Photo by Sylvia Kniss
The Tectonically Active Region of Northern New Zealand
by: Emma Dickinson
INTRODUCTION
It is essential to understand the natural history of any given location. Knowledge about the physical history of the land allows for inferences about how indigenous people there thrived prior to the modern era. Understanding these societal and cultural origins provides for a more informed individual when visiting a region and permits an appreciation for new ways of living. Furthermore, Geologic history can provide explanations for what is seen, and predict what may happen in the future—such as volcanic eruptions or mass wasting events, both of which have the potential to drastically impact human life. Because natural history often repeats itself, it is useful to know what to expect when choosing a long-term location to visit. Also, the natural landscape of a region largely determines diet. Perhaps the country does not import many foods because it is primarily landlocked. If that is the case, a dietary shift may be imminent due to climatic factors. Even something as basic as the economy of a location can be best understood in the context of its natural history. Some countries—such as Kenya, Costa Rica, and Ecuador—have economies supported by ecotourism. Others—like the United States, Saudi Arabia, and Russia—drill for oil. The natural environment strongly determines the way in which a country supports itself.
Time periods essential to New Zealand’s geological history as well as a brief explanation of their importance are as follows: in the Cretaceous period, from about 145.5-65.5 Mya, Zealandia separated from the supercontinent Gondwanaland. The Mesozoic era (252-66 Mya), Paleozoic era (541-252 Mya), and Quaternary period (2.58 Mya-Present) are when most of the bedrock was formed. In the Oligocene-Miocene (35.4-5.2 Mya), sedimentary rocks that make up the Waikato region were cemented. And finally, the Pleistocene (2.58 Mya -11,700 years ago) is when many of New Zealand’s volcanoes formed.
GEOLOGY
New Zealand is ultimately a fragment of Gondwanaland. During the Cretaceous Period, a rift formed, and a large landmass—Zealandia—separated from the East Coast of the Gondwanaland supercontinent. A body of water formed between the division—the Tasman Sea—and still exists in the modern era (Campbell et al. 2012). As Zealandia drifted Northeast, it cooled, becoming denser and losing buoyancy. This caused the landmass to subside dramatically, and it is estimated that about 1,500 kilometers of the landmass lie below sea level. The remaining land above the ocean is referred to as New Zealand.
The country sits atop two tectonic plates—the Pacific and the African—and the interaction between them is responsible for impressive landforms and features. According to a geological survey in 2012, 60% of New Zealand’s basement rock is composed of Graywake, metamorphosed gneiss, and the rest is other quartz-rich rocks (Campbell et al. 2012). A sample of 2.7 billion-year-old peridotite rock is the oldest rock in New Zealand, but the basement rock is much more abundant (Jamieson 2020). Most of the shallow sediments under Waikato are fluvial, from historic swamps, or derived from volcanic ash, and beneath that is sedimentary rock estimated to have formed during the Oligocene-Miocene epoch (Edbrooke 2005). Looking specifically at the Waikato/Hamilton region (located on the central West coast of North Island in Figure 1 -marked by the red star), it is evident that the lowest rock layer contains many faults and are mostly either from the Quaternary, Paleozoic-Mesozoic, or Mesozoic period (University of Waikato 2004). These ages correspond with the locations of active volcanoes on North Island, with strata ages increasing as distance from the feature increases (Becker et al. 2010).
Figure 1 (left). A geologic map of New Zealand depicting fault locations as well as basement rock age is denoted by colors labeled in the map key. Locations discussed within the paper are marked with red symbology. This map has been adapted from documents provided by the University of Waikato.
