Measure twice, cut once.

My dad was a design and technology teacher. I was exposed to the arts of woodwork, construction, design and so on as a child, and – while my brother went off and became an engineer – I have to say I’ve not particularly made use of those skills since I was doing my GCSEs. That said, I always enjoyed technical drawing, the precision and 3D spatial planning (and indeed, that same 3D spatial awareness that is so important in many aspects of geology).

While I was doing my PhD and had to design some flume equipment I had a flash of interaction with things again, but it was an absurdly simple three-part flume that a 7 year old could have designed and assembled.  For this current project, however, somewhat more time and effort has had to go into flume design. In fact, the full first month was spent doing little but designing and refining the flume, to ensure it was capable of producing the results I want to achieve without being blown apart by high pressure gases or collapsing under its own weight.

So I found myself with a ruler and protractor drafting out isometric sketches and trying to make sure everything fitted together. Then a stroke of genius hit and I booted up Google Sketchup. I’d used it a few times before, but I reasoned that while I could sketch by hand as much as I wanted, by producing a 3D model I would ensure that all the separate parts would fit nicely, and I could read the numbers for part ordering straight out of the model.

Sketchup models of some flume parts.

And I was right – in fact, it was even quicker than drafting by hand. A couple of people in the lab were quite impressed by these models I was producing and got interested.  I took images of the models down to our outstanding workshop engineer, and he was very pleased with the detail – illustrations of where cutouts needed to be made, clear ideas of where we would need PVC, where we would need aluminium, where perspex, and even where particular joins should be made (and how).  It enabled me to design the somewhat complicated hopper shape (do a Google search for ‘hopper geometry’ and you’ll quickly realise that simply whacking a great big box on top of a release mechanism is not the done thing), and was even able to ensure it would be of a certain volume and mass.

So I was ever so pleased with myself when the purchase order went off with all the outputted measurements for the 75 or so separately cut pieces of material, in a variety of materials and thicknesses.

I was less pleased this morning after an hour in the workshops ensuring that all the pieces fitted together nicely to discover that the 3000 mm x 100 mm x 10 mm  perspex flume base had been delivered at 3000 mm x 130 mm x 10 mm. Sounds trivial, but Perspex is really horrible to cut, even in a well equipped workshop. A 3 m length of it is unwieldy and impossible to deal with without some very specialist equipment.

I checked the purchase order. 3000 x 130 x 10. Bugger. How did they make that mistake. Why did I not notice it? I spent some time cursing myself for not checking the purchase order more carefully. I went and double checked again. Then I went and looked at the original paperwork. The spreadsheet I had specced everything on was correct. Then I checked the order email. I’d sent.  Hmm. That was wrong.

So, what had gone wrong? Idiot cut and pasting. I had copied the details from one part, and pasted them, then pasted the same values for the next part on the list.

In summary, after a morning of ferrying a 3m length of perspex to and fro between the suppliers and their enormous cutting machine to remove 30 mm of excess plastic, I propose a 21st century modification to the age-old adage ‘Measure twice, cut once’:

“Measure twice, cut once, paste once, check”.

At least it was cut too big rather than too small – that would have been both annoying and expensive.

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Tongariro Fireworks

Following the little spike of activity back in August, Tongariro in New Zealand reactivated today with a 5 minute explosive eruption jetting up a small plume and generating some very limited pyroclastic flows. With it being a daytime eruption, and with New Zealand getting firmly into its summer season there were, inevitably, a number of people attempting the Tongariro Crossing – a very popular hike that snakes past the dramatic Mt Ngaruhoe and up onto the nested craters of Tongariro proper.

Among this group of walkers was a pro film crew.  The net result is that some truly spectacular video got captured of the plume immediately after eruption, and showing some of the small PDCs generated from it. I strongly recommend going to have a look here. Not only do you get the joys of some lovely volcanology, but the added bonus of a soundtrack of overexcited and dramatically screaming children.

The volcano is at Alert Level 2 and Aviation Colour Code Orange.

EDIT: Here’s the seismics from Geonet for the last 24 hours. You can see the observed eruption a little before the 10 hour line (the drums are marked in hours before present, with present being about midnight New Zealand time, and the eruption going off at about 1.30 pm local time).  It looks like there’s possibly been a further pulse of activity just over 2 hours ago.

