of

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the Schlieren images. Nelly has been working independently and decided herself ona set of experiments. She was able to run experiments herself and process the mea-surements. She asked for help when needed, faced problems when they appearedand produced a large quantity of results, in two months only.

From a personal viewpoint, it was a great pleasure to work with Nelly Pons.She was always cheerful (even when experimental problems had to be sorted out)and always looked for solution and found them. With those qualities of efficiencyand commitment, I have no doubt that Nelly Pons will succeed in any of her futureactivities.

Finally, Nelly Pons wrote a report on her work (this was not required from heruniversity) where I could appreciate the clarity and precision of her writing. Insummary, I recommend warmly Nelly Pons for any practice work or other job sheapplies for.

Thierry AlboussiereChercheur CNRS,Responsable du theme ”Terre et Planetes”Laboratoire de Geologie de Lyon, France

Thierry Alboussiere

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