News & Views

Let’s talk about disability in geosciences

Katy Willis - edited by Iris van Zelst July 4, 2018

Geosciences should be accessible for everyone
Credit: Pixabay

Climbing towards outcrops during fieldwork for your undergraduate studies simply isn’t doable for everyone. However, this doesn’t mean that there are adequate alternative solutions available. This week, Katy Willis, PhD student on strain-localisation in the continental lithosphere at the University of Leeds, UK, discusses disability in the geosciences, because regardless of who you are a career in geosciences should be available to you.

On June 4th, 2018 at The Geological Society in London, the UK branch of the International Association for Geodiversity (IAGD) was launched under the name DiG-UK (Diversity in Geosciences, UK), and I was one of those in attendance. The IAGD focuses on the inclusion of people with disabilities within the geosciences, and DiG-UK has incorporated this aim along with championing a better representation of black, Asian, and other ethnic minority groups. Here, I am going to focus on the disability inclusion.

Before I go on – and it’s a shame that I have to type this in the 21st century – let me point out that just because a person has a mental or physical handicap it in no way detracts from their ability to study geosciences or advance in a career in either academia or industry. What hinders them is the barriers that are erected by others before their careers even start. There are a range of disabilities. Anyone may experience a temporary one, like a broken leg restricting your mobility. Some people may experience longer term issues, for example depression triggered by the death of a parent. It may be a health issue that has intermittent effects, such as Crohn’s disease. Or it could be a lifelong issue, such as partial blindness or complex mental health issues.

Geosciences is a broad term for anything from geology to paleo-climate, right up to geodynamics. The one thing that unites such studies, especially at an undergraduate level, is fieldwork. In the UK, an accredited geology degree requires a component of fieldwork, and graduation above a certain level may demand an extended independent fieldwork experience lasting weeks. This is all well and good if you are physically and mentally capable of doing such work, but each year a small proportion of students find themselves unable to go on fieldwork. The old “solution” was to give them a desktop study while the rest of the year went off to Cyprus, Scotland, or Spain. The field group would form close friendships while away, so that those left searching dusty library shelves felt partially excluded from their year group. Hardly an acceptable solution.

The inaugural DiG-UK meeting brought together academia and industry to discuss disability inclusion. An open session looking at how different organisations have got people thinking about disability inclusion and how to practically implement it got us all chatting and sharing ideas. I was delighted to see the approach the Open University had taken regarding fieldwork. It acknowledges that not all field locations are accessible to those with physical disabilities, but there is no need to prevent such students attending field trips because there will remain a number of locations that can be readily visited. For the inaccessible locations they set up a local WiFi network and use iPads so an able bodied person can stream a live image to those who can’t reach that particular outcrop. Genius!

Manchester Metropolitan University has developed a “Diversity Dash” game to help groups understand the many barriers that all students and staff can face. Each team is allocated a character, and a range of scenarios are presented (lab work, unexpected meeting on the top floor, taking notes in lectures). The teams then have to find realistic ways in which their character can take part in the scenario. The characters cover a range of people, from someone who has a pregnant partner through to the rich student that seems to have everything but certain issues are causing increased complications.

If universities automatically allow for the provision of disabled people in their fieldwork plans, then it allows students to continue their studies should they suffer a mild injury such as a sprained ankle. During my undergraduate time, I saw two people fail to finish their course because the university was unable to accommodate their disability needs. They were intelligent people, who knew that beyond graduation lay geoscience careers that did not rely on fieldwork, but they could not pass that barrier of obtaining the appropriate degree. In both cases a few simple adjustments would have allowed them to finish.

It behoves any institute to set up a framework that encourages practical and workable disability inclusion in the geosciences. Organisations such as DiG-UK and the IAGD can provide valuable information on how to do this. Our area of study – geodynamics – sees many of us sat in front of a computer, but a lot of us were required to carry out field studies at some point in our education. It added to our knowledge and experience and in my case it inspired me into the direction of geodynamics and the desire to understand the broader picture.

In September I am taking part in a field trip to Anglesey UK. There will be a range of people going and we aim to discover which methods assist inclusion and accessibility in the field (and which don’t!). Then the findings will be shared so real and practical ways of being inclusive can be implemented for geoscience fieldwork across the UK (and hopefully internationally).

So, go on. What are you going to do this month to help people with disabilities become more involved in geosciences?

Follow DiG-UK on twitter: @DiG_UK_IAGD

Going with the toroidal mantle flow

Luca Dal Zilio October 25, 2017

Topography and bathymetry in the region of the northwestern Pacific. This area characterized by multiple subduction zones as indicated by a deep trench (darkest blue), such as that along Japan. Credit: NOAA

Subduction zones host one of the most complex and fascinating tectonic systems on the planet. Numerical models by Király and colleagues recently published in Earth and Planetary Science Letters reveal that the strength of the toroidal flow depends on the mantle viscosity and the magnitude of the slab pull force while the characteristic size of the toroidal cells mainly depends on the size of the convecting mantle.

