The Roman “Invisibility” Cloak – A Triumph for Roman Engineering

I guess the title of this post is designed to be a little misleading, because you might be thinking of Klingons and invisible space ships, but let us stop and consider what an “invisibility” cloak actually means. In the case of Klingons, light does not come from somewhere else and be reflected off their ship back to your eyes. One way to do that is to construct metamaterials, which involve creating structures in them to divert waves. The key involves matching wavelengths to structural variation, and it is easier to do this with longer wavelengths, which is why a certain amount of fuss has been made when microwaves have been diverted around objects to get the “invisibility” cloak. As you might gather, there is a general problem with overall invisibility because electromagnetic radiation has a huge range of wavelengths.

Sound is also a wave, and here it is easier to generate “invisibility” because we only generate sound over a reasonably narrow range of wavelengths from most sources. So, time for an experiment. In 2012 Stéphane Brûlé et al. demonstrated the potential by drilling a two-dimensional array of boreholes into topsoil, each 5 m deep. They then placed an accoustic source nearby, and found that much of the waves’ energy was reflected back towards the source by the first two rows of holes. What happens is that, depending on the spacing of the holes, when waves within a certain range of wavelengths pass through the lattice, there are multiple reflections. (Note this is of no value to Klingons, because you have just amplified the return radar signal.)

The reason is that when waves strike a different medium, some are reflected and some are refracted, and reflection tends to be more likely as the angle of incidence increases, and of course, the angle of incidence equals the angle of reflection. A round hole provides quite chaotic reflections, especially recalling that during refraction there is also a change of angle, and of course a change of medium occurs when the wave strikes the hole, and when it tries to leave the hole. If the holes are spaced properly with respect to the wavelength, there is considerable destructive wave interference. The net result of that is that in Brûlé’s experiment much of the wave energy was reflected back towards the source by the first two rows of holes. It is not necessary to have holes; it is merely necessary to have objects that have different wave impedance, i.e.the waves travel at different speeds through the different media, and the bigger the differences in such speeds, the better the effect. Brûlé apparently played around with holes, etc, and found the best positioning to get maximum reflection.

So, what has this got to do with Roman engineering? Apparently Brûlé went on holiday to Autun in central France, and while being touristy he saw a photograph of the foundations of a Gallo-Roman theatre, and while the image provided barely discernible foundation features, he had a spark of inspiration and postulated that the semi-circular structure bore an uncanny resemblance to half of an invisibility cloak. So he got a copy of the photo and superimposed it on one of his photos and found there was indeed a very close match.

The same thing apparently applied to the Coliseum in Rome, and a number of other amphitheatres. He found that the radii of neighbouring concentric circles (or more generally, ellipses) followed the required pattern very closely.

The relevance? Well, obviously we are not trying to defend against stray noise, but earthquakes are also wave motion. The hypothesis is that the Romans may have arrived at this structure by watching which structures survived in earthquakes and which did not, and then came up with the design most likely to withstand such earthquakes. The ancients did have surprising experience with earthquake design. The great temple at Karnak was built on materials that when sodden, which happened with the annual floods and was sufficient to hold the effect for a year, absorbed/reflected such shaking and acted as “shock absorbers”. The thrilling part of this study is that just maybe we could take advantage of this to design our cities such that they too reflect seismic energy away. And if you think earthquake wave reflection is silly, you should study the damage done in the Christchurch earthquakes. The quake centres were largely to the west, but the waves were reflected off Banks Peninsula, and there was significant wave interference. In places where the interference was constructive the damage was huge, but nearby, where interference was destructive, there was little or no damage. Just maybe we can still learn something from Roman civil engineering.

