I am of a generation that, at mention of Laos, Vietnam and Cambodia, I recall images of intense conflict, thankfully long past. The images now are of jungle, peaceful villages nestled among ancient civilizations, and rivers; kayaks instead of gunboats. The coincidence between geology and river in Southern Laos (LDR) has created an area known as 4000 Islands. Here, Mekong River changes from a single channel to multiple braids that thunder across a spectacular array of waterfalls and rapids; a white-water kayaker’s idea of fun. Sam Ricketts, his friend Lachie Carracher, and a film crew (Luke McKinney and Lissa Hufford), converged, in December 2016, on Don Det, an island-town in the middle of 4000 Islands; their focus – Li Phi Falls. Continue reading
Omens, God’s wrath, or just plain misfortune; comets were seen by our Medieval forebears as a disturbance in the natural state of the heavens, portending disaster, pestilence, or famine, and if you were really unlucky, all three. Harold, Earl of Wessex and later King, before he did battle against William of Normandy in 1066, must have had some misgivings with Halley’s comet nicely lighting up the northern sky (we now know it was comet Halley); he probably should have kept both eyes on the battle. Portent indeed; the Norman conquest changed irrevocably the history of Britain.
It seems that the ancient Chinese were a little more rational in their deliberations on comets – they referred to them as brush stars, and as early as 613 BC were computing approximate orbits. In fact it is ancient Chinese astronomy records that have enabled modern astronomers to confirm calculated orbit periodicities for comets like Halley. Continue reading
February in New Zealand is mid-summer and this means beaches, swimming, BBQs, and generally chilling (often literally). One beach we frequent, a 50-minute drive, is Ngarunui. It is a popular surf beach near the coastal town of Raglan on New Zealand’s west coast. Here, the Tasman Sea rolls in, as it has done for millennia; the ancestral Tasman began to form about 80 million years ago, when the NZ subcontinent split from what then was a combined Australian – Antarctic continental block. The ‘Ditch’, as the Tasman is often called, is about 2000km wide so there is lots of space to develop a decent wave set. Continue reading
You never know what new treasures will be discovered strolling along a beach after a good storm. The beach may have changed shape; cusps, ruts and rills smoothed, some of the sand moved offshore beneath the waves, a few sand dunes cut in half. There’s flotsam and jetsam, a few bedraggled seabirds. And there are shells, mostly devoid of their original inhabitants.
Raglan (west coast New Zealand – i.e. the coast facing Tasman Sea) was a bit like that this week. One particularly neat find on our jaunt was a largish log completely covered in Goose Barnacles. It is usually the case that critters like these are dead by the time they wash up the beach. But this time all were still alive. The log was a slowly-seething mass of stalked shells, parched, and all looking for a way out of their predicament.
Goose barnacles, other than being fascinating to watch up close, have served the science of evolution. Charles Darwin’s book about them, published in 1851, contains many of the ideas he was formulating about species variations and embryonic development, laying some of the foundations for his ‘Origin of Species’.
Yes, that’s its zoological name. The common name ‘Goose barnacle’ has an interesting history that from a 21stC perspective seems slightly weird. The word derives from a 13th century usage for a seabird – the so-called Barnacle Goose, an Arctic migrant. Gaggles breed in the Arctic then migrate to spend a balmy winter on British shores. Coastal Brits, those that hadn’t been press-ganged into the Crusades, were never quite sure where the birds came from (they never saw the eggs). They surmised that the actual stalked barnacle looked a bit like the actual bird, and that the birds hatched in much the same way, from the planks of ships, whereupon they would fly off to join their gaggle.
Lepas attaches with a long fleshy stalk (a peduncle) to flotsam, logs, basically anything that floats; the Raglan examples were up to 20cm long. The stalk is part of the animal that can move the shell to take advantage of currents, light, or food. The animals live cheek-by-jowl, as you can see in the image. They are crustaceans like crabs and shrimp.
