Looking back at 145 years of the Manawatū Gorge road
For about 145 years travellers on the Manawatū Gorge road have wound their way through a prehistoric rift of steep rock, past piles of fallen debris and gurgling rapids. Karoline Tuckey looks back at some of the history and geography.
From the start: The deep chasm of the Manawatū Gorge divides the northeast-pointing Ruahine Range from the southwest pointing Tararua Range.
It was carved through brittle greywacke by the Manawatū River, on its way from the hills north of Norsewood, to empty into the sea at Foxton Beach.
Rangitāne legend says a giant supernatural being created Te Āpiti – the pass – by forcing a way between the two mountain ranges.
Māori crossed in waka, but it was known as a dangerous and difficult route.
The road is dug into the southern side of the gorge. It began as a precarious horse and foot track until a road was opened for carriages in 1872. Surveying for a rail corridor began about the same time, and the railway opened on the northern side in 1891.
Road versus rail: KiwiRail says since 2013, there's only been one closure of the track because of slips or debris, and only for three hours. The last major incident was a 10-day closure in 2010, when a milk train ran into a slip, causing $550,000 damage.
One anecdote says the rail corridor was built with pickaxes, but the road was built with dynamite that fractured the rock, leading to more slips and closures on the road side. But, with two substantial tunnels and a bridge on the rail side, explosives were also used there too.
In a Manawatū Times interview in 1955, Jim York, a horse-drawn coach driver during the 1890s, described warning signs when blasting was about to take place on the opposite banks, telling drivers to pull up and "hang on to their horses".
GNS Science engineering geologist Chris Massey says dynamite used in construction can cause "overbreak". "You break the rock and cause lots of fractures, and if you fracture your 'rock mass', that can in the future lead to faults.
"But the size of the landslides we are seeing in the gorge now is much bigger than what could be caused by dynamite. And they're old fractures that have been reactivated. They are much older than people with dynamite."
However, he says the road is not in the ideal place for stability. "The rail's got the pick of the places. On the rail side, the structure of the rock and the shape of the slopes is quite different." Crucially, it is less steep, with fewer overhangs.
The road and the regions: Former Woodville councillor and Tararua mayor Bill Bly has a strict view about the significance of the road.
"It's a vital link for the whole country, but locally it's critical," he says.
"The bulk of Tararua business goes through the gorge, including services, workers that use it, the movement of stock and produce. It's very much in everybody's minds right at the moment, as to what is going to be the final outcome."
The gorge is one of the standout beauty spots of both regions and a "lovely drive", he says.
Bly's grandparents regularly travelled it on horse and cart, and in their time it was common for people and stock to tramp the roughly 8-kilometre length.
"The Saddle Rd wasn't opened until the 1940s, so it's a recent alternative."
When Bly started farming in the 1960s, there was a stock yard at every rural railway station to send the animals for processing. Gradually, trucks became more efficient and cheaper, and heavy vehicle traffic through the gorge has grown, while rail has dropped.
A major upgrade in the 1960s and 70s made a big difference to the speed and ease with which cars could travel through the gorge road.
"Before that we never thought anything of it. It was windy and narrow, but everything was small and narrower and you just got on.
"When they put those new bridges in and took those little windy parts out that made a huge difference to the time and safety of the road. Some people don't like driving it, but there's very few accidents there."
The American myth: Another myth is that American troops stationed in New Zealand during World War II planned to build a viaduct or bridges along the route.
"It was talked about," Bly says.
"But it was probably something said over a pint of beer – 'well if it was American we would have bridged it'. But the need wasn't there then."
A Stuff search of official records has found no trace of the offer.
Early tales from the gorge: In a 1924 interview with the Manawatū Daily Times, Wi Duncan remembered walking the gorge track in 1870 as a child.
His iwi group was heading west to the mouth of the Pohangina River to harvest whitebait, karaka berries and eels.
European workers were working on the road at the Woodville end, and it was the first time he had met a Pākehā.
The scenery impressed him, but two years later it was marred by damage from the road's construction.
After the road opened in 1872, there was still no bridge at either end, so travellers faced precarious arrangements to cross the river.
In 1875, a toll for the road was introduced, taken at a small settlement called Gorge, at the Woodville end. At the same spot, a cable was strung across the river and travellers could be pulled across on a plank of wood, 20 metres up. A ferry ran at the Ashhurst end.
In 1885, an English visitor said it was one of New Zealand's "chiefest wonders". He describes landslides, howls of wind and the carriage's closeness to the cliff's edge as "not 10 inches to spare at many a jutting angle", but also the natural beauty.
"Giant totaras, ragged with age, draped with moss and lichen, tower in masses above the lower bush, which is thickly clung, with creepers innumerable.
"The clang of the hooves on the hard road, or the boom as we cross a culvert or bridge, echoes from cliff to cliff."
York said after six months travelling the narrow road it was still nerve-wracking, especially with scared commentary from passengers in the front seat.
The sheer drop was only inches from the wheels, and he would drive the coach and four horses "with the noses of the first horses pulled hard into the side of the bank".
Geology and the road: Massey says the stability of the road is affected by rock type, condition of the larger rock mass, steepness of the slopes, fault lines and earthquakes and the engineering of the road.
Greywacke is hard, but easily cracked, especially along fault lines. Cracks cause loose unstable ground. The Ruahine fault and Wellington fault both run under the gorge.
"The rock is being thrust upward by tectonic forces over many thousands of years while the river is cutting down. It generates these steep gorges and slopes, and at some point they become unstable.
"Greywacke – when you get defects, it can be really problematic. It's when you start cutting it and making it steeper, you can start causing things to fall down... You can get quite significant landslides."
In July, when the gorge road was closed indefinitely, NZ Transport Agency highways manager Ross I'Anson said geologists found the entire hillside showed signs of movement, at Kerry's Wall, 4.5km from the Ashhurst turnoff, and the slip was accelerating.
"That's an indication that a slip as large or larger than the [40,000 cubic metres] 2011 slip, which closed the road for 14 months, could come down at any time," he said.
Massey says early aerial photography over the gorge shows many landslides that could date back to ancient times.
In 1906, a large fire that burned off a lot of the vegetation led to a series of landslides because the natural plant anchoring disappeared. The road was not reopened until 1910.
"Landslides don't have to deposit lots of rock debris. They can just creep slightly over many years. It makes the mass weaker," Massey says.
"Earthquakes will continue to weaken the slopes and over time lots of small shakes with low levels of shaking can combine to damage the rock mass, and have detrimental effect on the stability."
Roading officials are now deciding on a new route between Manawatū and Hawke's Bay.
It is expected to be chosen by December, and could be completed within 5-7 years.