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

Happy International Year of Soils!

I’m not kidding.  The UN has declared 2015 the International Year of Soils.  And not before time.  Everyone should be preoccupied with dirt.  I know I am.  What is going in down there, under the ground? Are my veggies growing in podzol or mycelium? Hang on, that’s soil profiles in Minecraft, not in Berowra.

The CSIRO’s recently released Soil and Landscape Grid with its 3 dimensional digital soil attribute maps could resolve most Australian gardeners’ soil questions. In case you were wondering how these maps were developed, let me put you out of your misery:

“The spatial modeling was performed using decision trees with piecewise linear models and kriging of residuals. Fifty environmental covariates that represent climate, biota, terrain, and soil and parent material were used in the modeling. Uncertainty was derived using a bootstrap (Monte Carlo-type) approach to derive for each pixel a probability density function (pdf), from which we derived 90% confidence limits”

More kriging of residuals, I say!

Gags aside, this free online resource shows why Australia needs publicly funded science and why sacking researchers in the CSIRO to bankroll Gina Rinehart’s tax breaks is a major error (if you need more persuading, CSIRO scientists also invented WiFi, Aerogard, the permanent pleat, and the word petrichor, which describes the lovely smell of damp earth after rain).

After reading about the rocks in our neck of the woods, however, I’m not sure we are best placed to fully exploit the sophisticated visualising technologies of the Soil and Landscape Grid.  The geology around here is pretty danged boring. Other than the odd lens of shale, mostly on the ridge-tops (that is, under roads and houses) it’s Hawkesbury sandstone all the way down, 40 million years and 270 metres of it.  Or at least, all the way down to Berowra Creek where there’s an outcrop of more fertile Narrabeen Group of shales, sandstone and clays here and there.

Of course, we’re not alone in our preposterously deep beds of sandstone.  They’re on display in the Blue Mountains too, though with a few more layers clay and basalt intrusions to break up the tedium.

The humungous quantities of sandstone across a swathe of the Sydney Basin makes my sentimentality about the disappearing rock faces along the new railway cuttings of the Northern Line even more absurd.  After reading about the good exposures of Ashfield Shale between Hornsbury and Beecroft,  I’ve become a tiny bit obsessed with capturing the freshly exposed slices of Sydney Basin geology as they are revealed by the diggers and before they’re covered with nasty grey concrete.  Wordsworth was mortified by the ugliness of railway cuttings slashing their way through the nineteenth century British countryside.  Here am I mourning for disappearing railway cuttings, a slice of geological time revealed and then lost again.

Perhaps I should stop grieving the lost glories of the Pennant Hills trackwork and spend more time worrying about what my garden might be doing to the “quartz rich, nutrient poor” soils of Berowra.

My snake beans are kinda sallow – I reckon they need a side serve of well-rotted chicken manure.  But even as I contemplate emptying the compost tumbler, I can’t help but fret about where my vegetable garden sits, perched above the national park with its “rich and distinctive assemblage of species that thrive on poor soils” , “60-80 different plant species growing together on an area half the size of an average house block” (Benson, Howell, McDougall, 1996, 24-5).  Benson and Howell in their fascinating Taken for Granted: the bushland of Sydney and its suburbs (Kangaroo Press/Royal Botanic Gardens, 1990) mourn:

 “much of Hornsby’s rugged sandstone terrain remained undisturbed until after World War III when the increasing availability of the car and improved building technology made steeper, more remote sites available for housing.  As a result, bushland on ridge-tops and upper slopes has been totally destroyed, the bush remaining only where it is virtually impossible to built, and along steep gullies which have become drainage lines.  Virtually very catchment system includes some suburban development, stormwater run-off from which contains silt and nutrients.  These promote weed invasion of sandstone gullies… in newer areas such at Mt Colah and Berowra [the] invasion is beginning, and the consequences appear inevitable” (108)

And that’s us, in our mid-century twentieth century house, teetering on a steep slope in a fold of the hillside you might otherwise call a creek bed.  My painstakingly-made hot compost, my organic sugarcane mulch, the poo from my beloved chickens, all building nitrogen, carbon, phosphorus rich earth – garden alchemy.  I’m creating an anthroposol – a human made soil – and I’m not entirely sure that’s a good thing.

As a homage to the UN’s declaration, I’ve stared in a  incomprehending way at a schematic cross-section of Hawkesbury soils, I’ve thought long and hard about our B horizon (by staring even longer at this quite marvellous online introduction to soil classification – thanks again, CSIRO) and I’ve double-checked Minecraft’s definition of “podzolic” with the kids but I’m not sure how far it’s got me.

Maybe this is the chthonic thinking – thinking about the soil and the communities, plant and animal that grow from it – that my friend Kate urges us all to do in her fab blog about the Armidale Community Garden, but it’s not so much grounded me as taken me directly to Hades via the Field of Punishment.  This is a special special place of suffering for people who long to understand rocks and dirt but can never remember whether the Devonian comes before or after the Carboniferous, no matter how many times they read David Johnson’s splendid Geology of Australia.  And that’s without wrestling with the geopolitics of topsoil loss or the impact of international agribusiness on pesticide residues or the links between soil, country and indigenous chlthonic law

The only solution to this torment, I feel, is another variant of subterranean thinking: that sense of mindfulness I get sitting in a darkened vehicle with a swag of empty shopping bags, gazing tranquilly at the carefully preserved, sandstone rock exposures in the underground car park of Berowra Coles.

Happy International Year of Soils everyone!

Sprinter (not yet Sprummer)

Tim Entwhistle from the Royal Botanical Gardens suggests we add two seasons to the European standards: starting out with the clunkingly named Sprinter, to describe late winter and early spring when most things seem to burst into flower.  He reckons non-Indigenous Australians can’t handle the complexity of the diverse seasons observed by Kooris, Murris, Nunga, Noongar and all the first people of this place.

He’s probably right.  The D’harawal calendar – from people south of Port Jackson – says roundabout now is the time of Wiritjiribin – cold and windy. I think I saw Acacia floribunda blooming today, so that fits.  But maybe, since its getting warmer, it’s closer to the time of Ngoonungi, the time of the gathering of the flying foxes?  “They come in from the north-east, the north, the north-west and the west, and swirl over the Sydney area in a wonderful, sky-dancing display just after sunset”, says the D’harawal calendar on the BOM.  No signs here at least, in Dharug and Guringai country, of flying foxes yet.

Let’s face it: I’m clueless.  I’ve got no idea about the local wildlife, know nothing of how you might live off the land, can’t even figure out half the Latin names of the flowers in our neck of the woods – MuogamarraBerowra National Park, Lane Cove.

Ok, I’m cheating. Lane Cove is miles away, but I took some nice pictures there yesterday.  And it is (mostly) on Hawkesbury sandstone.  And they have a great website for the local flora.  Which is important because this is what our plant identification book looks like:

Destroyed Robbo rotated

All in all, I think I’m only up to Sprinter.