Welcome to one of Whangarei's iconic geologic formations that surprisingly, a lot of locals are unaware of. This may be because it is near the end of a steeper no exit street, that is mainly used only by local residents and their visiting friends and family.
There is parking available for two or three vehicles at the waypoint indicated. Please use this parking space, as the rest of the road is quite narrow and not really suitable. Also, when leaving, please continue on 100 metres to the end of the road and turn around in the cul-de-sac.
The limestone here in Northland is all called Whangarei Limestone Formation and is part of the Te Kuiti Group and is the same age as the limestone around Waitomo Caves, near Te Kuiti. The limestone started life as a shell bank that accumulated on the seafloor at water depths of 10-200 m. This was around 30 million years ago when New Zealand and Northland were mostly under the sea and any remaining land was low lying and very little sand or mud was eroding and being deposited on the sea floor. The loose shells were cemented together at depth.
When they were buried by at least 300-500 m of overlying rocks the deep ground water passing through them dissolved some calcite and recrystallised it between the shells cementing them together and creating the dense hard limestone. At this site the land has subsequently been pushed upwards and the overlying rocks have been eroded off exposing the limestone to acidic water and creating karst landforms.
The karst landforms at this site were formed by solution of limestone rock by slightly acidic ground water - usually acidified as rain water and ground water passed through humus and soil. Surface water running down the outside of the rock forms fluting. Water passing through the rocks along fractures will dissolve out passages or underground caves. Sometimes this solution will be so advanced along sets of joints, that high vertical pinnacles (without fractures) will be left standing up high on the ground.
In some of the karsts at this site, veins of calcite appear as layers of crystallized minerals within the rock. Veins form when minerals carried by an aqueous solution through fractures within the rock mass are deposited through precipitation and pressure. Typically these veins are less soluble than the surrounding limestone.
Information courtesy of Bruce Hayward ( Geologist )
To log this Earthcache, please complete the following tasks.
GZ is at the start of a deep narrow cleft.
1. Describe the texture and appearance of the walls as you walk through this cleft and any evidence you can see of how this limestone formed 30 million years ago.
2. How do you think such a deep narrow cleft was formed?
3. What feature ( or lack of ) has allowed the formation of these tall pinnacles?
At WPT One, there is a boulder that displays some classic calcite veins. Examine these carefully.
1. Describe the physical appearance of the veins and what would have caused them to form in this manner.
2. Approx how wide are the veins and why do you think they are this size?
3. Why do you think these veins protrude above the surrounding limestone?
Lastly, take a photo of yourself, ( mugshot optional ). or an essential piece of your geocaching equipment, with the karst formation of your choice. Post this with your online log only.
After you have messaged your answers to the CO, please feel free to log this cache straight away. There is no need to wait for confirmation. Please do not include the answers in your online log. If there is a problem with your answers, I will be in touch to work out how you can prove you have visited the location and genuinely attempted the logging tasks. If this cannot be done, then I reserve the right to remove your found log.