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Earth of fire

Actualité volcanique, Article de fond sur étude de volcan, tectonique, récits et photos de voyage

Publié le par Bernard Duyck
Publié dans : #Actualités volcaniques
Jenni Hopkins and the map of Auckland volcanic field. - Photo Victoria University of Wellington.

Jenni Hopkins and the map of Auckland volcanic field. - Photo Victoria University of Wellington.

A doctoral student from the University of Wellington, Jenni Hopkins, in collaboration with GNS Science and the University of Auckland, has reconstructed the history of the Auckland Volcanic Field.

This elliptical volcanic field of 140 sq km, and 29 km long, located in the peninsula of North Island in New Zealand
, was formed over the past 200,000 years. It consists of 53 structures, monogenetic, of which maars, tuff rings, small shield volcanoes and cinder cones. He mainly produces intraplate alkaline basalts to basanites.

Of the 19 eruptions in the last 20,000 years, only an eruptive center was active during the Holocene. The eruption Rangitoto, 600 years ago, was the largest and created the island of the same name, off 6 km., formed by a low shield, covered by multiple cinder cones and lava flows.

 

The agglomeration of Auckland, seen by Aster in 2006 above, and the location of the volcanic field structures down.
The agglomeration of Auckland, seen by Aster in 2006 above, and the location of the volcanic field structures down.

The agglomeration of Auckland, seen by Aster in 2006 above, and the location of the volcanic field structures down.

Auckland Volcanic Field - Mt Wellington - photo Peirsrenad.blogspot

Auckland Volcanic Field - Mt Wellington - photo Peirsrenad.blogspot

Auckland Volcanic Field - Rangitoto in the background, and North Head Volcano in the foreground. - Photo city of volc.

Auckland Volcanic Field - Rangitoto in the background, and North Head Volcano in the foreground. - Photo city of volc.

Although dormant today, it could present new breakouts to new sites in a period of a hundred years. As explained by Jenni Hopkins, " What remained unknown until now, that is the order in which the volcanoes erupted ... I wanted to establish to better understand the characteristics of the volcanic field and have a idea of ​​a future eruption. "

To do so, she examined the ash deposits of a series of lake cores to appreciate the thickness of layers and the order in which they are lodged. As part of the program Devora / DEtermining VOlcanic Risk in Auckland, the material was examined with an electron microprobe and laser ablation techniques (*) ... each layer has a unique geochemical fingerprint in trace elements, can be connected to the lava of issuers volcanoes. This allows you to see the distribution of the ashes of each eruption and assess the areas likely to be affected by the eruptions in the future, improve evacuation programs and helping local authorities to work towards a mitigation of damage infrastructure.

(*) The laser ablation is a technique for depositing thin layers. It complements the range of the physical methods of depositing thin layers, such evaporation, cathodic pulvérisatio or the sol-gel process.
The method comprises focusing a pulsed laser beam on a target consisting of the material to be deposited. The beam-target interaction causes tearing of the material constituting the target by sputtering, evaporation or mechanical fracturing, which may thus come to depositing on a substrate placed vis-a-vis of the laser spot.
The conditions for interaction fluence (energy of the pulse per unit area), pulse width, wavelength, to control the ablation path of the material (plasma, vapor, etc.) by modifying the absorption conditions of the laser energy by the target.
3Det sequence special effects simulation of a type of rash Surtseyan in the Bay of Auckland - Auckland Museum volcanic eruption video

These geochemical techniques will be applied in a subsequent study to examine the distal deposits of super-eruption of Taupo, which have not yet revealed all their secrets.


Script and direction of the flows of a future eruption - Doc. NZ Herald

Auckland Volcanic Field - Mt. Eden overlooking the city of Auckland - photo Geonet

Auckland Volcanic Field - Mt. Eden overlooking the city of Auckland - photo Geonet

 Script and direction of the flows of a future eruption - Doc. NZ Herald

Script and direction of the flows of a future eruption - Doc. NZ Herald

3D sequence and special effects of simulation of a type of Surtseyan eruption in the Bay of Auckland - Auckland Museum volcanic eruption video

These geochemical new techniques will be applied in a subsequent study to examine the distal deposits of the super-eruption of Taupo, which have not yet revealed all their secrets.

 

Sources :

- Victoria University of Wellington – Predicting the impact of an Auckland eruption - link

- Global Volcanism Program - Auckland field

- New Zealand Journal of Geology and Geophysics - Age of the Auckland Volcanic Field: a review of existing data - By JM Lindsay & al.

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