Tag Archives: Tides

Kimberley Day 3 – Talbot Bay and the Horizontal Falls

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If you’re not into the savage beauty of extraordinary rock formations, then there’s nothing here for you. Move on…

Oh, still here?  OK, then.

Thursday 15 August – Before anything else, some geological background to the Kimberley.

I’ll be honest, I didn’t know exactly what “The Kimberley” meant, except as the highly scenic destination for a lot of cruise ships. Courtesy of one of the onboard lectures, I have learnt a few basic geological nuggets.

  • Everyone knows that bits of the Earth’s surface have moved around; at one stage most of the land was in a single great mass which had since drifted apart.  What I learned is that Australia is not just one of these drifting land masses, but is actually composed of multiple cratons – micro-continents – which over the millennia have crashed into each other and got stuck together – “sutured” in geology-speak.
  • It’s a law of geology that rocks accrete vertically, oldest, therefore, at the bottom
  • When lumps of land collide, unsurprisingly the bits of land at the edges do not have an easy time of it, and compete for superiority. One edge “loses” and is either forced underneath the other, (a process called subduction) or over it (obduction).
  • The Kimberley is the verbal shorthand for the Kimberley Basin, a craton which collided with Australia and got stuck to it around two billion years ago.

So, you can see that the land round the edges of the Kimberly basin is going to be full of these subductions.

Still with me?  Oh, goody!

Today we had arrived at Talbot Bay, towards the left-hand edge of the Kimberley Basin. One would therefore expect the rock formations to be somewhat tortured by this subduction/obduction process.

One would be right.

Here is what the area looks like under the serene gaze of Google Maps.

Geologically, though, there’s a lot going on.

 

The land has been buckled and twisted in a very unusual way. Erosion has worked its way through the more easily weathered layers, thus exposing those underneath.

OK, so what? I hear you cry. Well, you get to see some rock layers that are normally buried under millions of years’ worth of other rock. More to the point, though, the landscape is visually arresting, particularly now I’ve set it up for you.

So, there now follows a large number of photos of rock formations.  You may care to leave at this point in the symposium, or, alternatively, to skip to the bottom where something slightly less dull happens.

We cruised around for a couple of hours, giving us a opportunity to take lots of photos.

I hope you can see the extraordinary angles the layers have been buckled to – some are almost vertical and others remarkably twisted and distorted.

This is my particular favourite – the colour of the rock just blazed from underneath the darkness.

The darkness in all of these images, in many cases just above the water line, is caused by cyanobacteria. These would normally be a blue green, but when exposed to the light they go into stasis and their colour changes to dark grey or black until they are covered by water as the tides go up and down.

Ah, yes. The tides.

The tides are the cause of a phenomenon that pulls in tourists from far and wide.  Some of them like us, would be in boats; others would take seaplane tours, from platforms rather unattractively parked in the middle of the bay.

What attracts them is the behaviour of the tidal currents through a couple of gaps in the rock, one of which

is sufficiently narrow to create whitewater rafting-style currents.

But not for us, sadly.

Once again, that old devil moon was spoiling our fun; we were here at neap tide, so the thrilling flood looked more like, well, a dribble, really. It may not have looked like much, but the guides attempted to make things more exciting for us by jockeying for position in the stream.

Had we been here at spring tide, this is how it might have looked.

Now you can see why it’s called the Horizontal Falls.

It is – at the moment – a popular tourist activity to race up through the channel.  Our Zodiacs did not, out of respect for the customs of the indigenous tribes, for whom this area, traditionally called Garaan-ngaddim, is a powerful, sacred place; their belief is that boats that pierce these gaps disturb Woongudd, the serpent who creates this wonder by gliding between the cliffs.

Others at the scene were less respectful.

This was a craft from the luxury cruising ship True North

which was in the area at the time.

The practice will fairly soon be banned. Out of respect for indigenous customs? Or because there was an accident a couple of years ago? Your call.

In any case, it was just as well that none of the passengers described in that accident fell into the water;

this was a very large crocodile which we spotted further up the bay.

As well as the croc, and a couple of crabs and mudskippers, which I totally failed to get decent pictures of, we saw a plant called the Kimberley Rose.

It’s a deciduous tree, also known as the Sticky Kurrajong, or Brachychiton viscidulus
to grown-up dendrologists.

The expedition wasn’t the dramatic thing it might have been at spring tide, but the area is beautiful and the rock formations very impressive.

The morrow holds in prospect a visit to Bigge Island.  On the other hand, I’ve developed quite a severe sore throat. I hope that doesn’t presage anything unpleasant…

Kimberley Day 2 – Montgomery Reef and Freshwater Cove

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Wednesday 14 August 2024 – Today saw a morning Zodiac cruise and an afternoon landing. The cruise was to see one of the many extraordinary phenomena that result from the geology of the Kimberley – tidal water movement at Montgomery Reef. The afternoon was spent walking at Freshwater Cove.

So, Montgomery Reef, then.

If you look at the track of our Zodiac cruise on Google Maps, it looks very dull indeed.

However, add the Satellite layer, and you begin to see what we were cruising through.

In detail,

you can see we were cruising up a creek. Because we were there as the tide was falling, it presented an amazing sight.

The range of tidal movement around Montgomery Reef is very high.  At Spring Tides, it can be a 12m (40ft) difference between sea levels at high and low tides.  We were there at Neap Tide, so the movement is much less – about 5.5m (17ft).  As the tide rises, the water rises above the reef; when it falls, the water has to go somewhere, and the shape of the reef means that it spills over in multiple channels. I stole an aerial photo which gives a clearer idea of what’s going on here.

It’s not just pouring out in the channels; it’s running over the surface of the reef everywhere.

