GD
Geodynamics

# Archives / 2017 / December

## The fluid dynamics of wine

The Christmas holidays: the one time of year that you don’t need to think about work. Instead, you are focussed on your family (including the in-laws), the massive amount of food still left (a miscalculation every year), and you’re starting to think about your New Year’s resolutions (because we give it a try every year, right?). So, this is definitely not the time to go and read a blog post (or write one, for that matter).
Lucky you: there is a blog post anyway! But, in the spirit of the holidays, it has a festive theme. We are concerned with geodynamics. In numerical modelling we even assume that the Earth flows like a fluid on geological timescales. So what could be more festive than looking at a different timescale today by looking at the fluid dynamics of wine (‘oenodynamics’)? Pour yourself another glass, swirl it around a bit, and sit back for a relaxing post about how the swirling of wine works.

If you are unfamiliar with the process of wine tasting, let me give you a short introduction (although I am by no means an expert): to fully appreciate and taste a wine, you need to follow five basic steps: color, swirl, smell, taste, and savor. To make this a bit easier to remember after a couple of glasses, these five steps are also known as the ‘Five S’ steps:

See, Swirl, Sniff, Sip, Savor

From a layman’s point of view, the see, sniff, sip, and savor might make some intuitive kind of sense. However, the swirling step might be less intuitive. This swirling of the wine releases the so-called bouquet (‘the total aromatic experience’) of a wine. You usually swirl a glass of wine by a gentle circular movement of the glass. This creates a wave along the glass walls, which enhances the oxygenation and mixing of the wine. The shape of this wave formed by the swirling of the wine (or ‘orbital shaking’: the motion on a circular trajectory, at a constant angular velocity, of a cylindrical container maintaining a fixed orientation with respect to an inertial frame of reference) has been investigated by Reclari et al., 2011.

Now before you ask why on Earth it would be useful to investigate this (other than to satisfy a healthy dose of academic curiosity), the authors provide a very sensible reason: this orbital shaking has been applied to large scale bioreactors for the cultivation of antibodies in cells. Of course, looking at the swirling of wine is a less expensive experimental setup to study the physics behind this orbital shaking and, let’s be honest: it just sounds like a really fun, slightly quirky, research project.

To simplify the experimental setup, Reclari et al., 2011 use cilinders instead of wine glasses. The free parameters that Reclari et al., 2011 consider are the inner diameter of the cilinder D, the diameter of the shaking trajectory ds, the elevation of the water at rest H0, and the angular velocity ω. Varying these parameters results in a variety of wave shapes. Reclari et al., 2011 identify three dimensionless parameters:

đsds/D,

Ħ0H0/D,

Fr22ds)/g

These dimensionless parameters define the wave shape of the wine and ensure the similarity of the free surface between experiments with the same dimensionless numbers.

For a comprehensive demonstration of their findings have a look at their video, which illustrates their methods very nicely and shows you lots of swirling wine. Hopefully, you will now have another interesting story to bring to the dinner table during the holidays.

