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The Sassy Scientist – Hyde: Lithosphere Dynamics

The Sassy Scientist – Hyde: Lithosphere Dynamics

Every week, The Sassy Scientist answers a question on geodynamics, related topics, academic life, the universe or anything in between with a healthy dose of sarcasm. Do you have a question for The Sassy Scientist? Submit your question here.

Senna asks:


I’m torn between mantle dynamics and lithosphere dynamics as a research topic. Which shall I choose?


Dear Senna,

I don’t know what came over me when writing last week’s post. Must have been something I ate. Sometimes I just get some crazy idea stuck in my head. For example, I completely misconstrued ideas on the relative importance of mantle convection over lithosphere dynamics.

Last week I was babbling on about plate tectonics, and how the focus on the lithosphere shifted attention away from mantle convection. To be clear: this was for good reason. Granted, McKenzie and Parker’s (1969) concept of rigid plates on a shell was simplified. That was also the point: it explains some first-order observations like relative plate motions and seismicity. No, plate boundaries are not necessarily narrow zones of deformation (Kreemer et al. 2014). Yes, plates can also be flexed through loads on top, or radial mantle tractions from below (Watts 2001). We know that the Earth’s lithosphere can generally be considered to be a visco-elastic plate that is primarily moved by forces acting at its boundaries. Does this preclude seismicity or deviations from principal stress directions far away from such plate boundaries? Of course not.

It is obviously a great idea to base model predictions on non-unique gravity and geoid observations, seismic tomography, and Earth’s normal mode undulations for structures 2500 km away from the surface. The surface. You know, that place where we actually have direct observations. Sure, just extrapolate some rheology measured on a rock sample down to the lower mantle using some equations of state. Should be similar, right? Do you have a kinematic plate tectonic reconstruction based on loads of geological and paleomagnetic data? Just pop it into a mantle convection model to see whether it is feasible. You measured some SKS splitting data? That’s definitely a measure of present-day mantle flow. You infer instantaneous dynamic topography at the surface in the order of a couple 100 meters? Mantle convection models predict kilometers of instantaneous dynamic topography, so you must have made a mistake in your observations.

Do you want to understand what’s driving deformation of the lithosphere? Choose lithosphere as a research topic. Do you believe in fairy tales? Look into mantle convection: it’s full of magic.

Yours truly,

The Sassy Scientist

PS: This post was written after recovering from a major headache from reading last week’s post.

PS2: I won’t be surprised if there is going to another post on this topic next week. How well do you know your Scottish literature?

References:
Kreemer, C., G. Blewitt, E.C. Klein (2014). A geodetic plate motion and Global Strain Rate Model, Geochemistry, Geophysics, Geosystems, 15, 3849-3889, doi:10.1002/2014GC005407
McKenzie, D., and R. L. Parker (1967), The North Pacific: An example of tectonics on a sphere, Nature, 216, 1276
Watts, A. B. (2001), Isostasy and flexure of the lithosphere, Cambridge University Press, 458 pp.

The Sassy Scientist – Jekyll: Mantle dynamics

The Sassy Scientist – Jekyll: Mantle dynamics

Every week, The Sassy Scientist answers a question on geodynamics, related topics, academic life, the universe or anything in between with a healthy dose of sarcasm. Do you have a question for The Sassy Scientist? Submit your question here.

Senna asks:


I’m torn between mantle dynamics and lithosphere dynamics as a research topic. Which shall I choose?


Dear Senna,

This is an easy one: mantle dynamics. Don’t you want to be part of cutting edge research, utilising state-of-the-art numerical modelling codes and high performance computing facilities? You can employ every solid rock rheology known to man and generate new lithosphere through volcanism. Nowadays the lithosphere and crustal layers are implemented so convincingly that we can easily match seismic tomography slices, passive margin architectures and even subduction zones to the scale of accretionary wedges. Inherited weak zones can lead to supercontinent cycles. The sky is the limit!

I am the first to admit that mantle convection has been overshadowed for quite a while by plate tectonic theory ever since the early days of Holmes (1931). Wilson’s (1965) tessellation of the Earth’s surface and the straightforward connection to relative plate motions (e.g., McKenzie and Parker 1967) and mid-ocean magnetic anomalies (Vine and Matthews 1963) resulted in a longstanding main focus on lithosphere dynamics (Forsyth and Uyeda 1975). Even though early work, by for example Morgan (1971), showed that simplified systematic mantle convection explained first-order observations as well, it took quite a while before mantle convection became more popular. To be clear, researchers from several fields studying the mantle didn’t help very much: lingering discussions on whole mantle convection vs. separate flow cells, whether slabs or plumes can penetrate the 660 km boundary, and problems with incorporating a realistic lithosphere with proper rheologies that produced surface deformation predictions similar to the actual Earth’s surface held back widespread acceptance that mantle convection can explain everything. Nowadays, computational prowess and numerical model sophistication is at a point where we have overcome these issues: once again, the lithosphere is simply the thermal boundary layer of the mantle convection system.

