Purewa Tunnel is a 800 m long rail tunnel on the North Island Main Trunk Railway (Eastern Line

Eastern Line, Auckland

The Eastern Line in Auckland, New Zealand is the name given to Auckland suburban part of the North Island Main Trunk. Suburban services are operated by Veolia under the MAXX brand...

) in Auckland

Auckland

The Auckland metropolitan area , in the North Island of New Zealand, is the largest and most populous urban area in the country with residents, percent of the country's population. Auckland also has the largest Polynesian population of any city in the world...

, New Zealand

New Zealand

New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

. It is located west of Glen Innes

Glen Innes

Glen Innes may refer to:* Glen Innes, New South Wales, a town in Australia* Glen Innes, New Zealand, a suburb of Auckland...

, in the suburb of Saint Johns

Saint Johns, New Zealand

 - to the north-east  - to the east  - to the south-east  - to the south  - to the south-west  - to the west  - to the north-west Kohimarama Saint Heliers Glen Innes...

. The tunnel is concrete-lined.

Construction

The tunnel was built in the 1920s by workers experienced in the 'hard school... [of] the notorious railway tunnels of North Auckland' (i.e. constructing the North Auckland Line). With the assistance of horse-driven carts, the mining workers, mostly British (with some Italians and Dalmatians in the groups preparing the approach cuttings), were reported to have made good progress, working in triple shifts, using gelignite

Gelignite

Gelignite, also known as blasting gelatin or simply jelly, is an explosive material consisting of collodion-cotton dissolved in either nitroglycerine or nitroglycol and mixed with wood pulp and saltpetre .It was invented in 1875 by Alfred Nobel, who had earlier invented dynamite...

 emplaced in drill holes to fracture the rock.

The tunnel, while lit by electric lights during the excavation, was described as hosting large amounts of glowworm

Glowworm

Glowworm, or glow worm, is the common name for various groups of insect larvae and adult larviform females that glow through bioluminescence. They may sometimes resemble worms, but all are insects .-Classification:Major families are:* Lampyridae , found around the world...

s giving it a 'weird and fantastical' appeal. Miners reported that the worms, likely to have entered from the nearby bush-clad gullies, were unlike anything they had ever reported in a working tunnel. Further, the tunnel was also strangely attractive to large amounts of sparrows that came to populated it, living from pilfered horse feed and becoming quite inured to the regular explosions.

Later work

The tunnel has in the past years experienced some significant water drainage issues, which have required remedial work, and the installation of speed restrictions. In 2010/2011, tracks within the tunnel were being lowered to allow the required clearance for the Auckland railway electrification

Auckland Railway electrification

The Auckland railway electrification has been proposed for several decades, but physical works only began in the late 2000s. After investment into new infrastructure and improved services created massive patronage gains on Auckland's commuter rail network in the middle 2000s, the long-discussed...

.