As evidenced by the relationships with strata age, New Zealand’s volcanoes dominate its geologic history. The volcanic arc across the center of North Island is composed of Tongariro, White Island, and Ruapehu. Mount Taranaki lies to the west of this arc, and is near Hamilton City, within the Waikato region. It is an andesite-rich stratovolcano, formed by the subduction of the Pacific Plate under the African Plate (Global Volcanism Program 2023). High volcanic activity in the Pleistocene resulted in pyroclastic flows across the landscape which deposited large amounts of pumice and volcanic ash across the region. Over time, this material weathered and became incorporated into the soil. The prevalence of volcanic material is crucial to understanding the culture of those that live there—namely, the abundance of grass-fed livestock. Much of the soil on the Northern Island is classified in the soil order Andisols, which are those that have formed among volcanic ash. Andisols are relatively nutrient-rich, which would generally support abundant crops. However, New Zealand’s climate, which ranges from subtropical to subantarctic, makes the country more suitable for grasses (Climate Change Knowledge Portal 2021). This makes sheep and cows ideal livestock for the region,largely dictating the traditional diet (Brown et al. 2022). Therefore, rich soils are utilized by grasses and support the agricultural lifestyle that continues today.
The extreme tectonic activity of New Zealand from its position over a plate boundary produces other features such as geysers and hot springs. Near the Waikato region is the Pohutu geyser, known for its frequent eruptions and impressive heights. Geysers, such as this, are formed initially by the heating of groundwater. Friction between the African and Pacific plates combined with pressure and nearby volcanoes are the main methods of heating in the Hamilton region of New Zealand. The second factor of geyser formation is pressure from gases, which causes the eruption. In the case of the Pohutu geyser, contact with a layer of limestone rock is essential. The water dissolves the limestone, releasing Carbon Dioxide gas into the confined area underground. This builds up extreme pressure, and results in spectacular eruptions—up to thirty meters high, and around twenty times a day. New Zealand’s hydrogeological features were a main factor in Maori culture. The people used the springs as the main features of a “health spa” and the resort gained lots of international attention (Philippa Smith 2012). One example of this is the Terume Hot Spring Resort. Today, these features are within the Te Puia Geothermal Park in Rotorua (marked by the red circle in Figure 1) and serve as a major tourist attraction.
CONCLUSION
New Zealand’s geology reflects intense tectonic activity below the surface. In Waikato, the subduction zone causes volcanoes and geysers which are major tourist attractions. Understanding these formations allows for a deeper appreciation of human history. The indigenous peoples of New Zealand—the Maori—have integrated these natural processes into their culture, representing years of adaptation and learning. New Zealand is a phenomenal example of humans utilizing the world around them to suit their needs and wants -as seen by the creation of spas, and livestock-based agriculture.
When visiting the Hamilton region, travelers can expect to see populations that reflect the environment around them. The prevalence of unique features, like volcanoes and hot springs, suggests heavy tourist attention. Grassy landscapes with flocks of sheep and cattle should be anticipated, as well as a diet largely composed of lamb, beef, and cheeses. In short, the geology of any travel destination is critical, because it dictates the lifestyle and social/economic atmosphere of the region. Understanding the processes that formed the ground beneath a civilization permits a deeper appreciation for the culture and traditions of those that live there.
Works Cited
Becker JS, Saunders WSA, Leonard GS, Robertson CM, Johnston DM, 2010, A Synthesis of Challenges and Opportunities for Reducing Volcanic Risk Through Land Use Planning in New Zealand: Australasian Journal of Disaster and Trauma Studies, v. 2010-1, no. 3, p. 1-27.
Brown R, Mackay S, Eyles H, Jalili-Moghaddam S, 2022, 2021 Annual Scientific Meeting of the Nutrition Society of New Zealand: Multidisciplinary Publishing Institute, ed. 1.
Campbell H, Malahoff A, Browne G, Graham I, Sutherland R, 2012, New Zealand Geology: Journal of International Geoscience, v. 35, no. 1, p. 57-71.
Climate Change Knowledge Portal, 2021, New Zealand Current Climate: World Bank Group.
Cooke P, Campbell A, Cass K, Earl K, 2004, The Geological History of New Zealand: The University of Waikato School of Science and Engineering.
Edbrooke, SE, 2005, Geology of the Waikato area: Institute of Geological & Nuclear Sciences.
Global Volcanism Program, 2023, Volcanoes of the World: Smithsonian Institution National Museum of Natural History Global Volcanism Program, v. 5.0.4
Jamieson, Debbie, 2020, New Zealand’s Oldest Rock Found at Lake Wānaka: Stuff Science.
Philippa Mein Smith, 2012, A Concise History of New Zealand, Cambridge Concise Histories: Cambridge University Press, ed. 2.