Bingi rocks

Tags

aplite, basalt, Bingi Bingi Point, dacite, dykes, geology, wedding anniversary

Forty six years ago, about now, J and I were occupied with our wedding, a low key event with a small guest list and a reception at my parents’ home. He nipped out from work at lunchtime to buy a suit. On Monday when his workmates said “Hey J, what did you do at the weekend?” he said, “Well, as a matter of fact I got married.” 

What began that Friday night led, 46 years later, via four children, four grandchildren, a couple of other partners, and deep unassailable companionship, to a glorious summer day rock-hopping at Bingi Bingi Point, not far from our respective homes, to indulge a shared interest in geology. We’re off to visit younger rocks today, volcanic in origin: aplite, gabbro-diorite, tonalite, dacite and basalt. We’re armed with a couple of mappings of the area’s geology, and we’ve already visited under the guidance of a couple of local geologists so we’re feeling unusually confident.

But before we proceed to rocky analysis, we watch entranced as a couple of whales leap and slap and blow close inshore, just off Bingi Bingi Point, defying photography in the glaring path of the sun. Once they disappear heading south, we focus on rocks. I’m acquiring, at last, a nimbleness that allows me to step over mini-chasms and up and down layers of rock that would usually have me bumming it. Everywhere are rocks I recognise and scapes with wonderful aesthetics.

The place is crawling with dykes: the sombre black shine of basalt, the pinky-apricot of aplite, and the astonishing orange angularites of dacite.

This slideshow requires JavaScript.

The dykes provide me with metaphors for our long relationship. It too was born out of molten passion and solidified into interweaving and intrusion. Who could have predicted that this …

… would lead to this?

Tentative postscript: A winding trail through the Penguin dictionary of geology suggests that we may actually have been standing on the earth’s mantle.

Eurobodalla beaches: 1080

Tags

geology, rocks

1080 is a poison, banned in many countries but still used in Australia in an attempt to eradicate foxes, rabbits and wild dogs. Edward Hoagland calls it “a drastic potion”. How come it is also the name of a beach in the Eurobodalla National Park, and a very beautiful beach at that? When we first moved to this part of the world, surfies J knew kept talking about this great beach called 1080. It was one of those nameless beaches around here that surfies identified using the name of the poison on warning signs. The name stuck.

We drive through bushland from Mystery Bay, the sign for 1080 invisible from the road, a familiar habit of National Parks and Wildlife NSW. The bushland opens out into a clearing on the headland, a scattering of picnic tables and short tracks leading to the edge of the cliff. There are long views south to Mumbulla Mountain and an emphatic sea empty of surfers. A wooden staircase leads down to the beach, and to the rocks that are of course the focus of our interest.

As with most of our weekend beaches we’re in sole possession as we move amongst the rocks, expecting to see something similar to rocks we’ve seen before. Not so. How to characterise these rocks? 

There are rocks in conjoined piles crowned by grass and sky; rocks displaying panels, parallel and differentiated in shades of brown and pumpkin and grey; and rocks sporting a blue line meandering past minute shelves where sand has settled.

There are clean-edged black basalt rocks stretching out into the turmoil of surf. They’re johnny-come-latelies on this coast, only 99 million years old and related in origin to the rocks of nearby Gulaga Mountain and the offshore island, Baranguba.

I’m delighted to spot a geological feature I recognise, a substantial dyke intruding into 470 million year old sandstone, if I’m to believe the results of a search. 

Perhaps the most distinctive feature of this rocky profusion are the wavy lines, unlike anything we’ve seen before.

Unfamiliar too are the frilled vertical layers, from some angles looking like old-fashioned bonnets.

I wander round contentedly as the tide begins to drop, relishing textures and patterns and colours; tiny pebbly coves gentled by crystomint wavelets; rocks vivid with orange lichen; and the view back to Mumbulla Mountain. A lowering sky does not, sadly, deliver on what looks like a promise of rain.



Granite country

Tags

boulders, flowers, geology, Girraween, Granite Arch, Granite Belt

Girraween National Park is not far from my daughter’s place near Stanthorpe. It’s in the Granite Belt which stretches for 250 kilometres from Warwick in Queensland to Armidale in NSW. 

For its creation story, take yourself back 240 million years. Two tectonic plates approach each other and compress the crust of the eastern side of whatever was sort-of Australia then. The heat is intense, and a molten mass of magma invades older rocks. Two kilometres below the earth’s surface, it cools very slowly, creating coarse-textured granite. It’s under an immense weight of older rock which is gradually eroded away. The upper face of the granite expands upwards and cracks and large slabs, sometimes metres thick, break away  from the mother rock. Gradually, where there are a lot of fractures, sheets break into blocks and the roughly rectangular blocks become weathered into rounded boulders, like the ones I’m walking through now. But there are less-fractured places in Girraween, now beyond my aging reach: broad slabs, steep domes and pinnacles of bare granite with names like The Pyramid and Castle Rock. The creation story continues today: chemical reactions dissolve the boulders into a mixture of kaolinite clay and quartz sand; each episode of freeze and thaw enlarges cracks; wind, water, animals, algae, bacteria, lichens and mosses also play a part in weakening and shaping the stone.

My  Girraween walk this visit isn’t a long one (less than 2km): it meanders between boulders, the legacy of the processes of long time, as it makes its way to today’s goal, the Granite Arch. I have two cameras slung around my neck and my sturdy walking stick, just in case I want to venture beyond the well-made track. 

The trail begins with a creek crossing, concrete bridges joining granite slabs. But the main beauty is the rockscape, everywhere rounded boulders, leaning over and resting on each other amongst the scrub, sometimes paddling in bright wattle, sharp leaved bell shaped heath flowers, a couple of white correas. Where the rocks are sparser there is plenty of moss and sundews. 

I round a corner, and there’s the Granite Arch: a huge rounded lintel-rock, supported by two doorposts. 

For once geological information is easy to come by, easily understood and accompanied by explanatory photos. I am grateful! For a photo gallery covering more of the park than my legs can manage, see here.

The panel near the Granite Arch was also informative, although geological processes satisfy me: I don’t need the handiwork of giants. It’s a pity too that the Thoreau quote is so apposite: David Henry is not my favourite person!