Baring Head Coastal Terraces

The two main terraces visible at Baring Head formed just underwater along the shoreline, as wave-cut platforms. The lowest and largest of the two at Baring Head, formed approximately 120,000 years ago, during what is called the ‘last interglacial period’. The older terrace, dating back to approximately 220,000 years, overlies the younger terrace, and formed during an earlier interglacial period. There is a remnant of a third, even higher terrace, but it is very indistinct.

An interglacial is a period during which the earth has a relatively warm climate. Conversely, glacial periods feature low global temperatures, during which significant volumes of earth’s H2O is stored in ice sheets and glaciers. The storage of water as ice on land rather than in the oceans leads to decreases in global sea level. When an interglacial period begins, the warmer temperatures melt the ice, leading to increases in sea level. The difference between interglacial sea level (close to what we have today) and glacial sea level is around 120 metres.

The initiation of the last interglacial would have seen sea level rise approximately 120 metres, eroding the coastline as it advanced and forming a flat, laterally continuous wave-cut platform at its highest level. This "high stand" is the surface that gets preserved when the sea retreats and re-advances once again in the next cycle . Continued tectonic uplift off the coast has lifted these old interglacial wave-cut terraces above modern sea level, which we recognise as part of the Baring Head landscape. Because the uplift is greater nearer to the fault ruptures (in this case the West Wairarapa Fault not far to the east), the terraces are tilted down to the west.

Baring Head is also the site of the Baring Head Clean Air Monitoring Station, operated by the National Institute of Water and Atmosphere (NIWA), one of New Zealand’s Crown Research Institutes. The station provides 24/7 air monitoring, and also collects samples when appropriate southerly winds are blowing - the monitoring station’s location, facing south toward the Southern Ocean, ensures southerly air is uninfluenced by local activity. Air is collected from masts above the ground, to avoid the influence of gases released from plants and the soil. The station monitors the presence of greenhouses gases and trace gases in the air, including CO2. These air samples are used in national and global climate studies, and are internationally significant.

Have a long look at the Baring Head terraces. Trace the lines of the ancient wave-cut platforms with your eyes, and think about the angles you observe. How far along the coast can you follow the terraces?

So the story of the Baring Head terraces is a little more complicated than simple erosion. We see a set of two terraces, raised well above modern sea level. Each one was created at the high sea level of an interglacial period and has since been uplifted by numerous earthquakes along with the whole landscape. When the sea advanced again as the world warmed up at the end of the glacial cycle, the uplift had put the most recent terrace beyond the reach of the sea

The earth is currently experiencing an interglacial period, meaning that a similar wave-cut platform has been developing along the coast of Baring Head over the last 7,000 years (when the sea reached its present level). Over time, the uplift and preservation of this platform will occur to produce yet another step like terrace along the coastline, and new land will rise out of the shallow coastal water nearby.