Yes, the lithosphere is tessellated and undergoes continuous reorganisation — we can model this with mantle convection. Yes, there are probably thermo-chemical piles in the lower mantle — we can incorporate these. Yes, we infer that India has moved faster than any continent does at present — just add a mantle convection cell. Yes, the surface has topography that we can’t explain with isostasy and flexure — it is induced by radial mantle flow. I’m forgetting other issues here, obviously. The point is: studying lithosphere dynamics is going to be an obsolete exercise in a couple of years. Join the mantle convection party and be prepared for the future!

Yours truly,

The Sassy Scientist

PS: This post was written after reading quite a bunch of lithosphere dynamics papers trying to explain surface observations without using the mantle!

References:
Forsyth, D.W. and Uyeda, S. (1975), On the relative importance of the driving forces of plate motion, Geophys. J. R. astr. Soc., 43, 163–200
Holmes, A. (1931), Radioactivity and Earth movements, Transactions of the Geological Society of Glasgow, Geological Society of Glasgow: 559–606
McKenzie, D., and R. L. Parker (1967), The North Pacific: An example of tectonics on a sphere, Nature, 216, 1276
Morgan, W. J. (1971). Convection Plumes in the Lower Mantle. Nature, 230, 42-43, http://dx.doi.org/10.1038/230042a0
Vine, F. J., and P.M. Matthews (1963), Magnetic anomalies over ocean ridges, Nature, 199, 947
Wilson, J. T. (1965), A new class of faults and their bearing on continental drift, Nature, 207, 343

The Sassy Scientist – Key Papers

The Sassy Scientist – Key Papers

Every week, The Sassy Scientist answers a question on geodynamics, related topics, academic life, the universe or anything in between with a healthy dose of sarcasm. Do you have a question for The Sassy Scientist? Submit your question here.

Luca asks:


What is (in your opinion) the key paper in geodynamics and why?


Dear Luca,

There is not one key paper. It is simply impossible to point at one paper and say: “This is the one that changed geodynamics”. Obviously, without the early work of Wilson, McKenzie, Froidevaux, Morgan, Turcotte, and Schubert (and many others, the list is enormous, don’t be offended if you’re not on it) the field of geodynamics wouldn’t even exist. However, unless you are a bachelor student, it should be fairly clear by now that (Earth) science is an evolving beast that can take many shapes and lead to many dead-ends. Well-considered concepts are continually overturned, contradicted or adjusted.

So, it seems to me that you are looking for a shortcut. Unfortunately this shortcut doesn’t exist and you’ll just have to go through the literature. Painstakingly and critically evaluating papers. And you’re right: most of the ones you’ll come across will not be qualified as ‘key papers’. But this is a good thing. It’s better to go through an abundance of small steps to move science forward than to take major leaps while overlooking small but significant details that take you across a decades-long detour…

Still interested in science?

Yours truly,

The Sassy Scientist

PS: This post was written after getting annoyed by stupid questions.

Happy blog birthday!

Happy blog birthday!

Can you believe it, people? We have been running this blog for 2 years! What a milestone! Time to celebrate and look back at a year of great blogging.

Who are the champions?

We are the champions, my friends!

That’s right! We actually won a prize this year: we won best blog post of 2018 by public vote for a post by one of our editors, Luca Dal Zilio, about a conference he attended in Singapore. So we are now an award-winning blog. Hell yeah!
Technically this post was written during our first blog year, but hey, we only got the prize in January, so I think we’re totally within our rights to mention it now. Since we won by public vote, we would like to thank all of you – our readers – for your support! It really means a lot to us and strengthens the idea that some people actually read this blog!

And talking about our readers…

Who are you?

Contrary to popular belief, there are actually people who read this blog! Although I don’t have any data to back this up, I think most of our readers are actually scientists from the geodynamics, tectonics and structural geology, and seismology divisions of EGU. So much for trying to do outreach. If I’m wrong, please let me know!
I do have some data on how many people visit our blog. On average, we have 37 unique visitors per day (and that’s quite something if you remember that we only post on Wednesdays and now Fridays). Our 100 most viewed pages (and this includes the homepage, author profiles, tags, etc. as well as individual posts) each have seen 150 unique visitors on average with some posts having over 2000 unique visitors in the past year! These popular posts are usually commissioned and promoted on social media by our editor Grace Shephard. Little gems of blog posts with many views from her hand include The Rainbow Colour Map (repeatedly) considered harmful, Thirteen planets and counting, and How good were the old forecasts of sea level rise?