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More on M 87

In my post regarding the M 87 black hole, I stated that you do not necessarily know what the black hole and its environs look like from that image. The popular image that seems to have taken over the web is just plain misleading because it focuses on radio waves very close to the event horizon. Katherine Bouma, who developed the algorithm that made the picture possible, explained that there were “an infinite number of possible images” that could explain the data, in part due to atmospheric disturbances of different kinds at widely dispersed sites, while the difficulty in getting good data intensity meant that there was an inherent uncertainty. On the other hand, the hole and the ring were valid. However, there is more that the black hole effects.

There is another image obtained from the Chandra X-ray telescope of the environs of the M 87 black hole You will see somewhere near the middle a small black dot that on closer investigation appears to be shaped like a cross. X marks the spot! This is exactly the case. The black hole, the radius of which is almost five times the distance from the sun to Pluto, is too small to register on this image. And whereas the first image was based on radio waves, this is recording x-rays.

Chandra2

As you can see, the effect covers a monstrous volume.

Why Xrays? This is because of the huge amount of energy being lost during a radiation event. To illustrate, a red dwarf star largely emits infrared radiation, and only a relatively low fraction is in the visible wavelength electromagnetic spectrum. Thus Proxima Centauri, which has a surface temperature of about 3,000 degrees K, puts out 85% of its emissions in the infrared spectrum (although flares do contribute some xrays) and its visible emissions are only 0.0056% as luminous as the sun (which has a surface temperature of about 5772 degrees K. Now, consider that five times the distance from the sun to Pluto does not really register on that image, this will give some indication of the power of the black hole. Those xrays are generated from the energy  given off by dust heating as they fall into the regions of the black hole and give off the extraordinary energy of an xray in the spectrum.

The dust accelerates, gets hotter than the surface of most stars as a consequance of collisions, and eventually becomes a plasma that is orbiting the black hole at relativistic speeds.  As an aside, this shows that the science fiction plots of a space ship suddenly coming across a lurking black hole is somewhat improbable. Observation should give good clues well in advance as the size of the Xray emissions around this one is comparable to the distance of most of the farthest stars we can see with the naked eye.

One of the most bizarre things about black holes is that sometimes you can see a jet of material travelling at relativistic speeds away from the polar regions of the black hole. The jets show only a few degrees of dispersion and these can travel up to millions of parsecs. One parsec is about 3.26 light years, so the nearest star to us, Proxima Centauri, is about 1.3 parsecs (4.2 light years) from the sun. The jets can leave a galaxy, and there are images from Hubble where the length of the jet dwarfs the galaxy from which it came. On the other hand, the black hole at the centre of our galaxy does not currently generate such a jet. In the Chandra X-ray image you can see the jet coming out of the M 87 system. (There will be another on exactly the other side of the system.)

This is one of the most powerful events that occur in the Universe, and while we have a qualitative idea of some of what might be powering it, the details are still to be worked out. One theory is that as the plasma spirals into the black hole, the magnetic field gets compressed and rotates, and this magnetic field then exerts a force on the plasma, with the net result that matter is ejected in a jet from the inner regions around the black hole. There is at least one alternative theory. Roger Penrose has proposed that the rotating black hole causes “frame dragging”, which can extract relativistic energies and momentum, essentially from the spin of the black hole. Of course the material being ejected did not come from the black hole, but rather some of the material falling into the black hole is caught before it reaches it and from whatever the cause is ejected at these fantastic energies. The net result is that energy and angular momentum are removed, which also aids the black hole to accrete more mass.

Which raises the question, why does the black hole at the centre of our galaxy not do this? The simple answer may well be that there is no matter close enough to fall in, and what is nearby is in stars that are stable and in a stable orbit. There is a lot we do not know about black holes, and we are unlikely to in the near future.

