At 1.25pm on 21 November 2012 Mt Tongariro let fly with a two kilometre plume of ash emanating from Te Maari Crater. This is the area that erupted on 6 August. The eruption only lasted five minutes but GNS are monitoring the situation. The volcano alert for Tongariro has been lifted to Level 2, which means ‘minor eruptive activity.’ The Aviation Colour Code is changed to red. Flights between Wellington and Taupo are cancelled.
A lot of snow has disappeared off the mountain and we now have many people circumnavigating the mountain as well as walking the Tongariro Alpine Crossing. There were several school groups on the mountain, some within one kilometre of the eruption. No injuries are reported.
Wow, it’s always exciting when one of our mountains goes off. At 11.50pm on 6 August Mt Tongariro erupted flinging ash and hot rocks into the air. Although there had been increased earthquake activity in recent weeks and slightly elevated gas signatures there was no real indication that the mountain was anything other than restless. It is thought the incandescent explosions emanated from the Te Mari Craters which are on the northern end of the mountain. Mt Tongariro last erupted in 1897.
Volcanic ash has trended east towards Napier and some flights have been suspended. Roads in the area have been reopened after being closed last night due to ash.
Police have set out this morning to check that no one is stuck in huts on the mountain.
My novel, Fire in the Mountain, is due out in three weeks! Great timing!
Mt Ruapehu produces eruptions of high explosivity, but they are not the biggest like the eruption that produced Lake Taupo 26,500 years ago. However, they can be larger than those that created Rangitoto Island 600 years ago in Auckland’s Hauraki Gulf.
This is due to the composition of the magma and the amount of water contained in it. Magmas are generated from partially melted source rocks which can include subducted oceanic crust and overlying sediments plus the lower continental crust. Andesites, which are the most common rocks produced by Ruapehu eruptions, are differentiated products of basaltic magmas that may have become contaminated and mixed with magmas generated by partial melting of the surrounding crust. In short, the higher the water content, the higher the explosivity of the eruption.
The fallout from eruptions is as follows:
Ash – less than 2mm diameter particles
Lapilli – 2-64mm diameter particles
Bombs – greater than 64mm diameter plastically deformed blobs of magma
Blocks – greater than 64mm diameter solid rock fragments
The temperatures of these rocks at eruption are 1100 – 1250 degrees Celcius
During the 1995/96 eruptions enough ash and lapilli built up on the rim of Crater Lake to allow an increase in lake water volume. This debris, termed tephra, is unconsolidated and allowed as much as 1000 cubic metres per day to seep out of the lake prior to the 18 March 2007 lahar.