About tsunamis

Waitakere City Council warning sign, New Zealand. In places with a high tsunami risk, like the coasts of New Zealand, there may be warning sirens, but if you feel tremors, play safe and go uphill.

In August 1805, The Sydney Gazette and New South Wales Advertiser reprinted a letter from Norfolk Island, a Pacific sub-colony, describing a ‘freak tide’ on 8 May 1805. At 3.30 pm, almost at low tide, all the water drained from a channel that usually had 2 to 3 fathoms (4 to 6 metres) of water in it, and in two minutes it was left dry. Suddenly, the water rushed back and came inland, reaching the military barracks, usually 20 metres above the high tide mark. Then, the water all ran out again.

You can read the story here: The Sydney Gazette and New South Wales Advertiser, 4 August, 1805, 1 – 2, https://trove.nla.gov.au/newspaper/article/626869

The “town of Sydney” that is mentioned there is now called Kingston.

This event was later called a ‘tidal wave’. In Japan, where this happened more often, people called it a ‘harbour wave’, or in Japanese, a tsunami. A tsunami is far bigger inside a harbour than it is out in the deep ocean, and it actually has nothing to do with tides. It is caused by movements in or under the sea.

English speakers adopted the Japanese name when we began to understand what causes these waves. Out at sea, a tsunami passes under boats without anybody on board noticing. The wave is not just on the surface: the disturbance reaches deep into the water and, as it approaches shallow water, the bottom of the wave touches the sea floor, it gets slowed down, and the water starts to pile up.

On Norfolk Island in 1805, the first warning of looming trouble came when the sea level fell. This often happens with a tsunami, and there will always be people who walk out onto the exposed seafloor when the sea goes out. If you ever see this kind of fall in sea level (with or without a starter wave), move quickly to high ground, because the several following waves will be larger!

In Sri Lanka, when the 2004 Boxing Day tsunami hit, the biggest wave was the third or fourth, which gave a British geologist time to warn people to leave the beach. In the ocean, those waves were a metre high, but their tremendous speed—almost 1000 kilometres per hour—is converted into extra height in shallow waters.

We live on top of a 65 metre hill (for primitive societies, that means 200 feet above sea level. Nonetheless a dodgy insurance agent tried to sell us tsunami insurance. and several fellow-residents scurried to sign, until I pointed out that any tsunami hitting us had to come through, 70 metres high, meaning that most of Sydney would be devastated, and the insurance company would be bankrupt, so we would never get any money back.

That aside, I told them, our coastline was unlikely to allow any surge to come our way. The most dangerous place to be during a tsunami is in a steep-sided inlet like a fiord or in a wedge-shaped bay. These shapes funnel the wave’s energy in, increasing the force and the danger.

In 1946, a magnitude 8.1 earthquake in the Aleutian Islands in the northern Pacific Ocean produced a tsunami that killed 96 people in Hilo, a town on a wedge-shaped bay on the eastern side of the island of Hawaii. The people of Hilo had two later tsunami warnings, in 1952 and 1957, but these waves were small and people had stopped worrying about mere waves. A few years later, in 1960, a magnitude 9.5 earthquake in Chile sent another huge wave into Hilo’s bay, killing 61 people. Seven hours later, the wave reached Japan where 142 people were killed.

Some of my Californian friends have just (December 5, 2024) been through a tsunami scare, and while they got off safely this time, there may be another quake that does produce a quake in the near future. Note the may. All I offer is a reasonable hypothesis.

A tsunami can happen when there is an earthquake resulting from a large part of the seafloor moving suddenly up or down; or when there is an earthquake or volcano that makes a large mass of rock tumble into the sea; or when a large solid piece of a meteor falls into the sea.

These days, people receive alerts if a tsunami is coming, but there was an insufficient warning system in place when the 2004 Boxing Day tsunami happened in the Indian Ocean, after a quake with a magnitude of about 9.1. In hindsight, that event might have been predictable, because a week or so earlier, there had been a powerful earthquake with a north to south sideways movement of the Australian Plate, south of New Zealand.

Sideways movements make no waves, but they transfer force and, sooner or later, the northern end of the Indian Plate had to slide under the Burma micro-plate, bumping it upwards. When the slide happened, 30 cubic kilometres of water were moved, leading to waves that were about one metre high, out at sea, but up to 15 metres high as they came ashore. With no warning, about 230,000 people died across 14 countries. 

This may perhaps happen off California: every seismic movement transfers stress to to a new place.

At other times nobody may notice. On 16 January 2022, Little Manly beach in Sydney harbour had repeated surges from a tsunami triggered by a volcano near Tonga. Only the present writer was aware of the continued one-minute ebb-and-flow, and my camera caught it: I managed to crop out members of the public and children, but they all remained blissfully unaware.

