The Napa Valley quake, and why California is (geologically) not part of America at all.

A post by Chris RowanIn the early hours of Sunday morning, the Napa Valley region north of San Francisco was shaken by a magnitude 6 earthquake, the largest to hit this region since the magnitude 6.9 Loma Prieta earthquake in 1989. An earthquake in wine country produces dramatic visuals of wine bottles thrown from the shelves and leaking into the street, and there was strong shaking and significant damage in the region close the the epicentre. But in the grand scheme of things, a magnitude 6 earthquake is not particularly large: it may have been strong enough to wake people up in San Francisco (as data from fitness trackers has rather cleverly been used to illustrate), but it didn’t pack enough of a punch to do any real damage there.

There have already been some excellent write-ups of the geology of the earthquake by Mika Mckinnon, Dana Hunter and Garry Hayes: in brief, the root cause of all earthquakes in California is its location on the boundary between two rigid but independently mobile bits of the Earth’s crust: the Pacific and North American plates. The Pacific plate is moving northwest relative to the North American plate at around 4 centimetres a year, and the focal mechanism for Sunday’s quake is consistent with right lateral strike slip on a northwest-southeast oriented fault, which is what we’d predict for a fault at this plate boundary. But interestingly, we are clearly some way (about 50 kilometres) to the east of the San Andreas Fault, which is popularly considered to be ‘the’ plate boundary in California.

Location of Napa Valley earthquake

Location of Sunday’s earthquake relative to the San Andreas Fault. Yellow lines mark faults thought to have been active in the last 130,000 years, according to USGS mapping. The red line is the rough surface trace of Sunday’s rupture, as mapped by Mike Oskin’s speedy students, which appears to be associated with a previously unmapped strand of the West Napa Fault Zone.

This event actually nicely illustrates the nature of the plate boundary in California: we are not looking at a single line in the crust, where you can step directly from one plate to another, but a broad deforming zone. Nowadays, we have some lovely data that shows this directly, courtesy of the abundance of GPS stations deployed all through the western US. The red arrows in the figure below show contemporary motion of the crust relative to North America measured at seven stations, the most westerly of which is on the seaward side of the San Andreas Fault, and can therefore be considered to represent the Pacific plate. Although there is a significant drop in the rate at which crust is being dragged to the northwest after crossing the San Andreas, the crust in this region is still moving relative to the stable interior of the North American plate at some fraction of the Pacific plate’s velocity. As you move inland, each time you cross one of the mapped fault systems – which are themselves complicated amalgamations of anastomosing fault segments – the measured GPS velocity drops further, indicating that these systems are all actively involved in accommodating plate motions.

GPS velocities in a E-W transect across Northern California.

GPS velocities (in mm/yr) for selected UNAVCO Plate boundary observatory stations in Northern California.

The astute amongst you will note that even as the GPS velocity seems to stabilise 60-80 km inland from the San Andreas, it is still not zero; even here, the crust is not fully attached to North America. To get to the stable, non deforming bit, we still have to get across the Basin and Range, and before we get to that we have to cross the apparently more rigid Sierra Nevada mountains. The plate boundary in the western US is far from a well-defined line. On the plus side, this makes it much more interesting geologically; on the negative side, a broad zone of many faults makes estimating the seismic risk much more ‘interesting’, too.

Categories: earthquakes, tectonics

Scenic Saturday: Crossbeds on the Edge

A post by Chris RowanSome of the famous features of the Peak District are not really peaks at all – but there is nothing more scenic than a wander along one of the ‘Edges’.

Birchen Edge near Baslow, Peak District, UK. Photo: Chris Rowan, 2014.

Birchen Edge near Baslow, Peak District, UK. Photo: Chris Rowan, 2014.

These sheer cliffs, scattered along the eastern and western edges of the National Park, are made of beds of angular, coarse-grained sandstones, locally known as the Millstone Grit. They form part of a Middle to Late Carboniferous (325–315 million year-old) sequence of sandstones and siltstones that were deposited on top of the limestones that now outcrop in the middle of the Peaks (where the porous bed of the River Manifold is located), as rivers flowing south from what is now Scotland build a large delta out into a shallow, tropical sea[1]. The harder gritstone layers have eroded more slowly than the surrounding siltstone units and the underlying limestone, creating the rock-climbers’ paradise we see today.

Another view along. Birchen Edge. Spot the sedimentary structures! Photo: Chris Rowan, 2014.

