Internship: Analogue of flowstones in the lab

Concretions that develop in caves or open air encompass a wide variety of forms and shapes as a result of different physico-chemical, thermal and hygrometric conditions, as well as flow rates and geometries. However, the influence of all these parameters is still far from being understood and quantified. To study these systems in the laboratory, under controlled conditions, one has to face a difficulty: natural carbonate precipitation takes place over very long time scales. Our approach is therefore to carry out experiments with analogue systems, which can capture at least part of the relevant physical processes. Here we are particularly interested in flowstones (Figure), which can be found in caves and hot springs (travertines). Similar shapes also result from the solidification of water in ice when waterfalls freeze, or with wax when a candle overflows.

The objective of the internship is to develop a new laboratory set-up using thermoplastic materials with a low fusion temperature (polyethylene glycol or PEG) to investigate the mechanisms of formation of a flowstone-like structure. Thermal solidification is then here the analogue of chemical precipitation. A molten PEG flow will be injected in an axi-symmetric fountain and the growth of the solidifying pattern will be monitored through image analysis and 3D scanning. We will measure the wavelength of the pattern, its growth rate and characterise its coarsening along the vertical direction. Flow rate, PEG molar mass and injection temperature will be varied to assess their influence on these measurements. We also plan to visit natural caves to acquire digital elevation models of flowstones, in order to compare to the laboratory results.

This interdisciplinary project is primarily experimental, combining with modelling and field data analysis.

Co-supervision: Anne Mongruel, Antonin Eddi and Philippe Claudin
Emails: anne.mongruel@espci.fr, antonin.eddi@espci.fr, philippe.claudin@espci.fr