New Zealand volcanoes going for gold

Posted on August 10, 2012

While they might be 19th on the medal table, the kiwis are doing a sterling job of heading up this weeks volcano news.

Both White Island and Tongaririo have shown activity this week. White Island was last active in 1980, and is a beautiful example of an andesite volcano. Tongariro is a volcanic complex, comprising numerous adjacent vents. Technically, it includes Ngauruhoe (a volcano I have spent some time on, and wrote about back in January).

This morning we then get news that a huge pumice raft has been spotted 1000 km North of Auckland, believed to have been generated by a submarine eruption from Monowai.

The first thing I should point out is that these three eruptions are not related. This is just one of those statistical anomalies that crop up with random scatter. All three volcanoes are associated with the subduction of the Pacific plate under the Indian-Australian plate, but their magma plumbing systems are completely unrelated. To put the magma plumbing in perspective, the crust is 35-40 km thick, and the distance between White Island and Tongariro (the closest two of these events) is about 220 km in a straight line. These two volcanoes lie at approximately the NE / SW extents of the Taupo Volcanic Zone (VTZ), and have the much larger features of Rotorua and Taupo separating them. Below is a map which plots the recognised features of the TVZ (taken directly from here and plotted in Google Earth), with White Island and Tongariro highlighted.

Importantly, the Monowai seamount – although associated with the same tectonic boundary (the Kermadec trench), is clearly not directly associated with activity over 1400 km away.

<SNIP>

http://lithics.wordpress.com/2012/08/10/new-zealand-volcanoes-going-for-gold/

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Great Alpine Fault Earthquake talks

This is a summary of the talk given by Associate Professor Tim Davies at Cromwell, Wanaka and Queenstown, 8-10 October 2007.

Natural event and human consequences in Queenstown Lakes and Central Otago.

Tim Davies, Canterbury University
Mauri McSaveney, GSN Science

Introduction

Earth has a mobile surface divided into "tectonic plates". The New Zealand continent is on one of the plate boundaries.

The Alpine fault connects two "subduction" margins where the ocean floor descends into the Earth's mantle. At this point the surfaces of the two plates making up the South Islands alpine fault meet.

The Pacific Plate on the easterly area of New Zealand is moving westwards and the Australian Plate, on the western side of New Zealand moves eastwards. They move at a relative rate of about 45mm per year.

As these two plates move against each other enormous pressure builds up which must eventually be released through earth movement. The result is a major earthquake along the Alpine fault. The pressure has been continually building for about 280 years since it was last released by a large earthquake in 1717 AD.

This earthquake is a normal part of New Zealand's evolution. We are a young country and learning to adapt to it is a necessity if you and your community are to get through.

The alpine fault earthquake will be but one event of many different types of natural hazard events that will occur in New Zealand's future.

<SNIP>

http://www.orc.govt.nz/Information-and-Services/Natural-Hazards/Great-Alpine-Fault-Earthquake/