01. Brisbane was a pleasant city. Cool evenings at this time of year (August - winter !). One day a front came through
bringing these dramatic clouds to the normally blue sky.
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02. Meeting a koala. They're not actually as cute as they look.
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03. Near Undara there is a fair amount of exposed granite in addition to the basalt flows. Here Jason stands for scale on this
spheroidal boulder. We climbed up one of the many volcanic cones here, saw wallabies and parakeets and other exotic wildlife.
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04. The Undara lava tubes are colossal - adding up the branches there are ~200km of them here - some a cavernous 20m tall, even
accounting for the dust that has accumulated over the 190,000 years since they formed. Such lava tubes exist on the moon and
Mars (as well as e.g. in Hawaii, Washington/Oregon, and Arizona)
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05. Forget the poisonous spiders and venomous snakes, what is most likely to kill you in the Outback is a road train - a truck
hauling up to 4 heavily-laden trailers. They don't (can't) stop - you just have to keep your wits about you and keep out of the
way. Lots of dust in the dry winter - but much of Northern Queensland gets impassable with mud and rivers across the roads in
the wet season, hence many vehicles have snorkels. (see
Jani's
video of us fording - just- a river between Lawn Hill and Mt Isa).
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06. After the long drive, a swim at Adels Grove. There are supposed to be archer fish and freshwater crocodiles ('considered
harmless, but may bite if provoked') but we didn't see any of them.
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07. As we drive into the Lawn Hill crater, Jani plots our GPS position in real time on the ERS-1 Synthetic Aperture Radar
image, so we can relate our view of the terrain out of the window to the remote sensing data (and by extension to comparable
structures on Titan). The ring of limestone hills is not the rim, but may be resistant deposits formed in a moat around the
central uplift (subsequently eroded) after the impact.
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08. The limestone hills are only a few tens of meters high, and the vegetation makes the structure quite subtle in optical
images. But the roughness at small scales (due perhaps to the fluted texture of solution erosion, as well as the fracturing and
brecciation) makes it prominently radar-bright. The limestone beds are rather jumbled in orientation, again consistent with an
energetic deposition immediately after the impact.
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09. There is a lot of breccia among the limestone. This would be consistent with a resurge in a shallow submarine impact,
ripping up the underlying shale and mixing it in with the limestone in a poorly-sorted deposit.
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10. Round geological features, upturned beds and breccias are all only weakly suggestive of impact, but here is the smoking gun
- lots of lovely shatter cones. These striated textures only form in the severe shock wave of impact (see pictures from my other
crater trips -
Vredefort in South Africa,
Wanapitei in Canada,
Waqf as Suwaan in Jordan, etc.)
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11. After exploring the crater, some canoeing. We power upriver, with Jason and Catherine in pursuit.
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12. The river has cut down through up to 140m of sandstone, forming a steep gorge (again somewhat reminiscent of the
Canyonlands in the southwest USA).
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13. A rather idyllic swimming spot by some waterfalls. Still no crocodiles.
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14. In places the sandstone preserves some (presumably marine) ripples - just below my feet.
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15. At the Riversleigh fossil deposit just south of Lawn Hill, Catherine points out some crocodile bones.
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16. The crew, by the rather corny dinosaur model in Hughendon on the long drive back.
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17. Murray Falls, a little inland from the Pacific coast.
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18. Not exactly geology, but an interesting formation nonetheless on the Pacific Coast at Mission Beach. It seems that a very
tiny crab rolls up these balls of sand to make its burrow, and the dendritic pattern is just incidental. My foot for scale.
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