Te Puia o Whakaari. White Island the dramatic volcano.

This post was originally published in September 2019. On 9th December 2019 the volcano explosively erupted while 47 people were on the Island. This blog post is dedicated to the memory of the 21  victims passed away as of 29 January 2020. I also acknowledge rescue and disaster recovery workers worldwide, and the work of volcanologists worldwide.

Te Puia o Whakaari/White Island, view from eastern Bay of Plenty 
looking into main crater with steam fumeroles visible just above sea-level. Source: Author (2017).

One of the most exciting things for me about living in the Eastern Bay of Plenty is the sight of one of New Zealand's most active volcanoes puffing and steaming away on the horizon. Recently I was very lucky to be able to make a boat trip out to White Island with a group of international exchange students thanks to the Eastern Bay of Plenty AFS intercultural exchange organisation.

While conditions in the Whakatāne Harbour were relatively calm, the hour and a half boat trip thanks to White Island Tours saw some fairly green passengers by the end of the trip  due to the rolling swell encountered as soon as the boat reached deeper water. Whakaari is in fact a large volcanic complex, approximately 16 x 18 km, the majority of which is underwater, with only the peak visible above water as the island we can see. The island volcano is part of a belt of volcanism that starts at Ohakune (part of a region commonly referred to as the Taupō Volcanic Zone (TVZ))  and continues  offshore to Whakaari.

If you would like to know more about the Taupō Volcanic Zone, and the geological forces that have shaped the Eastern Bay follow this link to a previous post "Ōpōtiki, the shifting and fiery land around us. A thrilling story of volcanism and tectonics...."

It may surprise you that approximately 70% of the Earth’s volcanic activity occurs underwater, and Whakaari is part of a chain of underwater volcanoes extending as far as Tonga called the Kermadec Arc. A distant perspective may give us a sense of the island as relatively small, but it is a significant landmass approximately 2 x 3km. Setting foot on the island gives one an entirely new perspective of this surreal and raw landscape, constantly changing and subject to the influences of volcanic activity, landslides and earthquakes, and influences of hydrothermal gases and liquids.

A group of people viewed from the distance gives one a sense of the scale of this volcanic landscape, 
shaped by huge mounds of ash and volcanic debris, landslide scars, and hydrothermal features. Source: Author (2019).

 

This detail of seafloor features surrounding Whakaari shows that
the island above water is just one part of a significant complex of volcanic features
and underwater canyons and sea-mounts. Source: NIWA (2019).

 

Diagram showing the majority of the White Island volcanic cone under water, and magma chamber and conduit during one of several types of eruptive phase typical of White Island. Source: Adapted from Cole et al. (2000). Magma origin and evolution of White Island (Whakaari) Volcano, Bay of Plenty, New Zealand. Journal of Petrology, 41(6), 867-895.

The Māori name Te Puia o Whakaari means “The Dramatic Volcano” or “that which can be made visible” and is explained in two Māori legends. One tells of Maui fishing the North Island out of the ocean, accidentally stepping on the land and some of the fire burning on it. Where he shook this off his foot into the sea this became Whakaari. Another legend tells of the arrival of Chief Ngatoro-i-rangi bringing fire from Hawaiiki. Leaving his sisters at Whakaari, he voyaged to Maketu and onwards to Tongariro. Finding it so cold at Tongariro he called on his sisters to send fire. Volcanic and thermal activity between Whakaari and Tongariro marks the route of the underground journey taken by spirits bearing fire. The volcano, most of which is underwater with the main crater only 30m above sea-level, has been continually active since human settlement of New Zealand, with one of the most the most active periods between 1976-1982. Presently the volcano is at an alert level of 1,  meaning minor volcanic unrest.

Report on sequence of eruptions occurring between 
1976 and 1982 when ash clouds several kilometres were
formed and lava bombs up to a metre in diameter were ejected.
Also significant changes to craters and vents took place. Source:
GNS.cri.nz

The name White Island was given by Captain Cook who only ever saw the island from a distance. The most commonly cited theory was it was referring to the ever-present white steam-plume. However, according to some researchers Cook noted the similarity of the rocks around the Island to the Needle Rocks, off the Isle of Wight, and marked our "White Island" on a chart prepared for Joseph Banks as "The Isle of Wight".

The island passed into the hands of European officers in the mid-19th century, allegedly for two hogsheads of rum. From 1885 onwards the island was the site of commercial sulfur mining, which continued till 1933 despite several miners being killed by a landslide from the crater wall in 1914. Understandably such a unique, dynamic, and relatively accessible volcanic feature has long been of interest, both for scientific interest and tourism , as can be seen in this photo of an early 20th century field trip to White Island.

