GD
Geodynamics

Iris van Zelst

Iris van Zelst is a PhD student at ETH Zürich in Switzerland. She is working on the modelling of tsunamigenic earthquakes using a range of interdisciplinary modelling approaches, such as geodynamic, dynamic rupture, and tsunami modelling. Current research projects include splay fault propagation in subduction zones and the 2004 Sumatra-Andaman earthquake. Iris is Editor-in-chief of the GD blog team. You can reach Iris via email. For more details, please visit Iris' personal webpage.

EGU GD Whirlwind Wednesday: Geodynamics 101 & other events

EGU GD Whirlwind Wednesday: Geodynamics 101 & other events

Yesterday (Wednesday, April 12, 2018), the first ever Geodynamics 101 short course at EGU was held. It was inspired by our regular blog series of the same name. I can happily report that it was a success! With at least 60 people attending (admittedly, we didn’t count as we were trying to focus on explaining geodynamics) we had a nicely filled room. Surprisingly, quite some geodynamicists were in the audience. Hopefully, we inspired them with new, fun ways to communicate geodynamics to people from other disciplines.

The short course was organised by me (Iris van Zelst, ETH Zürich), Adina Pusok (ECS GD Representative; UCSD, Scripps Institution of Oceanography, IGPP), Antoine Rozel (ETH Zürich), Fabio Crameri (CEED, Oslo), Juliane Dannberg (UC Davis), and Anne Glerum (GFZ Potsdam). Unfortunately, Anne and Juliane were unable to attend EGU, so the presentation was given by Antoine, Adina, Fabio and me in the end.

The main goal of this short course was to provide an introduction into the basic concepts of numerical modelling of solid Earth processes in the Earth’s crust and mantle in a non-technical, fun manner. It was dedicated to everyone who is interested in, but not necessarily experienced with, understanding numerical models; in particular early career scientists (BSc, MSc, PhD students and postdocs) and people who are new to the field of geodynamic modelling. Emphasis was put on what numerical models are and how scientists can interpret, use, and work with them while taking into account the advantages and limitations of the different methods. We went through setting up a numerical model in a step-by-step process, with specific examples from key papers and problems in solid Earth geodynamics to showcase:

(1) The motivation behind using numerical methods,
(2) The basic equations used in geodynamic modelling studies, what they mean, and their assumptions,
(3) How to choose appropriate numerical methods,
(4) How to benchmark the resulting code,
(5) How to go from the geological problem to the model setup,
(6) How to set initial and boundary conditions,
(7) How to interpret the model results.

Armed with the knowledge of a typical modelling workflow, we hope that our participants will now be able to better assess geodynamical papers and maybe even start working with numerical methods themselves in the future.

Apart from the Geodynamics 101 course, the evening was packed with ECS events for geodynamicists. About 40 people attended the ECS GD dinner at Wieden Bräu that was organised by Adina and Nico (the ECS Co-representative for geodynamics; full introduction will follow soon). After the dinner, most people went onwards to Bermuda Bräu for drinks with the geodynamics, tectonics & structural geology, and seismology division. It featured lots of dancing and networking and should thus be also considered a great success. On to the last couple of days packed with science!

EGU GD Informal Lunch

EGU GD Informal Lunch

Good afternoon. This is your correspondent, Iris van Zelst, reporting live from the EGU General Assembly 2018 in Vienna, Austria. Today, the first Early Career Scientist Geodynamics event of this week took place. Several young geodynamicists gathered at the Donau Zentrum (metro stop Kagran, 2 stops away from the conference centre) to have lunch. ECS Representative Adina Pusok, who initiated this meeting, is said to have explained the role of the ECS Representative and the many different activities in which ECS can become involved. Furthermore, inside sources confirm that a new blog editor and ECS Co-Representative have been found. We expect more details to become available in the near future. This was Iris van Zelst, reporting live from Vienna, Austria. Back to the studio.

Live reporting from EGU GA 2018

Live reporting from EGU GA 2018

As per usual (I mean, we reported Nethermod, right?), the EGU Geodynamics blog team will be reporting live from the 2018 edition of the EGU General Assembly. So, if you cannot attend this year: do not despair! We will keep you in the loop! Look out for updates on the social geodynamics events organised by our ECS GD representative Adina Pusok, interviews with attendees and updates on major sessions for the next two weeks. “Two weeks?!”, I hear you say. Yes, “two weeks”, because your faithful blog team might be a bit delayed with posting everything, as our schedule is pretty full as well. Also, what better time to give you a recap and the latest tips and tricks that we picked up ourselves during the conference than the week after? Exactly.

