Archive for February, 2006

Experiencing Tarawera’s Eruption

Monday, February 6th, 2006

Early in the morning of the 10th of June 1886 residents of the Bay of Plenty experienced, first-hand, the sudden eruption of a previously dormant volcano. The sudden eruption was so violent that residents of Gisborne district, 140 km away, heard the explosions, saw the rising ash clouds and received a coating of volcanic ash.

Near the opposite shore of Lake Tarawera from the mountain, residents and tourists had become alarmed during the evening of the 9th at the sudden onset of many earthquakes, some violent. Most of the tourists were spending the night at the hotel in the village of Te Wairoa which had sprung up to allow visitors to experience the thermal wonders of the area, and visit and bathe in the famous Pink and White Terraces at nearby Lake Rotomahana.

At the time, New Zealand was a growing colony of Great Britain, and the Victorian past-time of the “Grand Tour” brought a welcome boost to the growing economy. However, the tourism had its downside, bringing alcohol, money and young men looking for pleasure to the many Maori settlements in the area.

Maori communities were divided between those who wished to retain traditional ways and those who wished to move with the tide of change brought by the European. A local tohunga (Maori priest or knowledgeable person) had warned of impending doom, and the appearance of a phantom war canoe (waka) paddling across Lake Tarawera 10 days before the eruption added to the tension. The canoe was seen by Maori and European alike, and some observers reported the warriors had dogs heads, and that the waka mysteriously disappeared in the misty conditions at the time.

The eruption was a relatively small one by New Zealand standards and, though it only lasted 6 hours, the opening of a 17-km long rift through the three domes of Mt. Tarawera (Wahanga, Ruawahia and Tarawera Domes) was to have a profound effect on the area. Ash up to a metre thick was deposited up to 10 km away, and many tourist attractions were destroyed. European settlers counted 120 bodies, but the death toll may have been in the thousands as the ash affected many small villages occupied by Maori that Europeans never visited.

The story of the Tarawera eruption is thoroughly covered by exhibitions at the museum at the nearby city of Rotorua which grew from the initial settlement of Ohinemutu on the shore of Lake Rotorua. Many artifacts from the eruption are on display, and a short documentary describing the event plays regularly in a small alcove in the display area.

A feature of the current display is a longer video presentation which plays at 20 minute intervals in the main auditorium. The presentation covers the social, economic and geological aspects of the Tarawera eruption both before and after the eruption. Museum staff have gone to some lengths to make the presentation both informative and entertaining. But make sure that nervous adults and young children are supervised. The seating in the auditorium has been set to move abruptly in a most realistic way during the earthquake and eruption sequences on the video. Most perplexing is the very realistic rotational movement of the seating which caused a grandmother to hastily evacuate a distressed youngster from the auditorium when I was last there. Even so, the 15-odd minute presentation is not to be missed.

The Rotorua Museum is located in the refurbished Bath House, built as part of government investment in tourist facilities 1908. The opening of the spa rejuvenated the local tourism industry which had languished after the Tarawera Eruption. It is situated in the Government Gardens on the shore of Lake Rotorua, within easy walking distance of central Rotorua. The museum is well-signposted in the city, but foreknowledge is required to easily locate it once in the gardens, a small oversight.

One of the villages buried by the eruption’s ash, Te Wairoa, has been largely excavated and provides stunning insights into the effects of a volcanic eruption. From the lakeside nearby, the triple domes of the volcano responsible can be viewed.

For the more adventurous, it is possible to walk around and down into the rift craters of Mount Tarawera. Allow at least half a day if you wish to scramble down the scree slopes to the rift floor – a dramatic experience which rewards the adventurer with remarkable views. On a clear day, other nearby volcanoes can be observed from the top of the domes, of which Ruawahia is the tallest at 1111 metres. Access is via 4-wheel drive vehicle, and charges are steep as the volcano is on sacred, private land which is tightly managed and preserved. Several different tour options, one of which offers a return leg via helicopter, are available.

One Month’s Warning

Sunday, February 5th, 2006

Residents of Gisborne were given one month’s warning of the destructive earthquake which occurred just before noon on March 5th 1966.


Hangaroa Mud Eruption 1931

Saturday, February 4th, 2006

At the time of the magnitude 7.8 Hawkes Bay earthquake on the 3rd of February 1931, a mud blowout occurred many kilomteres north at Hangaroa, inland from Gisborne.

A loud report which was accompanied by a flash of flame as escaping gas ignited was followed by the eruption of an estimated 20,000 tons of mud at a property owned by Mr J. Barnes-Graham. The mud, which was finely crushed Lower Tertiary mudstone and sandstone, covered an area of approximately two and a quarter acres, and temporarily blocked the Hangaroa River as it flowed over the lip of the vent.

