The Remarkable Dry River at Ātene

THIS post follows on from my earlier one about the Whanganui River. In this post, I zero in on one rather unusual and especially scenic feature of the river, a cut-off meander or ‘oxbow’ that is still preserved as an obvious dried-up river channel, with a skyline walk around the tops that surround it.

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The Ātene Oxbow and skyline track, from NZ Topo Map, screenshot taken 22 October 2020, map ultimately sourced from LINZ, Crown Copyright Reserved. Scale box added for this post. North at top.

This remarkable feature is at a spot called Ātene, a missionary-bestowed name which is Maori for Athens. It is inhabited by Māori who farm the flat bottomland around the central hill and live at a small settlement called Ātene Pā. The dry channel and the hill in the middle, called Puketapu (‘sacred hill’), look like this:

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Which is why it’s worth doing the skyline track!

As you can see from the following map, Ātene’s not far from the city of Whanganui and also accessible by road.

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Yet this amazing scenic feature isn’t visited very often. A blog post which I’ll link to at the end says that:

If a quiet walk and the possibiliy of an empty campsite is what you’re after, this might be it. We didn’t see another soul (and it was a perfect weather Saturday) and you may well spen[d] the night all alone.

It really is obscure. As of the date of this post, there seem to be only two real-life videos on Youtube about the Ātene Skyline Track. The shorter one (quarter hour) is here:

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The longer one, at three-quarters of an hour, is here:

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I’d never heard of this natural curiosity, either. But now that I know about it, I’m determined to go and take some pictures of my own. If I do I’ll add them to this post.

This kind of dried up river loop with a hill in the middle is called a rincon, from the Spanish word for corner (rincón), and it’s normally only seen in a desert environment.

Here’s one on the Colorado River in the southwest United States. It has a mesa, a flat-topped hill, in the middle, looming some 600 to 750 feetabove the dried bed (180 to 230 metres).

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Puketapu has been rendered more pointy and less mesa-like by erosion since it’s on the west coast of New Zealand, which gets a ton of rainfall. In an environment like this the former riverbed, though cut off from the main flow, would still normally collect standing water to form an oxbow lake. So the combination of a dry rincon and a green verdant landscape is unusual, and extra-beautiful.

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How did a river flowing through such rough terrain as we see at Ātene end up meandering in the first place? Isn’t that normally a feature of rivers that flow sluggishly through dead flat countryside, like the Mississippi?

The meander actually developed when the area was flat, before being uplifted by earthquakes and subjected to erosion. As the land rose, the river with all its meanders gradually cut its way downward.

Eventually the river broke scoured its way through the neck of the meander and took a shortcut. This is what usually happens to river meanders sooner or later.

The meander probably became completely dry about 1,800 years ago, when the colossal Taupō volcano in the centre of the North Island erupted and blanketed the area in ash and pumice.

The Taupō volcano is like Yellowstone, except that it’s a lot more active. It has a big eruption every 1,000 years or so.

The pumice and ash from the Taupō eruption of 1,800 years ago ran off the hills and filled in the meander. It created a wide flat bottom that was above the level of the river and also free-draining, so no lakes or ponds could form.

With continued earth movement this dry bottom will get higher and higher.

So a river loop plus volcanoes gives us what’s possibly the world’s only green rincon, though I stand to be corrected on that score.

Interestingly enough, the skyline track wasn’t put in with hikers and sightseers in mind.

It was actually put in as a road by New Zealand’s Ministry of Works in 1959 as part of a hydroelectric scheme.

The plan was to block the Whanganui River with a very high dam just upstream of the rincon and create a lake which would have tailed back for at least 90 kilometres and perhaps as far as Taumarunui (accounts vary).

While the dam was being built, the river would have been diverted through a tunnel which would have gushed out into the rincon and pretty much destroyed its character.

The scheme never happened: in part because of objections from local Maori who were horrified at what was going to happen to their sacred river, and who also pointed out that a number of scenic reserves along the river had been gifted to the government on the understanding that they wouldn’t be interfered with.

But what really killed the scheme, apparently, was the lack of firm and continuous bedrock to hold the dam in place. Test bores kept turning up balls of pumice from past volcanic eruptions, and even old tree trunks, pretty much all the way down. It was the same at other sites that were looked at, as well.

So, the Whanganui River dodged a bullet. But it didn’t escape entirely, as the subsequent Tongariro Power Scheme stole its headwaters and diverted them northward into Lake Taupō, the huge lake in the centre of the North Island which occupies the caldera excavated by successive Taupō eruptions. Lake Taupō drains into the Waikato River, which flows north, so the Whanganui never sees those waters again.

Regarding Taupō’s eruptions, the next is about 800 years overdue. They are supposed to come every thousand years and we haven’t had another since the one that filled in the meander at Ātene 1,800 years ago. But that’s another story.

Notes

The blog post that I quoted is in a blog called Jogaroundtheblog, here. There’s also another interesting blog post in a blog called Leisure Life Larry, here. These posts have lots more photos as well.

A New Zealand Department of Conservation web-page with a downloadable brochure can be accessed here.

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