Alhambra on the Hawkesbury

The last few times I passed by Bujwa Bay, on my way downriver from Berowra Waters, it was shrouded in mist.

But last Sunday, in the golden light of late afternoon, there was a revelation.

I’m familiar with the Hawkesbury’s sculpture parks and sandstone art galleries.  But the fact that Berowra Creek had well preserved fragments of an ancient Moorish fortress – well, that was news to me.

When I went home and told RB I’d seen something very like the famous stucco inscriptions of the Alhambra on a estuarine cliffside at the end of Berowra Waters Road, his comment was “You’re barking!”.  And he’s probably right.

After all, the Alhambra is an artistic jewel, a masterwork of European Islam, preserved over the centuries after the Moors themselves were driven first into the mountains and then out of Spain altogether.  Its delicate carved plasterwork miraculously survived Christian conquerors, dodgy architectural restorers, squatters and tourists.  And the sandstone of Bujwa Bay is just, you know, rock.

But I’ve been reading about “thing power” and it’s given me a whole new angle on inanimate objects.  “Thing Power!” – sounds like a killer bathroom cleaner that will sort out all the disturbing life-forms, named and unnameable, in your shower cubicle.

But according to Jane Bennett, its “a creative not-quite-human force capable of producing the new [that] buzzes within the history of the term ‘nature’ ” (2010, 118).  Electrons, microbes, minerals, waste, all busily making and shaping things, inside, around, through, against and despite humans and their fancy-pants plans.  She reckons things and people rub along or against each other in a pattern that’s “not random or unstructured, but conforms to the strange logic of vortices, spirals and eddies” (2010, 118).

Kooky as it sounds, this is not a bad description of how the Bujwa Bay Alhambra came into the world, according to a paper coauthored, in a way that pleases my penchant for magical thinking, by a geologist from Granada, home of the famous palace.

Honeycomb weathering like this happens in all sorts of porous rocks, around the world – from Antarctica to Jordan – and maybe even on the surface of Mars. It might seem like  hollows would form in weaknesses in the rock, but it’s not necessarily so. Blistering heat, frost, chemical weathering and rain are all in the frame – with maybe a little help from the odd patch of algae or lichen. But mostly it’s about salt and wind.

Salty water – in this case from seaspray – seeps into the rock and crystallises, making tiny fractures. If there’s plenty of water, salt crystals forms on the outside surface to form efflorescence, a mineral flowers blooming on a cliffside or a cellar wall or a garden fence.  But the real damage is done deep in the rock.

According to Rodriguez and friends, once a depression is formed in the rockface, wind eddies and swirls inside the concave parts of the stone.  Faster breezes mean more evaporation and a super-saturated salt solution, meaning more salt crystals and more fretted stone. Eventually the rockface becomes lacework, without any intervention by a rock lacemaker.

Alhambra rocks 1 crop long

The other name for honeycombed rock is alveoli.  It’s stone with lungs.  Made of mineral flowers.  Not alive (or mostly not alive – sorry algae) but doing complicated and beautiful things.

Not immortal, invisible, unfathomable.  In fact, as fathomable as the waters of Bujwa Bay at low tide, that is, knee deep to a heron.  Just exceedingly hard to grasp.

And that’s not just me banging my head against a corroding brick wall of “Salt weathering: a selective review” – the geologists are still bickering over exactly how it works. In Bennett’s (possibly slightly loopy) words, it’s vital matter, “hard to discern… and, once discerned, hard to keep focused on.  It is too close and too fugitive, as much wind as thing” (119).  Or perhaps, in this instance, both wind and thing.

tiny crab and shadow.jpg

A crab wondering what I’m on about, on a beach near Bujwa Bay

References

Jane Bennett 2010 Vibrant Matter, Duke University Press

Eric Doehne (2002) “Salt Weathering: a selective review” from Natural Stone, Weathering Phenomena, Conservation Strategies and Case Studies. Vol 205, 51-64, Geological Society Special Publication

Carlos Rodriguez-Navarro, Eric Doehne,Eduardo Sebastian (1999) Origins of honeycomb weathering: The role of salts and wind, GSA Bulletin; August 1999; v. 111, no. 8; p. 1250–1255

Huinink, H. Pel, L, Kopinga, K. 2004 “Simulating the growth of tafoni” Earth Surface Processes and Landforms 29 1225-33

9 thoughts on “Alhambra on the Hawkesbury

  1. I love the Berowra Creek “Moorish fortress”! I keep heading out to White Rock mainly for the sandstone galleries and the other fascinating effects of weathering. “Thing Power” sounds rather appealing. I enjoy looking at interesting geological formations but don’t seem to be able to retain the knowledge of how they are formed. Thanks very much for the lesson in how these features occur and for the entertaining manner in which you share it. 🙂

    • Thanks Jane! Your pictures of White Rock on your blog are amazing – I completely share your love of the intricate patterns in sandstone. The funny thing about the geomorphology is they really don’t seem to have a clear idea of how honeycomb forms – there are a lot of unanswered questions! But I like this version…

  2. Both are impressive, but I feel a deeper connection with the sandstone.
    Thanks for the explanation; I’d wondered how it happens. Nature is fascinating!

    • Glad you enjoyed it, Dayna. I always find things (even beautiful things) much more satisfactory when I know more about them. I have to confess that the explanation I give here is the one in the Rodriguez paper – there seems to be quite diverse accounts of honeycombed rock/tafoni/stone lattice/alveoli depending on who you read. Salt weathering is at the heart of it, but all else is subject to debate it seems!

    • Thanks Robert! Your admiration for the Hawkesbury says a lot considering the amazing places you’ve been (and the fantastic photos you’ve taken of them). A read through your blog is always a tonic – love your recent cloud photos in particular!

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