Barnacle guts are contained within five shelly plates. They feed by filtering microscopic particles, plankton, and algae from seawater using delicate, feathery protrusions called cirri (hence the general classification as Cirripedes). In the video, our Raglan examples are extending their cirri in air – perhaps they can sense the incoming tide.
Darwin’s barnacles; sources of invention
He wrote four books on these critters; two on living groups (the stalked group and the sessile-attached group), and two volumes on fossil representatives. The first was on the stalked variety, including Lepas. A second volume on (living) barnacles that are more commonly cemented to rocks was published in 1854. His studies of these creatures provided him with insights into species variation and embryonic development. As Martin Rudwick illustrates in his wonderful book ‘The Meaning of Fossils; Episodes in the History of Palaeontology’, Darwin understood that both phenomenon would require cogent explanation to convince his audience of the central theme of his ‘Origins’; natural selection. Thus, his studious and systematic observations of barnacles, seemingly a dry topic, provided both the data and the wherewithal for creative thinking.
Prevailing 19th century thought on species development, postulated by pioneer biologist Jean-Baptiste Lamarck (1744-1829), was that species tended to progress toward improvement and complexity. Darwin’s recognized that regression was also an important adaptive process in evolution. He based this challenge to the status quo on the well-known fact that free-swimming barnacle larvae have legs (like other crustaceans), and that these appendages are converted “into an intricate food-collecting device, and lost many of the functions and organs associated with a free-swimming life.” (Martin Rudwick, p233). This feeding device is the cirri.
As is so often the case in science, the seemingly innocuous, tedious, but deliberate gathering of data can lead to startling invention and discovery. The humble Goose Barnacle has certainly done its part in shaping our ideas on the biological world. With our barnacle-covered log, we were witness to a microcosm struggling for survival; hundreds of individuals and a single community. Some days later, most are dead, scavenged by seagulls and demolished by waves. Perhaps all that’s left are a few broken, disarticulated shells.
Martin J.S. Rudwick. The Meaning of Fossils; Episodes in the History of Palaeontology. Second Edition, 1976, Science History Publications, Neale Watson Academic Publications Inc, New York.
There is a nice essay by Marsha Richmond (2007) on Darwin’s barnacles, written for Darwin on Line.
You can also find lots of interesting general information and teaching resources on Darwin, including his voluminous correspondence (more than 2000 letters), on Cambridge University’s Darwin Correspondence Project
CO2 has a bad rep. We can’t do without it (GOOD – it’s part of the photosynthetic process), but it looks like we’re upsetting the balance between having too little and producing too much (BAD). I take some of the blame for this: I drive a car (out of necessity), run a small boat (that I really enjoy), use a gas stove (the best cooking device ever), use a couple of lawn/orchard mowers (also necessary to keep the weeds at bay in our organic kiwifruit orchard), and take trips to Canada and beyond (which is life-affirming). I guess we all have our crosses to bear (INDIFFERENT), but I do take solace in the knowledge that my carbon footprint is more than offset by the biomass on my organic orchard.
Back to geology
Carbon moves through a grand cycle. The cycle is actually pretty complex and if considered in its entirety, takes 10s of millions of years wherein carbon moves through the atmosphere (mainly as carbon dioxide and methane), the biosphere (that includes us), the earth’s crust and mantle (i.e. soils, rocks, magma), and the oceans. The exchange of carbon through these systems can take place fairly quickly even on a human timescale, or it can take eons.
Climate change science tends to concentrate on the atmosphere-ocean part of the carbon cycle, probably because it is the most obvious and also because it is the most likely to influence our well-being in the short term (a few lifetimes). However, important parts of the carbon cycle also include processes that can take a very long time, such as the recycling of carbon, rock and fluid through the crust and mantle over 10s of millions of years, only to be rejuvenated when new crust is formed, for example by volcanoes. Carbon is also stored, or sequestered as rock and fluid and it is the use of some of these (coal, oil, gas) that has the potential to disrupt the natural cycle.
