February 13, 2017

Surveying the rugged beauty of Tasmania’s coast

Posted by llipuma

Our route to survey the east coast of the Tasman Peninsula, starting from Port Arthur and ending at Pirates Bay, near Eaglehawk Neck.

By Lauren Lipuma

Lauren Lipuma is AGU’s public information specialist. She is attending the AGU Chapman Conference on submarine volcanism in Hobart, Tasmania. Read previous blog posts from this trip here.

After our morning of watching Tasmanian Devils tear apart scraps of meat and me trying desperately to take a selfie with a kangaroo, we finished the mid-conference field trip with a 3-hour eco-cruise around the Tasman Peninsula. The peninsula has some of the most beautiful coastline in the world, which includes some amazing exposed rock formations, which our group of geologists were all too happy to see.

We started out in Port Arthur, a former convict settlement and Australia’s best preserved convict site. To get to Port Arthur, you have to drive through Eaglehawk Neck, a tiny isthmus of land only 30 meters (90 feet) wide at its narrowest point connecting the lower portion of the peninsula to the mainland. Tasmania fun fact: at the time Port Arthur was in use, convicts couldn’t swim, so the authorities placed a chain of half-starved dogs across the narrowest part of the isthmus to keep them from escaping.

The 85 of us split up between two massive speedboats and donned full-length red ponchos to keep ourselves (and our cameras) from getting wet. After setting out, our first stop was the Isle of the Dead – an island cemetery where Port Arthur convicts were buried. Interestingly, scientists used to use the isle to record sea levels, and measurements from the isle are the oldest sea level records in the Southern Hemisphere, according to our guides.

Here we are, ready to go!

The isle of the dead.

We then sped south out of the bay to the open ocean. It was a rocky but exciting ride, with the boat tilting upward and slamming down each time we hit a swell. (I was seated in the front, of course.) At Tasman Island we got our first glimpse of seals hanging out on the rocks.

Seals on the rocks of Tasman Island.

This guy didn’t look too happy to see us. (Or maybe that’s just his face.)

At this point there was nothing between us and Antarctica but open water!

Just a few thousand kilometers to Antarctica!

After Tasman Island, we turned north to see the east coast of the peninsula. We rounded Cape Pillar, where we saw columns of Jurassic dolerite – a volcanic rock similar to basalt. The rock laid down here, about 182 million years ago, is also found in Antarctica and South Africa. The majestic cliffs rise 300 meters (1,000 feet) above the ocean, making them the tallest sea cliffs in the Southern Hemisphere.

Pillars of Jurassic dolerite.

As the rock cools from above and below, cracks form because the rock transitions from ductile to brittle, leaving behind nearly vertical columns stacked next to each other, like giant bundles of spaghetti.

The cliffs at Cape Pillar, slightly eroded by wind and sea.

A close-up view of the dolerite cliffs, 300 meters high!

Two of the most impressive formations are the Candlestick and the Totem Pole – standalone dolerite pillars that are a favorite of rock climbers in Tasmania.

The Totem Pole (center) and Candlestick (right center).

Here’s the other boat next to the cliffs, for scale.

On the eastern side of the peninsula, in the Tasman Sea, we ran into several playful pods of dolphins. The dolphins were apparently happy to have us, racing along beside the boat for as long as we were there.

We also saw beautiful layers of sedimentary rocks laid down during the Permian Period, between 290 and 250 million years ago.

Sedimentary rock laid down during the Permian period, when the land was under water.

We continued north to Cape Surville. The sun finally came out and we saw a wedge of Devonian granite – roughly 400 million years old – intruding into the Jurassic dolerite and Permian sediments.

Devonian granite (pink wedge pointing right), sandwiched between Jurassic dolerite (lowest, left-pointing wedge) and Permian sediments (top).

The we turned back south and ended the tour at Pirate’s Bay and Eaglehawk Neck. We were windblown but smiling by time we got back on the buses. All in all an amazing day!

A thoroughly happy bunch of geologists.

—Lauren Lipuma is AGU’s public information specialist. She is attending the AGU Chapman Conference on submarine volcanism in Hobart, Tasmania. Follow her on twitter at @Tenacious_She and on Instagram at laurenthepuma.