EDIT 2: Quick and dirty compilation of the webcam images from Geonet / GNS Science, showing a lot of geothermal outgassing activity before and after the eruption. Available on YouTube here.

I’ll update as and when I get a bit more info.

Posted in Education, Geology, Hazard Assessment, News, Science, Volcanism | Tagged , , , , , , , , , | 1 Comment

Accretionary Wedge #52

Been a while since I had a chance to get in on the Accretionary Wedge, which – for those of you who are perhaps not familiar – is something of a geoscience blog carnival. Once a month, someone hosts a new topic for the rest of us geobloggers to wax lyrical about.  This month Vi-Carius is hosting, with a topic broadly about ‘geoscience courses you wish existed’

Now, it’s been a while since I was an undergraduate. In fact, I was away from geoscience for several years before coming back to do my PhD.  And that’s really where my dream course would have fitted in.

Rather than Geoscience 101, I’m thinking more a ‘Geoscience 999′. A short sharp kick-up-the-rocks for people who could do with a refresher. Maybe 5 or 6 hours of lectures, one each recapping the key details (and last 10 years developments in) each of half a dozen key subject (plate tectonics, palaeo, geochem, geophys, sedimetology and volcanology?). Broad strokes coverage, with updates of key concepts where necessary, each followed by 3-4 hours practical work getting back up to speed with stuff like microscopy, map drawing, strat logging, etc. That would really have made my life easier.

That said, I can understand that actually it’s only marginally useful for a lot of people. So that gets me wondering what would be most useful for the most people. And by most people, I’m extending the remit slightly to mean everyone. Not just geologists. Not even just university students. The whole bloody lot of you. The answer I have come to is informed by the experience I’ve had teaching, lecturing and demonstrating, and remembering one of the most useful lectures I’ve ever had.

That lecture was given by Dave Waltham – who ended up as my future PhD and eventual postdoc supervisor. His qualifications are in Physics, but he has diligently spent most of his career at the Earth Sciences department at Royal Holloway  University of London ensuring – among many other things – that there was a friendly face and a clear explanation awaiting any geologist who was at a mathematical or conceptual roadblock.

And the lecture was this: Ballparking. At its simplest, how to calculate a rough first-order approximation for any given calculation.  As professional researchers I think it is something that we get good at doing, and the ability to quickly estimate whether something is ‘about right’ or not is phenomenally useful in a vast array of situations. Eyeballing a recipe when you’ve only got 2 eggs instead of 3? Ballpark it. Trying to calculate how to split a restaurant bill? Ballpark it. Trying to work out how many cricket balls you can fit in a stadium?…. You get the idea.

The interesting thing is that it is a skill that I certainly find is absolutely lacking in many people. Knowing how to simplify what would otherwise be a complex calculation into a first-order accurate approximation you can do in your head – or at least in 20 seconds on the back of an envelope – is something that everyone would benefit from. Imagine the time that could be saved!  Everything from working out whether a cheap but high mpg car is better value than expensive low mpg one, to arguing about how many whales you could fit in the oceans.

Ballparking is not necessarily an intuitive skill, and there’s plenty of shortcuts and tricks that a taught course should pass on. When you can and can’t round numbers, and by how much, what are reasonable simplifications, and which are not. Giving everybody the confidence to look at a number presented to them in context and the ability to judge whether the data are good would – I think – be a huge boon to society.

So that’s my wish. Quick and dirty maths for the masses.

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The insanity of the Italian legal system

Well, it’s official.

The Italian courts have found half a dozen scientists and a government official guilty of manslaughter over the failure to accurately predict the risks of the 2009 L’Aquila earthquake which killed 309 people.

This has been rumbling along for years now, indeed here’s a previous blog post where I outlined the case in more detail.

I am actually stunned by the utterly ridiculous conclusions of this hearing, let alone the fact these men now have 6 years in prison to look forward to for failing to predict the unpredictable.  Presumably we can shortly expect a series of high profile cases of bookmakers taking their employees to court for gross negligence for inaccurately determining the outcome of future sporting events.

I jest.