Cheers!

```Reference
Reclari, Martino, et al. "Oenodynamic": Hydrodynamic of wine swirling. arXiv preprint arXiv:1110.3369 (2011).
Reclari, Martino. Hydrodynamics of orbital shaken bioreactors. (2013).```

## Remarkable Regions – The India-Asia collision zone

Every 8 weeks we turn our attention to a Remarkable Region that deserves a spot in the scientific limelight. This week we zoom in on a particular part of the eastern Tethys as Adina Pusok discusses the India-Asia collision zone. She is a postdoctoral researcher at the Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, UCSD, US.

Without doubt, one of the most striking features of plate tectonics and lithospheric deformation on Earth is the India-Asia collision zone, largely comprised of the Himalayan and Karakoram mountain belts and the Tibetan plateau. What makes this collision zone so remarkable? For one, Tibet is the largest, highest and flattest plateau on Earth with an average elevation exceeding 5 km, and it includes over 80% of the world’s land surface higher than 4 km. Then, the bordering Himalayas and the Karakoram Mountains include the only peaks on Earth reaching more than 8 km above sea level.

It makes one wonder, how can such a mountain belt and high plateau form? Most of the major mountain belts and orogenic plateaus on Earth are found within the overlying plate of subduction and/or collision zones (e.g. the Alps, the Andes, the American Cordilleras etc.). When an ocean closes and two continental plates meet at a destructive (subduction) boundary, the continents themselves collide. Such collisions result in intense deformation at the edges of the colliding plates. Neither continent can be subducted into the mantle due to the buoyancy of continental crust, so the forces that drive the plate movement prior to collision are brought to act directly on the continental lithosphere itself. At this stage, further convergence of the plates must be taken up by deforming one or both of the plates of continental lithosphere over hundreds of kilometres [Figure 1]. Mountain belts can form under these circumstances.

Figure 1 Global map of surface velocities and the second invariant of strain rate (from Moresi [2015]). The surface velocities show the location and extent of plates, and the strain rate map highlights the fact that most of the deformation is concentrated at plate boundaries (high strain rates), while the continental interiors have little or no deformation (low strain rates). In some places, deformation occurs over broader regions, especially following mountain belts. These boundaries are called diffuse plate boundaries. The white rectangle roughly indicates the extent of the India-Asia collision zone.

The Himalayas and the Tibetan plateau are no different. Following the closure of the Tethys ocean (see earlier blog post), the Indian continent collided with Eurasia around 50 million years ago (e.g., Patriat and Achache [1984]), thus giving rise to this anomalously high region. This tectonic boundary is complex and changes character along its length. The Tibetan plateau is a collage of continental blocks (terranes) that were added successively to the Eurasian plate during the Paleozoic and Mesozoic [Figure 2]. The boundaries between these terranes are marked by scattered occurrences of ophiolitic material, which are rocks characteristic of oceanic lithosphere. The Himalayas represent the traditional accretionary wedge formed by folding and thrusting of sediments scraped off the subducting slab.

Figure 2 Simplified tectonic map of Tibet and surrounding region showing approximate boundaries of the major terranes, suture zones, and strike-slip faults (from Ninomiya and Bihong [2016]). Blocks and terranes: ALT-EKL-QL: Altyn Tagh–East Kunlun–Qilian terrane; BS: Baoshan terrane; HM: Himalayan terrane; IC: Indo-China block; KA: Kohistan Arc terrane; LA: Ladakh arc terrane; LC: Lincang–Sukhothai–Chanthaburi Arc terrane; LST: Lhasa terrane; NCB: North China Block; NQT: North Qiangtang terrane; QT: Qiangtang terrane; SP: South Pamir terrane; SPGZ: Songpan-Ganze terrane; SQT: South Qiangtang terrane; TC: Tengchong terrane; TSH: Tianshuihai terrane; WB: West Burma terrane; WKL: West Kunlun terrane. Suture zones: BNS: Bangong-Nujiang Suture; EKLS: East Kunlun Suture; ITS: Indus-Tsangbo Suture; JSS: Jinsha Suture; LSS: Longmu Tso–Shuanghu–Menglian–Inthanon Suture; WKLS: West Kunlun Suture. Basins: QB: Qaidam Basin; KB: Kumkol Basin. Faults: ALT: Altyn Tagh Thrust; ALTF: Altyn Tagh Fault; KKF: Karakorum Fault; LMST: Longmen Shan Thrust; MFT: Main Frontal Thrust; NQLT: North Qilian Thrust; RRF: Red River Fault; SGF: Sagaing Fault; XXF: Xianshui River–Xiaojiang Fault.

Interestingly, the India-Asia collision orogen is not just the youngest and most spectacular active continent collision belt, it is also the most studied research area on Earth. Studies on this region span a wide range of topics and methods for over more than 100 years. I am not sure if it is the fascination with the highest mountain on Earth (Mt. Everest was actually climbed for the first time as late as 1953 by Tenzing Norgay and Edmund Hillary), similar to our fascination for exploring the Moon, Mars and the other planets in our Solar System nowadays, or the hope that studying the youngest orogeny will help us decipher the older ones (soon to realize different mountain belts evolve differently).

To understand the magnitude of the work done in the past 100 years, a simple search of the keywords “India Asia collision” on Google Scholar yielded ~90k results, and a more focused geosciences search on Web of Science (where I filtered the results to those from geophysics, geochemistry, geology, geosciences multidisciplinary only) yielded >1600 results for the same keywords (other keywords: “Himalaya” > 5600 results, “Tibet” > 6500 results, “India Asia” > 2200 results). These numbers can be intimidating to a new student taking on the topic, but it is a topic worth studying and I’ll explain why below.

From a general perspective, it is important to study the India-Asia collision zone due to the interaction between tectonics and climate and the formation of the Indian monsoon [Molnar et al., 1993], but also because it is a highly populated area (>200 million people in the Hindu Kush Himalaya region) regularly shaken by natural phenomena, such as earthquakes, floods or landslides. For example, the last large earthquake in Nepal, the Gorkha earthquake (Mw 7.8) in April 2015 caused more than 9000 deaths.

From a geophysics point of view, understanding mountain-building processes and the driving forces of plate tectonics has been one of the long-term goals of solid Earth sciences community. The India-Asia collision zone is one of the best examples in which subduction, continental collision and mountain building can be studied in a global plate tectonics perspective. Prior to plate tectonics theory, Argand [1924] and Holmes [1965] thought that the Himalayan Mountains and Tibetan Plateau had been raised due to the northern edge of the Indian craton underthrusting the entire region, causing shortening and thickening of the crust to ∼80 km. This perspective remains widely accepted, but recent ideas suggest that other processes are equally important (more below).

