Waipu Caves

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.

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.

Enter the limestone cave and use your torch to find stalactites and stalagmites. Which are on the ceiling and which on the floor? How were they formed?
How was the cave formed? Does it have anything to do with the stream?
Explore the exquisitely dissolved karst features on limestone next to the reserve entrance.