Book Discount

From April 18 – 25, Athene’s Prophecy will be discounted to 99c on Amazon in the US and 99p in the UK. Science fiction with some science you can try your hand at. Have you got what it takes to actually develop a theory? The story is based around Gaius Claudius Scaevola, given the cognomen by Tiberius, who is asked by Pallas Athene to do three things, before he will be transported to another planet. The scientific problem is to prove the Earth goes around the Sun with what was known and was available in the first century. Can you do it? Try your luck. I suspect you will fail, and to stop cheating, the answer is in the following ebook. Meanwhile, the story.  Scaevola is in Egypt for the anti-Jewish riots, then to Syria as Tribunis laticlavius in the Fulminata, then he has the problem of stopping a rebellion when Caligulae orders a statue of himself in the temple of Jerusalem. You will get a different picture of Caligulae than what you normally see, supported by a transcription of a report of the critical meeting regarding the statue by Philo of Alexandria. (Fortunately, copyright has expired.). First of a series. http://www.amazon.com/dp/B00GYL4HGW

The M 87 Black Hole

By now, unless you have been living under a flat rock somewhere, you have probably seen an image of a black hole. This image seems to be in just about as many media outlets as possible, so you know what the black hole and its environs look like, right? Not necessarily. But, you say, you have seen a photograph. Well, actually, no you haven’t. That system is so far away that to get the necessary resolution you need to gather light over a very wide array, so the image was obtained from a very large number of radio telescopes and the image was reconstructed by a sequence of mathematical processes. Nevertheless, the black sphere and the ring will represent fairly accurately part of what is there.

No radiation can escape from a black hole so the black bit in the middle is fair, however the image as presented gives no idea of its size. Its radius is about 19 billion km, which is a little under five times the distance from the sun to Pluto. This is really a monster. Ever wondered what happens to photons that are emitted at right angles to the gravitational field? Well, at 28 billion km or thereabouts they go into orbit around the black hole and would do that for an infinite time unless they get absorbed by dust falling in. The bright stuff you see is outside the rotating photons, and is travelling clockwise at about half light speed.

The light is obviously not orange and the signals were received as radio waves, but when emitted they would be extremely high energy photons. We see them as radio waves because they have lost that much energy climbing out of the black hole’s gravitational field. One way of looking at this is to think of light as a wave. The more energy the light has, the greater the frequency of wave crests passing by. As the energy lowers due to gravity lowering the energy of the light, the wave gets “stretched” and the number of crests passing by lowers. At the edge of the black hole the wave is so stretched it takes an infinite amount of time for a second crest to appear, which means no light can escape. Just outside the event horizon the gravity is not quite strong enough to stop it, but a gamma ray wave might take 100,000 of our years for the next crest to pass when it gets to us. The wave is moving but it is so red-shifted we could not see it. Further away from the event horizon the light is a little less stretched, so we see it as radio waves, which is what we were looking at in this image, even if it still started as gamma rays or Xrays.

It has amused me to see the hagiolatry bestowed upon Einstein regarding this image. One quote: “Albert Einstein’s towering genius is on display yet again.” As a comment, I am NOT trying to run down Einstein, but let us be consistent here. You may note Newton also predicted a mass at which light could not escape. In Newtonian mechanics the energy of the light would be given by E =mc^2/2, while the gravitational potential energy would be GMm/R. This permits us to calculate a radius where light cannot escape as R = 2GM/c^2, which happens to be exactly the same as the Schwarzchild radius from General Relativity.

Then we see statements such as “General relativity describes gravity as a consequence of the warping of space-time.” Yes, but that implies something that should not be there. General Relativity is a geometric theory, and describes the dynamics of particles in geometric terms. The phrase “as a consequence of” should be replaced with “in terms of”. The use of “consequence” implies cause, and this leads to statements involving cosmic fabric being bent, and you get images of something like a trampoline sheet, which is at best misleading. Here is another quote that annoys me: “Massive objects create a sort of dent or well in the cosmic fabric, which passing bodies fall into because they’re following curved contours (not as a result of some mysterious force at a distance, which had been the prevailing view before Einstein came along)”. No! Both theories are done a great disservice. Einstein gave a geometric description of how bodies move, but there is no physical cause, and it has the same problem, only deeper, than the Newtonian description had, because you must then ask, how does one piece of space-time know exactly how much to distort? Meanwhile, Newton gave a description of the dynamics of particles essentially in terms of calculus. Whereas Einstein describes effects in terms of a number of tensors, which most people do not understand, Newton invented the term “force”.