Today, the challenge lies in refining our understanding of the dynamics of India-Asia collision by elucidating the connections between the wealth of observations available and the underlying processes occurring at depth. Decades of study have produced data sets across various disciplines, including: active tectonics, Cenozoic geology, seismicity, global positioning system (GPS) measurements, seismic profiles, tomography, gravity anomalies, mantle-crustal anisotropy, paleomagnetism, geochemistry or magnetotelluric studies. Of these, the GPS data stands out as it clearly shows the distributed deformation across the entire collision zone and suggests that this is a highly dynamic area [Figure 3].

Figure 3 Horizontal GPS velocities of crustal motion around the Tibetan Plateau relative to stable Eurasia from Liang et al. [2013].

Collectively, all these observation data sets stand as a different piece in the puzzle of the India-Asia collision. However, the same data sets can support a number of competing and sometimes mutually exclusive mechanisms for the uplift of the Tibetan Plateau. For example, the mantle lithosphere beneath Tibet has been proposed to be cold, hot, thickened by shortening, or thinned by viscous instability. Other controversies include the degree of mechanical coupling between the crust and deeper lithosphere and the nature of large-scale deformation. It is no surprise then, that several hypotheses emerged over time trying to explain the anomalous rise of the Himalayas and Tibetan Plateau [Figure 4]:

1. Figure 4 Schematic cartoons of tectonic models proposed to explain the thickening and uplift of the Himalayas and the Tibetan Plateau. (Source: personal institutional web page of A. Ozacar).

Wholescale underthrusting of the Indian plate below the Asian continent [e.g. Argand, 1924].

2. The thin-sheet model or distributed homogeneous shortening [e.g. England and McKenzie, 1982].
3. Homogeneous thickening of a weak, hot Asian crust, involving a large amount of magmatism [e.g. Dewey and Burke, 1973].
4. Slip-line field model to account for the brittle deformation in and around the Tibetan Plateau and to explain extrusion of SE Tibet away from Indian continent [e.g. Molnar and Tapponnier, 1975]. The same group also proposes a time-dependent model for the growth of Tibetan plateau [e.g. Tapponnier et al., 2001], in which successive intracontinental subduction zones maintain the stepwise growth and rise of the plateau.
5. Lower crustal flow models for the exhumation of the Himalayan units and lateral spreading of the Tibetan plateau [e.g. Royden et al., 1997, Beaumont et al., 2001].
6. Delamination or convective removal of the lithospheric mantle that induced isostatic movement, lifting the Tibetan Plateau [e.g. Molnar, 1988].

These models were applied either to the Tibetan Plateau or the Himalayan mountain belt and were able to explain the formation of specific tectonic and geological features. However, there is no conclusive answer on which of the hypotheses works best for the entire orogen, and instead, more questions arise:

• Which forces are at work during continental collision and mountain building?
• What is the deformation history and evolution of this plate boundary?
• How was the subduction accommodated in the Neo-Tethys?
• How does subduction evolve during continental collision?
• What drives the present-day fast convergence (~4-5 cm/yr) between India and Eurasia?
• Which forces propagated India northwards between 70-50 million years at anomalously high speeds (up to 16 – 20cm/yr)?
• How can you form such large elevations over such extended areas?
• What is the effect of surface processes on uplift?
• What is the structure at depth beneath the Himalayas and Tibetan plateau?
• How do the Indian and Eurasia plates deform during collision?
• How is the deformation accommodated during continental collision?
• How do mountain belts form and why not all mountain belts look the same?
• How did the crust beneath Himalaya and Tibet reach double-crustal thickness (normal continental crust is 35-40 km thick, whereas the crust beneath the Himalaya and Tibet is 70-100 km thick)?
• Which mechanisms help sustain the high topographic amplitudes?
• Why should an area as broad as the Tibetan Plateau be uplifted so high compared to other mountain belts following collision?
• Did the Tibetan Plateau and Himalayan mountain belt rise continuously or diachronously?
• Which the proposed models [Figure 4] can be applied, and where?
• How do lithospheric heterogeneities and rheology affect the deformation pattern?
• What is the degree of mechanical coupling between the crust and deeper lithosphere? Is it the “jelly sandwich” model (e.g., Burov and Watts [2006]) or the “creme-brulee” model (e.g., Jackson [2002], see earlier blog post)?
• Why do the Himalayas have a convex curvature?
• What about the high deformation of the prominent Himalayan syntaxes (the inflection points of the Himalayan belt): Nanga Parbat in the west and Namche Barwa in the east?
• What is the effect of the India-Asia collision on climate? Do the Himalayas affect the Indian monsoon or is it the other way around? A chicken-and-egg question.

Seriously, can I even stop asking questions? The question that fascinated me the most during my graduate studies was “Why is the Himalayan-Tibet region so high and broad compared to other mountain belts?”. If we tune our models to Earth parameters, can we build such large elevations in computer simulations? Which factors and forces are at play? Using 3-D numerical models to address this question [Pusok and Kaus, 2015], we were able to obtain distinct topographic modes (different types of mountain belts) [Figure 5] and to show that building topography is an interplay between providing the energy to the system and the ability of that system to store it over longer periods of time. We also suggest that the reason why Himalaya-Tibet is different from the Alps, for example, is because the shape and elevation of mountain ranges can vary depending on the boundary conditions (plate driving forces that control convergence velocity and lithospheric heterogeneities such as the Tarim Basin) and internal factors (rheology), but also on the evolution stage they are in.

To sum up, it is clear that many of the above questions remain unanswered. But I think this is good news, meaning that in the future, exciting new results will shape our understanding of this remarkable region.

Figure 5 3-D Simulation results showing different modes of surface expressions in continental collision models. Modified from Pusok and Kaus [2015].