Another view along. Birchen Edge. Spot the sedimentary structures! Photo: Chris Rowan, 2014.

Exploring these cliffs, and the more eroded tors scattered around on top of them, you can also see a lot of very impressive cross-bedding – the preserved signature of the currents that shaped and built that Carboniferous delta.

Multiple layers of cross bedding in the Millstone Gri

Multiple layers of cross bedding in the Millstone Grit, Birchen Edge. Photo: Chris Rowan, 2014.

A closeup of one layer of crossbeds in the Millstone Grit

A closeup of one layer of crossbeds in the Millstone Grit – you can just about see some of the coarse sand grains that this unit is composed of. Photo: Chris Rowan, 2014.

Cross beds in one of the more eroded tors on top of Birchen Edge.

Cross beds in one of the more eroded tors on top of Birchen Edge. These tors actually form part of a monument to Lord Nelson erected in 1810. Photo: Chris Rowan, 2014.

Looking past some cross-beds in the Millstone Grit, over Bichen Edge.

Looking past some cross-beds in the Millstone Grit, over Bichen Edge. Photo: Chris Rowan, 2014.


  1. If you want a bit more geological info, this fact sheet (pdf) is a good starting point  ↩

Categories: geology, geomorphology, Palaeozoic, photos

Fieldwork should be safe and welcoming for all. Currently, it’s not.

A post by Chris RowanHow prevalent is sexual harassment and assault during fieldwork? A paper in PLOS One that grapples with this question is getting some justified attention in the press and online at the moment, and the answer is of concern to anyone who works in a field-based science like geology. In the paper, Kate Clancy and coauthors Katie Hinde, Robin Nelson and Julienne Rutherford present ‘the first systematic investigation of field site work environment and experiences, particularly as they relate to sexual harassment and assault’. The results, from interviews of more than 600 people working in 32 different field-based disciplines[1] are not pretty:

  • 64% of all survey respondents stated that they had personally experienced sexual harassment.
  • Over 20% of respondents reported that they had personally experienced sexual assault.
  • The primary targets of harassment and assault were women trainees[2], and they were predominantly targeted by their male superiors.
  • Few respondents were aware of mechanisms to report incidents, and most who did report were unsatisfied with the outcome.

This is a difficult subject to get totally accurate data on, and the authors acknowledge there are risks of some self-selection in a study based on a voluntary survey (although this cuts both ways: they could be as many or more people choosing not to participate because their experiences were too traumatic, as were motivated to participate because of their experiences). But really, the absolute frequencies are unimportant. They are clearly a long way from being zero, and even one incident of harassment or assault is one too many. Also, whilst this might be the first attempt to systematically study this problem, there is a certain lack of surprise at the outcome which is almost as terrible as the numbers themselves.

This is a serious issue. The very nature of the geosciences, where time in the field is still an essential part of earning your undergraduate degree, and many graduate degrees and later research are fundamentally tied to field work, means that career progression requires women to enter and persevere in environments where they are at measurable risk of experiencing harassment – or worse. If we wish to undo the highly-skewed-to-white-male post-PhD gender ratio in the geosciences (which is measurably worse than in many other sciences), we are not exactly presenting the safe and welcoming culture that will make it happen.

So what to do? Kate Clancy has previously listed some suggested actions, which boil down to:

  • making sure that you know your institution’s sexual harassment policy and reporting mechanism, and ensure that your colleagues and students are also aware of it.
  • Investigating the issue of pre fieldwork training for researchers[3].

This is a good start, but I don’t think it can end there. If our aim is to truly make the climate within our field more friendly to women and other minorities, I don’t think we can sit back and say that because there is a policy and a process for reporting and resolving complaints, we have no other responsibility. Our frontline defence against sexual harassment and assault should not be forcing people to compound the trauma and emotional damage that they have already suffered to bring people to account for their behaviour – with the additional risk of having their reputations and their future prospects in their field damaged, with no guarantee of a good outcome[4]. We can, we must, be more proactive than that. We need to attack this behaviour at its root, by making it clear upfront that it is not acceptable, that a complaint will be taken seriously, and that people who do break the code of conduct will be dealt with harshly. The latter two may require taking an uncomfortable look at our own behaviour and actions: how often are we inclined to turn a blind eye, or brush off troubling behaviour as nothing of consequence? This is a particular risk in the peculiarly intense environment of field trips, which can skew perceptions and standards of acceptable behaviour, whilst simultaneously isolating the vulnerable from their normal support network, and increasing the perceived power differential between students and mentors. Our oversight is dulled, precisely when we should be more vigilant. Perhaps that is something training can effectively address.

