The Ring of Fire is active

Quakes shake lower North Island

Two earthquakes - the second a strong 5.2 magnitude - have struck near Masterton causing the lower North Island to "roll".

Photo: GeoNet

Radio NZ,

12 May, 2016

The latest was a 5.2 magnitude 15km west of Masterton, which struck at 7.55am. It was felt in Blenheim, Wellington and Lower Hutt, among other places.

The first quake, a magnitude 4.7 quake was centred 20km west of Masterton.

It struck at about 7.15am and was felt from Wellington to Whanganui, GeoNet said.

A Whanganui resident texted to RNZ that the quake was a slow, rolling motion.

Another, in Tauherenikau, said he thought a tree had fallen on the house: "The whole room seemed to shift a couple of feet and then spring back."

Within 20 minutes of the main quake there had already been two aftershocks - neither strong enough to be felt. Geonet said aftershocks could continue for weeks.

There had also been several earthquakes in the same area the hour before the 5.2 quake.

Martinborough olive grower Ray Lilley said his house shook "quite sharply" in the biggest quake.

"The windows all rattled. A couple of items fell over inside the kitchen and the dogs came running through to say there's an earthquake going on. We knew that already," Mr Lilley said.

Ruapehu on alert after 20C rise

Ruapehu's crater lake temperature has risen about 20C since mid-April. Photo / Maurice Costello

Mt Ruapehu's risk of eruption may have increased, but GNS volcanologists say nearby residents should not feel concerned.

GNS today announced the mountain's crater lake temperature had doubled in the past few weeks, rising from 25C to between 45C and 46C over the past couple of days.

Duty volcanologist Geoff Kilgour says scientists made two visits to Ruapehu yesterday, one flight to measure the gas output and other to sample the crater lake water and make additional ground-based gas measurements.

"Volcanic gas measurements indicate an increase in the amount of both carbon dioxide (CO2) and sulphur dioxide (SO2) output ... Seismic activity at Mt Ruapehu is usually dominated by volcanic tremor. Since the volcanic earthquakes in late April the seismicity has been dominated by volcanic tremor at varying levels. The level of tremor has increased but is not exceptional in terms of the last few years.

The Ruapehu crater lake in 2013. Photo / Geonet

"It's got nothing to do with weather. And White Island, they're [volcanoes] all independent of each other."

Mr Scott says the activity is caused by molten lava getting trapped inside the volcano itself.

"When that new pulsar heat and hot rock comes into the volcano it's whether or not it can flow through the volcano and get out of it and if the holes in the volcano aren't big enough to let the gas through it just over pressurises and pops."

And for those in surrounding towns worried that a lahar will swamp them, Mr Scott says debris is unlikely to travel more than a few kilometres from the volcano itself.

"One of the biggest eruptions, in 1995, only a few blots got past the 3km or 4km mark and that was really rare. Being away from the volcano is very safe and even the standard places you can go. Different story if you go and climb the thing and you're camping at the crater lake or something."

As for where it travels, Mr Scott says the majority head out towards the Desert Rd but there have been some eruptions producing lahar on the northern side.

"If you're at the ski lodges, they're safe as. Ruapehu only affects within about 3km of the lake and the nearest part of the ski fields are about 4km or 5km away so it does make it a fairly safe environment and the rest, once off you're off the bottom of the volcano, nothing can touch you."

Mr Scott says Ruapehu Alpine Lifts has shifted all of its infrastructure - ski tows, towers, cafes - out of the valleys in case it did head in that direction.

As for how the volcanic unrest occurs? "That's the $64,000 science question of volcanologists all over the world."

The Department of Conservation also issued a warning to climbers and trampers on the mountain, to not enter the Summit Hazard Zone on Mt Ruapehu until further notice.

The Summit Hazard Zone is the area within 2km of the centre of the crater lake.

It encompasses all the peaks in the summit area, with Te Heuheu Peak at the north end of the summit area at the edge of the zone, and the upper Turoa skifield at the south.

Climbers and trekkers should refer to the Summit Hazard Zone map or use their map and GPS reading skills, to determine when they are approaching the zone.

"We recommend climbers, trampers and walkers do not enter the zone," said Paul Carr, DoC's operations manager for Tongariro.

"Guiding companies should also heed the advice and not take people into the zone."

No ski areas, other facilities or roads on Ruapehu or elsewhere in Tongariro National Park - including the Tongariro Alpine Crossing - are affected by this warning

Possibility of further eruptions on White Island remains high

The view of White Island from the crater floor after an eruption on April 27. Photo / GNS Science"

10 May, 2016

Last month's eruption at White Island likely would have killed anyone standing close to the floor of its Crater Lake, scientists say.

Fortunately, the eruption happened late at night and no one was on the island when a surge of ash was thrown across the crater floor late on April 27.

In a blog post, GNS Science volcanologist Brad Scott said the steam and gas driven eruption from the offshore volcano created a new crater, caused landslides and excavated some of the lake.

Much of the crater floor was covered with a green-tinged ash - but Mr Scott and his colleagues have been able to confirm that none of the material contained magma from deep within the active volcano, which rises 1.6km from the ocean floor off the coast of Bay of Plenty.