Belmont viaduct blown up

The towering Belmont railway viaduct, which bridged a deep gully at Pāpārangi, north-east of Johnsonville, Wellington, had been built in 1885 by the Wellington and Manawatu Railway Company (WMR). Unused since 1937, when the Tawa Flat deviation was opened, it was demolished by Territorial Force engineers.

The original wooden viaduct formed part of the WMR line between Wellington and Longburn, near Palmerston North, which was completed in November 1886. Standing 38 m high and 104 m long, this was the largest wooden trestle bridge in New Zealand, and one of the largest in the world at the time. Its construction required 212,000 superficial feet of kauri timber.

In 1903 (in part because of concerns over the risk of fire) it was replaced by a steel viaduct, which was built around the wooden structure without requiring any closures of the line. In 1908, when the WMR was bought by the government, its line – including the Belmont viaduct – became part of the newly completed North Island Main Trunk Line.

By the 1920s, the steep, twisting line between Wellington and Johnsonville was unable to handle the demands of main trunk traffic. Work on the Tawa Flat deviation out of Wellington, which included two long tunnels passing under Cashmere, Newlands, Pāpārangi and Grenada, began in 1927; it was opened to freight traffic in 1935 and to passenger trains in June 1937. The old WMR line was then cut off at Johnsonville and became a suburban commuter line, operated from July 1938 by New Zealand’s first electric multiple units.

The Belmont viaduct, now bypassed, was left to rust for 14 years. In October 1951, due to concerns about public safety, the decision was made to demolish the derelict structure. Territorial Force engineers were given the job as a training exercise. On 15 December, after standing for 66 years, the Belmont viaduct was destroyed by 44 kg of TNT. Today, its original concrete abutments are all that remains in the regenerating bush of Seton Nossiter Park.

Image: Detail from blowing up Belmont railway viaduct slideshow