The implications of this finding however, are more worrisome. Given this outcome, who could blame Italian seismologists for being reluctant in the future for getting involved in the forecasting business at all.  Public service science in Italy may have been irrevocably damaged by this judgement, and it’s going to be a while before we know how badly. The only winners in this case are the lawyers who have no doubt earnt a pretty penny in the 3 years this case has now been building for.

Shame on you, Italy.

Posted in Earthquakes, Geology, Geophysics, Hazard Assessment, Media & Perception, Not even wrong, Science | Tagged , , , , , , , , | 1 Comment

Scaling new horizons

Mayon, Phillipines, 1984. Gravity currents, in the form of pyroclastic flows, propagate down the flanks of the volcano. From

It’s fair to say that when most people ask what I do, I simply reply “volcanologist”, “sedimentologist”, or “geologist”, depending on the audience. On the infrequent occasions they ask further what I do, it usually gets summed up as “I see how well things go downhill”, or “I study how different flows behave”. I might even go into detail about the hazard mitigation or petroleum reservoir potential of some of these studies.

The fact is though, that on the whole, I try to keep it absurdly simple.  And, on the whole, that serves the needs of the casual question, and lets us get on with the business in hand (which, to be fair, is quite often “having a beer”).

However,  since I discovered I was moving to France for this new postdoc I have found a more insistent repetition of “what is it you’re actually going to do?” The temptation is often to pull a Barney Stinson

But, apparently I don’t wear enough suits to get away with it. So, here we go. I’ll be spending my time running scaled models of gravity currents. The interesting thing is that everyone seems to ask about the ‘gravity current’ bit, and just take the ‘scaled’ part for granted. However, the ‘gravity current’ is actually in many ways the dull and straightforward bit – very simply, dense stuff goes down hill. You put dense fluid at the top of a slope, and gravity moves it down that slope. I just record the flows and measure the deposits.

Far more important is the ‘scaled’ part of this little world of sedimentological wonder. It is easy enough to imagine that building a small model of a volcano and pouring stuff over it might produce realistic results. However, the fact is that this is very far from the truth. While it seems obvious that you can model the behaviour of large particles in a big flow by using smaller particles in a smaller flow, there is a question firstly of ‘how big do the new particles have to be’.  But there is also a question of ‘what happens with things like gravity?’.  No matter how big or small I make the flow, gravity is a constant I can do little about.

And that’s not all. Things like particle friction, and fluid viscosity also don’t change (or change in non-linear ways). So now, if you change the volume of the flow, you’re not actually changing all the parameters at the same time.  As you might imagine, this means a flow at one scale can behave completely differently to a flow of identical materials and relative height and width at another scale.

Then you get all sorts of other interesting little problems creeping up. For example, when you work with sand-sized particles, there’s a number of weird sorting mechanisms that occur. If you try and use even finer particles, you start getting cohesion – where everything from humidity to van-der-Waals forces starts to stick particles together.

In short, scaling is probably one of the biggest challenges in any kind of geophysical modelling. The scaling problems become less pronounced as you make your models bigger and bigger, but cost and practicality then become your adversaries.

There’s a number of solutions (or at least workarounds) when you’re looking at scaling of experiments, and it comes down to trying to describe the various parameters of the flow using dimensionless quantities. As the simplest example, I can look at the aspect ratio of a flow (how long it is, divided by how tall it is). Because both are measured in meters, the aspect ratio is a simple number with no dimension. Hopefully, the aspect ratio of the flows in the model would be the same as the aspect ratio of the flows in real life. And we do that for everything from particle densities, to pore-pressure and fluid viscosities.

It’s worth noting that you will almost never achieve a perfectly scaled model. But, with care, you can get close. In the words of George Box: “All models are wrong, but some are useful.”

So what do I do?

Well, for the first month of this particular project, I’ve been spending a lot of time doing the calculations and designing the equipment to ensure that the experiments I’m going to be running can actually inform us about flows which – rather than being a few meters long and centimeters high, are kilometers in length, and tens of meters high.

Posted in General, Geology, Hazard Assessment, Physics, Science, Sedimentology, Volcanism | Tagged , , , , , , , , | Leave a comment

The end of the hiatus

I know, I know.

