Jens Niclaes

Here is a short presentation of my research topic: 

In 1980, happened the catastrophe of the volcano Mount Sint Helens. Until this day, it is the largest landslide ever recorded. It displaced nearly 3 kilometers cubed of geomaterials at more than 250 kilometers per hour, erasing more than 600 kilometers squared off the map, causing tens of death and more than 3 billion dollars of damage. Sadly, that kind of event is not isolated. Most of the volcanoes lived such phenomena cyclically in their life. When it happens in remote areas, like Mount Sint Helens, it is mainly a question of material damage. But it may cause much more problems if the volcano is close to a city or the sea where its instabilities may cause a tsunami.

Some investigations were conducted on the site of Mount Sint Helens, it appeared that the deposits of the volcanic debris avalanche were altered. It means that the microstructure of the volcanic rock had evolved over time and that the mechanical properties had weakened. The main explanation for this is hydrothermal alteration, which is the chemical and mineralogical changes induced via, generally acidic, hot fluids. Hydrothermal alteration is very common in volcanoes. Effectively, it may happen wherever fluids coexist with a heat source that dissipates its energy by fluid circulation. 

Thanks to or because of the sad event of Mount Sint Helens, awareness was brought to the scientific community of the natural instabilities of volcanoes. Some people would say that the volcanoes are rotten from the inside. There is a need to predict such catastrophes. 

This research focuses on the influence of hydrothermal alterations, which are thermal, chemical, and hydrologic phenomena, on volcanic flank stability. Hence, it aims to propose a mechanical model for large volcanic flank collapses including thermo-hydro-chemo-mechanical couplings at different scales. The idea is to fully understand what happens at the micro-scale, i.e. the variation in the microstructure, mechanical properties, etc. caused by the hydrothermal alteration. Then, to implement it into a larger scale model to assess the macro-variation at the volcano scale. Ideally, these models would directly interact with each other. 

As said, the research aims to produce a final model combining sub-models working at different scales. The microscale model, which represents the first part of the research, tends to fully understand the effect of the type and intensity of hydrothermal alteration on volcanic rock. It will be calibrated thanks to experimental data, which may be classified into two kinds. The first one gives volcanic rock mechanical properties from compressive tests on hydrothermally altered rocks. The second one offers volcanic rock microstructural information from tomographic imagery and (geo)physical tests. Thanks to the combination of these mechanical and mineralogic analyses, predictions of the mechanical properties of volcanic rocks regarding the type and intensity of hydrothermal alteration are possible. 

In the second part of the research, several macroscale models will be developed. A hydrothermal system model will interact with the microscale one to understand the volcanic rock properties variations due to the hydrothermal activity. Finally, once the areas of the volcano are characterized, a mechanical model will determine the failure surface and instabilities of the volcano. These models will be coupled to understand the interactions between these phenomena. 

The model of the role of multi-physical couplings across scales on the mechanical instability of volcanic flanks (the name of the thesis) will be able to predict how and when a volcano will collapse. Because yes, all volcanoes will collapse sooner or later, the only questions are how and when!