Kaikoura peninsula was an island, created by limestone escarpments pushed skywards by tectonic action. It's directly on the faultline between the Pacific and the Indo-Australian plates, and is being pushed upwards by about 10mm a year. Erosion keeps the heights roughly constant. Silted gravel has created the narrow spit which now connects to the mainland.
Folded limestone created the great plates that jut out into the sea, the rocks that encircle the coast and the vertiginous cliffs. It is full of nutrients, so plants can flourish even in tiny cracks of the rocks where they get hit by salt spray and baked in the hot sun of this dry east coast.
The beaches alternate between the black of volcanic dust and the blinding white of limestone, all littered with rubble, boulders, strands and tangles of bull kelp and innumerable balls of seaweed. Your steps clatter and rustle between sand, shingle, and the popping of the weed, a little like unwrapping accompanied by stress relief sessions with bubble wrap.