Lake Waro

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.
Waro Lake is formed from an old limestone quarry which operated between 1922 and 1974. The Limeworks quarried 26-27 tonnes of limestone a day which was then railed through to Portland, Whangarei to be mixed with muddy limestone in the manufacture of Portland Cement. In 1974 the quarry was closed and gifted to the Whangarei District Council
In the 1920s and 1930s large blocks of limestone here were sawn up into facing blocks and sent around teh country by rail for use in numerous public buildings. Waro Marble, as it was called, can be seen in the foyer of Wellington Railway Station for example.
Underground coal mining was a major industry in this area in the late eighteenth and early nineteenth centuries. Heaps of waste rock from several mines can be seen close to the access driveway. The coal is slightly older (35 million years) and underlies the limestone.

Walk around the lake and imagine it when it was an active quarry. Why do you think the limestone here was quarried away and not Waro Rocks in the reserve?
Can you see a waste heap of rock from an old coal mine back nearer Kings Rd? Where else in Northland were there coal mines?
Look closely at some of the broken limestone faces near the far end of the carpark - can you see large fossil oysters?