More updates now available at the newer post – click here
Update 3; OK this is getting more interesting and alarming by the day. The pumice debris in the ocean comes from a third erupting NZ volcano – Mt Monowai. This undersea volcano has one of the fastest growth rates of any modern volcano.Like with Krakatoa it is possible the pumice could find its way all the way to the Americas.
Meanwhile there is a 50% chance of further eruptions at Tongariro with a couple of thousand tonnes of sulphur dioxide gas having been emitted by the Volcano with lava bubbling under the surface.
Meanwhile it has been stated by scientists that previous eruptions in the Taupo volcanic zone would have been visible from Sydney Australia – such was the magnitude of them.
Update 2; Volcanic debris the size of Belgium found floating off the coast of NZ. More here
Update; Magna bubbles under Tongariro – further eruptions likely.
1800 years ago Taupo volcano in New Zealand had the largest volcanic eruption in the world for the last 5000 years. Taupo ejected over 30 cubic kilometers of material including a pyroclastic flow that moved at 600-900km/hr, traveling up mountains to a height of 1500m .
But even that massive eruption was dwarfed by the huge Taupo eruption just 26,500 years ago which plunged the earth into a volcanic winter & wiped out 60% of the population. From wikipedia;
The Oruanui eruption of the Taupo volcano was the world’s largest known eruption in the past 70,000 years, with a Volcanic Explosivity Index of 8. It occurred around 26,500 years ago and generated approximately 430 km³ of pyroclastic fall deposits, 320 km³ of pyroclastic density current (PDC) deposits (mostly ignimbrite) and 420 km³ of primary intracaldera material, equivalent to 530 km³ of magma.   
Tephra from the eruption covered much of the central North Island with ignimbrite up to 200 metres deep. Most of New Zealand was affected by ash fall, with even an 18 cm ash layer left on the Chatham Islands, 1,000 km away. Later erosion and sedimentation had long-lasting effects on the landscape, and caused the Waikato River to shift from the Hauraki Plains to its current course through the Waikato to the Tasman Sea.
This eruption was the largest volcanic eruption in the world in the last 70,000 years. When you consider the pyroclastic flows from this eruption were up to 100m deep (yes the height of a 30 story building), and extended up to 100km from the volcano then this is a volcanic area to keep a close eye upon. Especially as this volcano erupts every 2000 years and erupted around 1800 years ago.
Taupo volcanic zone is one of the most active in the world, The last 3 months has seen many small earthquakes around Taupo but there seems an increase in tectonic activity in recent years with a 6.5 quake just last year and another 5 quake last month. With volcanic eruptions Tongariro erupted unexpectedly this week with White Island erupting yesterday.
In 2006 Geologists warned Rotorua, Taupo and Whakatane are set to be wiped out in a massive overdue earthquake. An Alpine fault quake is a certainty where East Cape would rip away from New Zealand, destroying the plateau that Rotorua is based on and taking Taupo and Whakatane with it. It is only a matter of when. “The interval since the last event (in 1717) is longer than any interval between known earlier events.”
As Christchurch keeps getting hit with earthquakes & liquefaction is New Zealand waking up in accord with it’s cycles? There is also speculation that volcanic activity coincides with low sunspot activity – with solar cycle 24 flat-lining it will be nteresting times ahead!
The east coast of Australia is at risk from tsunami