Holiday recommendations – blog break summer 2018

Holiday recommendations – blog break summer 2018

Even dedicated workaholics such as the editors of your EGU GD Blog Team sometimes deserve a break! Let me clarify that by saying ‘an intentional break’ (because uploading every Wednesday is hard!). We will be ‘on holiday’ during August, so there won’t be any new blog posts then. But don’t worry: we will be back stronger than ever in September and we already have a lot of very good blog posts in the pipeline for you. To start the holidays properly and to get you in the holiday spirit as well, the EGU GD Blog Team shares their geodynamical holiday recommendations with you. Enjoy & relax!

Iris van Zelst – Edinburgh

Hutton’s Section with a very young me (in 2012) for scale

Go. To. Edinburgh. Seriously: Edinburgh is the place to be for anyone who has an affinity with the Earth sciences. In this beautiful, historic city, James Hutton – the founder of modern geology, who originated the idea of uniformitarianism – lived and died. Everywhere in the city you can find little reminders indicating this iconic scientist lived there. You could, for example, visit his grave, and hike to his geological section on Edinburgh’s Salisbury Crags. There are also little plaques spread around the city that mark significant James Hutton places and events. The city itself is also steeped in a mix of geology and history: Edinburgh Castle, situated on the impressive volcanic Castle Rock, boasts an 1100-year-old history and towers over the city. Directly across from the castle, connected by the charming Royal Mile is Holyrood Palace, where you can soak up even more history – Mary Queen of Scots lived here for a while. Nearby, there is Holyrood Park where you can find the group of hills that hosts Hutton’s Section and a 350 million year old volcano named Arthur’s Seat. Climb it when the weather is nice and you will have the most amazing view of Edinburgh. The whole park is perfect for day hikes and picknicks.
Even if you (or your travel buddy) are not that into Earth Sciences (or history), Edinburgh has plenty of other attractions. It is the perfect place for book and literature lovers with the large International Book Festival every August and a very rich literary history with iconic writers such as Walter Scott (Ivanhoe), Robert Louis Stevenson (Strange Case of Dr Jekyll and Mr Hyde; Treasure Island), Arthur Conan Doyle (Sherlock Holmes), and – more recently – J. K. Rowling (Harry Potter). Theatre fans will also love Edinburgh, particularly during August when it hosts the Edinburgh Festival Fringe – the largest arts festival in the world.
I totally should’ve booked a trip to Edinburgh this year… Learn from my mistakes and enjoy it in my stead!

The view of Edinburgh when you’re standing on top of Arthur’s Seat: a more than 300 million year old volcano. Pretty epic.
Picture by me in 2012 (also: proof that the weather can be good in Scotland!)

Luca Dal Zilio – Aeolian Islands

My recommendation? I vote for the Aeolian Islands! Smouldering volcanoes, bubbling mud baths and steaming fumaroles make these tiny islands north of Sicily a truly hot destination. This is the best place to practice the joys of “dolce far niente“: eat, sleep, and play. The Aeolian Arc is a volcanic structure, about 200 km long, located on the internal margin of the Calabrian-Peloritan Arc. The arc is formed by seven subaerial volcanic edifices (Alicudi, Filicudi, Salina, Lipari, Vulcano, Panarea, and Stromboli) and by several volcanic seamounts which roughly surround the Marsili Basin. The subduction-related volcanic activity showed the same eastward migration going from the Oligo-Miocene Sardinian Arc to the Pliocene Anchise-Ponza Arc and, at last, to the Pleistocene Aeolian Arc. My favourite island, Stromboli, is one of the few volcanoes on earth displaying continuous eruptive activity over a period longer than a few years or decades. I like Stromboli because it conforms perfectly to one’s childhood idea of a volcano, with its symmetrical, smoking silhouette rising from the sea. Most of this activity is of a very moderate size, consisting of brief and small bursts of glowing lava fragments to heights of rarely more than 150 m above the vents. Occasionally, there are periods of stronger, more continuous activity, with fountaining lasting several hours, violent ejection of blocks and large bombs, and, still more rarely, lava outflow. I can’t quite explain what made it so special to me. It may be because Stromboli itself is an island, and all the time during the hike I enjoyed splendid sea views (with a beer in my hand). It may be the all encompassing experience, where I could see, hear and literally feel the lava explosions. It was simply fantastic.

