Last week’s discovery of yet more unstable cliff-side tells me the Manawatu Gorge is at its use-by date as a road. Damn – it’s a fantastic scenic area.
I’m not surprised. It’s one of the few places in the world where a river goes through a mountain range – and the river, the Manawatu, was there first. As the Tararua and Ruahine ranges rose up under the tectonic forces of what’s generally known as the Kaikoura Orogeny, from about 5 million years ago, the river kept flowing, cutting through the rock as fast as it rose. This also means that the slopes of the gorge, right up to the peaks, are essentially old river bed – alluvial. Go figure.
For almost all of that time New Zealand was uninhabited by humans – a real ‘lost world’ that still had most of its late-Cretaceous era biota in the form of forests and birds, among other things. But even then Polynesians arrived around 1280 AD there wasn’t much change to the gorge. Maori, who emerged indigenously from the Polynesian settlements, used the river as a regular transport route, man-handling their waka (canoes) upstream against thrashing torrents.
Enter Britain. By the 1850s, settlement was expanding on each side of the gorge, and that meant not just road and rail – but also the wholesale destruction of a good deal of bush, including forests that grew on some of the lower slopes of the gorge entrance. Pictures from the 1890s are very different from those of today. Since then the road has become the main through-route between the Manawatu and southern Hawke’s Bay, fuelling the town of Woodville which is just to the northeast of the eastern gorge entrance.
The problem has always been the road. For a while it wasn’t too big a problem, but it can take years sometimes for water to seep through cracks in rocks and for changed drainage patterns to make themselves felt. Progressive widening and other work didn’t help. By the 1980s, as far as I can remember, there were problems with slips in increasing numbers. All sorts of remedial work was done, including putting steel netting across the worst of the slopes to stop motorists being hit by random boulders.
Then in 2011 about a cubic kilometre fell in, closing the gorge for 14 months. And now there’s more – multiple slips since April, which now can’t be cleared because it turns out the slopes above aren’t stable. They pulled out the clearing teams for safety last week.
What now? I guess it’ll come down to money, but there’s now talk of upgrading the alternative route across the south Ruahines. That’ll come as a relief to Woodville residents, who need the gorge through-traffic – and whose nearest large town is Palmerston North, on the other side of it.
Still, it’s pretty clear to me what’s happened. It’s taken a century or more, but the act of monkeying with the southern slope of the gorge to put a road in has destabilised the whole thing. Figures. Back then we were so arrogant as to suppose humanity could dominate nature. The reality? Nature bites back. Always.
Copyright © Matthew Wright 2017