The Future of the Canterbury Plains

The Canterbury Plains lie along the eastern side of the Southern Alps on New Zealand’s South Island.They also lay near the Alpine Fault, a transform boundary fault between the Indo-Australian and Pacific tectonic plates that slips laterally. The Indo-Australian plate also subducts under the Pacific plate near the south part of the island, causing vertical slip and uplift of the Southern Alps.
Figure 1:
The red lines show the transform fault boundary; however, the black line near bottom shows where the Indo-Australian plate subducts under the Pacific plate, causing the vertical slip and uplifting of the Southern Alps. High rates of erosion keep the Alps around 4000m tall (GNS). Invisible branches of the fault system (Marlborough Fault system) covered by layers of soil and debris carried down by erosion from the deformation of the Alps. The Canterbury Plains’ placement along the fault makes it more susceptible to earthquakes.
Figure 2: This figure shows the historical progression of some of the geographical processes that set the stage for current day landforms and erosion (Wallis).


The Plains were formed as quaternary moraine type gravels  (Greywacke) were deposited during Glacial periods in the Pleistocene epoch (Gage). As glaciers melted in the present interglacial period, the water moves downward toward base level, eventually becoming the braided rivers
(Allen 3).


Figure 3: Braided Rivers, such as the one shown above, are created by multiple tributary channels crossing the broad flood plains, carrying alluvium (here, gravel deposits of greywacke) down from the Alps. The small gravel is carried along down the stream via suspension, which is partially what causes the width of the braided rivers (Allen 2017 2). (Deckchair)
Topography of New Zealand in 10,000 Years

I believe that 10,000 years from now, there will still be human civilization on earth. Humanity will hopefully have learned to better fortify structures from earthquake damage in the Alpine Fault region, as earthquakes will have been occurring around an average rate of once every 330 years. As the Alpine Fault moves at a rate of about 30m/1000 years (GNS), this will cause the Canterbury plains to shift south with the Pacific plate 300 meters over time. The rate of vertical uplift from the transform boundary fault will continue lifting the Southern Alps but will also be eroded by processes of heavy precipitation from the moist prevailing westerlies winds that causes deformation of the rocks from rainsplash. Sediment from rainsplash erosion and faulting is then carried down via fluvial processes to the plains.

.

Figure 4: This picture shows what what the action of the tectonic plates may have looked like 10 million years ago, giving some idea of what kind of shifts may be possible 10 million years into the future given the current rates of fault movement (McSaveney).

Image result for alpine fault new zealand
Figure 5: The difference between pictures 4 and 5 give some idea of the dramatic changes that can affect topography over geologic time. The different colors show approximately where the break along the island will occur as plates continue sliding overtime.

If humanity continues to contribute to climate change, oceans will continue to rise; in 10,000 years, the sea level will have risen by 34 meters, flooding parts of the Canterbury Plains, particularly near the coast. There is a high likelihood that this will destroy a great amount of farmland as the water levels continue to creep in.

Image result for graphic oceans rise climate change
Figure 6: CO2 and Greenhouse Gases circulating through the atmosphere causes glacial melt, making the oceans rise at an average rate of 3.4mm/yr (Frost ). throughout the atmosphere will cause snow melt from the arctic (Easy Science for Kids). 


 Topography of New Zealand in 1,000,000 Years

The ocean will continue to rise at a rate of 3.4mm/year, rising to a height of .34 kilometers, effectively covering the Canterbury Plains. As the Alpine Fault continues its transform boundary lateral movement, it will progress another 30 kilometers from its current position; the northwestern part of the island (on the Indo-Australian plate) will shift northeast along the moving plate, with the southeastern part of Island moving in the opposite direction.  

Topography of New Zealand in 10,000,000 Years.


If we apply the same processes to what’s left of the Canterbury Plains, we can assume they will be 300km underwater; the Alps may have experienced 1,666 km in growth (minus erosion processes [Hales]), likely leaving only the mountains exposed above the water. As heavy faulting has been occurring for millions of years, we can assume there have been many earthquakes that will now take place underwater, potentially causing tsunamis for any nearby landforms.