There have already been some interesting geodynamics sesssions at the EGU General Assembly (GA) 2018. Yesterday (Monday, April 9th, 2018), was a subduction filled day with continuous oral and poster presentations from 8:30h to 19:00h during the session: “subduction dynamics from surface to deep mantle”. Many interesting talks and posters (and karaoke?) later, we are now ready for Tuesday with some more interesting sessions and our first social event!

Convection in eggs

Convection in eggs

Happy Easter everybody! It is that time of year again when you wake up excitedly on Easter Sunday and run into the garden to find the chocolate eggs the Easter Bunny hid for you! What? That’s just me? Hm. Well, in any case, you will probably have a couple of extra days off from work and this should be celebrated with a themed blog post! As you know, geodynamics is about the large scale dynamics of the Earth. One of the most important and most studied processes in geodynamics is mantle convection. However, convection processes are not only present on this large (mantle) scale. In fact, you can find convection processes everywhere around you. Think for example about adding cold milk to your hot tea or coffee: a more beautiful example of a(n analogue) model of convection you will only rarely find. However, for this happy Easter occasion, we will focus on the convection in eggs! Yes, your eyes do not deceive you: real eggs!

What is convection?

Let’s start with the definition of convection. Feel free to skip this section if you are a diehard geodynamicist already. For those of you that are not: convection is a natural process of heat transfer where material flows (convects) due to material density differences that are caused by a difference in temperature. To go back to our coffee analogy: the coffee is hot, and therefore less dense than the cold milk. If you pour the milk in the coffee, the milk is denser (~heavier) than the coffee and thus sinks to the bottom of your cup driven by buoyancy contrasts. This heat transfer via the movement of liquids is called convection. It happens in your coffee cup, and it also happens in the mantle of the Earth. And is an egg really that different? Imaging that the egg white is the mantle and the egg yolk the core and we have a nice analogy (okay, the yolk can move, I know. Cut me some slack).

Why would you study the convection in eggs?

Good question. I also didn’t have no clue at first. However, as it turns out, studying the convection in eggs is very important for the food processing of eggs. People like to cook with actual, intact eggs, but there is always a risk that raw eggs contain salmonellae. Apparently there are pasteurised ‘liquid egg’ products on the market, but they can not be used in as many different ways as real, intact eggs. So, in order to make sure that you can safely lick the spoon used to make the cake batter, the idea of ‘pasteurisation of intact eggs’ was born. By pasteurising intact eggs, the illness-inducing salmonellae is killed, without actually compromising the great versatility of the egg. In order to determine how long you should heat an egg at which temperature to kill all the salmonellae (and without accidentally boiling the egg), one needs to know how heat is transferred inside the egg. Hence, one should study the convection of an egg.

So what does convection in eggs look like?

Denys et al., 2004 conducted a numerical study into the computational fluid dynamics of conductive and convective heat transfer in eggs. They used three model setups:
• a reference egg without a yolk
• an egg with a yolk in the middle
• an egg with a yolk at the top

They looked at the time evolution of heating of the egg, while also keeping track of the coldest point in the egg (which is a measure of the pasteurisation process). The initial egg was at a uniform temperature of 24.5 ℃. They then simulated the placement of the egg in a 59.4 ℃ water bath. The calculated velocity fields and time evolution are shown in the figures below.

Calculated velocity field (top) and contours (bottom) after 30s of food processing in a water bath for the three types of model setups: a) no yolk, b) yolk in the middle, c) yolk at the top. Figure from Denys et al., 2004.

Time evolution of the temperature in the model of an egg with a yolk in the middle after being heated in a water bath for a) 5s, b) 10s, c) 30s, d) 80s, e) 150s, and f) 300s. White line is the 53 °C temperature contour and the cross represents the coldest point in the egg. Figure from Denys et al., 2004.

Denys et al., 2004 conclude that the convection in the egg changes the location of the coldest point in the egg: if there was only conduction at play, the coldest spot would be at the geometrical centre of the egg, but the convection forces the slowest heating zone to the bottom of the egg.

This conclusion is of course not applicable to the Earth: the core doesn’t move through the mantle, like the egg yolk can move through the egg white. Still, studying the process of convection systematically across all natural scales ultimately leads to a better understanding of the convection process, which is beneficial for everyone studying the physical process of convection on whatever scale.

So now you know what happens during convection in an egg. It’s not quite the Earth, but with a bit of festive imagination we can go a long way. Hopefully this piece of convection trivia will come in handy during the long Easter weekend. Enjoy!

Reference
Denys, S., Pieters, J. G., & Dewettinck, K. (2004). Computational fluid dynamics analysis of combined conductive and convective heat transfer in model eggs. Journal of Food Engineering, 63(3), 281-290.