Montgomery Reef is somewhat different to a regular coral reef. Whilst coral reefs are usually composed of limestone from coral skeletons, shell fragments and the remains of calcareous algae, Montgomery Reef is an ancient terrestrial tableland created from the same rocks as the surrounding Kimberley Basin. Covering the existing features of the rock is a more recent layer of marine sediment, including calcareous coral, shell and algae. Calcareous algae in the form of rhodoliths (the yellowish chunk in the picture)

are the predominant reef building organisms on Montgomery Reef. Rhodoliths are unattached, photosynthetic organisms made of coralline algae, which aggregate to form complex communities and in the case of Montgomery Reef, act as a long barrier across the reef. (Tom, our guide for the cruise, explained some of this detail, and I got the rest from this fact sheet).

The water in the channel appears to have a problem that would be labelled “pollution” were it seen in the UK – scummy froth on the surface.

However, it is entirely natural. Because the reef spends so much (i.e. half) of its time exposed to harsh sunlight, the corals that have colonised the reef have developed a natural protective substance which acts as a sunscreen, and this finds its way into the water with the fall of the tides.

The creek we cruised along is the feeding ground for green sea turtles, and we saw several heads pop up as we went along, as well as some swimming beside the Zodiac.  Annoyingly, they were always on the shallow side so we (seated as we were on the other side of the craft) rarely got to see anything.  Our optimism that we would surely see some turtle action on the way back was dashed as we returned up the other side, so we never got our turn at looking for turtles nearby. The best I got was this bit of video, which shows a turtle basking in the shallows.  Yes it does.

The afternoon saw our first landing, which was at Freshwater Cove.

An indigenous family lives there, and every group was welcomed with a speech from the niece of the family and her sister, who narrated a story from the Dreamtime and anointed everyone with a dab of ochre on their cheeks – the dark colour of the ochre was explained by the story we heard. The building top left in the photo is an artist’s hut, where punters can relax and (preferably) buy souvenirs, such as the hand-painted T-shirts, decorated in traditional style by family members.

It was a wet landing, and the nice folk at APT had ensured that there would be towels for people to dry their feet in order to change into shoes suitable for the rest of the afternoon.  A couple of walks were on offer: a short one along the beach; and a longer one (2km out and back, up a hill) to see some aboriginal rock art.  We had opted for the latter. Dain, the expedition leader had stressed in yesterday’s briefing that some of the going was over rocks and boulders, and that there would be reasonably large rocks to clamber up and down. (He had laid a test, which was that people had to be able to step up on to the stage in the Laperouse Theatre without any assistance as a prerequisite for anyone wanting to do the longer walk.)

There was a reasonably well-defined track for most of the walk

and people obediently trudged along it.

Inevitably, for a group like this, progress was at a gentle pace, but it gave us a chance to appreciate the remarkable rock formations we passed.

We had to squeeze through a narrow gap between two substantial boulders.

This is known as the “dessert gap”, as it’s a test as to whether someone has gone heavy on the puddings during the cruise. (Spoiler alert – there is a way round for the portly!)

At the top, our group rested for a few minutes

because another group was below us looking at the rock art.  When they surfaced, we clambered down past a scene that looked like something out of Picnic at Hanging Rock,

but which was actually the roof of a wide-mouthed cave, on which one could see the rock art.

“Where is it, then?”, you might well ask on seeing that photo. “Digitally removed”, is the answer; we had been briefed that respect for the native traditions dictated that while it was OK to take photos for our own records, these were not to be shared or published on social media: it is not for us to tell their stories. That’s why you can’t see any of the paintings in the photo above. Something you can see, however, is the colonies of native bees nesting in the blackened holes along the top of the back “wall” of the overhang, whose honey is harvested by the local people.

The father of the family, a chap called Neil, described the history behind the cave, which was known as the “cyclone cave” for the protection it afforded when the weather got uppity. When asked how old the paintings were, Neil said they go back 65,000 years.  I did some intensive research asked ChatGPT about this and discovered that, generally speaking, Kimberley rock art could stretch back as much as 17,000 years;  so the figure that Neil used could well be the folk memory which inspired some of the paintings, as there is broad understanding that Aboriginal peoples have been in Australia that long. Whatever, the paintings have great historic and cultural import for the indigenous people. They depicted various aspects of life – stingrays, turtles, fish, cyclones and even the cautionary tale of a little boy, who had disobeyed his mother’s instructions and gone out on a fishing expedition, only to be sadly killed in an accident. So the pictures give lessons as well as tell stories. The art is touched up by the family every so often to keep it fresh but new paintings are not added

Jane and I didn’t find the walk at all arduous; I should jolly well hope not – the temperature was “only” in the upper twenties – we’ve walked much further in far hotter conditions – and the going was by and large not at all challenging bar the final scramble. However, a couple of members of our group were unfortunately not up to completing the walk back to the shore without issue. To be frank, I’m not surprised; some of the people on this cruise are quite crocked in various ways – aged, frail or otherwise not in good shape. APT had, though, prepared for this eventuality, and a medical team was despatched from the beach – at a run, complete with stretcher – to support the two who were having problems, and they both eventually made it back to the boat OK.

After we returned to the ship, we didn’t have long to wait for the evening briefing; just long enough to pick up a drink at the bar, actually.  Dain explained what we would be seeing tomorrow, a combination of interesting geology and further unusual tidal action, this time in Talbot Bay.  APT had organised a casino evening in the lounge, which we really weren’t all that interested in, so after a bite of dinner al fresco we repaired to our cabin and tried (with not a great deal of success, it has to be said) to get an early night, as we had to be up betimes-ish for the Talbot Bay activity. Which will be revealed, of course, in the next thrilling installment, which I hope you would like to read in the fullness of time.