Now you will often see the argument that light is bent around the sun and that “proves” General Relativity is correct. Actually, Newtonian physics predicted  the same effect, but general Relativity bends it twice as much as predicted by Newtonian physics, so yes, in that sense General relativity is correct if the bend is correctly found to be twice that of Newton. You will then see statements along the lines this proves the bent path is “due to the warping of spacetime”. That is, of course, nonsense. The reason is that in Einstein’s relativity E = mc^2, which is twice that of the Newtonian energy, as you can see from the above. The reason for the difference appears to be the cosmic speed limit of light speed, which Newton may or may not have considered, but had no reason to go further. Why do I say Newton might have considered it? Because as a postulate, the fundamental nature of the speed of light goes all the way back to Empedocles. Of course, he did not make much of it.

Finally, I saw one statement that “the circular nature of the black hole again confirms the correctness of Einstein’s theory of General Relativity. Actually, Aristotle provided one of the first recorded reasons why gravity leads to a sphere. Newton would certainly have predicted a basic sphere, and of course the algorithm used to make the image would not have led to any other result unless there were something really dramatically non spherical. The above is not intended to downplay Einstein, but I am not a fan of the hagiolatry that accompanies him either.

Asteroid (101955) Bennu

The results of the OSIRIS-REx probe have now started to be made public, and while this probe was launched to answer questions about carbonaceous asteroids, and while some information has been obtained that is most certainly interesting, what it has mainly done, in my opinion, is to raise more questions. As is often the case with scientific experiments and observations.

Bennu is a carbonaceous asteroid with a semimajor axis of about 1.26 AU, where 1 AU is the Earth-Sun distance. Its eccentricity is 0.2, which means it is Earth-crossing and could collide with Earth. According to Wikipedia, it has a 1 in 2700 chance of impacting Earth between 2175 – 2199. I guess I shall never know, but it would be a threat. It has a diameter of approximately 500 meters, and a mass of somewhere in the vicinity of 7 x 10^10 kg, which means an impact would be extremely damaging near where it struck, but it would not be an extinction event. (The Chicxulub impactor would have been between five to seven orders of magnitude bigger.) So, what do we know about it?

It is described as a rubble pile, although what that means varies in terms of who says it. It is generally not considered to be an original accretion, and it is usually assumed to have formed inside a much larger planetoid which provided heat and pressure to form more complex minerals. Exactly why they are so sure of this is a puzzle to me, because we do not know what the minerals are, and how they are bound into the asteroid. Carbonaceous asteroids usually are found in the outer asteroid belt, and the assumption is this was dislodged inwards as a result of the collision that formed it. Standard theory assumes there were such collisions, but it also assumes such collisions led to planetary formation, and the rather awkward fact that there are no planets in the asteroid belt tends to be overlooked. These collisions are doing a lot of work, first making protoplanets then planets, and second, smashing up protoplanets to make asteroids, with no explanation why two different results arise other than “we need two different results”. Note that the collision velocities in the asteroid belt would be much milder than for the rocky planets, so smashing is more likely the closer to the star. Its relevance to planetary formation may be low since it did not form a planet, and there are no planets that have compositions that could realistically be considered to have come from such a chemical composition.

It is often said that Earth was bombarded with carbonaceous chondrites early on, and that is where the reduced carbon and nitrogen came from to sustain life, as well as the amino acids and nucleobases used to create life. Additionally, it is asserted that the iron and a number of other metals that dissolve in iron that we have on the surface must have come from asteroids, the reason being that in the early formation of Earth, the whole was a mass of boiling silicates in which such metals would dissolve in iron and go to the core. That we have them means something else must have brought them later. This shows one of the major faults of science, in my opinion. Rather than take the observation as a reason to go back and question whether the boiling silicates might be wrong, they introduce a further variable. Unfortunately, this “late veneer”  is misleading because the advocates have refused to accept that we have fragments of asteroids as meteorites. Their isotopes show they could only have contributed the right amount of metals, etc, if they were emulsified in all of Earth’s silicates. But wait. Why would these be emulsified and not go to the core while the original metals were not emulsified and did go to the core?