Image result for south island new zealand canterbury plains
Figure 7: A view of the plains nestled against the Alps (Te'Ara)

The Canterbury Plains on the South Island have stunning views, but the South Island's precarious geographical position near the Alpine Fault means it will face constant change. As people continue to think about climate change, preserving places like New Zealand from the threat of rising oceans could motivate people to more closely consider their environmental impact.

Citations:


Allen, Casey. "Faulting and Folding Earth, Parts I & II." Intro to Physical Geography. University of Colorado Denver. Spring 2017.


Allen, Casey. "Tectonics." Intro to Physical Geography. University of Colorado Denver. Spring 2017.


Allen, Casey. “Fluvial Processes.”  Intro to Physical Geography. University of Colorado Denver. Spring 2017.


Allen, Casey. “Hydrology.”  Intro to Physical Geography. University of Colorado Denver. Spring 2017.
Arthur, Jessie M., and Don C. Lawton. "Seismic Interpretation of the Canterbury Plains, New Zealand." CREWES Research Report 25 (2013): n. pag. 2013. Web.
Chu, Jennifer. "Short-lived Greenhouse Gases Cause Centuries of Sea-level Rise." MIT News. Massachusetts Institute of Technology, 09 Jan. 2017. Web. 05 May 2017.
Freitas, C. (1987). Perspectives on the impact of short-Term climatic change in new zealand. New Zealand Geographer, 43(3), 169-176. doi:10.1111/j.1745-7939.1987.tb01118.x  
Frost, Emily. "Sea Level Rise." Ocean Portal. Smithsonian's National Museum of Natural History, 31 Aug. 2016. Web. 05 May 2017.
Gage, M., (1969), 'Rocks and Landscape', in The Natural History of Canterbury, edited by Knox, G. A., Canterbury Branch of the Royal Society of New Zealand, A H & A W Reed, Wellington, page 35
Gillingham, Alan. “'Soils and regional land use', Te Ara - the Encyclopedia of New Zealand. n.d. Web. 5 May 2017.


GNS Science. “Improved Understanding of the Alpine Fault.” GNS Science, n.d. Web. 29 Mar. 2017.
GNS Science. "Alpine Fault." Alpine Fault. GNS Science, n.d. Web. 02 Apr. 2017.
Graham, Ian. "A Continent on the Move: New Zealand Geoscience into the 21st Century."GSNZ Miscellaneous Publications 24 (2008): 388. University of Canterbury. University of Canterbury. Web.
Hales, T., and J. J. Roering. "Estimates of Erosion Rates for the Central Southern Alps, New Zealand." AGU Fall Meeting Abstracts. Vol. 1. 2002.
Herman, F., and J. Braun (2008), Evolution of the glacial landscape of the Southern Alps of New Zealand: Insights from a glacial erosion model, J. Geophys. Res., 113, F02009, doi:10.1029/2007JF000807.
Jongens, R., et al. "Faulting and folding beneath the Canterbury Plains identified prior to the 2010 emergence of the Greendale Fault." New Zealand Journal of Geology and Geophysics 55.3 (2012): 169-176.


Figure Citations:

Figure 1: Rowan, Chris. "Alpine Fault." Highly Allochthonous. All-Geo.org, 4 Sept. 2010. Web.
Figure 2: Wallis, Graham P., et al. "Transverse Alpine Speciation Driven by Glaciation." Trends in Ecology & Evolution 31.12 (2016): 916-926.
Figure 3: Deckchair, Danny. "Braided River, Canterbury Plains, South Island, New Zealand. Panoramio. December 2003
Figure 4: E. McSaveney and R. Sutherland, New Zealand adrift. 2nd ed. Lower Hutt: Institute of Geological & Nuclear Sciences, 2005
Figure 5: University of Otago. "Alpine Fault." University of Otago, n.d.
Figure 6: Easy Science for Kids. "Climate Change." Easyscienceforkids.com. n.d.
Figure 7: Te'Ara. "Canterbury Plains and South Island high country." Teara.gov.nz. 2010



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