The history of sulphur mining and the associated loss of life and injuries on the island are well documented, and I have added here some links that tell the grim story of the brutal conditions, efforts to make mining profitable, and the loss of lives.

White Island: A Place of Hope and Despair. By Stephanie Smith

Disaster at White Island. Works Overwhelmed: All Dead. By Vaughan Yarwood

New Zealand Geographic.

   

"The island gives its few visitors an almost fearful sense of loneliness — a place where time could be cut short. And no wonder, for everyone who does come here is all too well aware of its grim history ... of how the 1911 company’s efforts to work the island’s sulphur deposits came to a disastrous end"

– From the narration, on the 11 men killed on the island in 1914 

The island remains in private ownership, and is now classified as a scenic reserve. Monitoring of the volcano measures ground deformation, while regular monitoring also measures composition of volcanic gases and hydrothermal fluids. Landing on the island is limited to several certified tour companies, which provides a unique opportunity to walk in the active crater of a volcano, and experience the surreal landscape consisting of ash, freshly erupted rock and lava, and colourful hydrothermally altered minerals. 

Approaching the island an Australasian Gannet colony is visible,
making a home on a mat of native ice plant. Source: Author (2019).

The Island is also home to a colony of grey-faced petrel, also known as ōi,
kuia, or the northern muttonbird. You can read more about this bird
at this earlier post. 
Ōi, our burrowing seabird neighbours, the northern muttonbird
by Paul Cumming.

New Zealand fur-seals lounge in the sun on the rocks around the island.
The water's support rich web of fish, sea-birds, and marine mammals.
Source: Author (2019).

Remains of the sulphur mining industry provide a stark reminder of the
difficult conditions here, with metal rapidly corroding in the acidic and 
salt-laden atmosphere. Source: Author (2016).

Above and below. A surreal and stark landscape is formed by stratified
layers of ash, land-slip scars, and lava outcrops, all showing signs of 
hydrothermal alteration and precipitation of minerals from liquids and
gasses. Source: Author (2019).

Above and below. Silica-rich minerals are a common sight, precipitated
from mineral-rich hydrothermal fluids and volcanic gases. 
Source: Author (2019).

Above and below. Sulphorous minerals provide a bright yellow splash of colour in this
otherwise stark landscape coloured grey by andesitic ash and unweathered
rocks forming the landscape. Source: Author (2019).

Above and below. Crystalline sulphur precipitated from volcanic gas fumeroles form 
distinctive, surreal, and beautiful "chimneys". Source: Author (2019).

A lava bomb deposited in ash shows signs of recent deposition,
with a small impact depression around the lava still visible in the ash.
Source: Author (2019).

A "breadcrust"lava bomb shows a distinctive crust, caused by very
rapid cooling of lava as it travels through the cold air. Source: Author (2019).

A lava bomb demonstrates the rapid rate of mineralisation and 
crystalisation on surfaces, with the andesitic lava bomb barely
visible beneath a thick crust of volcanic minerals. 
Source: Author (2019).

The main crater undergoes regular changes through eruptions, crater
wall collapse, and movement of multiple vents and fumeroles. The extremely
acidic hot lake also undergoes regular changes in level.
Source: Author (2019).

Several cameras monitor activity in real time, and a 10 minute 
snapshot can be seen at the GeoNet website. Monitoring also 
includes seismometers (earthquake activity), UV spectrometers 
(SO2 emission rate), and GNSS (ground deformation).

Visit the GeoNet monitoring website here.

A  retort lies abandoned and corroding, one of several remains of 
the mining endeavour that attempted to extract profitable sulphur from this 
harsh and unforgiving landscape. Crushed rock was heated in the retort
to extract sulphur, with a worker being killed in the very early days of 
mining when a large retort exploded. Source: Author (2019).

As one leaves the island the remains of the sulphur works provide a stark
reminder of the precariousness of human life and endeavours on an
active volcano. Source: Author (2019).

Stratified layers of volcanic layers exposed in crumbling and 
unstable cliffs leave a lasting impression of the ceaseless volcanic 
activity on the island and a dynamic landscape that tells a story of land 
being formed and destroyed before our eyes in a geological instant.
Source: Author (2019). 

Part 2 of Ōpōtiki, the shifting and fiery land around us. A riveting story of volcanism and tectonics.

Click here for part 1, read on for part 2 of Ōpōtiki, the shifting and fiery landscape around us.....