These asteroids are also believed by many to be the origin of life. They have very small amounts of amino acids and nucleobases, but they have a much wider range of amino acids than are used by our life. If they were the source, why did we not use them? Even more convincing, the nitrogen in the meteorite fragments has more 15N than Earth’s nitrogen. Ours is of solar composition; the asteroids apparently processed it. There is no way to reduce the level of heavy isotopes so these asteroids cannot be the source.

Now, what does a rubble pile conjure up in your mind? I originally considered it to be, well, a pile of rubble, loosely adhering, but Bennu cannot be that. First, consider the escape velocity, which is more than 20 cm/sec in the polar regions but reduces down to 10 cm/sec at the equator, due to the centrifugal force of its rotation. That is not much, and anything loose would be lost in any impact. Yet the surface is littered with boulders, three more than 40 m long. Any significant shock would seemingly dislodge such boulders, especially smaller ones, but there they are, some half buried. There are also impact craters, some up to 150 meters in diameter. Whatever hit it to create that and excavate a hole 150 m in diameter must have delivered a shock wave that should impart more than 10 cm s−1 to a loosely lying boulder, although there is one possible exception, which is when the whole structure was sufficiently flexible to give without fragmenting and absorb the energy by converting it to heat while adding to the kinetic energy of the whole.

Which brings us back to the rubble pile. Bennu’s relative density is 1.19, so if placed in water it would not float, but it would not sink very quickly either. For comparison, it is less than half that of granite and about a third of many basalts. CI asteroidal material has a bulk density of 1.57, while CM asteroidal material has a bulk density of 2.2.  Accordingly, it is concluded that Bennu has a lot of voids in it, which is where the concept of the rubble pile comes to bear. On the other hand, there is considerable stiffness, so something is restricting movement.

So what do we not know about this asteroid? First, we have only a modest idea of what it is made of, although a sample return might be possible. It may well be made entirely of large boulders plus the obvious voids put together with something sticking the boulders together, but what is the something? If made of boulders, what are the boulders made of? It never got hot enough out there to melt silicates, so whatever they are must b held together by some agent, but what? How resilient is that something, and how many times can it be used before it fails? This is important in case we decide it would be desirable to alter its orbit to avoid a collision with Earth. What holds the boulders together? This is important if we want to know how planets form, and whether such an asteroid will be useful in any way. (If, for example, we were to build a giant space station, the nitrogen, organic material and water in such an asteroid would be invaluable.) More to do to unravel this mystery.

Some Shortcomings of Science

In a previous post, in reference to the blog repost, I stated I would show some of the short-comings of science, so here goes.

One of the obvious failings is that people seem happy to ignore what should convince them. The first sign I saw of this type of problem was in my very early years as a scientist. Sir Richard Doll produced a report that convincingly (at least to me) linked smoking to cancer. Out came a number of papers rubbishing this, largely from people employed by the tobacco industry. Here we have a clear conflict, and while it is ethically correct to show that some hypothesis is wrong, it should be based on sound logic. Now I believe that there are usually a very few results, and maybe as few as one specific result, that makes the conclusion unassailable. In this case, chemists isolated the constituents of cigarette smoke and found over 200 suspected carcinogens, and trials with some of these on lab rats were conclusive: as an example one dab of pure 3,4-benzopyrene gave an almost 100% probability of inducing a tumour. Now that is a far greater concentration than any person will get smoking, and people are not rats, nevertheless this showed me that on any reasonable assessment, smoking is a bad idea. (It was also a bad idea for a young organic chemist: who needs an ignition source a few centimeters in front of the face when handling volatile solvents?) Yet fifty years or so later, people continue to smoke. It seems to be a Faustian attitude: the cancer will come decades later, or for some lucky ones, not at all, so ignore the warning.