To the left of those pictures lies North Head, covered in a deep layer of aeolian (wind-blown) sand from the last ice age, but there is at least one Australian geologist who claims the sand was deposited there by a tsunami. If I were to assess this, I would need to use rude words. Let me just say excreta tauri...

Just a note about the height of the water in the lower shot: a "king tide" in March 2025 was about 40 cm lower than this.

This draws on my recent and about-to-be-pitched What on Earth: behind earth science.

So to my Californian friends, I advise a degree of vigilance.

The case of the sensitive seismometer

This is a short excerpt from What On Earth?

This is a guide to how earth science works, because many parts of earth science leave lay people asking questions like How can we know what a once in a thousand years flood looks like.

Actually, I have already covered that one, and I used part of that blog entry in What on Earth?

There is a seismometer in Spain which has often detected odd things. It is 500 metres away from the Camp Nou stadium in Barcelona, in the basement of the Institute of Earth Sciences Jaume Almera of the CSIC (in Spain, it is called ICTJA-CSIC).

In May 2016, Bruce Springsteen and The E Street Band held a concert at Camp Nou. When 65,000 spectators danced to their songs, researcher Jordi Diaz found that the seismometer recorded the vibrations caused as the crowd jumped together. Here is the seismic record of the Springsteen concert:

The graph that appears below this shows the seismometer readings during Springsteen’s performance. Can you work out when he went from one song to the next?

At other times, the same seismometer has detected underground trains, traffic patterns (including the rush hour in Barcelona) and nearby fireworks, but the best of all was when the instrument detected Catalan enthusiasm at a football game in May 2015. The football club FC Barcelona, whose home ground is the Camp Nou stadium scored three goals in the last 15 minutes of a Champions League semi-finals game against Bayern Munich, and the fans’ celebrations showed up clearly.

This story was republished with the assistance and permission of Jordi Diaz and ICTJA-CSIC.

A history of climate change.

Jens Galschiot's installation, Unbearable, in Copenhagen

In the savage illustration on the right, the J-curve that is skewering the polar bear reflects the graph of the unstoppable rise of atmospheric carbon dioxide, and the curve is made from lengths of oil pipe. Sometimes, art and politics go together very well. 

We have known about what we used to call ‘global warming’ for quite a while, since the 1950s, though it was predicted (as a theory) in the 1820s and explained in the 1850s. Now reputable atmospheric scientists all believe human activity is driving the modern warming of our climate. All the same, they agree that global warming is a bad description, so we call it ‘climate change’. Under any name, it’s the same beast, and the same looming disaster. The problem used to be that there was not a lot of hard science in the arguments, which come down to logic, reason, careful modelling—and interpretation that is likely to be biased by a generous serving of self-interest among the nay-sayers.

In 1856 at the AAAS Annual Meeting, the work of Eunice Foote was presented, showing that carbon dioxide is a heat-blanketing greenhouse gas that in the atmosphere could warm the Earth. This was years before the work of the men usually credited with the finding (Tyndall in England and Arrhenius in Sweden, and we will come to them in a bit). Her work was in a short piece in The American Journal of Science and Arts for 1856 begins on p. 382, and says: “An atmosphere of that gas [carbonic acid, CO2] would give our earth a high temperature …”

Even before that, in the 1820s, Joseph Fourier had realised that heat-trapping by what we now call greenhouse gases might occur. Then in 1856, Foote identified carbon dioxide as the most likely threat, before John Tyndall said much the same thing in 1861. Back then, nobody thought much about it, then Svante Arrhenius reminded us in 1896 that both water vapour and carbon dioxide were ‘greenhouse gases’ (escaping that bad analogy is hard) and so water and carbon dioxide would play a role in making the planet get warmer.

He also considered that changes might be happening, and consulted Arvid Högbom, who just happened to know all about carbon dioxide sources and sinks. Carbon dioxide was coming from animals when they breathed, from volcanoes, and from humans burning fossil and other fuels. Arrhenius thought the human additions were a very small part of the total in the air already, perhaps one part in a thousand was added by the burning of coal, and there were probably checks and balances. Arrhenius estimated that in 3000 years, the atmospheric levels of carbon dioxide would double, but that such a doubling would raise world average temperatures by 5 to 6°C.

In 1896, the CO₂ level was around 290 parts per million: in 2016, the value was estimated at 396 parts per million: we had travelled one third of the distance in 120 years. In 2018, it was 407.4 ppm, and in May 2023, it reached a seasonal peak of 424 ppm. My back-of-the-envelope scribblings suggest we will double the 1896 value by the 2070s, after about 180 years, rather than 3000 years.

To Europeans back then, the warming effect seemed nothing to worry about, because nobody had stopped to consider the cascades, the flow-ons that might be driven by that rise in temperature. A thermodynamics expert, Walter Nernst, even wondered if it would be feasible to set fire to uneconomical and low-grade coal seams, so as to release enough carbon dioxide to warm the Earth’s climate deliberately!