Damage caused by magnitude 6.5 earthquake at Edgecumbe, 1987. Damage was so extensive because the earthquake occurred at a very shallow depth, causing damage in Matata, Thornton, and Kawerau. Source: Archives New Zealand (2015). https://www.flickr.com/photos/archivesnz/16552659081/in/photostream/

Last week was quite an introduction to the shifting and unstable landscape we inhabit, when a series of earthquakes originating offshore in the vicinity of Wharaaki White Island were felt across the Eastern Bay of Plenty. In part 1 of this post I explored the volcanic events and processes that have shaped this region and will continue to into the future. In this post I would like to explore the underlying structural process of plate tectonics that reminds us of its presence with regular shakes concentrated around the shifting and grinding plates that form Aotearoa. 

Aotearoa sits on the “Pacific Ring of Fire” formed by the boundary of the Pacific plate, one of the largest tectonic plates on the globe. When first proposed, the theory that the continents were continuously moving relative to each other was originally considered near impossible, until a growing body of evidence demonstrated that the crust of the Earth is formed from a series of plates that ride atop the semi molten mantle, and are continuously shifting and recycled through the  process of plate tectonics. A significant  piece of evidence that confirmed the boundaries of the plates is the global pattern of earthquakes and volcanoes,  that can be seen to be more frequent at plate boundaries in the map below.

Global distribution of earthquake epicentres, with areas of highest activity shown to follow tectonic plate boundaries. New Zealand on the Pacific Ring of Fire sits on the right edge of the map. Source: https://commons.wikimedia.org/wiki/File%3AQuake_epicenters_1963-98.png (2017).

Tectonic plates of Earth and their boundaries with active volcanoes, with the Pacific Ring of Fire marked. New Zealand sits at the southwestern end of the Ring of Fire, where the Pacific Plate meets the Indo-Australian plate. Source: Source: http://vulcan.wr.usgs.gov/Glossary/PlateTectonics/Maps/map_plate_tectonics_world.html (2017).

However, our country does not passively ride atop these plates, it is torn, twisted and uplifted by the subduction of the Pacific Plate diving westwards beneath the Australian plate at the Hikurangi subduction zone offshore from Eastern New Zealand at a rate of 40-60 mm per year. At the same time, the  Pacific plate relentlessly grinds past the Australian plate at an average relative rate of 45mm per year along the 600km long Alpine Fault  of the South Island, pushing the Southern Alps up by 10mm a year. Offshore of the South Island the plate roles are reversed and the oceanic crust of the Australian plate dives beneath the continental crust of the Pacific plate.

New Zealand in relation to plate boundaries forming southwestern end of Pacific Ring of Fire. Also visible is the Taupo Volcanic Zone in the central North Island, extending offshore into the Bay of Plenty and  the Tonga-Kermadec Trench. Also shown the is the North Island fault belt, extending from Wellington to the Eastern Bay of Plenty. Source: Waikato Regional Council (2017).

With all these incredible structural processes shaping our country, and the Pacific plate diving into the mantle beneath our feet, it is no wonder this part of the country is regularly rocked by earthquakes generated at the large number of onshore and offshore faults in the area. Improved detection and mapping techniques have seen the number of known offshore faults increase from 14 faults acknowledged in 2000, to 166 in 2006. The series of quakes that shook our region last week had their epicenter near Wharaaki White Island. The map below shows the number of offshore faults in the Bay of Plenty region mapped by scientists from NIWA, while the second map shows onshore faults in the Eastern Bay of Plenty and recorded earthquakes, onshore and offshore, between 2000 and 2015.

Offshore faults in the Bay of Plenty, as mapped by NIWA using seismic data and seafloor imaging. Onshore faults are visible in red. Source: NIWA (2006). https://www.niwa.co.nz/news/study-reveals-166-offshore-earthquake-sources-bay-plenty

Earthquake map of Bay of Plenty showing recorded earthquakes from 2000-2015. Faults are marked by red lines. Faults running south of Whakatane are part of the North Island Fault Zone extending to Wellington. The belt of smaller faults NE & SW of Rotorua are associated with the Taupo Volcanic Zone, where the crust is spreading and thinning. Source: GNS (2015) https://www.shakeout.govt.nz/bayofplenty/

Subduction is the process whereby the dense oceanic crust of the Pacific plate is forced beneath the more buoyant continental crust of the Australian plate. This takes place to the East of the North Island at the Hikurangi subduction zone. Most faults producing earthquakes such as those we experience in the Bay of Plenty occur in the brittle crust of the Australian plate forming the North Island as it accommodates the myriad stresses and strains generated by subduction. The most damaging  quake of this type in the Bay of Plenty was the magnitude 6.5 Edgecumbe earthquake of 1987.

