Kilauea, Science, and Crawfish at Rice University (Houston, TX)

7 Jul

by Fiene Matthies, PHD student at the PRE-COLLAPSE research group, GEOMAR

Within my PhD project I am investigating the stability of volcanic edifices from a geomechanical point of view. How stable is a volcanic edifice? What are the prerequisites that cause an unstable edifice?

My methods are laboratory experiments and computer models, more specifically direct shear experiments and finite-element models, respectively. The direct shear experiments will be carried out on intact and powdered samples at Marum in Bremen together with Matt Ikari. The samples will then be evaluated with respect to rate-and-state friction. This allows us to identify the frictional behavior of the rocks, i.e., we get an understanding of the strength of the rocks. Moreover, we can evaluate how the rocks behave at different velocities and if failure of the rocks is promoted or prevented during earthquakes. The results of the direct shear experiments will be implemented into a finite-element model. This is used to evaluate the stress field within the volcanic edifice, from which we can then infer the stability of the volcanic edifice.

In April 2024 I flew to Houston (TX, USA) to visit Julia Morgan, Professor and Chair at the Earth, Environmental and Planetary Sciences department at Rice University. Julia Morgan is working on Kilauea volcano in Hawaii (USA). During multiple dives herself and colleagues have over the years collected many rock samples from the submarine flank of Kilauea.

The goal of our visit was to discuss and understand the system of Kilauea volcano and to choose those samples of the submarine flank that can serve best to answer research questions relevant to the PRE-COLLAPSE project.

Puzzling geology of Kilauea’s submarine flank

The geology of Kilauea’s unstable submarine flank is particularly puzzling. In general, the submarine flank is mobile and can be divided into three distinct regions. Researchers found that the northernmost part of the submarine flank behaves seismically, i.e., earthquakes occur on this part of the flank. The central part of the flank hosts a basin which is referred to as the Midslope Basin. The Midslope Basin is said to have formed due to an ancient landslide as the hummocky morphology at the toe of the flank suggests. The westernmost part of the submarine flank which is bounded by an offshore lineament to the west has not experienced landslides in the past but it is observed to slide seaward with a rate of ten centimeters every year. The part of the flank that is constantly moving seaward is referred to as Hilina Slump. The Hilina Slump is buttressed by thrust faults at its toe that the movement of the flank has formed. As earthquakes occur on the northernmost part of the flank, the Hilina Slump moves faster and movement of the rocks at the thrust faults was observed. However, up to now even the 1975 earthquakes with a magnitude of 7.2 did not cause failure of the Hilina Slump, i.e., the earthquake did not cause a landslide into the ocean. If the Hilina Slump one day however would fail, the tsunami that would result from it could cause destruction at the coastlines surrounding the Pacific Ocean. Since failure of the Hilina Slump is hazardous it is important to understand what might cause instability of the flank. Flank stability is governed, among other things, by the mechanical properties of the rocks building the flank. Analyzing Julia Morgan’s submarine flank samples will help our understanding of the mechanical properties of Kilauea’s flank and to infer the role of the mechanical properties on flank instability.

Hands on geology in Houston

For the first three days of my trip, Morelia Urlaub joined me in Houston for discussion and a first look at the samples. During my two-week visit, together with Julia Morgan, we discussed about the rock samples and Kilauea, described the rocks, looked at thin-sections, and chose the samples to take home. By describing samples and using the microscope I was able to do hands on geology which is not usually part of my PhD project but was a nice change of topics. Moreover, I got a better understanding on how different volcanic rocks that originate from the same submarine volcanic flank and/or volcanic island can feel and look. While some rocks would fall apart as soon as you touch them, others were very hard. Some rocks showed alteration, some did not. Some contained a lot of air and were very light and others were heavy, without air. At the end of the trip we decided on 16 samples that we shipped back to Germany. For the sample selection, we focused particularly on the thrust faults at the toe of the flank that buttress the Hilina Slump and we made sure to cover the large variety of lithologies that can be found at Kilauea.

Besides working on the samples, I also had the opportunity to meet faculty and PhD students at the Earth, Environmental and Planetary Science department at Rice University. I listened to many talks, presented my own research and participated in the events organized by the university and the department. I went to the Moody Festival and the Big Crawfish Boil where I was first introduced to crawfish, a typical dish of the “Deep South” of the United States. I was introduced to local beer, ate lots of Tex-Mex food, and enjoyed the sun and warm weather. After the trip I also had the opportunity to do my first road trip in the Unites States and explore Louisiana and eat even more crawfish.

It was a really fun trip. I enjoyed meeting all the people, listening to other people’s research, and learning about Kilauea. I am grateful I had the opportunity to visit Houston and I am looking forward to the next trip!