The motion of Earth’s tectonic plates—the lithosphere—is driven by the subduction of relatively cold and dense oceanic plates into the mantle. Subduction zones are some of the most striking features on Earth. They represent one of the two types of convergent plate boundaries, in which one tectonic plate sinks underneath another one into the Earth’s mantle. The resulting forces induce mantle flow around the subducting plate, but the manner in which this happens is still a matter of debate.

Below the tectonic plates, the mantle moves in a slow and unseen manner—as cold slabs sink, hot upwellings rise, and convection slowly rids the Earth’s interior of its primordial heat. Much of our knowledge of mantle flow patterns is indirect, inferred from geodynamical models or seismic tomography images.

Seismological and geochemical investigations suggest 3D subduction-induced mantle flow around lateral slab edges from the sub-slab zone towards the mantle wedge^[1]. Such flow has also been observed in laboratory experiments^[2] and numerical models of subduction^[3]. In particular, geodynamic numerical models of subduction demonstrate that back-arc extension at narrow subduction zones is driven by rollback-induced mantle flow^[4].

Observations of seismic anisotropy—the directional dependence of seismic wave speed—provide us with tantalizingly direct information about mantle flow direction. For example, crystals of olivine, which is the most common upper-mantle mineral, tend to become aligned by the mantle flow, and seismic anisotropy is an indicator of this alignment.

To apply the laboratory-derived viscosity laws to nature, they must be extrapolated over 10 orders of magnitude, which introduces uncertainty. Moreover, it is unclear to what extent experiments on centimeter-scale samples are representative of the crust and lithosphere.

The viscosity distribution of the lithosphere and the surrounding mantle is therefore one of the least certain parameters in geodynamics. Alternative ways to determine viscosity on geological time scales are thus needed.

Schematic diagram of a subduction zone, showing the dominance of 3D flow beneath the slab and the competing influence of 2D and 3D flow fields in the mantle wedge. Credit: Long and Silver, 2008, Science.

Writing in Earth and Planetary Science Letters, Király and colleagues^[5] present a cutting-edge numerical model that shows how the strength and length scale of the toroidal flow vary with the mantle viscosity and the magnitude of the slab pull force. Király and co-workers highlight some remarkable implications of these effects: around subducting plates, the characteristic length, axis, and shape of the toroidal cell are almost independent of the slab’s properties and mainly depend on the thickness of the convecting mantle. The independence of the shape of the toroidal cell on the slab width can appear controversial with respect to previous studies^[6–7] that showed that the overall mantle flow is dependent on the slab width. However, as Király et al. point out, these differences can be explained with the model setup adopted and the range of slab widths investigated.

In order to characterize the flow—in terms of its geometry and strength—Király and co-workers analysed the vertical component of the mantle vorticity as well as the ratio between the vertical and the trench parallel component of the vorticity vector. With a series of numerical experiments, they find that subduction-induced mantle flow is highly three-dimensional, and that the toroidal component is sub-horizontal with some vertical flow components. According to the authors, this vertical flow around the slab edges has significant implications, as it can be responsible for the presence of the off-arc volcanism around several laterally confined subduction zones.

The numerical experiments by Király et al. represent another step forward in our understanding of how mantle circulation plays a relevant role in the shaping of tectonic features around subduction zones, and they provide evidence that the slab properties only impact the vigour of the flow around subducting slabs. The extension of these numerical experiments to a range of different parameters will allow for a fuller characterization of the olivine fabric, which in turn will allow seismologists to relate their measurements of seismic anisotropy to flow directions and, ultimately, to mantle processes.

References:

1. Long, M. D., and P. G. Silver (2008), The subduction zone flow field from seismic anisotropy: A global view, Science, 319, 315-318.
2. Funiciello, F., C. Faccenna, and D. Giardini (2004), Role of lateral mantle flow in the evolution of subduction systems: insights from laboratory experiments, Geophy. J. Int., 157, 1393-1406.
3. Jadamec, M. A., and M. I. Billen (2010), Reconciling surface plate motions with rapid three-dimensional mantle flow around a slab edge, Nature, 465, 338-342.
4. Sternai, P., L. Jolivet, A. Menant, and T. Gerya (2014), Driving the upper plate surface deformation by slab rollback and mantle flow, Earth Planet. Sci. Lett., 405, 110-118.
5. Király, A. Capitanio, F.A., Funiciello, F., Faccenna, C. (2017). Subduction induced mantle flow: Length-scales and orientation of the toroidal cell. Earth Planet. Sci. Lett., 479, 284–297.
6. Funiciello, F., Moroni, M., Piromallo, C., Faccenna, C., Cenedese, A., Bui, H.A., 2006. Mapping mantle flow during retreating subduction: laboratory models analyzed by feature tracking. J. Geophys. Res., Solid Earth 111, 1–16.
7. Stegman, D.R., Freeman, J., Schellart, W.P., Moresi, L., May, D., 2006. Influence of trench width on subduction hinge retreat rates in 3-D models of slab rollback. Geochem. Geophys. Geosyst. 7.

