Geosciences on Earth and elsewhere in our solar system
Landscapes on other planets have an eerie resemblance to landscapes on Earth. Comparing terrestrial to planetary landscapes therefore provides us with the opportunity, in conjunction with novel laboratory experiments, to understand how landscapes and materials develop over time and how planetary bodies evolve.
Glaciovolcanic glass in Iceland and on Mars
The comparative approach has been the main focus of my PhD research. Below are a few examples of my previous scientific work. On Earth we commonly find glaciovolcanic glass in the sandy deserts of Iceland. These sediments formed during eruptions of volcanoes underneath icesheets and some turn out to be stunningly colourful (such as the green rhyolitic hyaloclastite seen in the photo from the Grænagil in Landmannalaugar, Iceland). Interestingly, on planet Mars glassy sediments are formed by similar processes and under comparable conditions. Dunes in the vast sand seas of the northern lowlands were found to be composed of large quantities of glass-rich volcanic sands. Studying the alteration of volcanic glass can help us in understanding the behavior of these materials on other world; both by studies in-situ in the field, but also in laboratory experiments to understand the effects of frost weathering, thresholds of aeolian (wind-blown) transport and alteration of these grains using special experimental set-ups. In short, I have a broad interest in the transport and physical alteration of geologic materials in different (planetary) environments. Below you can find more highlights that were part of my PhD work. For my PhD I received the Andreas Bonn medal from the Society for the promotion of Natural Sciences, Medicine and Surgery.
Andreas Bonn Medal 2013. Once every 5 years the Society for the promotion of Natural Sciences, Medicine and Surgery (GNGH) awards the Andreas Bonn medal in the fields of natural sciences, exact sciences and medicine for original PhD research. Sebastiaan de Vet received the medal in the domain natural sciences on 29 November for his PhD thesis ‘When the glacier left the volcano’. Read more in this news article.
Aeolian processes in low-density atmospheres
If you have ever walked high up in the mountains and fell short of breath, you have experienced the effects of atmospheric density (caused by the lower atmospheric pressure). The lower atmospheric density also affects the flowing wind and causes it to pack less of a punch to detach sand particles. In essence it becomes more difficult to blow away sand particles if you reduce the atmospheric density (you need much higher wind speeds). We can study the effects of atmospheric density on aeolian (wind-driven) processes inside special hypobaric (low-pressure) wind tunnels, in order to understand the conditions that permit sand to be blown away on Mars. This is a very topical challenge as sand dunes migrate much faster on Mars than science thought was possible. Interestingly, sand deposits in the mountain ranges on Earth are also subject to lower-density conditions, so the insights gained can be applied on two planets at the same time.
Wind tunnel experiments used the AWTS-1 at Aarhus University in Denmark. (a) Observations of sediment detachment were made via the top access port via photographic time lapse. This view of the interior is along the length axis of the wind tunnel. Photo credit: Sebastiaan de Vet.
Sand grains as flowmarkers
Sand grains have the unique ability to collectively record wind flow patterns. During wind-blown transport, grains tend to streamline to the local wind flow direction. This caused grains to obtain a ‘preferred orientation’ that is recorded in the sediment fabric. This is by far the smallest physical scale at which wind directions can be inferred from geomorphic features, i.e. smaller than aeolian bedforms such as ripples and dunes. We can measure the wind direction by looking at the shapes, sizes and orientations of sand grains in geological thin sections of aeolian sediments. We first started to develop this method using thin-section of sand deposits from inland dunes found in Brandenberg, Germany. Interestingly, the method developed is not only applicable to dune sands on Earth, but also to aeolian sediments on planet Mars that can be imaged using e.g. the microscope imagers on the robotic arms of NASA and ESA Mars rovers.
Studying sand in hypo- and microgravity
Granular materials avalanche when a static angle of repose is exceeded and the motion of the sediment is arrested when it reaches the dynamic angle of repose. These processes occur with different materials on all planetary bodies in our solar system. We studied this form of gravity-driven transport using research platforms such as the Large Diameter Centrifuge (1-20 g) of the European Space Agency and during parabolic flights on board a Cessna Citation II research jet of the TU Delft/NLR. During the 54th ESA parabolic flight campaign we studied the dissipation of energy during collision of weightless sand particles in microgravity, to understand water repellent coatings. These coatings contribute to soil water repellency; a phenomenon caused by forest fires or as a result of desertification and this makes it a compelling societal and scientific problem.
Free-floating in microgravity. Sebastiaan served as project- and technical lead on the ARID experiment that was flown on the 54th ESA parabolic flight from the Bordeaux airbase. Photo credit: Lieke Mulder.
Projects in hypergravity
I have consulted and supported a several student projects that used hypergravity in their experimental approach. The experiments were selected in a European competition and were made possible by the educational programme ‘Spin Your Thesis’. These selected projects addressed topics in analogue glacier flow modelling, hatching of sponge gemmules and granular avalanches.