Ocean – Atmosphere exchange
CO2 is absorbed quickly in water. You can see this in your soda-stream maker or can of fizzy pop. When you open a bottle of soda water CO2 is released as bubbles. If you put the bottle cap back on the bubbles will continue for a while but gradually decrease until all bubbling ceases. This is the point at which the CO2 pressure in the air space is in equilibrium with that in the water. This doesn’t mean that there is no exchange of CO2 between the air and water in the bottle, but that the amount of CO2 going in or out is the same; there is an equilibrium, or balance.
Exchange between the oceans and atmosphere accounts for about 43% of CO2 in the air. However, we need to remember that the exchange is not a one-way journey. There is an approximate equilibrium between the two sources of CO2 – the atmosphere and the oceans, that means there is as much CO2 going into the atmosphere as there is CO2 going into the oceans. This balance can be upset, but even when this happens the tendency is for the atmosphere-ocean system to establish a new equilibrium.
It is estimated that 36 giga (billion) tons of CO2 were released into the atmosphere in 2013. The oceans are capable of absorbing massive amounts of CO2 but there are limits; many scientists now think those limits have been reached. This may well be the case, but we do need to take stock of some other factors in the ocean-atmosphere exchange story.
- When CO2 exchanges with seawater, some of it remains as CO2 in water (it is absorbed), and some of it dissolves forming the following products during chemical reactions: H2CO3 (carbonic acid – a weak acid), HCO3 (bicarbonate), CO3 (carbonate), H+ (acid). Carbon is removed from seawater itself when calcite and aragonite precipitate (as shells, skeletons and so on). Under normal conditions there is a balance between these chemical components such that in seawater the index of acidity, the pH is maintained at about 8.2 i.e. slightly basic (the neutral acid-base value is 7). In other words, the chemistry of carbon in seawater acts to buffer (maintain) the pH.
- CO2 is absorbed or dissolved into ocean surface waters. It takes time for these waters to mix with deeper oceanic water masses. In fact, some deep oceanic circulation systems can take several 100 years to move to shallower depths. This means that there are some pretty old deep waters that may contain pre-industrialization concentrations of CO2. So for example, if a process like ocean acidification is taking place it will not affect all shallow and deep ocean water masses at the same time. How long it might take to ‘homogenise’ ocean pH is not well known.
- Cold water will absorb more CO2 than warm water. As ice sheets melt, the cold water outflow will tend to have higher CO2 concentration than warmer waters, especially those in the tropics. The geographic distribution of these differing CO2 concentrations will depend on ocean currents and ocean mixing. The short and longer term impacts of mixing on ocean acidity are not that well understood at present although some evidence has been presented for a slight lowering of pH in shallow Great Barrier Reef waters.
Volcanoes; The Recycling Depots
CO2 is a common component of volcanic gasses. The US Geological Survey has calculated that about 200 million tonnes of CO2 are contributed annually by land and submarine volcanoes. The CO2 emitted by volcanoes is dissolved in magmas deep in the earth’s crust and mantle. Like the soda-stream bottle experiment, the gas is released from the magma as it rises to the surface and the gas pressure decreases. The most prominent submarine volcanic systems are the mid-ocean ridges, or spreading ridges where new crust is formed by rising magma. Large volumes of CO2 are released there into the ocean waters. Some of this CO2 will also react chemically with the new rocks produced by the rising magma and these CO2 + Water + Rock reactions will tend to remove carbon from seawater.
The volume of CO2 calculated by the USGS may be underestimated because it has also been discovered that CO2 is also released through faults associated with these large, linear rifts and not just the volcanic vents themselves. Nevertheless, the amount released by volcanic processes, even if underestimated by a factor of 2 or 3, is only a small fraction of the total CO2 added by burning fossil fuels.
A natural ‘sink’ for carbon and CO2 in the oceans is the formation of calcium carbonate as either the mineral calcite or aragonite, that is precipitated by organisms such as plankton, certain types of algae, shellfish, corals, bryozoans and crawling-swimming critters. When calcite or aragonite forms, the chemical reactions remove CO2 from seawater.