```References:
Argand, E. (1924). La tectonique de l’Asie. Proc. 13th Int. Geol. Cong., 7:171–372.

Beaumont, C., Jamieson, R. A., Nguyen, M. H., and Lee, B. (2001). Himalayan Tectonics Explained by Extrusion of a Low-Viscosity Crustal Channel Coupled to Focused Surface Denudation. Nature, 414:738–742.

Burov, E. B. and Watts, A. B. (2006). The long-term strength of continental lithosphere: “jelly sandwich” or “crème brûlée”? GSA Today, 16(1):4.

Dewey, J. F. and Burke, K. (1973). Tibetan, Variscan, and Precambrian Basement Reactivation: Products of Continental Collision. The Journal of Geology, 81(6):683–692.

England, P. and McKenzie, D. (1982). A Thin Viscous Sheet Model for Continental Deformation. Geophys. J. R. astr. Soc., 70:295–321.

Holmes, A. (1965). Principles of Physical Geology. The Ronald Press Company, New York, second edition.

Jackson, J. (2002). Strength of the Continental Lithosphere: Time to Abandon the Jelly Sandwich? GSA Today, 4–9.

Liang, S., Gan, W., Shen, C., Xiao, G., Liu, J., Chen, W., Ding, X., and Zhou, D. (2013). Three-dimensional velocity field of present-day crustal motion of the Tibetan Plateau derived from GPS measurements. Journal of Geophysical Research: Solid Earth, 118:1–11.

Molnar, P. and Tapponnier, P. (1975). Cenozoic Tectonics of Asia: Effects of a Continental Collision. Science, 189:419–426.

Molnar, P. (1988). A Review of Geophysical Constraints on the Deep Structure of the Tibetan Plateau, the Himalaya and the Karakoram, and their Tectonic Implications. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 326(1589):33–88.

Molnar, P., England, P., and Martinod, J. (1993). Mantle Dynamics, Uplift of the Tibetan Plateau, and the Indian Monsoon. Reviews of Geophysics, 31:357–396.

Moresi, L. (2015). Computational Plate Tectonics and the Geological Record in the Continents. SIAM News, 48:1–6.

Ninomiya, Y. and Bihong Fu, B. (2016). Regional Lithological Mapping Using ASTER-TIR Data: Case Study for the Tibetan Plateau and the Surrounding Area. Geosciences 2016, 6(3), 39; doi:10.3390/geosciences6030039.

Patriat, P. and Achache, J. (1984). India-Eurasia collision chronology has implications for crustal shortening and driving mechanism of plates. Nature, 311:615–621.

Pusok, A. E. and Kaus, B. J. P. (2015). Development of topography in 3-D continental-collision models. Geochemistry, Geophysics, Geosystems, 16(5):1378–1400.

Royden, L. H., Burch el, B. C., King, R., Wang, E., Chen, Z., Shen, F., and Liu, Y. (1997). Surface Deformation and Lower Crustal Flow in Eastern Tibet. Science, 276(5313):788–790.