Credit: Flickr

Anne Glerum – Montenegro

In case you don’t make it to Montenegro/Serbia this summer, it’s fun in winter too. And yes, it’s fun in spring too – there’s snow, mountains and a younger me on a tiny sled. Photo courtesy of Cyriel de Grijs

My geo-holiday-destination: Montenegro!
A summer without beach-time is not a summer to me (already got one beach-day in this year, phew). Being Dutch, a proper holiday also requires some proper mountains – or hills at least. And no trip is complete without cultural and culinary highlights to explore.
Montenegro is a country that ticks all the boxes. Situated along the Adriatic Sea it hosts a score of picture-perfect beaches; quiet or taken over by the jet-set, intimate coves or long stretches of white sand, take your pick.
Further inland, you reach the Dinarides orogenic chain, the product of 150 My of contractional tectonics and later collapse during the Miocene. Traversing the chain into neighboring Serbia will lead you past complete ophiolite sequences, syn-orognic magma intrusions and major detachment zones of the extensional orogenic collapse.
Visit the centuries old fortified coastal cities of Budva or Kotor or one of the many churches and frescoed monasteries spread around the countryside. For more bodily sustenance, enjoy the fresh fish dishes, rich meats or the regional cheeses and yoghurts. Seasonal fruits are eaten for dessert or, even better, turned into wine and rakija. Ehm, why I am not going there again this year – this time in summer?

Not-so-sunny spring view from St. John’s fortress onto Kotor along the Bay of Kotor. Photo courtesy of Cyriel de Grijs

Diogo Lourenço – CIDER Summer School

This year, my favourite geodynamical destination is CIDER 2018! It’s far from holidays… but it’s really cool! For the last three weeks (one week to go), we have been intensely learning about heterogeneity in the Earth, and trying to understand it in an interdisciplinary perspective with contributions from geochemistry, geodynamics, and seismology. Quite an intense schedule and a lot of information to process, but I think we are all learning a lot, and hopefully in the future we will use more constraints coming from other fields into our own work. Oh, and did I mention that it is happening in Santa Barbara? Great Californian weather, beautiful coastal landscapes, barbecues by the beach, and swimming in the ocean, all sprinkled with scientific discussions! Quite the geodynamical destination, no?

Just had to cross the street from the KITP building where the conference is happening to take this photo…

Grace Shephard – Svalbard

Geoscientists are no strangers to travelling to exotic places and many of us take the opportunity to turn a work-related trip into potential holiday scouting. My suggested destination is most probably the northernmost point you can quite easily travel to on this planet – Svalbard.
Svalbard is an Arctic archipelago located around between 74-81°N latitude. It is sometimes confused with Spitsbergen, which is actually the name of the largest island where the main settlements, including Longyearbyen and Barentsburg, are situated. The islands are part of Norwegian sovereignty, though with some interesting taxation and military restrictions (the Svalbard Treaty of 1920 makes for some pretty interesting reading). Svalbard is host to a stream of tourists and scientific researchers year-round, and this week I will travel back to Longyearbyen as a lecturer for an Arctic tectonics, volcanism and geodynamics course at the University Centre in Svalbard (UNIS).
Geologically speaking, Svalbard makes for a very interesting destination. It offers a diverse range of rock ages and types; having experienced orogenic deformation events, widespread magmatism, and extensive sedimentary and glacial processes.
If you’re after a more usual tourist package amongst the draw cards are of course iconic polar bears (though please keep your distance), stumpy reindeer, arctic foxes, whales, birds and special flora. There are many glaciers – in fact around 60% of Svalbard is covered in ice – as well as fjords and mountains, former coal mining settlements… the list goes on. You are even spoilt for choice between midnight sun or midday darkness, depending on the time of year, so prioritise your activities wisely. Plus, did I mention those miles and miles of unvegetated, uninterrupted rock exposures to keep any geology enthusiast happy?… if you’re lucky you might come across some incredible fossil sites.

Itinerary recommendation, tried and tested: Whale watching and fjord cruising to a Russian mining ghost town (Pyramiden) followed by an important sampling of the world’s northernmost brewery.

Thirteen planets and counting

Thirteen planets and counting

Apart from our own planet Earth, there are a lot of Peculiar Planets out there! In this series we take a look at a planetary body or system worthy of our geodynamic attention, and this week we move back to our own solar system. Many of us will clearly remember the downgrading of Pluto as a planet nearly 12 years ago to the month. In this informative and witty post, Laurent Montesi from the University of Maryland makes a case for reinstating Pluto of planetary status, plus a handful of others, or at least a review of definitions. Bring on Club Planet! 

Laurent Montesi

A planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit. When Resolution 5A was passed by the International Astronomical Union (IAU) during the closing ceremony of its 2006 General Assembly, Pluto was “demoted” from the rank of the true planets to a dwarf planet. Children’s eyes filled with tears over the injustice made to “poor little Pluto”, textbooks were rewritten, and the Nine Pizzas that My Very Excellent Mother Just Served Us turned to Noodles.

