How flat is Australia?

We recently drove down the coast to Mackay, then inland and South to Carnarvon Gorge before returning home via Clermont and Charters Towers. I will write about Cape Hillsborough and the Gorge in due course but first I will share my overwhelming impression from the 1800 km, twenty hour, trip: it’s flat!

Really, really, flat!

We have known for a long time that Australia is flat – old, worn down, eroded, etc – but there’s a difference between book-knowledge and body-knowledge.

Body-knowledge, seat-of-the-pants knowledge, now tells me very clearly that you can drive for a couple of hours along the Bruce Highway from Townsville to Bowen without going higher than 20 or 30 metres above sea level except for a couple of bumps. When you get there, Bowen’s topography is like Townsville’s: flat and low-lying with a few big bumps in the distance. Most of the run from Bowen to the Cape Hillsborough turn-off is the same again: swamps, lagoons, floodways, and an average altitude of perhaps 20 metres.

Heading inland from Mackay towards Emerald there’s more flat coastal land, rather like the Burdekin irrigation area, before (wow!) hills. Up and up and … flat again. Not quite as flat, admittedly, but far from hilly. And the trip from Springsure to Charters Towers is flatter again: hundreds of kilometres with wide, level, horizons and altitudes varying not-at-all-wildly between 250 and 300 metres according to the car’s onboard map.

Porcupine Gorge region
Looking over the savannah from a low hill on the road from Hughenden to The Lynd – much like the landscape between Clermont and Charters Towers

Relief maps

All of which took me back to my childhood, sitting (somewhat bored) in a Victorian primary school classroom and contemplating the globe on the teacher’s desk. It might have been a 12 or 15 inch globe, and its surface was ridged with mountain ranges. Surely the Himalayas should be higher than that? Mount Everest was 29,000 ft high, I knew, and that was very high, wasn’t it?

So I did the sums: diameter of the earth = about 8000 miles, so the scale of the globe was 1 inch to so many miles, Everest was … five and a half miles high (oh! that’s not much compared to the size of the earth) so Everest at the scale of the globe should be … only about one thirtieth of an inch high! Barely detectable, in fact, and such a surprise that I’ve remembered it ever since.

To bring it up to date, one thirtieth of an inch is a little less than a millimetre and, since all the rest of the earth’s surface is much lower than the Himalayas, a relief globe which was truly to scale would be smooth to the touch.

A relief map of Australia

Which brings us back to Australia. Let’s make a relief map of this flat old land, in imagination at least.

It’s about 4000 km from East to West and 3200 from North to South. Let’s reduce that to one metre by 750 mm to be manageable but leave us plenty of room to work with, and let’s base it on this map from Geoscience Australia because it’s so clear and simple:

topographic map of Australia
Australia’s elevations

Here we go:

  • One table-top, blue for choice, for the sea we’re girt by.
  • One sheet of paper (a nice dusty peach colour) for all the land that’s less than 300 m above sea level. How thick? If 4000 km = 1000 mm, 300 m = 0.075 mm which turns out to be the thickness of the lightest copy paper (60 gsm rather than the standard 80 gsm) from our local supplier. Cut out the continent and Tasmania and spread them carefully on the table.
  • Two big cut-outs (a slightly darker brown) and a few smaller ones  for the land between 300 and 600 metres. How thick? 60 gsm again.
  • Eleven little cut-outs (a nice red-brown) for the land above 600 metres How thick? Let’s use 60 gsm again.
  • What about the mountains? Well, Kosciuszko is 2200 metres high and that reduces to 0.55 mm at the scale we’re using. Our three sheets of paper add up to 0.23 mm, so we only need another one-third of a millimetre. A sparse sprinkle of fine sand over the darkest of our three layers of paper would be about right for the highest mountains.

And we’re done.

That Great Dividing Range doesn’t look very high any more. You could drive clear across the continent from Brisbane to Shark Bay without going over 600 m, and come back from Port Hedland via Mt Isa to Rocky just as easily.

Even more remarkably, you could go almost directly North-South, from the tip of Cape York to the point where the Vic-SA border touches the coast, without going over 300 metres. The high point of the trip would be the watershed which divides Gulf rivers from the Lake Eyre basin, somewhere near Hughenden, and it would be almost exactly the same height above sea level as the top of Townsville’s Castle Hill (286 metres).

Mount Stuart, also overlooking Townsville, has an elevation of 584 metres. That makes it higher than at least 90% of the continent.

Yes, it’s a flat old country!

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