A similar situation is occurring now with climate change. The critical piece of information for me is that during the 1990s and early 2000s (the period of the study) it was shown there is a net power input to the oceans of 0.64 W/m2. If there is a continuing net energy input to the oceans, they must be warming. Actually, the Tasman has been clearly warming, and the evidence from other oceans supports that. So the planet is heating. Yet there are a small number of “deniers” who put their head in the sand and refuse to acknowledge this, as if by doing so, the problem goes away. Scientists seem unable to make people fact up to the fact that the problem must be dealt with now but the price is not paid until much later. As an example, in 2014 US Senate majority leader Mitch McConnell said: “I am not a scientist. I’m interested in protecting Kentucky’s economy.” He forgot to add, now.

The problem of ignoring what you do not like is general and pervasive, as I quickly learned while doing my PhD. My PhD was somewhat unusual in that I chose the topic and designed the project. No need for details here, but I knew the department, and my supervisor, had spent a lot of effort establishing constants for something called the Hammett equation. There was a great debate going on whether the cyclopropane ring could delocalise electronic charge in the same way as a double bond, only mre weakly. This equation would actually address that question. The very limited use of it by others at the start of my project was inconclusive, for reasons we need not go into here. Anyway, by the time I finished, my results showed quite conclusively that it did not, but the general consensus, based essentially on the observation that positive electric charge was strongly stabilised by it, and on molecular orbital theory (which assumes it initially, so was hardly conclusive on this question) was that it did. My supervisor made one really good suggestion as to what to do when I ran into trouble, and this was the part that showed the effect the most. But when it became clear that everyone else was agreeing the opposite and he had moved to a new position, he refused to publish that part.

This was an example of what I believe is the biggest failing. The observation everyone clung to was unexpected and needed a new explanation, and what they came up with most certainly gave the right answer for that specific case. However, many times there is more than one possible explanation, and I came up with an alternative based on classical electric field theory, that also predicted positive charge would be stabilized, and by how much, but it also predicted negative charge would be destabilized. The delocalization concept required bothto be stabilised. So there was a means of distinguishing them, and there was a very small amount of clear evidence that negative charge was destabilised. Why a small amount of evidence. Well, most attempts at making such compounds failed outright, which is in accord with the compounds being unstable but it is not definitive.

So what happened? A review came out that “convincingly showed” the answer was yes. The convincing part was that it cited a deluge of “me too” work on the stabilization of positive charge. It ignored my work, and as I later found out when I wrote a review, it ignored over 60 different types of evidence that showed results that contradicted the “yes” answer. My review was not published because it appears chemistry journals do not publish logic analyses. I could not be bothered rewriting, although the draft document is on the web if anyone is interested.

The point this shows is that once a paradigm is embedded, even if on shaky grounds, it is very hard to dislodge, in accord with what Thomas Kuhn noted in “The structure of scientific revolutions”. One of the points Kuhn noted was if the paradigm had evidence, scientists would rush to write papers confirming the paradigm by doing minor variations on what worked. That happened above: they were not interested in testing the hypothesis; they were interested in getting easy papers published to advance their careers. Kuhn also noted that observations that contradict the paradigm are ignored as long as they can be. Maybe over 60 different types of observations that contradict, or falsify, the paradigm is a record? I don’t know, but I suspect the chemical community will not be interested in finding out.

Global warming and rain.

One day when I was a boy in Hokitika (West Coast, South Island, New Zealand) it was raining when I went to school and it got worse, so I had to walk home through water lying everywhere. The water was up to my ankles everywhere, and deeper in lower lying areas. This did not come from the river, but merely from the rain falling, and in nine hours, from memory there was nine inches of rain (a little under 23 cm). This was regarded as exceptional rain then, a once in a hundred year flood.

