The New Zealand of today has an abundance of notable geographic forms and processes. As a portion of the subcontinent Zealandia, the islands currently lay atop a convergence zone between the Pacific and Australian plates. On North Island, subduction of the oceanic Pacific plate has played a major role in earthquakes and volcanic land forms such as volcanoes. From these volcanoes ash, tephra and lava have created rich andisol soils resulting in fertile farmland and prosperous agricultural trade for New Zealanders. On South Island, the continental-continental convergence beneath the Alpine Fault both formed and continues to uplift the Southern Alps approximately 7mm per year. Consequently this mountain range acts as a major barrier to the prevailing westerly winds, creating orographic lift, adiabatic cooling and leaving the leeward side of the mountains much drier. An important variable for weathering on the islands is their maritime tropical (mT) climate which has plentiful moisture and warm temperatures.
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| Map of Subduction Zones and Fault Lines in New Zealand Here we can see the convergence of the Pacific Plate under the Australian in the north, the Australian underneath the Pacific in the south and Alpine Fault inbetween. Image courtesy of: http://www.otago.ac.nz/geology/research |
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| Satellite Image of New Zealand, Plate Boundaries and Interaction Included This dynamic view shows the oceanic boundaries in blue and continental in red with volcanoes in red triangles and earthquakes in orange. Image Courtesy of: http://modernsurvivalblog.com/earthquakes |
New Zealand in 2022 (+10 yrs)
In only a decade, changes to New Zealand's geography will occur, however they will not be as extreme as changes 100 or 1000 years into the future. The islands are a coastal landscape surrounded by ocean waves and subject to frequent tropical cyclones, therefore the coastline of New Zealand will recede in many places and wave cut formations will grow. In 10 years we could see at least 1 devastating storm as well as multiple smaller systems. During a cyclone a combination of raised sea levels, intense rainfall, and 100+ mph winds would batter the shores. The resulting floods would be a strong catalyst for erosion, creating powerful inland currents heavy with sediment and debris. Although the global climate is currently in an interglacial warming period the temperature increase in 10 years would be minimal and sea level rise will be insignificant.
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| A Storm Surge on Wellington Coast Breaks through a Seawall (1972) A scenario like this is likely to happen again when the next large Cyclone strikes, perhaps in the next ten years. Image Courtesy of: http://www.teara.govt.nz/en/coastal-erosion/3/5 |
New Zealand in 2112 (+100 yrs)
After a century there will be opportunities for less frequent geological events to occur. The Taupo Volcanic Zone is one of the most active volcanic sites in the world with Mt. Ruapehu at the center. Being a stratovolcano of andesitic composition and having had a last major eruption in 1995 it is possible that a larger eruption of 100+ year frequency will occur. Due to the higher levels of felsic or viscous material present the build up of heat, gases and pressure will result in a violent eruption. Perhaps the greatest danger to the population is the abundance of snow and ice in the current caldera. After a large eruption melts all the snow and ice, fast moving, dense and destructive lahars will form and race down the mountainside. If the eruption is uneven and not directly upwards Mt. Ruapehu will jettison a pyroclatic flow of hot ash and tephra even faster towards the cities of North Island.
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| A Violent Eruption of Mt. Ruapehu with Resort in the Foreground (1995) Characteristic of andesitic volcanoes, another major eruption could repeat or surpass the magnitude of this one in the next century.
Image Courtesy of:http://www.prints.co.nz/page/fine-art/PROD/8351
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New Zealand in 3012 (+1,000 yrs)
On a geographic timeline 1,000 years has more potential for altering the landscape of New Zealand. The Pacific and Australian plates themselves will have shifted 50-100 meters. This means the Southern Alps will have risen over 30 meters and the width of South Island will have decreased as the western continental mass converges with the eastern. North Island will have increased in mass as the continued subduction of the Pacific plate melts the continental crust into rising magma eventually emerging as lava through extrusive processes such as volcanoes. The global temperature will rise several degrees celcius resulting in melted glaciers and sea level increase. Higher seas will cause a steep decrease in coastline and land area. Many of New Zealand's over 3,000 glaciers will recede because the amount of ablation due to melting will be greater than accumulation. This will leave glacial land forms such as deep u shaped valleys, erratics and large moraines.
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| Image of a Hanging Valley In New Zealand Many more glacial features like hanging valleys will be common around the Southern Alps after the glaciers recede. Note the wide U shape formed from a large glacier
Image Courtesy of:http://glaciers1011r1.wikispaces.com/Hanging+Valley
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In conclusion it comes as no surprise to see such dramatic changes to New Zealand in the future. The islands fall into the categories of coastal, glacial and even fluvial, all of which bring elements of weathering and deposition. Another final factor to equate is the future effects of humans on the landscape. From anthropogenic land repurposing to the complete decimation of native flora due to the farmland cultivation, humans will have a profound effect on New Zealand after 10, 100, or 1000 years.
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| Figure Comparing Native Forest Coverage Before and After Polynesian Settlement The Maori were a 3rd world culture with only fire as a tool to clear forests. Imagine the impact after 1,000 years of modern industrial logging techniques. Image Courtesy of:http://envirohistorynz.com/2009/12/ |
Dr. Casey Allen