Truly catastrophic earthquakes of magnitude 8 or greater can be generated by sudden releases of energy from the two plates moving past each other, generating a “megathrust” quake. Despite the frequency and intensity of earthquakes experienced in Aotearoa, we have yet to experience the devastation caused by ground shaking (potentially 2000 times more energy than the 2011 Christchurch earthquake) and tsunamis generated by megathrust quakes. Examples of the catastrophic and destructive power of megathrust quakes were seen in the magnitude 9.0 Great East Japan Earthquake and devastating tsunami of 2011, the magnitude 9.1  Boxing Day Earthquake and Indian Ocean tsunami of 2004, the magnitude 9.2 Great Alaska Earthquake of 1964, and the largest earthquake since modern recording began, the magnitude 9.5 Great Chilean Earthquake of 1960. The fascinating short video below describes the devastation wrought by the Great Alaska Earthquake, and how studying it in the context of the new theory of plate tectonics led to an understanding of megathrust quakes (USGS).

  

Shaky ground is not the only consequence of our position torn between two plates. As the Pacific plate sinks into the mantle pressure increases on the rocks of the subducting plate, driving out water. This water rises and in turn reacts with rocks of the overlying plate leading to melting and formation of magma, which rises to the surface due to buoyancy.  And so, we come to the last piece of the puzzle forming our dynamic volcanic landscape. The Taupo Volcanic Zone is a result of the rising magma and heat generated by the subducting Pacific plate on its journey into the mantle for recycling. 

Diagram of the Pacific plate subducting beneath the Australian plate, with magma rising from the subduction zone forming the volcanoes of the central plateau. Source: Benjamin Moorhouse (2016). https://sciblogs.co.nz/shaken-not-stirred/2016/06/30/ruapehu-continues-fidget/

The Taupo Volcanic Zone is the southern-most part of a chain of volcanoes and islands running to Whakaari White Island, and beyond to some 90 submarine volcanoes found in the Tonga-Kermadec Arc, with the majority of the volcanoes fully submerged.

Seafloor depths have been used to construct this 3D model of The Monowai submarine volcanic complex, approximately 1000km northeast of New Zealand and one of the most active volcanoes in the Tonga-Kermadec Arc. A mid-2011 eruption added approximately 79m to the underwater summit. Source: GNS (2012).

 

Subduction related activity produces a gassy and viscous magma with a high silica content, meaning eruptions are extremely violent and explosive, often producing steep sided cones called stratovolcanoes, built up from alternating layers of lava and ash. Typical stratovolcanoes in Aotearoa are Ngarauhoe, Taranaki, and Whakaari White Island (with the majority of its cone underwater). Other volcanic subduction zones on Pacific Ring of Fire can be found at Japan; the American Northwest and Alaska; and Central and South America.

Large ash cloud rising from crater of Ruapehu during 1995 eruption. Chateau Tongariro in foregorund. Source: Tim Whittaker, Hawkes Bay Today, Ref. VR6326.

The Sakurajima volcanic complex in Japan, formed from three separate volcanoes, with Minami-dake pictured erupting here.Source: Kimon Berlin (2015). Flickr.com

Fire fountaining and lava bombs seen at night erupting from Tangarahua volcano, Ecuador. Source: Alcinoe Calahorrano, US Geological Survey (1999).

Due to the magma generated deep underground the Taupo Volcanic Zone has one of the highest rates of heat transference from the mantle to the crust in the world. As this heat energy and magma rises, the crust above is measured to be spreading at approximately 9mm per year. However, this spreading does not necessarily take place at an even rate. The 1987 Edgecumbe Earthquake increased the distance between Matata and Whakatane by 1.2 metres! And so, the forces working beneath our feet continue to work together, bringing heat, steam, and volcanic gasses to the surface of a continuously shifting, shaking, and shuddering landscape.

A sure sign that something is simmering away down below. Pohutu Geyser and Geyser Flat at Te Puia, Whakarewarewa. Source: Carl Lindberg (2002).

If you are interested in a more in depth exploration of the geology of the Bay of Plenty, the GNS Qmap of Rotorua is highly recommended. Comes with a fold-out geological map of the Bay of Plenty and a very informative and well illustrated booklet. Maps and publications are available on line from GNS at  https://www.gns.cri.nz/Home/Products/Publications

For a great base from which to explore the volcanic plateau and it's stunning sights, check out Tāwhiri, Waiouru for comfortable and friendly acommodation.