Pancake Rocks and Blowholes

The Pancake Rocks are a heavily eroded limestone formation where the sea bursts through several vertical blowholes during incoming swells, particularly at high tide. The limestone was formed in the Oligocene period (around 22–30 million years old), a period in the geological history of New Zealand where most of the continent of Zealandia was submerged beneath shallow seas.[2] The limestone rocks of the Punakaiki region began forming on the sea floor in warm coastal waters, offshore from a group of low-lying islands. There was a great profusion and diversity of marine organisms growing in these waters, and when these animals died, their shells settled on the sea floor along with small amounts of sand and mud eroded from nearby islands. Over millions of years, vast quantities of shell debris accumulated on the sea floor, eventually forming a thick deposit of nearly pure calcium carbonate.[3]

About 25 million years ago, at the beginning of the Miocene, there was a phase of upward movement of the Earth's crust (known as the Kaikoura Orogeny), that led to the formation of the Southern Alps. Large amounts of sand and mud were eroded from the emerging land and deposited on the sea floor, on top of the shell debris. Over the following 20 million years, as the uplift of the crust continued, the older shell debris became buried under a great thickness of accumulated sand and mud. The high pressures created by the new layers expelled water from the shelly sediment, and this gradually became cemented and lithified to form limestone rock. In the Pliocene, a few million years ago, the Kaikoura Orogeny led to slow folding and faulting of sedimentary layers in the Paparoa region, raising them above sea level. Following this uplift, erosion processes stripped away most of the sedimentary rocks which covered the region. However, at Punakaiki, a downwarping of the crust preserved much of the sedimentary layers. Where the limestone now appears at the surface at Dolomite Point, erosion has removed all the younger mudstones and sandstones. Subsequent erosion of the limestone headland has created the unusual karst landscape.[3]

The regular layering that can be observed in the Pancake Rocks results from a process called stylobedding. Under the influence of high pressure and compaction, small imperfections in the calcium carbonate that forms the limestone tend to aggregate in horizontal planes, in a process known as grain boundary diffusion. This leads to regular bands of stronger rock separated by weaker and more erodable mudstone rock.[2] Thousands of years of rain, wind and spray have mechanically weathered away the surface of the mudstone layers, leaving the limestone layers in relief.[3]

Uplift of the crust is continuing and its recent effects can be seen at Dolomite Point. The flat surface of the headland is in fact an old beach surface, formed at sea level 100,000 years ago and since uplifted by around 35 metres (115 ft). Patches of beach gravel and sand can be found on the headland.[3]