Pancake Rocks on the West Coast

The Pancake Rocks is located on the West coast of the South Island.When traveling on the West Coast, we are framed to our right by the sea and to our left by the mountains in going in the South. On the way, many magnificent places are worth visiting, such as the Fox Glacier, Lake Matheson, etc … The rock that is mostly seen is limestone. This rock was formed more than 25 million years ago (Oligocene) when it was deposited in the ocean. Limestone is formed by the deposit in the seabed of shells and skeletons of marine animals. Its mineral composition is predominantly calcite and aragonite.

Calcaire — Deposits of shells and skeletons in the seabed. Different strata can be observed following deposition for thousands of years.

For all definitions: go to this page.

For the time scale is here!

The Pancake Rocks

Pancake Rocks is a popular destination. Located west of the New Zealand Alps (not European ones), the formation is due to the deposition of calcareous sediments during the Oligocene then to elevation before ending by an erosion.

This term is used because one has the impression of having a stack of rocks one over the other when one observes the Pancake Rocks. But this is only an impression! Indeed the rock is composed of different deposits one over the other over the years for more than 25 million years under the ocean having made it possible to form the rock.

The formation of Pancake Rocks

Five million years ago, the collision between the Australian and the Pacific plate led to the rise of the land.It is important to note that the formation of the land on the South Island is very different from that of the North Island. Indeed, if in the North Island we had a subduction leading to the formation of volcanoes and the island. The South Island is due to the collision between the same plates which caused a push up, causing the land to be immersed.

Collision between the Australian plate (left) and the Pacific plate (right). The collision resulted in the formation of the Southern Alps

If we use the name of the Southern Alps, it is because its formation is identical to that of our Alps in Europe.

125,000 years ago, in the back of the ice age, the Pancake Rocks were a beach. Since the earth has not stopped to go up.

During this reassembly, the rock will be eroded. What is specific to pancake is that due to a fine horizontal stratification, during erosion, only certain strata will be eroded. This is called differential erosion.

érosion différentielle — Here is an example of differential erosion. The different strata are more or less resistant.
Differential erosion can be defined as erosion of more tender / fragile parts compared to much more resistant parts. This will make it possible to create erosion figures that can be from a few centimeters to several kilometers.

It is several thousands of horizontal erosion figures that give this form of pancakes.

Blowhole

The attraction of the Pancake Rocks is, during the high tide, the blowhole. These sea geysers are orifices on the ground, at the edge of sea, where water is projected in height. This water is projected as a result of the ebb and flow of the sea in an underground gallery whose shape allows the compression of the air.

When the sea enters the subterranean channel, it compresses the air in the end of the cave. When the sea retreats, the compressed air pushes the water back violently. If there is an orifice communicating with the ground, part of the repelled water can be broken at the orifice.

For all definitions: go to this page.

For the time scale is here!

Source

“The field guide to New Zealand Geology, An introduction to rocks, minerals and fossils”; Jocelyn Thrnton, Pinguin Books

“In search of ancient New-Zealand”; Hamish Campbell & Gerard Hutching; Pinguins books