Geological time frame is not always easy for students to conceptualise. In fact, drafting maps and diagrams is a great start, along with the use of analogies. I remember being told by my teacher, that plate tectonics move at about the speed that your fingernails grow, which is actually the plate tectonic movement in New Zealand. Of course, not correct for all plate tectonic movements, but it’s a great start to visualising the geological time scale. This blog covers material specific to New Zealand’s teaching units of physical principles related to the Earth System and extreme Earth events in New Zealand.
Let’s look at New Zealand – it is quite the geological laboratory. We can thank the collision of the Australian and Pacific Plates for this. It’s an ancient story. Let’s reverse 500 million years ago, to a time when a super-continent called Gondwanaland existed. A lot has happened since then, with continents South America, Africa, Madagascar, India, Antarctica and Australia splitting apart 160 million years ago. New Zealand began its identity 85 million years ago when it separated from Australia and Antarctica. Well, that’s the geologist’s story according to plate tectonic theory.
Tectonic forces have significantly sculptured New Zealand’s landscape. It’s complex, but it is a masterpiece. The turbulent battles between the Pacific and Australian tectonic plates have created volcanoes, tsunamis and earthquakes. The two plate tectonics are seriously twisted like a corkscrew. In the North Island the Pacific plate is descending below the Australian plate, yet the reverse is happening in the South Island, with the Australian plate descending below the Pacific plate. In the centre of the South Island, the Southern Alps are being formed as both plate boundaries are colliding and sliding past each other. It’s very twisted indeed.
Volcanoes form in three ways; divergent plate boundaries spread mid-oceanic ridges apart and magma rises from the mantle; subduction plate boundaries melts solid rock aided by super heated water; and lastly a plume of magma rising to the surface through convection known as an hot spot. Intra-plate volcanoes are considered hotspots and not specifically related to plate boundaries and plate movements. As plate tectonics move across a hot spot, a chain of oceanic islands are created such as the Hawaiian and Galapagos Islands. Yellowstone’s volcanic hot spot in the United States is unique in that it has evolved on thin continental crust. New Zealand’s hot spot volcanic activity shares an equally unusual story.
So where is the hotspot volcanic activity in New Zealand? Currently, there are no active volcanoes in the South Island. However, if we rewind time, basaltic volcanic activity was alive and often produced scoria cones and lava flows. This was the case in the formation of Otago’s peninsula and Banks Peninsula approximately 10-16 million years ago. Auckland’s volcanic field is another example of an intra-plate hot spot. Each volcano will usually erupt once, with the magma finding a new way to the surface each time to create a new volcano. However, this makes volcanic predictions more difficult, a challenge considering Auckland’s volcanic field is still active.
A large majority of volcanoes in New Zealand have been formed from the subduction of one plate beneath another. It causes rock to melt in the mantle from the heated water that is pushed down, and eventually that energy is released to produce a volcano. Both andesitic and rhyolitic volcanoes are found in the subduction zone of the North Island. White Island, Mount Ruapehu, and Mount Tongariro have been andesitic volcanic eruptions, forming steep strato-volcanoes. There has been a bit of action lately, with Ruapehu erupting about once a decade. White island is very active, erupting on a frequent basis. Rhyolitic volcanoes erupt more violently, often producing calderas such as Lake Taupo and Lake Rotorua. You would want to stand right back from such action.
Hawaii, Mauritius and Canary Islands
Warm, lush vegetative islands, with sandy beaches paints a picture of paradise. The landscape is inviting. Hawaii is a hot spot – in fact it is one of the most heavily studied hot spots in the world. Underwater volcanoes will continue to form; some will build to become islands as the Pacific plate gradually glides it way across the hot spot. Currently several volcanoes are either active or dormant and more than 100 are extinct – they continue to be eroded by ocean waves to form coral reefs and atolls. The lava is predominantly igneous basalt, indicative of oceanic hot spot activity. Jaggered hilly terrain on the islands, paint a landscape full of volcanic history.
The island of Mauritius located just 20 degrees south of the equator is also a tropical paradise. Volcanic activity from the Reunion hot spot plume has created an island comprised entirely of volcanic rocks. On first impressions, visiting Mauritius reminded of the landscape in Hawaii. The jaggered crated rims and lush vegetative crops are feed by rich volcanic soils. Although this time I was seeing plenty of sugar cane grown as opposed to pineapples. The highlight was seeing Chamarel, the seven colours of the Earth, formed by ancient lava flows. Without the sunlight, it was slightly duller, but it was still visible to see the unique colour bands running through the soils.
Tenerife is part of the Canary Islands that I visited last year in 2015. It’s a stratovolcano and it is assumed to have resulted from hot spot activity, although other theories exist. Tenerife entertains a complex history of volcanic eruptions that became more explosive as the island grew in height above the ocean floor. The last recorded eruption occurred in 1909 and is still regarded as an active volcano. It is a strange appearance, as if we had landed on Mars. But it is different, and striking for it. In fact, scientists use Teide National Park as a reference point for studies related to Mars, in particular analysing environmental and geological formations. Now wouldn’t that be an adventure – a journey to Mars. But then that is a whole new story of scientific adventure to behold.