Visiting is a bit of an exaggeration. We basically stopped in the middle of the road. The road runs through the middle of the dolines, and we tried to look at them from the street. They did not disappoint.
We learned about the dolines from our recently-acquired book by Bruce Hayward – “Mountains, Volcanoes, Coasts and Caves, Origins of Aotearoa New Zealand’s Natural Wonders: 2022“. It is a fantastic book, with great explanations of the features we are seeing and some wonderful photos, thanks to Lloyd Homer, who has done some great photography.
According to the title of the chapter, the Pareora Dolines are “fields pockmarked with limestone sinkholes”. Their story is amazing.
Where to find the dolines
The dolines, rated as awesome by the book, are to be found near Timaru.
The story of how the dolines came about
About 24 million years ago, a 30-m thick band of sand and shell was accumulating in a shoal. A shoal is a submerged, relatively flat, or gently sloping part of the sea floor close to the water’s surface, found typically in shallow coastal regions. There was sand, gravel, and other sedimentary material often found in estuaries, bays, or near the mouths of rivers. Shoals get made as sediment accumulates, being carried by currents or waves and gradually building up to create these shallow zones.
As time went by, another 9 million years brought with them a 350 m layer of silt and sand covering the shoal. By about 15 million years ago, this new layer buried the shoal area, dissolving and recrystallizing the shell into sandy limestone. Five more million years passed, and the shoal got compressed, lifted, and folded into what now is Craigmore Hill. Extending to the Paerora River and Elworthy’s ridge, Craigmore Hill is where we stopped the car to see the sinkholes.
As the hills were being lifted, the softer mudstone and sandstone progressively eroded, and the limestone fractured in places. A forest now covered the ridge. Rainwater went down through the forest and turned slightly acidic. It dissolved out narrow passages along fractures in the limestone down to the base of it. Emerging spring water entered these fractures beneath the forest soil, gradually widening the entrance. The passing water carried the dissolved carbonate and insoluble grains away through the underground passages, further widening the entrances into funnel-shaped depressions.
According to Bruce Hayward, dolines can be anywhere between 1 and 13 m deep and have a diameter from 3 m to 72 m across.
Inside the dolines are small oases of cabbage trees and Muehlenbeckia complex, by the looks of it.
Often, when we teach about space and astronomy, people struggle with the idea of deep time. These dolines are young in geological time, younger than the dinosaurs. This was when sabertooth tigers emerged at the predator apex, and early apes and monkeys were evolving in Africa. The climate was turning cooler and drier, leading to the expansion of grasslands and the decline of tropical forests.
We highly recommend the book and are determined to visit every chapter in it. 🙂
Happy tramping
Hari and Sam