Over long periods of time the dead shell-skeletal material accumulates on the sea floor, is buried and hardens to limestone. Most of the limestones we see today are acting as vast storage facilities for carbon – they have sequestered carbon.
An analogous process takes place with land plants that accumulated in bogs and swamps, were buried and converted over millions of years to coal. Hydrocarbons (oil and gas) also represent the long-term sequestering of organic carbon that, through geological history will have been present in the ancient atmosphere, oceans and organisms. At a quicker pace, modern soils sequester carbon that is used both by plants and micro-organisms.
Permafrost – more tenuous sequestration
Arctic permafrost covers about 24% of the northern hemisphere land area; it also extend beneath the sea floor. Permafrost consists of ice, frozen soil and sediment. Although some CO2 is present in the ice, most permafrost carbon is locked in frozen organic matter. Melting has the potential to release carbon; some will be consumed by soil microbes and plants, and some will be released as CO2 and methane CH4, depending on the metabolism of the microbes. Groundwater chemistry may also change as CO2 and cations like calcium or sulphate are released. Indeed, the chemistry of Arctic drainage systems like Yukon and MacKenzie rivers seem to be undergoing some changes to their chemistry as a result of permafrost melt.
Debates over climate change, whether they are directed towards agreement or denial, encapsulate positions that at one end of the spectrum are ideological and political, and at the other scientific. Ideological positions, regardless of stripe, contribute little to the debate other than providing a vent for one’s spleen. Ultimately, questions about the veracity of the science will be answered by science.
The USGS has calculated that, in 2013, 36 giga tons of CO2 were added to the atmosphere-ocean system; this is a humongous volume. It seems to dwarf the natural CO2 inputs from volcanoes, soils, organisms and so on.
The problem, if we encapsulate it in a single sentence, is that the rate of CO2 emissions into the atmosphere-ocean system is far greater than the rate at which CO2 can be consumed or sequestered by all natural processes. Does this mean that climate will change? Regardless of one’s position on Climate Change it seems eminently sensible to allow the science to continue gathering data that will test the veracity of hypothesis and theory. Afterall, many-most of us will have grandchildren and I for one would like to be more certain about the kind of world I’m leaving them.
Most of us at some time have gleefully created our own liquefied puddle by stomping on wet beach sand. I once showed my kids, intent on explaining the scientific intricacies of liquefaction, but being teenagers at the time they walked off in embarrassment. But liquefaction is much more than a trick at the beach; it is a process that can have devastating consequences for built structures and natural slope stability.
Earth movement during an earthquake is cyclic; each back-and-forth or up-and-down motion is one cycle. There can be many cycles during those few terrifying seconds. One way to express the intensity of the movement (and earthquake magnitude) is to measure the acceleration of ground displacement (called Peak Ground Acceleration, PGA). A useful analogy is a car that, when the gas pedal is depressed, accelerates to some maximum speed; the acceleration is the rate at which this speed increases. Take your foot off the gas pedal and the car decelerates; your vehicle has completed one cycle. A PGA value is usually expressed as a fraction of ‘g’ (the acceleration due to gravity); the greater the fraction, the greater the intensity. During severe earthquakes most damage occurs because of physical, mechanical shaking. However, there is another process that, in some circumstances, produces severe and widespread damage to buildings and infrastructure – liquefaction.
Of the two major earthquakes to hit Christchurch, New Zealand (M7.1 September 2010 and M6.2 February 2011) the second, lower magnitude (but greater intensity) event resulted in the most damage and loss of life (because the epicentre was less than 10km from the city and high PGAs). Christchurch lies on a relatively flat, low elevation flood plain that is underlain by unconsolidated (soft) layers of silt, clay, sand and gravel. The watertable is less than 2m beneath much of the city area. During the 2011 earthquake, liquefaction resulted in water and sediment expulsion (to the surface) over about a third of the city, damaged about 15,000 buildings (6000 beyond repair) and buried water-sewerage pipes, and deposited more than 400,000 tonnes of sand and silt on streets and backyards.