I don’t really care.

I see where the IAU came from when crafting this definition, and to some extent, I agree with it. But it is not relevant to me. The thing is, I am not an astronomer. I recognize the authority of the IAU to name geological features on planets and other worlds, but I’m a geologist. Pluto, like many other solar system objects, has too much exciting geology to be ignored!

Figure 1: The five Dwarf Planets currently recognized by the IAU, proud members of Club Planet.


To me, a dwarf planet is first and foremost a planet, and what interests me in planets is their geological activity. If, as stated in part b of the IAU definition, an object is able to “overcome rigid body forces” (whatever that means), that should leave a geological trace. I don’t care if the planet cleared its neighbourhood or not.

So, I take the IAU definition as an invitation for Ceres, Pluto, Eris, Haumea, and Makemake to join the exclusive Club Planet (Figure 1). They all bring interesting geology to the Club. Look at the results of the Dawn and New Horizons missions! Ceres has mountains, fractures, oddly hexagonal craters, and a remarkable bright spot beckoning explorers to study its water-rich interior. Pluto has become a superstar of planetary exploration, with oceans of frozen nitrogen, diverse terrains, large rifts, perhaps a giant ice volcano, and the cutest heart tattoo in the solar system.

I’d like to go even further and open the door of the Club to many satellites (Figure 2). Our Moon is the doorway towards understanding the early evolution of terrestrial planets like the Earth. It taught us about giant impacts and magma oceans. If you want to find liquid water (and possibly life) today, go to Europa or Enceladus. If you are looking for alien plate tectonics, check out Ganymede and Europa. Are you searching for a thick atmosphere, rivers, and lakes? Welcome to Titan. Who has the most volcanic activity today? Please stand up, Io. What incredible rifts you have, Miranda and Charon! From a geological standpoint, satellites are as rich as any planet.

Figure 2: Knocking at the door of Club Planet are several of the satellites of the solar system: Earth’s Moon, the four Galilean Satellites Io, Europa, Ganymede, and Callisto, the large moons Titan and Triton, as well as numerous smaller, but geologically interesting satellites. They are led by Pluto’s moon Charon.


So, what actually is a planet? To the ancient Greeks, they were dots of light wandering against the rigid background of the night sky. These dots then turned out to be balls. Galileo saw four satellites around Jupiter, and in the redesigned solar system, planets could only orbit the Sun. Eventually, so many objects were found that it was decided that it mattered whether a planet “cleared their planetary neighbourhood” or not. Some objects were not enough of a bully to be regarded as a full planet, so they were called dwarfs. All along, astronomy guided our thinking about what is a planet and what is not.

Interestingly, the 2006 IAU definition merges astronomy and geophysics: what does it matter to an astronomer that the object has reached hydrostatic equilibrium? That is a geophysical criterion. Perhaps it matters in the sense that the interior is fluid enough that one should consider how dissipation influences orbital evolution. If that is the case, though, can tidal interaction with satellites be regarded separately?

I don’t know why the IAU was interested in hydrostatic equilibrium, or even if that is a valid question to consider, because, once again, I am not an astronomer. I’m a geologist. I study the geological activity and the interior evolution of… well… planets… and dwarf planets… and satellites… perhaps exoplanets one day… although not the ice giants and gas giants because, as far as I am concerned, they are different beasts altogether.

The fact is, the IAU definition does not help me. Perhaps there could be a geological definition of a planet, or whatever you want to call the various objects I am interested in. Perhaps the International Union of Geodesy and Geophysics (IUGG) — which, like the IAU, is a member of the International Science Council — could propose a definition more in line with my research interests, but as far as I know, there is no discussion of that.

In the meantime, resistance to the IAU definition is growing in our community. David Grinspoon and Alan Stern recently published a Perspective in The Washington Post1. Around twenty scientists got together to discuss a “Geophysical Planet Definition” at the start of the 2018 Lunar and Planetary Conference. One major point of agreement was that no one should feel obligated to follow the IAU’s definition (we are all rebels now), or any other definition.

At the 2017 Lunar and Planetary Conference, Kirby Runyon and coworkers proposed the following “Geophysical Planet Definition”2: A planet is a sub-stellar mass body that has never undergone nuclear fusion and that has sufficient self-gravitation to assume a spheroidal shape adequately described by a triaxial ellipsoid regardless of its orbital parameters. I find there is a lot to like with this proposal. For example, it would allow me to consider satellites as planets. If I focus on internal evolution, it doesn’t really matter what object my planet is orbiting. Of course, this influences the possibility of tidal heating, but I can regard that as an external energy flux, like the energy of accretion for impacts.

