Here you can see the construction of the tunnel portals. What is not visible is the sense of the full height nor the floor - which was flat.
An interesting feature is the large square cross section stone which protrudes slightly into the tunnel profile at the right and just above the water line. The one to the left can be discerned through a dried weed.
These blocks are long - running back some 1400mm into the tunnel.
They are there so that any vehicle such as a cart or wheelbarrow or barge (yes truly) which bumps against the portal when exiting cannot knock this stone out of the arch and dislodge all the stonework. Barge! Well, no barge ever passed through these tunnels but if you look at photos of barge tunnels from Europe and the UK you will see the design feature replicated in every case. The stone masons at Oamaru were not just good at their job but also immersed in the technology of it. There are a few engraved names in the tunnels but dates are uncertain. In this tunnel (number 2) there is a section in the centre where the rock was fractured and stonework has been erected to support the roof. For most of their length all the tunnels appear to have been in basalt.
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Photo taken in Pukeuri, New Zealand
Misplaced? Suggest new location