The Chatham Rise

The Chatham Rise is a plateau formed by an extension of the continental shelf. It is found on the ocean floor off New Zealand's south island (Herzer and Wood., 1992). The plateau runs roughly 1400 kilometers east of Banks Peninsula and 620 miles east of the Chatham Islands and west of Southern Island. Furthermore, Chatham Rise is roughly 3000 meters deep from the ocean surface. It is made up of large ridges that are 350-450 meters below the sea surface. Hikurangi Trench is located to the northeast of the Chatham Rise. This trench is an extension of a considerably deeper trench called Kermadec. The Kermadec lies approximately 3000 meters or 9800 feet from the New Zealand Coast. Furthermore, Chatham Rise borders the Hikurangi Plateau (Wright, 2007). Biologically, Chatham Rise is an interesting place due to its large commercial fisheries and because it acts as a feeding ground for Hoki.

Location and Size

Chatham Rise rises from the east of New Zealand at 44 degrees and spanning 14 degrees of longitude. The subtropical front of Chatham Rise encircles the Southern hemisphere at 35 degrees to 45 degrees south and at act the point of transition between warm and saline subtropical water and the less salty and cooler subantarctic water to the south (Poynter, 1983). The extension is approximately 400-500 kilometers wide and is bounded by salinity and temperature fronts at it southern and northern edges. The plateau stretches to about one 1400 kilometers to the east of Banks Peninsula (Herzer and Wood., 1992). Chatham extends to about six hundred and twenty miles from near the Chatham Islands to the east and Southern Island to the west. The plateau for the part of Zealandia continent. Besides, Chatham Rise approximately 3000 meters in depth from the ocean floor. It comprises of broad ridges that lie within a range of 350-450 meters below the sea surface. To the northeastern part of the Chatham Rise lies Hikurangi Trench. This trench is an extended section of a much deeper trench Kermadec. The Kermadec lies approximately 3000 meters or 9800 feet from the New Zealand Coast. Furthermore, Chatham Rise borders the Hikurangi Plateau (Herzer and Wood., 1992).

Geological Formation

Geologically, Chatham rise and other plateaus in New Zealand such as the Hikurangi Plateau were formed as a result of rifting (Herzer and Wood., 1992). It was separated from the Gondwana continental margin in the mid to Late Cretaceous period through the process of rifting and extension. Chatham Rise comprised of large half grabens. These were formed through the dip-down throw listric fault of several kilometers to the south. The faulting process paralleled the strike of Chatham Rise. Thus the rise submerged due to thermal relaxation in the Paleogene. The sedimentation of Clastic in early post-rift phases and the Cretaceous rift led to deposition of greensand and authigenic limestone in the Paleogene. The erosion and starvation of sediments in the Neogene have resulted in a narrow volcanoclastic and authigenic sedimentary part of the Chatham Rise crest (Herzer and Wood., 1992). Furthermore, Neogene uplift of the Southern Alps that occurred later along the Indo-Australian/Pacific plate boundary resulted to clastic sedimentation of the rise to the west.

Economic Importance

Chatham Rise plays a vital economic role in New Zealand. It also acts as a source of food for and a habitat for other small aquatic animals. The rise can host many birds of different species who move there to feed. The submerged plateau attracts a large number of sea birds of various kinds from the world. The Rise is vital for birds because it lies on the convergence zone for the southern sub-tropical convergence. Thus birds come from the northern and south regions to look for foods. It hosts up to 20 percent of seabird species that is approximately 30 species at a given time (Herzer and Wood., 1992). Some of these are rare species such as the Chatham Islands tāiko that has only 20 breeding pairs in New Zealand. Besides, Chatham Rise has significant biodiversity such as unique animals and threatened corals. It is a habitat for such animals as Campylonotus, Squat lobsters, sabre prawns and Munida gracilis among many others. The area also provide an habitat for big ocean mammals such as whales.

Mining and Fishing

Chatham Rise also acts as a mining center for phosphate and sand. The Rise walls provide a suitable condition for the formation and growth of phosphate. The phosphate is a precipitate of sea water over an extended period (Wright, 2007). The precipitation creates little bumps on the sea flow. These precipitation (phosphorite) are vital mineral. Studies have shown that the seabed covered by the Chatham Rise has approximate 100 million nodes that average 21% phosphate. Thus the rise has acted as major phosphate mining center in New Zealand despite the legal cases that have been brought against mining activities in the area (Poynter, 1983). For example, Chatham Rock Phosphate Limited (CRP) has a license that allows it for mining 820 kilometer square of Chatham Rise area. The company extracts the phosphorite nodules from Chatham Crest half way between the Chatham Islands and Banks Peninsula (Teleki et al., 1987). The Chatham Rise phosphorite nodules play an essential role in the manufacture of phosphatic fertilizer used in New Zealand. The rise also acts a mining zone for iron sand (Poynter, 1983). These sands are brought to the shore by strong waves. The sand is used in construction industry and steelmaking in New Zealand.

Moreover, Chatham Rise acts as a fishing ground. The rise is most productive for the growth of fish and is estimated that it has more than 180 fish species. The fish species thrive due to the mixing of the warm subtropical water from the north and cold subtropical water from the south. These two waters of different temperatures meet in the vicinity of Chatham Rise to create a subtropical front (Wright, 2007). The zone contains adequate nutrients for the fish food such as planktons. It has ideal temperature for fish breeding. Rare species of fish such as Hoki grow in this zone. Other species that can be found along the Chatham include squid, hake, orange roughy, ling, and silver warehou. The fishing in the formed front lead to 60% of the fish catch in New Zealand. The waters in this region are shallow thus accessible to both large and midsize trawlers. Chatham is the most crucial fishing region in New Zealand.

Work Cited

Herzer, R. H., and R. A. Wood., 1992, Tectonic History, Sedimentation, and Changes in Relative Sea Level: Chatham Rise, New Zealand: Chapter 5: Southwest Pacific and Eastern Indian Ocean Margins. P. 55-73.

Wright, I., 2007, Marine Minerals - Phosphates, iron sands, and sands Te Ara - the Encyclopedia of New Zealand,

Poynter, F. A., 1983, The Chatham Rise phosphorite resource, offshore New Zealand: risks associated with development and implications for policy (Doctoral dissertation, Lincoln College, University of Canterbury).

Teleki, P. G., Dobson, M. R., Moore, J. R., & Stackelberg, U., 1987, Marine Minerals: Advances in Research and Resource Assessment. Dordrecht: Springer Netherlands.

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