Category Archives: Kid’s stuff

Rip currents – you’ve been warned

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A rocky mound, 1500m above, and 119.44 km straight-line distance from the sea, is about as far as one can get in New Zealand from either the Tasman and Pacific coasts. The location is in central Otago, southern New Zealand, a region better known for its Pinot Noir. No one lives at this farthest point from the beach.  In fact, most New Zealand folk live only a few kilometres from the sea. Hence, the summer exodus. Any nostalgia for those snow-bound, icicled, northern hemisphere winter solstice festivities is short-lived, banished by squealing kids and crying gulls.

I don’t like putting a damper on this general sense of merriment, but, despite all the signs that warn, all the cautions and reminders of potential dangers, people drown. New Zealand has one of the worst records for preventable drownings, of any OECD country (113 in 2015).  Most drownings occur at seaside beaches, where rip currents are the leading cause of strife for swimmers – there were over 1300 rescues in 2015 (NZ), and most of those were plucked from rip currents.  These statistics are repeated the world over.

Beach witness.

As waves approach the shore, they begin to interact with the sea floor, growing in amplitude (wave height) until they break. Waves in the surf zone move the water mass onto the beach. Gravity requires that all this water then moves down the beach slope, back to the surf zone. On all beaches, the return flow, or backwash, produces an undertow that flows beneath the incoming waves. Undertow occurs everywhere along a beach. Its influence is generally confined to the surf zone, and for the most part is not dangerous (although it can be quite a strong flow).  Undertow IS NOT the same process as a rip current. Rip currents are not that same as tidal currents.As water moves back into the surf zone, it commonly shifts sideways across the beach, a process referred to as along-shore drift. Most swimmers will have experienced this ‘drift’ when they find themselves farther along the beach from where they started (this is usually where the local surf lifeguard starts waving at you to return to the flagged swimming area). Rip currents form when the returning seawater is diverted and focused by shallow holes and sand bars on the sea floor. If the sand bars extend onto the beach, then the waterline will have a kind of point-like shape along the beach (as shown in the images here). These channel-like currents frequently extend beyond the surf zone. Rip currents are narrow flows (a few 10s of metres wide) that move rapidly offshore; current speeds of 4m/second have been recorded, speeds that are well beyond the ability of even the strongest swimmer. The currents are powerful because so much water is being focused through a relatively narrow gap. Rips can appear suddenly on any beach where there is appreciable wave activity. They can also form adjacent to rocky promontories.Rip currents are best viewed from an elevated vantage; they are not easily seen from the water’s edge. Useful identifying features include:

  • The surface waters of a rip tend to be relatively calm or rippled,
  • The current cuts through the surf and is usually clear of large breaking waves,
  • Currents commonly carry flotsam (including swimmers) or sediment offshore, and hence may appear cloudy, and
  • A point-like, or cuspate shape to the waterline along the beach may indicated submerged sand bars – such features increase the likelihood that rip currents will form.

While swimmers and life guards tend to view rip currents with (respectful) dislike, people who study coastal processes see them as one process among many, that shape coastlines. On sandy coasts, sediment is constantly being transferred among the deeper offshore regions of the sea bed, the shore and beach, and sand dunes.  Sometimes the beach or dunes are in sand deficit, and at other times in surplus.  Breaking waves tend to move sand onshore, whereas undertow and rip currents tend to move sand seaward. There is generally a balance between the onshore and offshore transfer of sand, but this can be disrupted by seasonal changes in tidal currents and storm tracks, by decadal cycles in the movement of ocean water masses, and by longer-term rises or falls in sea-level.  Rip currents, despite the risks they pose, are an important part of coastal sand budgeting and transfer .  They are a geological phenomenon.

The advice normally given to anyone caught in a rip is DON’T PANIC (perhaps more easily said than done), and don’t try to swim against the current – you will not win that contest. Swim parallel to the beach and you will eventually exit the current. Surf life-saving folk put up flags where they assess the safest stretch of beach to be. It is common for these flags to be moved up or down the beach, as rips come and go.  But these common-sense warnings are ignored by too many – if they’re lucky, that they won’t enter the books as another statistic.

Surf Life Saving Australia has produced this useful video

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Polar bears do not live in the Antarctic, there are no Penguins in the Arctic. The asymmetry of the poles

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This post is about asymmetry – the Arctic and Antarctic polar regions. They are the most frigid places on Earth, but that is about all they have in common; with one other exception –  they are both stunningly beautiful. I can attest to this for the Arctic, or at least the Canadian Arctic Islands where I spent several summers; but I’ve never been to Antarctica. Visual treats everywhere. And silence – above the wind and the hum of a few insects – silence.

There is an intriguing asymmetry in their respective geographies, the timing of ice accumulation, present climates, the flora and fauna. What follows are a few comparisons and contrasts. Continue reading

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Class 5; The falls and cataracts of Li Phi, southern Laos

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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

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Comets; portents of doom or icy bits of space jetsam?

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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

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Burnt soles: black sand beaches in New Zealand

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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

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A Gaggle of Goose Barnacles

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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’.

 

Lepas anatifera

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.

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Martin J.S. RudwickThe 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

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CO2 – the Good, the Bad, and the Indifferent

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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.

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