An underwater volcano
Ancient volcanic activity formed Cape Wanbrow, the headland next to Ōamaru Harbour. Volcanic rocks at Boatman's Harbour (at the head of the cape) record the geological history of underwater volcanic eruptions. Limestone accumulated during periods of volcanic inactivity. The sequence at Boatman's Harbour dates from around 38 million years ago. It includes pillow lava, tuff, limestone and pillow breccia. During this time, more of Te Riu-a-Māui/ Zealandia was submerged beneath the sea than today. Headlands along the present day coast - such as Kākaunui/Kakanui and Moeraki Peninsula, are also remains of ancient volcanic events.
Annotated photo fo simplified sequence of rocks at Boatman's Harbour
Hot lava meets cold water
Underwater volcanic activity erupted lava onto the seafloor. The surface of the hot lava cooled quickly when it came into contact with the cold water - forming a crust of dark volcanic glass. The lava within the crust continued to ooze and cooled more slowly. This type of lava formation is called pillow lava.
At Boatman's Harbour cross-sections of these ancient pillow lavas are exposed underfoot and in the cliff face - the gaps between are filled with light-coloured limestone.
Cape Wanbrow formed as an ancient underwater volcano.
Pillow lavas still form in places on the seafloor today.
Please be aware the following hazards include: slippery surface, rock pools, undercutting, falling debris, uneven surface, wildlife, tides, and no cell coverage. Tsunami risk – if an earthquake is strong or long, get gone.
Latitude: --45:11:27.69 Longitude: 170:98:23.61
Scenic views & Photo opportunities
Head to Ōamaru's Lookout Point and follow the Cape Wanbrow walking track, past the gun emplacement and onto the Department of Conservation's Second Beach track. Please follow the advice on the signs. The pillow lavas can be seen from the track. If tides and wildlife allow, you can also go down to the beach and see them up close.
Protection and guardianship are at the heart of the Geopark philosophy. We ask you to treat this site with respect, do not remove anything from this site and preserve it for our future generations.