Now we have global warming so what do we expect? You hear lots of talk about drought, and yes in some parts of the world there will be drought, but in others there will be more rain. The reason is, if the oceans get warmer more water should go into the air. By itself that may not matter too much if the air gets warmer as well, but problems arise if such warm air meets cooler air. This is the sort of thing that causes rain, but now there is more water in the air.

What happens next depends on exactly how the cause behaved. The obvious thing is the rain falls, but when the humidity collapses into rain drops, its going from the gas phase to liquid releases a lot of energy. If there is enough cold air, it might just heat it, especially if the cold came from mountains forcing the air upwards relatively slowly so that it cools and rains on one side of the mountains. That is what happens around Hokitika. Now the hot air blows a strong warm wind over the land to the east, the so-called föhn wind. If the energy cannot be dissipated that way, then stronger circular winds are generated. The tropical cyclones are examples. There was one recently in Madagascar recently that did extreme damage.

So, how will global warming affect these? The short answer is, there will be a variety of ways. Stronger cyclones, more frequent cyclones (because milder systems that get stronger enter the classification) but the more obvious one is more rain because more water has been evaporated. Which gets me back to Hokitika. They have just had a weather system pass over that lasted about a day and a half of continuous rain, and dumped 800 mm of rain in that period (about 31 ½ inches). That is as much as some places get in a year. A little way inland, in the same period they got 1,082 mm, and that is almost 43 inches.

There has been a variety of flooding around the place. A number of houses were inundated because the storm-water drains could not cope and one woman died. Apparently she was driving; she did not like the speed of the water flowing down the road, so she got out. If when driving you see rapidly flowing water of unknown depth ahead, stop and sit it out, or turn back to higher ground. Do not enter. If you are correct in your fear that a car cannot maintain its grip on the road, you walking would be in a worse position. The force of rapidly flowing water will sweep you off your feet, and if it is deep, you are lighter and therefore have less grip. Your grip depends on your weight.

Probably the most frustrating situation has been for tourists south of the Franz Josef glacier, where they are stranded. To the south, the road is apparently cut off around Haast, and to the north of the Fox Glacier, the Waiho bridge was washed out by a river carrying down quite large boulders. A little earlier there were sightseers walking on the bridge, but fortunately they all got off before the bridge went. To give some idea of the water, here are links to two videos of the bridge going: https://www.youtube.com/watch?v=ldCjVqfkKFk   and  https://www.youtube.com/watch?v=wPf49aaomYI The first one also gives a brief example of the New Zealand accent, and the vernacular. Note the bridge was a Bailey bridge and is in principle not expected to be permanent.

Once something like this happens, the blame game starts. One argument was that the river has a history of flooding and of eroding out the land and changing course, so why build a more permanent bridge? Another was the crossing is situated on a major fault and apparently the land is not good for foundations. I suspect that since it is in a very low population area, money is also a relevant issue. Where I live, there are a number of bridges across the Hutt river, and it runs along a major fault line, but being in a major metropolitan area, bridges are built. However, another more pertinent accusation came from a local who had complained a few days before that someone excavating the riverbed a little upstream had created a channel that would direct the heaviest rocks in a flood in the direction of the first supports to give way. Oops! No doubt more will follow.

When I wrote that (yesterday), the weather system was still to the south of here but working its way north. Yesterday we had wind gusts of up to 120 k/h, and while the system was working its way north, apart from some heavy rain last night, it had run out of steam. Today it is quite warm, sunny, no problem.

So is this a sign of climate change? A single incident is not, however I note that the “one in a hundred year rain event” in my youth has happened again now, and apparently in the 1980s. This time it has dumped almost four times the amount of water, and the Tasman Sea is about two Centigrade degrees above average this summer. You form your own opinion.