In December 2019, Australia recorded its six hottest days ever, and 2023 now looks to be set to be the hottest ever, around the globe, but the trend was apparent even in 1950, when George Kimble reported in Scientific American that the northern limit of wheat-growing in Canada had moved northward some 200 or 300 miles (call it 400 kilometres), adding that farmers in southern Ontario were experimenting with growing cotton. While the Canadian cotton industry seems not to have taken off yet, he reported another trend that continues to this day, the northward retreat of the permafrost:

In parts of Siberia the southern boundary of permanently frozen ground is receding poleward several dozen yards per annum.

The matter open to question back in 1950 was the cause. Kimble noted that the Domesday Book listed 38 vineyards in England in 1086, in addition to those of the Crown. He pointed to the Greenland colony which was frozen out, back around the mid-1400s and other evidence that climates change. He looked also at Biblical evidence on the distribution of date palms to suggest that conditions in 1950 were much like those of Biblical times, providing a picture of a climate that fluctuates around a mean. Nothing to see here…

In the 1990s, global warming was in much the same position that “continental drift” had been in, a generation earlier, with some of the scientists arguing furiously, even when they agreed on the main principles, and as in the puzzle of the wandering continents, the key evidence was all there. The problem is that once again we were stuck with a bad analogy, just as the early 1960s saw us hung up on “continental drift”.

Mind you, when I covered the 2002 Spring Conference of the American Geophysical Union, there were no nay-sayers there on plate tectonics or climate change. The problem is that so long as people can get away with saying “global warming”, we are once again stuck with a bad label, just as the early 1960s saw us hung up on “continental drift”.

Scientists are always slow to move to a new model, a new way of understanding, something called a paradigm, and I lived through the plate tectonics paradigm shift, and saw some of the brawling. There was fuss and bother along the way, but in the end, the good science was recognised and accepted.

Now about the ‘greenhouse effect’: in cold climates, a greenhouse is a glass shed which allows sunlight to shine in, where much of the energy is absorbed and changed to heat. Glass is less transparent to heat than it is to light, but a greenhouse does not just trap warmth that way: it also holds a body of warm air around the plants, and protects them from wind-driven evaporation. So while we still speak of ‘greenhouse gases’, it is rare to hear anybody mention the greenhouse effect these days.

In the last ten years we have seen how the climate spin-doctors were using the same crooked tactics that were used to hide the harm that tobacco does. Nowadays, nobody denies that the Earth is getting warmer, because the evidence is there, but we stay with the less-easy-to-lie about climate change.

Why? Mainly, the cost of disagreement and bickering is higher in this fight. It mattered not at all if people disagreed about plate tectonics (except, perhaps, that it makes tsunamis like the 2004 Indian Ocean tsunami easier to understand), but global warming will be a major disaster for humanity, and any delay has the potential to cost lives. To understand this, we have to accept some puzzling propositions.

To take one example, the formation of cold salty water in the Norwegian Sea is probably what stops Dublin and New York being iced-in each winter. This is because of the cold brine that drives a current known as the Conveyor, which in turn drives the Gulf Stream. The Gulf Stream takes warm water from the Caribbean and swirls it up around the North Atlantic, contributing to fogs and breaking icebergs loose, but keeping many ports warm and open, even in winter.

Just as the prion proteins of mad cow disease have more than one stable form, so do weather patterns, and if the weather once drops into a new pattern, we may not be able to bounce it back to where it started. A golf ball in a wok lies at the bottom, and if you move it and let it go, it will roll back down. That is a stable system. A golf ball, sitting on a long cardboard tube doesn’t fall, so we might say it is stable, but if you knocked it over, it wouldn’t come back to this position. We say it is metastable.

The golf ball on the tube is stable to small nudges, but only within limits. Humpty Dumpty had two positions, one on the wall and one off it, and according to the nursery rhyme, the second was a position of no return. On the wall, Humpty Dumpty was metastable, but beside the wall, he was stable, and broken.

Climate patterns are either stable or metastable. If they are pushed too hard, they may ‘flip’ into a new metastable pattern (or even break), and only then, too late, do we discover that they were metastable (or even breakable). The best example of a probably metastable pattern is the monsoon system that waters much of Asia and the north of Australia, but El Niño and Indian Ocean Dipole are other possibles.

Climate scientists worry that severe changes may deliver a push that will take a metastable pattern away from what we know, and there might be no way of returning to the original pattern. The good news is that as northern Europe freezes over, the glaciers which are now melting away fast will be replenished, lowering sea levels. The increased snow cover will also increase the reflectivity of the northern hemisphere, and that may cool the planet down a little. We just have to hope it does not trigger a new stable pattern that happens to be an ice age.