Interestingly, the draft “Geophysical Planet Definition” does not explicitly mention hydrostatic equilibrium. In the IAU definition, the hydrostatic equilibrium criterion implies that planets have a minimum size. It also assumes that the planet behaves as a fluid. In that case, what are we to do with the solid planets, like the Earth? We have evidence of frozen hydrostatic bulges, especially for the Moon. In other words, geological bodies can be strong enough to support a significant deviation from hydrostatic equilibrium. Hydrostatic equilibrium is not the best way to define a planet from a geological standpoint.

Figure 3: Ratio of relief scaled by planetary radius against mean radius based on best fitting triaxial ellipsoid for a variety of solar system objects, drawn following Melosh (2011). The maximum relief is controlled by friction for objects smaller than ~100 km in diameter and by strength for larger objects. Note that some objects like Mercury and Venus do not appear on this graph as they have no measurable flattening, due to their small rotation rate. Gas and ice giants appear to deviate from the trend of solid planets.

Where the IAU definition focuses on the driving force, it may instead be useful to focus on the strength of the planet. In his Planetary Surface Processes book, Jay Melosh discusses the relation between strength and gravity3. He concludes that for small bodies, relief (quantified as the difference between the maximum and minimum radius of an object, divided by the average radius) is independent of size, whereas it decreases inversely with the square of the average radius for larger solar system objects. In these larger objects, relief is limited by the strength of the body. The transition between these two trends is a planetary diameter of 200 to 400 km (Figure 3). This division leaves all of the objects for which we have evidence of geological activity driven by internal processes safely within the category of planets. Ancient planetesimals were probably big enough to be regarded as planets, and indeed, evidence for internal differentiation suggests that their interior was quite active.

So, in my view, a planet is simply a body large enough to have small relief as compared to its radius. This is evidence of relatively low internal strength, which allows geological activity to take place. I don’t need to consider where it orbits, and if it cleared its “planetary neighbourhood” or not, as that doesn’t affect geology. The pitfall of my very inclusive view of what is a planet is the consequentially large number of objects to consider, but variety is the spice of life. Why limit the diversity of geological activity to consider?

There can be subcategories, as Alan Stern actually advocated: gas giants, ice giants, terrestrial planets, dwarf planets, satellite planets, even exoplanets. From a geological standpoint, the ones I am least likely to study are actually the giant planets, whose activity is dominated by atmospheric processes. But feel free to consider them.

Perhaps I should leave the term “planets” to the astronomers, and advocate instead for a new term, “geological worlds”. What remains is, whichever classification you choose to adopt should be adapted to the research you do. For me, I want to embrace the geological diversity of our solar system.



Further reading: 

David Grinspoon and Alan Stern (2018), Yes, Pluto is planet, Speaking of Science – Perspective, Washington Post, May 7

Runyon, K.D., S.A. Stern, T.R. Lauer, W. Grundy, M.E. Summers, and K.N. Singer (2017), A Geophysical Planet Definition, Lunar and Planetary Science XLVIII, Abstract 1448

Jay Melosh (2011) Planetary Surface Processes, Chapter 3, ISBN 9780511977848 

The rock whisperers…

The rock whisperers…

The Geodynamics 101 series serves to showcase the diversity of research topics and methods in the geodynamics community in an understandable manner. We welcome all researchers – PhD students to professors – to introduce their area of expertise in a lighthearted, entertaining manner and touch upon some of the outstanding questions and problems related to their fields. This month, Manar Alsaif, PhD student at Université Montpellier, discusses actual rocks and field work!

In a discipline increasingly shaped by models, what can the rocks still tell us?

Flicking through your typical geodynamics bodies of work, most of the papers are on some kind of modelling – be it analogue, numerical, or something using seismic data. This is hardly surprising considering that geodynamics is all about the depths of the Earth, where we cannot make direct observations. But at some point, we need to check the results of these models, and checking them means looking for the observables. This is ok for the global scale – we can measure gravity and magnetism and the like, but what about smaller scales? And more detail? And the kind of complexity we cannot yet model? Our observations are restricted to the Earth’s surface – but this is actually not a bad place start. There is still a lot that we can learn from good old fashioned field work. And in fact, a lot of the motivation for models comes from an observation of something not understood, or not previously thought of.
So if you need a little inspiration for your next research project, I implore you to literally take a hike!

