New Zealand's Climate

According to the Koeppen classification system New Zealand has a Cfb climate ("New Zealand"). This means it has a mild mid-latitude climate that is wet all year with mild winters and warm summers. Because the New Zealand islands are small, they experience relatively little temperature variation. The average variation between summer and winter is only about 10 degrees Celcius (Mullen).

This climograph of Auckland clearly demonstrates there is relatively little temperature variation between its coldest month (July) and its warmest month (February).
http://www.auckland.climatemps.com/

Due to its location between about 35 to 50 degrees south, one of the biggest factors affecting New Zealand's climate are the Westerly winds (Mullen). Because air moves from areas of high pressure to low pressure, the Westerlies originate in the warm high-pressure horse latitudes and move towards the cool low-pressure air near the poles. The Coriolis effect, which is caused by rotation of the Earth, steers the winds in New Zealand so that they tend to blow from the west and northwest ("Westerlies").

The arrows show the direction of the average wind from data collected between 1971 and 2000. The Westerlies are aptly named as the wind in New Zealand tends to come from the West.
 http://www.teara.govt.nz/en/diagram/7746/winds-over-the-southern-hemisphere

Cyclones are traveling low-pressure systems that sometimes develop in the Westerlies. These cyclones often bring rain and stormy weather to New Zealand (Mullen). However, the mountain ranges which run the length of the country create orographic precipitation and wind patterns. When the air rises over the mountains, it cools until it reaches the dew point, which results in precipitation. For this reason, many parts of the Southern Alps receive over 300 inches of rain a year, while some areas just east of the Alps receive an average of only 24 inches ("New Zealand Climate"). This is often referred to as a rain shadow.

Note the high rainfall on the west coast of the South Island. This is the windward side of the Southern Alps. Also notice that the areas east of the mountains receive much less rain.
http://www.teara.govt.nz/en/map/19595/new-zealand-annual-rainfall

Orthographic lifting sometimes creates foehn winds in the South Island. As the water vapor in the rising air condenses, latent heat is released so that the descending air is much warmer and dryer. In October of 2010, a weather station on the western side of the Southern Alps recorded a temperature of 57 degrees Fahrenheit. At the same time, the temperature at a weather station east of the mountains was 77 degrees Fahrenheit ("The Foehn Wind").

This animation demonstrates how a Foehn wind can create much warmer temperatures on the leeward side of a mountain range than on the windward side.
http://blog.metservice.com/2010/10/the-foehn-wind/

Works Cited

"Climate Data and Activities". NIWA Science. N.p., n.d. Web. 11 Nov. 2014.

"New Zealand". Weather Online. N.p., n.d. Web. 11 Nov. 2014.

"New Zealand Climate". MetService. N.p., n.d. 11 Nov 2014.

Mullan, Brett, Andrew Tait, and Craig Thompson. "Climate - New Zealand's Climate". Te Ara- The 
         Encyclopedia of New Zealand. N.p. 13 Jul. 2012. Web. 11 Nov. 2014.

Webster, Chris. "The Foehn Wind". MetService Blog. N.p. 18 Oct. 2010. Web. 11 Nov. 2014. 

"Westerlies". Wikipedia. N.p., n.d. Web 11 Nov. 2014.

Volcanism in New Zealand

New Zealand experiences significant volcanic activity due to its location along the subduction zone of the Pacific and Australian plates. As the subducting plate is heated, it releases its surface water into the mantle above, which lowers the mantle’s melting point and causes magma to form. The magma rises to the surface and erupts, forming volcanoes like Mount Ruapehu (Smith).

This diagram demonstrates how the subduction of the Pacific Plate beneath the Australian Plate produces magma, which erupts on the surface in volcanoes like Mount Ruapeu and Taupo.
http://www.cdemhawkesbay.govt.nz/hawkes-bay-civil-defence-emergency-management-group/earthquakes_idl=2_idt=496_id=1814_.html

Ruapehu is classed as a stratovolcano (or composite volcano) because it was formed by a mixture of andesite lava and ash layers. When Ruapehu erupts, the magma cools and breaks up quickly within the crater lake, spewing ash and larger tephra such as bombs and blocks into the air (Ruapheu). In the video below, watch as tephra rains down during the 1996 eruption.

In 1953 a mix of lake water and volcanic material broke through the crater and created a lahar, which flowed down the volcano and took out a railroad bridge just as a train was crossing, killing 150 people (Mount). Below is a photo of a more recent lahar on Ruapehu.

 

In 2007, a lahar broke through the tephra which had previously contained it within the crater and ran down the side of the volcano. Since the 1953 disaster, early warnings systems have successfully prevented any additional lahar fatalities.
 http://www.radionz.co.nz/collections/u/when-the-siren-goes/volcanoes/lahars

Further north along the subduction zone is Lake Taupo’s giant rhyolite caldera. The caldera was formed following the Oruanui eruption 26,500 years ago when the volcano collapsed upon its empty magma chambers. 

 

The Orunanui eruption created the Taupo caldera, which is now filled with water. At over 600 square kilometers, Lake Taupo is the largest lake in New Zealand.
http://www.stuff.co.nz/dominion-post/news/6784815/Taupo-super-eruption-secrets-revealed

The most recent major Taupo eruption was in 200 AD and was much smaller. Still, ash spewed over 50 kilometers into the air and a 100 meter-deep pyroclastic flow enveloped the surrounding area (Taupo). Luckily, New Zealand was not yet inhabited by humans. The diagram below compares the volume of Oruanui and Taupo to other major eruptions.

The Oruanui eruption produced 1000 times the volume of the 1980 Mt St Helen's eruption.
http://www.teara.govt.nz/en/diagram/8716/taupo-eruptions

New Zealand’s largest city contains over fifty cinder cone volcanoes. They are monogenetic, meaning that they only erupt once. Unlike Taupo and Ruapehu, they were created by a hot spot, an area of weak crust where magma sometimes rises to the surface. As the earth's crust moves over the hot spot, a new volcano could form in Auckland, which would be devastating for the city (Auckland).

Imagine if Mt Eden erupted today. Luckily that will probably never happen because it is a monogenetic volcano, but the hot spot beneath Auckland is still active, meaning that a new volcano could form within or near the city.

Works Cited

“Auckland Volcanic Field.” GNS Science. N.p., n.d. Web. 13 Oct. 2014.

“Mount Ruapehu Erupts.” Waikato Regional Council. N.p., n.d. Web. 13 Oct. 2014.

“Ruapehu.” GNS Science. N.p., n.d. Web. 13 Oct. 2014.

Smith, Richard, David J. Lowe, and Ian Wright. “Volcanoes - Pacific Ring of Fire.” Te Ara - The

    Encyclopedia of New Zealand. N.p. 13 Jul. 2012. Web. 13 Oct. 2014.

“Taupo.” GNS Science. N.p., n.d. Web. 13 Oct. 2014.