The actual changes that might follow any breaking point are hard to predict. They are unlikely to be spectacular and major, and probably they will do their harm stealthily, when roads, bridges, port facilities and cities are flooded, or when agricultural land is lost, either by being covered by the sea or as a result of drastically changed rainfall patterns.

If rock is exposed in Antarctica, this could lead to a low pressure zone over the icy continent that could change weather patterns around the world. It hasn’t happened yet, but we need to learn from history. Ten years ago, no politician would take a long-term view and force the changes needed in the next thirty to forty years, when most of them are elected for a mere three to four years, before they face the voters again.

It is easier to bleat plaintively that there is no real agreement among the scientists yet (there is, actually), or that some eminent scientists (they aren’t eminent: just look at where their funding comes from) believe there are other explanations. That saves the politicians from having to act—and the honesty of scientists in saying that they cannot be sure just how things will go wrong allows devious short-term opportunists to prattle that “the scientists aren’t sure…”.

Politics is a marvellous human discovery. It is a pity that politicians still have to discover humanity and consider its prospects. It is likely that politics, dithering, duck-shoving and shilly-shallying will make this disaster happen, and many of the effects will seem to be unrelated to the climate.

Take dengue (pronounced den-GAY) fever, which is caused by the dengue fever virus, which is transmitted by the Aedes aegypti mosquito. The geographic range of Aedes aegypti is limited by freezing temperatures that kill overwintering larvae and eggs, so dengue virus transmission is limited to tropical and subtropical regions.

Aedes albopictus is also capable of spreading dengue fever. As a rule, the Aedes mosquitoes are recognizable by their striped legs (which give Aedes albopictus its nickname of ‘tiger mosquito’), and the fact that they bite by day.

Dengue fever involves an internal haemorrhage that sometimes leads to shock—a drop in blood pressure and failure of blood cells to meet the metabolic demands of the body. It is a leading cause of death among children in Southeast Asia, killing about 1% of all cases. It includes four distinct viruses or serotypes, dengue 1 through dengue 4. As in the case of malaria, mosquitoes become infected with dengue after taking a blood meal from a dengue-infected person.

People infected with dengue virus develop dengue fever or dengue haemorrhagic fever. Dengue fever is also known as ‘breakbone disease’ because of severe headache and joint pain associated with it. Dengue haemorrhagic fever is far more serious than the rarely fatal dengue fever.

After a short incubation period of 1 or 2 weeks, the mosquito can transmit the infection to a susceptible person. An infection with any of the four serotypes confers protective lifelong immunity, but only to that serotype. The risk of developing haemorrhagic dengue appears to be increased among people later infected with a different serotype. In recent years, haemorrhagic dengue has become increasingly common in tropical America.

Climate change is expected not only to increase the range of the mosquito but would also reduce the size of the mosquito’s larval size and, ultimately, its adult size. Since smaller adults must feed more frequently to develop their eggs, warmer temperatures would boost the frequency of double feeding and increase the chance of transmission, which will happen when the first person bitten is carrying the virus.

Warmer temperatures reduce the incubation time for the virus. The incubation period of the dengue type-2 virus is 12 days at 30°C, but seven days at 32 to 35°C. Half the world’s population is currently at risk from the disease, and it has recently become a serious problem in Latin America. Brazil alone had a quarter of a million cases in 1997.

Dengue is hard to eradicate once it is established. In Australia, it reappeared in north Queensland in 1981 after being absent for some 25 years, and it spreads each year through the areas of northern Australia where the Aedes aegypti mosquito is found, though cases are reported from across Australia each year, as a result of people being infected in either the north of the continent or overseas.

There have been suggestions in the past that global warming could lead to a spread of the Aedes aegypti mosquito, and thus the disease, but at the moment, Australian cases seem to be limited to about 200 a year. There is, however, a massive increase in cases across the whole of the western Pacific. Our turn will come…

I like to light fires

No, not bushfires, silly, though as readers of my new book Survivor Kids: get Ready for Wild Australia (released April 1, 2020) will learn, I used to light bush fires for research, under very tightly controlled conditions.

(I was a junior research assistant, supervised by senior scientists, and one of them did the actual lighting. Each day, we had tankers, up to 30 crew, knapsack sprays and tools, and the work we did gave rise to the present six-point bushfire danger scale.)

My recent silence is because I have been in New Zealand, playing with my grandkids and other kids, and thereby lies a tale of lighting a fire in the hearts of three anonymous children.


My wife and I decided to take in the Auckland Art Gallery, a superbly designed building with delightful Jura Grey limestone floors and stairs from Bavaria, all highly polished, and chockers with fossils.

Now as the people who travelled with me last year in Spain, Portugal and Morocco can attest, I keep my head down when on marble or limestone, watching out for fossils like the ones seen here.

(The second is a belemnite, an extinct squid-relative, the others are ammonites, and they are all from the Jurassic.)

I always lay down an Australian 50 cent coin for scale: the coins are 32 mm across.

