Submitted by admin on April 22, 2009 - 21:20
Events on Land
The slow rise of the land that was going on during this time (the late Tertiary and Quaternary) was achieved mainly by the displacement of large crustal blocks along fractures, called faults. The blocks that rose were carved by streams into a landscape pattern of mountains, hills, and valleys; the sinking blocks were buried by gravels worn from the higher lands.
The Kaikoura Orogeny began, and tapered off, earlier in some areas than others. In Northland it started in the Miocene; today few earthquakes have their origins there, no active faults have been recognised (diagram 8), and erosion has reduced the area to one of low relief. Central and eastern Otago is another region relatively free of earthquakes and active faults. The most powerful mountain-building movements of the Quaternary have been in a “mobile belt” that follows the Southern Alps, Marlborough, and the main North Island mountain chain. The main faults shown by diagrams 8–9 have remained active. All the major faults of this zone are “transcurrent”, that is to say, the crustal blocks adjacent to them slide horizontally along the faults, as well as vertically. Evidence of vertical movement on these faults is shown by the prominent fault scarps that border them: examples are the huge dissected scarp that rises from the Alpine Fault, the scarps of the Wairau, Awatere, and Clarence Faults in Marlborough, and the scarp of the Wellington Fault at Wellington and Lower Hutt. Transcurrent movement is recorded by the displacement of rock groups, by the offsetting of stream courses, and by the presence of fault ponds, shutter ridges, notched spurs, and other minor but revealing landscape features.