I don’t have any easy answers to all this, but what I do know that just as anywhere else, women working in the field have a right to feel – and be – safe and secure. Currently they are not, and the onus is on us to change that. A discussion of how to do so is already taking place within anthropology, as evidenced by this study, and in other field-based sciences like ecology. Geoscientists should be part of this important conversation too.


  1. 4% of the respondents identified as geologists. Overall, the survey was dominated by anthropologists, who were the original targets of the survey, and were more likely to have been reached by the authors’ recruitment efforts.  ↩

  2. Harassment and assault were documented for both men and women, but women were 3.5 times more likely to report having experienced sexual harassment and more than 5 times as likely to report having been assaulted.  ↩

  3. At least in geology, as far as I know, fieldwork risk assessments do not routinely address this particular risk, but there’s no reason it could not be added.  ↩

  4. For example. It’s no surprise that many people do not get to the stage of making a complaint in the first place.  ↩

Categories: academic life, fieldwork

Now you see it, now you don’t: the disappearing and reappearing waters of the River Manifold

A post by Anne JeffersonA post by Chris RowanWe’re just back from a couple of weeks in the UK, which included a week exploring the scenic Peak District in northern England. Interesting geological features abounded from day one, when we took a hike along part of the very well-named River Manifold.

The Valley of the River Manifold, looking North from Thor's Cave. Photo: Chris Rowan, 2014.

The winding valley of the River Manifold, looking North from Thor’s Cave. Photo: Chris Rowan, 2014.

At least, the ‘Manifold’ bit seems apt: the channel is indeed very windy. Where we first started off, though, the ‘River’ bit seemed a bit shaky, since the channel was completely dry. It rather reminded Chris of the dry-except-in-a-once-in-a-blue-moon-flash-flood channels he saw in Namibia. But this is Britain, which has a reputation for being a little more soggy, shall we say (and indeed, the day before it had been raining rather heavily). So where was all the water?

Anne standing in the channel of the River Manifold. No waders required. Photo: Chris Rowan, 2014.

Anne standing in the channel of the River Manifold. No waders required. Photo: Chris Rowan, 2014.

A bit more hiking upstream, and we heard the sound of running water; a bit of clambering back into the river bed, and we saw the rather interesting sight of a fairly full channel of water suddenly disappearing into the ground through a number of sinkholes.

The river caught in the act of disappearing underground into a sinkhole. Photo: Chris Rowan, 2014.

The river caught in the act of disappearing underground into a sinkhole. Photo: Chris Rowan, 2014.

Anne poses next to a sinkhole. Photo: Chris Rowan, 2014.

Anne poses next to a sinkhole. Photo: Chris Rowan, 2014.

There is a geological reason for this vanishing act, which you may have already guessed from all of the light-coloured debris in the channel bed: the bedrock here is made of early Carboniferous (around 325-360 million years old) limestone. Limestone is prone to dissolving when it comes into contact with slightly acidic rain water, creating of fissures, sinkholes, and underground channels and caves that surface water can escape into (regions where the landscape is dissolving and collapsing in on itself like this are known as karst. Also important in this are is the fact that soon after being deposited, the limestone was deformed in the continental collision that formed Pangaea, opening up lots of tectonic joints and fractures that water can also flow into (and probably enhancing the rate of karst formation).

The interesting thing about the River Manifold is that a clear, continuous channel does exist, indicating that at times of very high rainfall water is being fed into the channel at a higher rate than it can drain underground. Not a hard thing to imagine in this part of the world, and recent heavy rainfall might explain why we found the river disappearing some way downstream of some of the sinkholes (also called swallets) referred to in many guidebooks, and this handy Geotrail Guide.

Of course, having discovered where the river disappeared, our resident water nerd was very keen to find where it came back to the surface again. It is commonly stated that it reappears a few miles downstream in the grounds of Ilam Hall, and when we visited it was easy to find a lot of water being added to the channel at an obvious spring (or ‘boil hole’).

Water refilling the surface channel of the Manifold River from a backside spring. Photo: Chris Rowan, 2014.

Water refilling the surface channel of the Manifold River from a backside spring in the grounds of Ilam Hall. Photo: Chris Rowan, 2014.

The view from the opposite bank. Photo: Chris Rowan, 2014.

The view from the opposite bank. Photo: Chris Rowan, 2014.