This often draws attention when people only see me picking up the coin after getting a shot, and I have been known to claim that it's a form of magic, but really, it's just for scale purposes.

Let me tell you, though, that joy is discovering that the floors and stairs at the  are of fossil-stuffed limestone.

True joy is finding a father and three children interested enough to ask what I was photographing.


Sheer blissful joy is walking out the front door later to hear the oldest one, a girl of 8 or 9, giggling with glee at finding yet another fossil in the outdoor paving.


I think I won that one.


So yeah, my hobby is lighting fires.


And by the way, there's another book about to emerge as an e-book, previously announced as Not Your Usual Rocks.


It now has a new name and is now called Mistaken for Granite.  It's for older readers and armchair travellers who prefer not to hike over 3 km of blasted heath in stinging rain, only to be lowered down into a volcano. We did that, for the sake of the book.

School geology notes part 2

There appears to be a limit to the number of pics, so I had to split the entry in two.

  Once seen, never forgotten. Two examples of joints near Fairlight.

Geologists don’t really know how joints are formed, but they think it has to do with stresses being released as rocks above weather and erode away. And THAT brings us to weathering.

Weathering

All rocks break down in what geologists call “weathering”. This involves the decay of the rocks, combined with all the ways the planet has found for moving rock debris, erosion in other words, are both necessary for the rock cycle to operate. A lot of the most spectacular scenery emerges because some parts of the rock resist weathering, like Drawing Room Rocks near Berry, down the coast.

Here, the sandstone has accumulated an iron-rich layer near the top, but at a guess, water was able to get in through the joints, rock chipped away, and we ended up with this sort of pattern, with ‘occasional tables’.

In geology, nothing is completely permanent. For starters, there is no such thing as insoluble. Many of the minerals in rocks resist being dissolved, but over time, given enough time, no mineral is ever totally insoluble. Some minerals are rather more soluble, and if one mineral in a rock breaks down and washes out, it will only be a matter of time before the hard rock begins to crumble.

Air, heat and cold also play a major part in this breakdown, which is referred to as weathering. Geologists recognise two types of weathering: physical weathering, though this is sometimes called mechanical weathering, and this name probably tells us more about how it works.

All of the sandstone around the school shows clear signs of weathering. The sandstone face below and east of the library is a good example of one form of physical weathering caused by feet.

In 1969, just after major fires in the Royal National Park, I was sent out, in full ranger uniform, partly to see if the old tracks were visible, but also to ‘show the flag’. Where a track passed over sandstone, the path to walk was much lighter than the other rock: human feet had weathered the rock.

Lightning

There used to be a poor example of a lightning strike in the old nature area, but I think we lost that. No matter, it was unimpressive unless you knew what to look for.

   

Around the world, there are about 100 lightning strikes, somewhere, each second. That adds up to a lot of energy hitting things.

When lighting fails to hit a building, a tree, a foolish kite flyer or an unwise golfer, it usually hits rock. Lightning often comes with rain, and when the water has already soaked into a rock, the instant heat of a lightning strike turns that water to steam, flaking off a surface layer. Once the rock is in small pieces, other weathering effects can take over.

Note that these blasts happen on high places in storms. The traces are best sought for in good weather. If you are on a high place in lightning, move away! The danger signal comes when long hair starts to float up into the air, but by then, it may be too late…

And now for my favourite rock forms, which appear in the school grounds only in minor and beginning forms, visible only to a prepared eye.

Honeycomb weathering

Geology shapes our scenery, sculpting the rocks around us, and one of the delights of my home area is honeycomb weathering, sometimes called alveolar weathering by people of French background, while others call it fretting, stone lattice, or most poetically, stone lace.

Honeycomb weathering in Hawkesbury sandstone, some of it cross-bedded, near Box Head, north of Sydney.

Much of the best-exposed sandstone near Sydney is close to the coast, and around the world, it is common to blame salt spray for honeycomb weathering. The idea is that salt spray lands on and soaks into the stone, but when the water evaporates, salt crystals are supposed to wedge sand grains off.

There is definitely more to the picture and that, and while salt spray probably plays a part, as a young man, I saw honeycomb weathering in the Budawang Ranges, 40 km from the nearest sea coast. I have no surviving photographs from that time, but I do have something rather similar from the flanks of Uluru, on the far side from where the climbers used to start.

A curious but entirely natural weathering effect on the side of Uluru.

   

Ant lions

Ant lions were the first insects I ever studied, and they make neat pits in sandy soil. There used to be lots of them under the old demountables, and there should be some under the trees. They are the larvae of lacewings, alias Myrmeleontidae (Neuroptera). The name ‘lacewings’ describes their pretty wings quite well, but ‘ant lion’ is a good name for the larval stage. Instead of hunting like lions though, they dig pits in the sand and sit at the bottom, waiting for an ant to fall in.