In my defense, the last months have been insanely busy. There was the usual dip in activity as the summer arrived and I was able to focus on some research problems. Then, as summer got going, I discovered that the postdoc fellowship at the Laboratoire Magmas et Volcans in France was going to happen, and from that point onward finding time to dedicate to this became somewhat secondary to the numerous other things which needed my attention.  With the turbidity modelling postdoc finishing at the end of September, and the France postdoc starting three days later, it is really only now – 12 days after my arrival  - that I’ve got myself sufficiently settled and arranged that I can begin getting back to a regular schedule.

So, my apologies for absence, and an assurance that normal service is now resuming.

I’m thoroughly enjoying the new work – although at the moment it’s focussing a lot on getting back up to speed with the literature related to fluidised gas-particle currents, and designing the flume apparatus that I’ll be using over the next 12 months.  Oh, and getting my French slightly above the abysmal pit in which it currently resides.

C’est la vie.

See, it’s coming along already.

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New Zealand volcanoes going for gold

While they might be 19th on the medal table, the kiwis are doing a sterling job of heading up this weeks volcano news.

Both White Island and Tongaririo have shown activity this week. White Island was last active in 1980, and is a beautiful example of an andesite volcano. Tongariro is a volcanic complex, comprising numerous adjacent vents. Technically, it includes Ngauruhoe (a volcano I have spent some time on, and wrote about back in January).

This morning we then get news that a huge pumice raft has been spotted 1000 km North of Auckland, believed to have been generated by a submarine eruption from Monowai.

The first thing I should point out is that these three eruptions are not related. This is just one of those statistical anomalies that crop up with random scatter. All three volcanoes are associated with the subduction of the Pacific plate under the Indian-Australian plate, but their magma plumbing systems are completely unrelated. To put the magma plumbing in perspective, the crust is 35-40 km thick, and the distance between White Island and Tongariro (the closest two of these events) is about 220 km in a straight line. These two volcanoes lie at approximately the NE / SW extents of the Taupo Volcanic Zone (VTZ), and have the much larger features of Rotorua and Taupo separating them. Below is a map which plots the recognised features of the TVZ (taken directly from here and plotted in Google Earth), with White Island and Tongariro highlighted.

Importantly, the Monowai seamount – although associated with the same tectonic boundary (the Kermadec trench), is clearly not directly associated with activity over 1400 km away.


The Kermadec/Tonga trench is itself an interesting feature. At over 10 km deep in places, it is one of the deepest trenches known, and with a closure rate of 24 cm per year at the northern end, and perhaps as low as 4.5 cm per year at the southern, is something of an anomaly.

The eruptions we’ve seen from Tongariro and White Island have been small. The Tongariro event was particularly interesting as while there was some indication of rising activity 2-3 weeks ago, there was no immediate precursor activity. The seismic trace below is for the 24 hour window in which the eruption started.  The drum is timestamped in the top right, and each horizontal trace represents 1 hour (numbered in hours before timestamp). All seismic traces here courtesy of GNS Science.


That lack of build up activity is good to highlight. One of the biggest issues volcanologists face is trying to provide some level of forecasting for eruptions. The simple fact is (and this event proves) that while we can monitor all we like, even with light-speed communication, eruptions are not nice orderly events which lend themselves to easy forecasting.

Below are two more seismic drums, from the last 24 hours at two separate locations on Tongariro.



The red lines indicate points where the signal was stronger than the drum could record. You can see the constant activity in the second trace 7-14 hours ago, which is likely to represent magma movement within the plumbing system, similar to that demonstrated at El Hierro for example. The alert level at Tongariro is 2 (minor eruptive activity), and its aviation colour code is down to yellow  (down from red at the onset of eruption).

The White Island eruptions are somewhat more significant – not least because while Tongariro (exluding Ngauruhoe) has not been active for over 100 years, White Island was last active in 2001, following 25 years of activity. This is the seisimic trace from White Island:


And it’s looked like that pretty much constantly since Sunday.

So, with everything from rhyolite/obsidian eruptions, to the largest eruption seen on Earth in the last 5000 years, the TVZ is a fascinating study. It is related to a complex plate boundary system, as it transitions from subduction to transform (before reversing its subduction direction West of South Island), and on the whole a great place to do some geology.


There’s some great videos and images collated by Erik Klemetti over at the Eruptions blog which are well worth having a look at.

Posted in Geology, Hazard Assessment, Science, Volcanism | Tagged , , , , , , , , , , , , | 1 Comment