Most of the damage from earthquake shaking takes place above the land surface; most of the damage from liquefaction occurs below it.
What is liquefaction?
Under normal conditions sand deposits have strength, imparted by all those sand grains being in contact with other grains around them; this is the reason you can walk along a beach without fear of sinking up to your neck. This condition also applies to sands below a watertable but in this case all the pore spaces between grains are filled with water. The groundwater fluid pressure in this situation is normal.
Earthquake shaking applies a cyclic external force to the sand grains and the ground water. If shaking is strong enough the sand grains begin to separate until they reach a point where most are ‘floating’ in the surrounding water. At this point, the fluid now consists not only of water but also the floating grains and a consequence of this is that fluid pressure increases. The sand is now liquefied. In this state it no longer has sufficient strength to support surface loads and their foundations sink. Buried pipes will also move, some breaching the land surface.
The excess fluid (water + grains) in liquefied sediment is at a higher than normal pressure and will flow towards the surface as boils or sand volcanoes. The 2011 Christchurch earthquake provided some excellent examples of this process (although pretty disheartening for those directly affected). As water plus sediment is expelled the sand grains beneath the surface begin to settle and eventually the process stops. Another spectacular example of foundation failure took place during the 1964 Niigata earthquake on Honshu, Japan. Here, entire 4- and 5-storey apartment blocks literally fell over because of liquefaction beneath the buildings.
Liquefaction beneath the waves
Sediment beneath the sea or lake bed can respond in a similar way to seismic shaking. However, seismic events are not the only cause of submarine liquefaction; the impact of storm waves on the seabed can also produce liquefied sediment. Like earthquake events, this process is also cyclic where fluid pressures increase and decrease as each wave passes. Liquefaction of seabed sediment can result in serious damage and movement of structures such as pipeline, cables, oil rigs, reclaimed land and jetties; it can also trigger submarine landslides and bottom-hugging flows of mud, sand and gravel.
A simple experiment
The inset demonstrates a simple experiment where a structure, comfortably resting on a sandy surface, will sink during an experimental seismic event. All you need is a suitable container, sand, water and Lego (or whatever takes your fancy for a surface structure).
I always feel a sense of unease when hearing of natural disasters. I live in a country where earthquakes, volcanic eruptions, landslides, floods and the threat of tsunamis all occur within a relatively small land area. In Canada, I lived on a small island (a daily ferry commute), nestled in a typical West coast fiord near Vancouver and more than once I pondered the possibility, even inevitability of those towering rock walls suddenly obeying the laws of gravity.
Fiords exist because of ponderous gouging and plucking of the solid earth by rivers of ice; testaments to ancient glacial climates and the forces of nature. Fiord landscapes are stunning, beautiful in and of themselves and, I suspect because they invoke a sense of awe. But this is a façade. Rock walls, almost vertical in places and towering 100s if not 1000s of metres are inherently unstable; any glaciers at the head of the fiord or hanging off the valley walls exacerbate the problems. Landslides, rockfalls and glacier calving inevitably end up in the sea and the resulting tsunamis can be terrifying. The video here shows these guys had a lucky escape after venturing a bit too close to a calving, Greenland glacier.
All that energy focused through a narrow gap
Terrestrial or submarine landslides that occur on open coasts can produce locally massive tsunami waves (10s of metres high) but these tend to dissipate radially. There are well known examples on oceanic volcanoes like Canary Islands and Hawaii. From the North Sea, the Storegga submarine landslide about 8000 years ago must have devastated parts of Britain and northern Europe coasts with wave run-up locally 20m and more. The Youtube Video here shows a recreation of this event.
Tsunamis generated in fiords react differently because the wave energy is focused, generally along the length of the fiord. Some of the largest waves on record, either observed directly or the immediate aftermath, have been generated in fiords. There are many examples – historical and prehistoric. The three I have chosen are well documented and pretty spectacular. They provide a sober reminder of what can happen when nature casually flicks a finger at us.