Pre-plate-tectonics on early Earth: How to make primordial continental crust

Luca Dal Zilio July 5, 2017

Artistic representation of the Earth in the Archean. Credit: Richard Bizley (www.bizleyart.com).

The sequence of events before continental crust formation has long been contested. Numerical simulations performed by Rozel and colleagues imply that the key to the puzzle could lie in the intrusive magmatism.

Despite several decades of research on the topic, the trigger of proto-continental crust formation on early Earth remains an enigma. However, magmatic processes may hold the key to unravelling what controlled the pre-plate tectonic dynamics of Earth.

The hidden shreds of evidence narrating Earth’s geological history are located deep within the interiors of old and thick cratons or even deeper in the Earth’s mantle – there lies the answer to the non-trivial question: how does the Earth machine work? Synthesizing these clues requires gathering a vast array of data, and geodynamic simulations are required in an attempt to reproduce the processes that gave rise to continents on early Earth.

Writing in Nature, Antoine Rozel (ETH Zürich) and colleagues provide a first global picture of Archean geodynamics by exploring continental crust formation on the early Earth with numerical modelling. Attempting global simulations of the early Earth is challenging as the models must satisfy petrological constraints and must be able to explain field data in Archean (~4 to 2.5 billion years ago) provinces.

Rozel and colleagues use cutting-edge software (the global convection code StagYY) to investigate different magmatism scenarios. Eruptive or intrusive magmatism differs in the way in which magma is deposited, namely cold at the surface or warm at the bottom of the crust. This is important as the primordial continental crust can only be produced in small windows of pressure-temperature conditions.

Rozel and colleagues simulate the thermomechanical evolution of early Earth (0–1 billion years), and find that the tectonics model dominated by volcanism is not able to produce Earth-like primordial continental crust, because of a too low crustal temperature. In contrast, a tectonics regime dominated by intrusive magmatism results in a higher crustal temperature, resulting in a stable continental crust. Commenting on the research, Antoine Rozel said:

Our models explain how continental crust might have been formed.

This work illustrates that the sophistication of numerical models has now reached a level where crusts of various types as well as depleted mantle can form self-consistently. Such models have the potential to distil geological and geophysical knowledge into complex process models that allow geoscientists to investigate a very exotic, pre-plate tectonics Earth. However, the specific results of Rozel and colleagues depend on the details of the pre-defined hypothesis assumed in their model. Specifically, they assume two critical parameters: the eruption efficiency (as opposed to intrusion efficiency) and the strength of the lithosphere.

Via a systematic parameter study, they found that a volumetric melt eruption efficiency of <40% leads to the production of the primordial crustal, both in terms of quantity and composition. Despite inevitable uncertainties, co-author Charitra Jain (ETH Zürich) said:

The production of the expected amount of the main primordial crustal compositions is in agreement with data constrained from fieldwork.

The impact of the emplacement mechanism (eruption vs. intrusion) on the geotherm (modified from Rozel et al., 2017, Nature – doi: 10.1038/nature22042). (a) 100% eruption efficiency; (b) mix of eruption and intrusion and (c) intrusive emplacement only. The grey envelopes in the right-hand-side plots show the temporal evolution of the geotherm.

Whether or not the formation of primordial crust gave birth to plate tectonics will no doubt remain contested. Scientists have previously suggested numerous ways to understand when and how plate tectonics began. For instance, the apparently quiescent phase between the Paleo- and Meso-Archean (~3.2 billion years) seems to have been followed by a geological era of intense deformation. This has been interpreted as the onset of plate tectonics, although this question is beyond the scope of the work presented here.

Rozel and colleagues have thus provided a fresh perspective on the long-standing problem of understanding the sequence of events that led to the formation of continental crust on early Earth. However, whether these events have driven the initiation of plate tectonics is likely to remain controversial for some time. An important missing ingredient in this study is the formation of strong continental roots (cratons), which is now under investigation in the Geophysical Fluid Dynamics team at ETH Zürich.

REFERENCE:

Rozel, A. B., Golabek, G. J., Jain, C., Tackley, P. J., & Gerya, T. (2017). Continental crust formation on early Earth controlled by intrusive magmatism. Nature, doi: 10.1038/nature22042