I once saw one of these animals capture a small weevil, but usually, they eat ants. Whatever the prey is, once the unlucky animal reaches the bottom, the ant lion seizes it in its pincers and sucks it dry. In the end, it flicks the empty husk of the prey out of the pit. Ant lions are neat!

To find these curious creatures, look for a small conical pit, 1–3 cm across in dry sandy soil. The soil may be close to one of those gum trees with sap that kills grass, or inside a hollow tree, along the edge of a building or under a rocky overhang. Sometimes, you can even see ant lion pits, right out in the open in the dry season on Cape York, in the summer around Myall Lakes in NSW and in dry areas. All they need is dry sandy soil.

A large ant lion can be 6 mm long, but 1.5 mm of that length may be the nippers that it uses to seize its prey. It digs a pit by backing into the sand and moving in a circle, flicking sand out with its head. Recent research on fossils in amber suggests they have made pits for 100 million years.

Dry sand only piles up to a certain slope, called the angle of rest, and this is the slope of the sides of every pit. At this angle, the sand is unstable and ready to tumble down if a small animal walks near the edge. As soon as sand grains hit the bottom, the ant lion starts flicking sand up from the bottom of the pit. Some sand falls down again, knocking its prey down the slope, but if the ant lion flicks enough sand out from below, the whole slope begins to slide down, carrying the food animal with it. Ant lions are easy to keep but they aren’t geological.

A moral tale for kids:

Whenever people in the outback dug a well in a sandy river bed or climbed a dune, they were in the same position as ants, except that there was no monster waiting to grab them and suck them dry. The real danger came as they dug down close to water, because damp sand will hold together, and they could dig a steep-sided hole. Then when the sand dried, it would collapse.

Each year in Australia, one or two children are killed when a sand cave collapses on them. No explorers were ever killed that way, but probably a few needed their companions to dig them out.

As you can see, in science, everything is connected. We teach them to read the rocks, and weave a web around them!

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A small advertisement: some of the illustrations appearing here will be in my upcoming Not Your Usual Rocks. This is now moving into final editing, and will either be the subject of a contract for a coffee table book by mid-June, or it will be issued as a delicious e-book by April 2020.

School geology notes part 1

I work as a volunteer 'visiting scientist' at a local K-6 school, and the last two years have been turmoil as it was rebuilt to meet climbing population figures. In the process, some beautiful nature was destroyed, but the place is bouncing back, and I saw that there was now some exciting sedimentary geology to play with.

Today was the last day of the year, and I was there to show the teachers what is available to use, and I wrote these notes before I went.

Stories

Rocks tell stories, and some of these stories are at a simple THE CAT SAT ON THE MAT level. Other stories that the rocks have to tell are more like Virginia Woolf on a bad day.

Getting kids started on reading is a bit like edging them onto a slippery slope on a bicycle and keeping them on an even keel as they get up to speed, carried along by natural forces. OK, that’s a stretched analogy, but slippery slopes are one of my long-term temporary obsessions. All you need, in order to play is a sand dune, but a Vegemite jar half full of sand will do as well.

Once seen, never forgotten: I had to learn this sort of stuff for myself, but each bit, once I acquired it, became part of my ongoing observations. The linking theme here is that sand that is piled up collapses to form a fixed angle (for that sort of sand), and that angle shows up in dunes, rocks, sandbanks, pits and holes in dry sand and more.

When we try to pick out anything by itself, we find it hitched to everything else in the universe.
—John Muir, My First Summer in the Sierra, Boston: Houghton Mifflin, 1911, chapter 6.

A slippery slope in a jar

The thinking for this began when I had an idea to try something. I was getting ready to work on the track with Stage 2, I think. Our topic was flowers and stuff, but I spotted the rock on the right, and saw one of my favourite simple stories: current bedding or cross bedding.

I will explain what that is shortly, but let’s walk before we gallop down the slope, OK? Just watch how all of the bits come together, in the end.

Advancing dune, Sahara

Ant lion pit, coin for scale

Current bedding, as I prefer to call it, tells us something odd about sand. If you tip dry sand out of a funnel in the sandpit, it will

form a conical pile, and I can predict to within a couple of degrees the angle that the sand will lie at. We call this angle the angle of rest, and that’s the last bit of jargon.

Angle of rest in a jar. Use a cylindrical
and clean, very dry sand.

Ant lions (I will talk about them later) make pits in dry sand, like the one on the left, and the sides also lie at the angle of rest, as does the front of an advancing dune in the Sahara.

So there I was, clutching a Vegemite jar, half full of dry sand. I always carry this in case somebody happened to need a jar of dry sand, and a full jar is too heavy… I bounded onto the rock, declared that I was sitting on a 205 million-year-old fossil, then moved among the kids and showed them the jar, rolling it.