We have a global readership! Most of our readers are accessing the website from the US, the United Kingdom, Germany, China, and Spain. Interesting list of countries, right? Apart from that, we also have some geodynamicists in Turkmenistan, Rwanda, Pakistan, Myanmar, and Mozambique. Or maybe that is just a result of geodynamicists being on holiday in exotic places who are dying to read geodynamics news to distract themselves from their amazing holiday destination. Who knows?

Who are we?

We have a lovely blog team and it’s quite a big team as well! Currently, there are 7 regular editors, one mysterious, anonymous editor under the name of ‘The Sassy Scientist’ and one Editor-in-Chief (yours truly). Who would’ve ever thought there would be 9 people in the blog team? Last year, we were 5, so we have grown a lot. If you have already forgotten who we are, you can check out our recent introduction post.

But, these 9 amazing editors don’t have the time (or the expertise) to write all these blog posts themselves. Therefore, we heavily rely on the most amazing guest authors. During the past year, we had 20 guest authors who contributed one or more posts. So here is a big shout out to all the guest authors of the past year:

• Manar Alsaif
• Marie Bocher
• Daniel Bowden
• Kiran Chotalia
• Robert Citron
• Lorenzo Colli
• João Duarte
• Rene Gassmöller
• Lars Gebraad
• Antoniette Greta Grima
• Charitra Jain
• Kirster Karlsen
• Maria Koroni
• Laurent Montesi
• Andrea Piccolo
• Adina Pusok
• Nico Schliffke
• Paul Tackley
• Katy Willis
• Jonny Wu

Thank you so much. We couldn’t do it without you!

Behind the scenes

During our first 1.5 years of blogging we had a system in place where we had regular types of posts, such as Geodynamics 101, Remarkable Regions, Peculiar Planets, and Wit & Wisdom posts. Additional content that did not fit in any of these categories, would go into our News & Views or Conferences. This meant that all the editors were encouraged to find posts that fitted into a certain topic and then we hoped for the best. In practice, most of the responsibility lay with yours truly: the Editor-in-Chief. I was in charge of keeping an eye on the schedule and asking the editors to contribute. In the end, I wrote and commissioned most of the posts myself.

That was clearly unsustainable.

Whenever I had a lapse of vigilance, holes were more likely to appear in the schedule, because no one else in the blog team felt responsible for posting (and rightfully so). This lead to the infamous gaps in content around February (which seems to be a recurring yearly theme).

Again: clearly unsustainable.

So. This year, I got inspired at the EGU Blog Editor meeting a few days before the General Assembly and I thought of a complete new blog strategy during EGU. I know: I spent my time at EGU wisely…

We recruited a bunch of new editors and we have now successfully implemented a new schedule: all 7 regular editors are responsible for a blog post for 1 week in a 7 week cycle. They can commission blog posts, write them, give their slot to another editor who might have more blog posts lined up, or whatever they want to do, but they are – in the end – responsible for uploading a blog post on Wednesday. I still keep an eye on the schedule and fill gaps where necessary, but at least now I have someone to address whenever there seems to be an empty slot. We also added some extra repercussions to increase the responsibility of our regular editors: if they fail to upload a Wednesday blog post on time in their scheduled weeks twice within one year, they will automatically stop being editors. Of course, we want to keep everyone in the team, so everyone is encouraged to help each other out, if a gap in the schedule threatens to appear.
The Sassy Scientist is responsible for weekly Friday Q&As, which is a lot of work actually: 52 blog posts in a year is a lot. So for these posts, we are working with a backlog of at least 5 blog posts at all times to ensure that our Sassy Scientist can sometimes take a holiday. Currently, I am editing all the Sassy Scientist blog posts, but I’m hoping they can fly solo soon! One of the most difficult things is getting questions for the Sassy Scientist to answer. So far most of the questions have been asked by editors, although some wished to remain anonymous, so their names were changed. Therefore, we ask everyone to just e-mail the Sassy Scientist a question, leave a comment to one of the blog posts or on social media. You will remain anonymous, if you so desire, and we will make sure that your question gets answered soon (i.e., we will adapt the schedule accordingly).
The new system works well so far. Let’s see if we can keep it up!

So now what?

Well, onwards and upwards, don’t you think? We will try to keep providing you with geodynamics news on Wednesdays and Sassy Scientist Q&As on Fridays for another year. That’s twice as much content as in our first year! Theoretically. We have lots of great posts lined up as well as some very impressive, new guest authors who are dying to pen down their thoughts. If you would like to contribute to the blog, don’t hesitate to contact us by sending us an e-mail. Until then: enjoy the read!