However, although the surface flow was very clearly a lot more anaemic upstream of the spring than it was downstream, there was still some water in the channel for at least a mile – perhaps also a sign of recent heavy rains, or more minor springs. Still, despite shifting about a bit, the dry section of the Manifold, particularly where it remerges, seems fairly constant, suggesting that the well-formed channel at the surface is matched by a fairly clear ‘Subriver Manifold’ running through the limestone around here as well.

Upstream from the Ilam Boil Hole: not completely dry, but much less water in the channel. Photo: Anne Jefferson, 2014.

Upstream from the Ilam Boil Hole: not completely dry, but much less water in the channel. Photo: Anne Jefferson, 2014.

Both the disappearance and reappearance of water in the channel show up clearly in the current Google Maps satellite imagery, when you zoom in: explore for yourself downstream of one of the major apparent sinkholes near Wetton Mill, and near where it starts to reappear near Ilam.

Categories: by Anne, geology, hydrology, photos

10 years of scientific career evolution: from springs to stormwater, student to teacher

This summer, I’m involved with a super-cool Research Experiences for Undergraduates (REU) program focused on aquatic-terrestrial linkages in urban impacted ecosystems. Undergraduate students come to Kent State for 10 weeks to design, undertake, and present a mentored, independent research project, which is a huge boost for graduate school applications or just figuring out whether scientific research is the right path for you. In the first few weeks, our REU students also take field trips to various natural and urban green areas in the region. I got to help with a trip to Cleveland Metroparks Watershed Stewardship Center and some surrounding neighborhoods, where Metroparks has been undertaking efforts to distribute storm water management through rain gardens, rain barrels, and bioretention cells. A MS student working with me is focused on the hydrologic impacts of these efforts, and the REU student I’m mentoring will be adding to our knowledge about how soil moisture and plant conditions affect bioretention performance. Here I am telling the group about how bioretention cells are built and what we know about how well they are working:

I was tickled when I saw this photo and its accompanying tweet, not only because of the nice pun, but also to think that a bioretention cell is now “the field” for me and my students. It doesn’t seem so long ago when this was me in the field:

Anne in a stream

Anne measuring discharge at Olallie Creek, March 2005, photo probably by Sarah Lewis.

My PhD research focused on the hydrology of massively spring-fed streams in the Oregon High Cascades, how they are a function of the young volcanic landscape in which they are found, and how the springs, their streams, and the landscape co-evolve over geologic time.

I think these two photos nicely capture some fundamental features of scientific careers.

First, your whole career won’t be defined by topic of your PhD. Your interests, and the opportunities that are available, will evolve over time as you move geographically and professionally and as the field changes along with you. I dimly recall my undergraduate professors telling me something like this, but I didn’t really understand it until much later. I’ve written before how the move from Oregon (volcanoes, big springs, and snow) to North Carolina (none of the preceding, but lots of interesting urban streams) altered my perspectives. I still work a little on topics related to my PhD, but its clear that my professional trajectory has moved in a different direction. Some movement is also necessary if you want to establish yourself as a scientist independent of your former advisors, and that’s often a tenure requirement. A lot of people don’t shift course as radically as I have, but few researchers will go their whole careers with a single narrow focus.

Second, the field won’t always be your focus. At some point you stop being the student and become the teacher. In that transition, you’ll probably stop doing the frequent and hard physical work in the field and instead make only occasional forays to field sites, during which you are liable to be caught pontificating. This is a bit bittersweet for me. I love mentoring students and helping them to develop into scientists and professionals in their own right, and my job and life are now multi-faceted enough that frequent or extended field work would be hard to manage. But I miss getting to spend long summer days in the field, measuring streamflow or soils, writing data in a rite-in-the-rain notebook, and being the very first person to ever know some infitesimally small piece of knowledge. I miss the intimate connection with my field areas, watching them change subtly with passing storms and seasons. Fortunately, I’ve been haunting the isotope lab lately, getting to intimately know the quirks of the isotope analyzer, and being the first person to look at the data coming off each run. It’s not the same as the field, but it gives me some of the same thrill of discovery.

On our day in the field last week, a colleague said “When we come back in 10 years and measure this…”, it gave me a big pause. My colleague is right, 10 years on, these bioretention cells will have lots of interesting traits they don’t have now, and I can’t wait to see them evolve. But my career will be evolving too, and I might be studying both bioretention and something else entirely by then.

Categories: academic life, by Anne, fieldwork, hydrology