Talfjord, Norway, 1934
On April 7, about 2 million cubic metres of rock fell about 700m into the fiord. Displacement of water instantly created a wave that initially was 62m high near the landslide impact. By the time the wave had reached the village of Talfjord some 5 km away it was still 16m. It was about 3am and most in the town were asleep. Geological mapping has shown that there have been at least 10 landslides along a 7km stretch of the fiord, and along the adjacent Storfjorden 108 rockslides have been identified, all occurring since deglaciation about 14,500 years ago (Source: Harbitz et al. 2014, Coastal Engineering, v 88). It was common knowledge at the time that the rock mass above the fiord was unstable, where tension cracks were forming. Unfortunately, there are no real geotechnical solutions to a problem like this, other than monitoring.
A similarly unstable, but much larger rock mass in Storfjorden (about 50 million m3) has been monitored for several years. Signs of instability include tension gashes that seem to become larger every year. Early warning systems are in place although the warning time for the closest villages is likely to be no more than a few minutes. Fingers are crossed.
Paatuut, Greenland, November 21, 2000
A large landslide at Paatuut located in a fiord on Greenland’s west coast, moved about 90 million m3 of rocky debris about a third of which splashed into the fiord. The landslide was initiated 1000-1400m above sea level. No one witnessed the landslide but the resulting tsunami was recorded in a small village about 40km away. On the side of the fiord opposite Paatuut an abandoned mining town (Qullissat) about 25km away was almost destroyed. Wave run-up at Qullissat was 28m (observed in the lines of debris) and it is estimated that the wave near the landslide itself had a run-up of about 50m. Seven kilometres northwest of Paatuut several icebergs were left stranded up to 700m from the coast on an alluvial fan. Fishing crates and other flotsam were stranded to 800m inland and 40m above sea level.
Lituya Bay, Alaska, July 9, 1958
One of the largest waves ever observed (and survived) took place in Lituya Bay, Alaska during a 1958 magnitude 7.8 earthquake along the Fairweather Fault (Fairweather Fault is part of an extensive system of active faults that mark the boundary between the Pacific and North American plates – it is a fundamental structure in the Alaskan Panhandle.).
The tsunami was triggered by a 30 million m3 rock mass falling more than 900m into Gilbert Inlet at the head of Lituya Bay. It seems likely that collapse of the glacier front at the head of the Bay also played a role in generating massive waves. The wave nearest the landslide had an incredible 524m run-up (1720 feet), but subsided to about 10m near the entrance to the open sea. Wave run-up was easily mapped along Lituya Bay by the line of devastated forest; also known as trimlines.
Howard Urlich and his 7 year-old son, from their fishing boat anchored in a sheltered bay, provided first-hand accounts of what must have been a terrifying experience. They awoke to a wall of water, that from their estimates was 50-75 feet high (15-22m) coming at them. The boat was anchored in about 10m of water. Unable to release the anchor Urlich let the anchor chain run free – it snapped at about 40 fathoms (73m – note however that the boat would have been carried forward at this point in their adventure and the 73m does not indicate true wave height; but it does give some indication). The boat was carried along the front of the wave over the adjacent shore and several metres above the trees. It was then washed back into the bay, still upright. A couple of other boats in the bay didn’t fare so well. The Youtube video shows a dramatic reconstruction of events.
The list of terrifyingly spectacular fiord tsunamis goes on. For example, a more recent event at Taan Fiord Alaska, October 17, 2015 – as if Lituya Bay wasn’t enough; this one is still under investigation, but it looks like the wave was capable of hedge-trimming activities to about 150m and tossing boulders even higher.
The day I wrote this post ended with a magnitude 7.5 jolt in northeast South Island, New Zealand (north of Christchurch). We live about 800 km north of the epicentre and our house shook and swayed, trees swayed, and water in the pool sloshed over the sides. No damage to us, but considerable building and infrastructure damage farther south. Some aftershocks have been greater than magnitude 6. A rude awakening…