I explained that when sand is pushed along by wind or water, it gets pushed over the front, and this creates (drum roll please!):

Current bedding

Once you know what you are looking for, it’s everywhere, and any kid who has been shown the secret will be able to share it with others. Any cutting, any cliff is likely to reveal beds of sandstone, laid down as sand banks: the picture geologists have of Sydney in the Triassic (~205 million years ago) is a giant sandy river delta, a bit like Bangladesh today.

Three examples of current bedding: (top) Old Man’s Hat, Inner North Head; (centre) Sydney Road Fairlight, Manly side of the shops; and Malabar.

The shots above are easy to spot: the ones around the school need a trained eye. Let the training begin!

(A note to my teachers, less relevant to others: In all of these shots, I have left background in place, so you can come back and look at them.)

 

 

 

 

 

As you can see, the layering is more subtle when it comes to bush rock. The right-hand shot éabove is on the cycle track, and every cyclist going along there is running over 205 million-year-old fossils.

But how do we know the age? We don’t, not really, but the rock is Triassic, making it between 180 million and 220 million, and the sandstone is early to middle Triassic, so 205 million years is near enough for government work. Talk to me if you want more, because explanations require lots of hand waving..

 

On the western side of the school, the sawn stone has nice banding, and this is a Virginia Woolf sort of story, so here’s the Classics Illustrated/Cliff Notes version/. Iron occurs in compounds in two forms that old chemists called ferrous, which is soluble and ferric which is insoluble.

Banded iron in sandstone.

The ferrous form is now called Fe²⁺, and the ferric form is Fe³⁺. The key thing is that one can change into the other, Fe²⁺ seeps away, but when it changes to Fe³⁺, it stops where it is. Chemists say that iron II is oxidised to iron III and iron III is reduced to iron II.

Iron banding and Liesegang patterns

I didn’t find any Liesegang patterning around the school, but this is the same iron II/iron III story.

     

The same explanation applies to the iron banding we can see, and some of that is spectacular:

 

Joints

I was tricked when I thought I had found a joint in the sandstone. Joints are planes of weakness that are seen in most rocks, but they are particular important in the shaping of Sydney, because when sea levels fell, streams and rivers were directed along the jointing patterns, which is why the city has so many east-west and north-south valleys.

When the sea rose at the end of the last Ice Age, it flowed into those valleys, and we say that the fern leaf pattern of the harbour is a drowned river valley. Anyhow, those ‘joints’ were cut with a saw, but they give you some fresh rock to look at. There are no joints that I can see in the school grounds now, but below are some local joints:

  

Above: three examples of joints: (top) Old Man’s Hat, Inner North Head; (centre) Sydney Road Fairlight, north side; and on the way to Fairy Bower.

There appears to be a limit to the number of images I can insert, so this is continued in part 2.

What geologists think, part 3

8. The standard principles of science

These are ideas that all scientists just assume, but they are rarely stated explicitly for students or the public. There is enough information here to tell you what each idea is about, and you will find enough terms to let you look the idea up, if you need to. There are lots of ins and outs, and working scientists spend their lives mastering them. They will, I hope, recognise that this is Science Lite.

Atoms and molecules

All matter is made up of atoms, and the properties of any piece of matter will depend on what atoms are present, and how they are arranged and connected. Many atoms join up to form regular frameworks that we call crystals. Sometimes, atoms join into tight standard groups, like water, quartz, salt and sugar. We csll these groups molecules.

The laws of thermodynamics

For general purposes, heat flows from hot to cold, perpetual motion is impossible, and there is no such thing as a free lunch. By the way, if you want to drive a politician or an arts administrator to distraction, ask him or her to explain (or even just to state) the second law of thermodynamics. Trust me: it matters!

A good many times I have been present at gatherings of people who, by the standards of the traditional culture, are thought highly educated and who have with considerable gusto been expressing their incredulity at the illiteracy of scientists. Once or twice I have been provoked and have asked the company how many of them could describe the Second Law of Thermodynamics. The response was cold: it was also negative. Yet I was asking something which is the scientific equivalent of: Have you read a work of Shakespeare’s?
—C. P. Snow, Rede Lecture The Two Cultures and the Scientific Revolution (1959).

 If you want a simple version, it says that differences in temperature, pressure, and density tend to even out, after a while. More detailed discussion involves entropy The simplest available version of that: entropy is a thermodynamic function that measures randomness or disorder. If you like, entropy is a measure of untidiness.

 

Most of the principles of science are what scientists call counter-intuitive. In lay terms, they seem to go against our gut reaction; the earth as we experience it looks flat, and our intuition tells us the sun and moon circle around us once a day, but ignoring intuition, all scientists agree that the world is a globe, we orbit around the sun, and the moon orbits around us once a month.

Entropy is slippery, rather than counter-intuitive, and you have to note the qualifications which limit entropy to inside a closed system. Under those conditions, entropy, or disorder, increases, which is how scientists say that over time, everything gets more random, more dispersed.