Tapponnier, P., Zhiqin, X., Roger, F., Meyer, B., Arnaud, N., Wittlinger, G., and Jingsui, Y. (2001). Oblique Stepwise Rise and Growth of the Tibet Plateau. Science, 294(5547):1671–1677.```

## 2017 AGU Fall Meeting

The largest Earth and Space science meeting in the world is taking place in New Orleans, Louisiana.

As usual, once a year AGU gathers the best and brightest minds from around the globe in the pursuit of high quality science, knowledge, and a more sustainable future. In particular, AGU allows to share your science, advance your career, and gain visibility and recognition for your own scientific efforts alongside the world’s leading scientific minds. With more than 20,000 oral and poster presentations, scientists can get the latest in groundbreaking research from every field and gain inspiration for your own work.

A classic crowded poster session at AGU

This fall meeting is a great way for early-career professionals to make connections. Not only are attendees exposed to thousands of presentations filled with emerging science and new research, but they have the opportunity to attend countless events and workshops that can equip them with the right tools to build a sustainable career. Presenters get constructive feedback in real time from experts and established scientists in the field. Presenting is a great way to test-drive your research before publishing in a peer-reviewed journal.

French Quarter by night. One of the great things about the French Quarter is that it sits beside the mississippi river, which turns out is beautiful at night!

But not only that! This meeting gives the opportunity to explore the city’s world-famous French Quarter, Jackson Square, and Saint Louis Cathedral. New Orleans is the birthplace of jazz and a mecca for gospel, the rock and pop we love today. Strolling through the French Quarter you can enjoy many live music performances ranging from swanky lounges to tiny honky-tonks – enjoy!

## Conferences – so near and yet so far

Attending conferences is expensive and time consuming, so going to all the conferences relevant for your research topic(s) is an impossible mission. One solution might be to attend (parts of) conferences remotely. Suzanne Atkins, postdoc at ETH Zürich, Switzerland, discusses the pros and cons of remote conferencing.

Last month the Geological Society of London live-streamed their celebration of 50 years of plate tectonics. Here at ETH we joined the love-in, camping out in the lecture theatre for two days. This follows the trend of many conferences to live-stream sessions or make them available on-line afterwards. But can video conferences replace the real thing? And would we want them too?

On paper, there are so many reasons to support video conferencing and replays. The most obvious one is financial. Many students are limited to local conferences and even professors have to watch their expenditure. The eye-watering cost of a large conference like EGU makes annual attendance unfeasible for many scientists, especially when extras like beer are factored in. If you’re only interested in one or two sessions, dropping in remotely makes far more sense than dragging yourself halfway across the continent for an afternoon.

But there are plenty of other reasons. Here at ETH, our flights make up around 60% of the department CO2 budget. Yes, I could take the train but I’m too lazy and impatient (I know, I know), especially if I’m only interested in half the conference. This doesn’t even take into account the vast carbon footprint of the hospitality industry, to which we are contributing every time we stay in a hotel or eat at a restaurant. Remote conference attendance is therefore the only really defensible environmental option.

The attraction of attending a conference where I can sleep in my own bed is high, but for academic parents, or even just academics with a life outside work, the benefits of cutting a few trips off the yearly circuit without missing out are obvious. Especially in the summer season, when we’re all trying to cram in holidays and a bit of teaching-free research time, the seemingly endless round of meetings and workshops can end up feeling more of a chore than a pleasure.

This brings me to my final point in favour. For a remote conference, etiquette is far more flexible than in person attendance. No one at the conference can see you checking your emails, or dipping in and out to talk to students. The university WiFi is nice and reliable. And the quality of the coffee is just so much more … predictable.

So, what are the drawbacks? Why don’t we all switch over immediately? Obviously attending conferences remotely can make it difficult to present your own work and get feedback, which is invaluable for us. We will never be able to fully replicate digitally the experience of a long poster discussion, chatting to someone after a talk, or the serendipitous meeting in the coffee queue.

But there may also be some subtler disadvantages. At cash-strapped institutes, remote conferencing will allow staff and students who otherwise couldn’t attend to see the talks. But it might also lead to pressure, particularly on students and junior researchers, to cut expenditure by never leaving the building. That deprives them of the networking and presentation opportunities that conferences offer. The flip-side of this is that conferences would get boring scientifically. The same few faces would attend every time, starving the community of new ideas and input. Both of these seem somewhat extreme endpoints, which could be guarded against by careful management within institutes and by conference organisers, and the availability of grants and scholarships for attendance.

So all in all, I think I have to conclude that live streaming conferences seems a sensible way to go. I can even head off to my post-conference Friday beer in the common room afterwards. Cheers!