Apart from a source of inspiration, where does field work fit into a geodynamics workflow? I’d say it fits on top (no pun intended), since all geodynamic processes have a surface expression (at least to some degree).
Take plate motion, for example. Whether a plate moves laterally or vertically, that motion is recorded in the rocks. Palaeomagnetism will trace lateral motion, while thermochronometry will give you a vertical history of the rocks. More often than not, it will reveal a complex history of the rocks and the plate in which they lie. This complexity includes a myriad of processes e.g. fluid action, metamorphism, deformation, diagnesis, etc. These are all processes that are still not fully understood but which we can address by picking up a rock and looking at its mineralogy, its texture, its veins, its contact with its surrounding rocks, its P-T history, its fractures, their strain patterns, etc.

This is by no means an exhaustive article on field methods, I merely mention some examples of how field methods can be useful. So if field geology can be so useful, why are there fewer and fewer scientists doing it? Well, there’s the popular misconception that field geology is only geological mapping, and that the world’s geological surveys have more or less taken care of that already. In reality, some geological surveys have done a marvellous job at mapping out the rock units, but half of a geological map is actually interpretation. This interpretation will constantly change with new understanding of processes and with new data, especially where rock exposures are few and/or flighty.

Apart from the misconception that all field geology has ‘been done’, there are some practical reasons why geodynamicists veer away from field studies. Firstly, there is a mismatch of scales. Generally, the smallest scale a geodynamicist will deal with is a plate – that is already a scale which is too large for field work in practice. But as we argued above, field studies can tell you so much, so what do you do? Go strategic! Pick a few practical locations on your plate, where you might find the products of the processes you’re looking at. For example, if you are looking at obduction, go look around the high pressure rocks, which have probably already been mapped – thank you, local geo survey. If you’re looking at active faulting, use topography and satellite data to help guide you, and then a little thermochronometry can go a long way. If you’re looking at processes behind magmatism, look around your magmatic rocks, and then let the powers of geochemistry come to your aid. There are so many other examples that field geologists do and new tricks that we could start to do with a little creative thinking.

Drone field geology, bridging geo-scales. Tectonic study of Northern Scandinavia by CEED U. Oslo researchers Hans Jørgen Kjøll and Torgeir Andersen. Picture provided by Hans Jørgen Kjøll.

This is all made much easier by using satellite data as a first line of attack. Never before have we had such fine satellite data to simply strategising as we do now.
So maybe it’s also time to move on from old fashioned geological mapping – especially where pretty good maps already exist- and move on to more comprehensive, strategic field campaigns. And remember, technology can be our friend, we need not shy away from it. The photo here is not merely a gorgeous landscape, it is a drone picture by Hans Jørgen Kjøll and Torgeir Andersen of CEED, U. Oslo (seen as the people-looking lines in the middle of the photo). They are seen here flying a drone to get high resolution field data in rugged, inaccessible northern Scandinavia, while simultaneously bridging the scale of typical field work to large scale tectonics.
Similar advantages can be had by using LIDAR, various GPS methods, shallow logging techniques, etc. Perhaps it’s time to stop thinking of geologists as the hammer-hand lens people, and of geophysicists as the gadget people, and of geodynamicists as the code people. Perhaps it’s time to blur the lines, work together and learn from each other.

All of this might eventually give us more real data to plug into our models, perhaps refine some of the parameterisation, or at the very least, give us something against which to compare our model predictions.

After all, George Michael said it best: “Let’s go outside”!

50 years of plate tectonics: then, now, and beyond

50 years of plate tectonics: then, now, and beyond

Even if we cannot attend all conferences ourselves, your EGU GD Blog Team has reporters that make sure all significant geodynamics events are covered. Today, Marie Bocher, postdoc at the Seismology and Wave Physics group of ETH Zürich, touches upon a recent symposium in Paris that covered one of the most important milestones of geodynamics.

On the 25th and 26th of June, the Parisian Collège de France was celebrating the anniversary of the plate tectonics revolution with a symposium entitled 50 years of plate tectonics: then, now and beyond. For this occasion, the organizers Eric Calais, Anny Cazenave, Claude Jaupart, Serge Lallemand, and Barbara Romanowicz had put together a very impressive list of presenters, starting with Xavier Le Pichon, Jason Morgan, and Dan McKenzie during the first morning!

The very impressive program of the 50 years plate tectonics symposium

Needless to say, it was a blast, and a great occasion to focus on the big picture and reflect on the evolution of Earth sciences within the last 50 years.

Watch it online!

But don’t panic if you missed it: all the presentations are available online now on the Collège de France website. So relax, brew yourself a cup of coffee, and enjoy the symposium from the comfort of your own home 🙂

Xavier Le Pichon
Image courtesy of Martina Ulvrova

Important panel
Image courtesy of Martina Ulvrova

Dietmar Müller
Image courtesy of Marie Bocher