There can be no exceptions to the rule that entropy, the disorder of things, always increases, but life, at a local level, can be an anti-entropy agent, making some things more ordered at a local level, even as entropy is increasing on a larger scale. In simple terms, animals and plants gather up and concentrate certain elements in our bodies.

Across the universe, every change leads to an increase in the total entropy, but the delight lies in the details, and a lot of geological science comes down to explaining how, on a local level, the process of concentration in elements or minerals is driven.

If [your pet theory of the universe] is found to be contradicted by observation—well, these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation.
—Sir Arthur Stanley Eddington, The Nature of the Physical World (1928), chapter 4.

Conservation of mass and energy

In simple terms, matter and energy can neither be created nor destroyed. There is No Such Thing As A Free Lunch.

Equilibrium

As a rule, things are in balance, but that is not the same as saying they are unchanging. The number of oxygen molecules in an open jar may vary slightly over time, as molecules whizz in and out, but at any practical level, the entries and exits cancel each other out. If I have crystals of salt sitting in a saturated brine solution, some of the chloride and sodium ions in solution may attach to the crystals, but on average, just as many ions will leave the crystals. We say the solid and the solution are in dynamic equilibrium.

The law of large numbers

There is no such law, but it is convenient to pretend that it exists. Given time, every atom of a sample of radioactive carbon-14 will break down. We cannot say when a given atom will decay, but with large numbers of atoms, we can say that half of all of the atoms that we start with now will have decayed if we come back in 5730 years from now. We say that carbon-14 has a half-life of 5730 years.

Evolution

Evolution also hangs on large numbers. You won’t evolve, I won’t evolve, but our species, like every other species, does evolve. Don’t worry: some of your genes will carry forward, and some of them may be more common in a future population.

(I anticipate, for example, that in a thousand years, the descendants of today’s Australians will have a skin color darker than mine, due to the selective effects of melanoma.)

(Note that this can  be negated because humans, uniquely in an evolving world, can apply social changes to limit selection effects.)

Falsifiability

Every part of science is able to be falsified by evidence, and if some idea can’t be tested and potentially falsified, it just isn’t science. That doesn’t mean science is all false, it just means every assumption is always considered open to testing and being found wrong.

If we found dinosaur fossil bones and human fossil bones in the same rock, this would mean we probably had to revise large parts of what we think we know about geology and biology, though the first step would be to check carefully that somebody hadn’t just pulled off a hoax.

Scientists are always on the alert for contradictions like that, even though they don’t really expect to find any. One way to become a famous scientist is by finding a red-hot contradiction to what everybody believes.

Ockham’s Razor

Then again, maybe we wouldn’t need to revise anything. William of Ockham made it a lot more complicated, but his basic notion was that if there are two possibilities, you should take the simpler one. If we found human and dinosaur fossils in a single rock, a simpler explanation would be fraud. We would at least look for evidence of fraud first, but if there was truly no evidence of fraud, it might be time to start a rethink.

9. Caveats

I am not a geologist, but I know how to think, where to look, and what questions to ask. My undergraduate studies were mainly in the areas of botany and zoology, so I may, from time to time, be in error. As a professional science writer, I am used to checking my facts, but even when I get the latest opinions there is still one gotcha remaining.

Science changes, and geological science does change—and I saw it happen. When I was an undergraduate, I picked up one year of formal geology training, enough to appreciate that the rocks yield the soil that my precious plants flourish in, plants that feed my equally precious animals.

One day, one of our geology lecturers urged us to attend certain sessions of ANZAAS, the Australian and New Zealand Association for the Advancement of Science. “Listen to Sam Carey,” he told us. “He’s quite mad: he thinks the continents are moving.”

That was in 1962, and I did indeed hear Sam Carey talking about such wild ideas. He seemed to make a reasonable case, except that we all knew the idea was crazy. Just three years later, plate tectonics was all the go.

In fairness, Sam Carey was only partly right, because his notion was based on some false assumptions, but the key thing to note is this: in 1962, moving continents was madness, by 1965, it was pretty much the orthodox model.

I have tried in this book to stay with the best and safest bits of orthodoxy, but at any time, that which was orthodox can be defeated of overturned by a simple paradox. One new discovery is all it takes, as T. H. Huxley said while discussing historical work on the spontaneous generation of life:

But the great tragedy of science—the slaying of a beautiful hypothesis by an ugly fact—which is so constantly being enacted under the eyes of philosophers, was played almost immediately, for the benefit of Buffon and Needham.
—T. H. Huxley, Presidential address to the British Association in September, 1870.

My book (meaning Not Your Usual Rocks, still to be published) is about the facts—though I will later discuss a maverick theory about the origins of oil. I don’t believe it, but it is both entertaining, and instructive to consider as a way of seeing how science works.

By the time you are done, all of these will make perfect sense.