The report of the event in the New Zealand Department of Scientific and Industrial Research Bulletin No. 43 (p 78) stated that there were numerous examples of extinct and active mud volcanoes in the Gisborne district.

Earlier, in May 1930, an extensive blowout occurred at the cold mud springs in Waimata Valley, near Gisborne. J. A. MacKay in “Historic Poverty Bay and the East Coast, N.I. N.Z.” (p 370) states that they had erupted on previous occasions but the 1930 event was more extensive. “Explosions of gas brought up sufficient mud to raise the height of an area of some acres by, in places, as much as from 10 to 15 feet [3 to 4.5 metres]. The gas produced a steady flame when ignited.”

Lest We Forget

Friday, February 3rd, 2006

In the 14 years from 1929, New Zealand was relentlessly hammered by nine viciously large earthquakes and their associated aftershocks, causing major damage to infrastructure; and death, injury and personal hardship in an economy reeling from depression and the onset of war.

They were:
1929, March 9th, Arthur’s Pass, magnitude 6.9, felt over the whole country.
1929, June 16th, Buller (Murchison), magnitude 7.8, locally destructive, 17 deaths.
1931, February 3rd, Hawkes Bay, magnitude 7.8, severe regional damage, firestorms, 256 deaths.
1931, February 13th, Hawkes Bay aftershock, magnitude 7.3.
1931, May 5th, Poverty Bay, magnitude 6+, damage in Gisborne.
1932, September 16th, Wairoa, magnitude 6.8, damage in Gisborne and Wairoa.
1934, March 5th, Pahiatua, magnitude 7.6, damage in Hawke’s Bay and Wairarapa, 1 death.
1942, June 24th, Southern Wairarapa, magnitude 7.0, damage in Wairarapa and Wellington.
1942, August 1st, Southern Wairarapa, magnitude 7.1, local damage.

Today marks the 75th anniversary of the Hawkes Bay earthquake and Napier firestorm of the 3rd of February 1931. It is a timely reminder that New Zealand has enjoyed a lengthy period free from large earthquakes close to populated areas. Logic tells us that this cannot last, and that we should plan ahead so that we can manage the effects of the next large earthquake to reduce the disruption that will surely result.

Rural Fire Service Works Late

Thursday, February 2nd, 2006

Crews from the Rural Fire Service were working late tonight, damping down hot spots in the fire south of Tawa.

Just after 6-30 p.m. fresh crews were leaving their base at Tawa to carry out clean-up work, and a tired-looking crew passed me in their truck on Main Road just after 9 o’clock on their way back to base.

Thanks folks. The work you do as volunteers is much appreciated.

I suspect that, after three large fires in two nights, you’d like a rest. Fine misty rain is occasionally falling, but the temperature still sits on 20°C with 86% humidity. Uncomfortable for us lounge lizards, but even worse for fire-fighters in all their kit. Not only do they have to work in such uncomfortable conditions, but it does little to reduce the chance of a flare-up.

Scrub Fires Near Tawa

Thursday, February 2nd, 2006

Two scrub fires burning near the motorway at Tawa caused the closure of the northbound Tawa off-ramp on State Highway One, and Middleton Road between Tawa and Churton Park this afternoon.

As many as 10 fire appliances were in attendance, and two helicopters ferried water in monsoon buckets from a supply set up nearby.

Commuter rail services were interrupted for a time, and the flight path into Wellington International Airport was adjusted to the east while the helicopters were operating.

Fire Services attended a scrub fire in a park near Linden last night, and a bigger blaze in scrub which spread to a pine plantation near Upper Hutt.

Fire danger in the area has risen to moderate after several hot days, and 7 days without rain.

U.S. Geological Survey Enhances Services

Thursday, February 2nd, 2006

The United States Geological Survey (USGS) has enhanced the earthquake monitoring services offered by its National Earthquake Information Centre (NEIC).

In recent weeks, the NEIC has changed to a 24 hour per day, seven days per week, operation. The round-the-clock operation is expected to dramatically reduce the amount of time taken to analyse and report on earthquakes globally.

The USGS co-operates with a number of countries to collate data from seismometers in order to determine earthquake epicentres. This information is useful in assessing possible damage, and is a key element in improving world-wide monitoring of seismic waves, tsunami.

The USGS is currently trialling a new seismic event processing system called HYDRA which identifies, locates and measures earthquakes. It is expected that HYDRA will be fully operational sometime during March this year.

These enhancements will increase our knowledge of seismic events in the South Pacific and in New Zealand territories. Whilst our Institute of Geological and Nuclear Sciences operates Geonet to monitor earthquake activity within New Zealand, it still has some shortcomings. Geonet’s seismometers provide good coverage for earthquakes occuring up to moderate depths within New Zealand, but the long, narrow nature of the country makes it difficult to accurately pinpoint deep earthquakes. The triangulation calculations require the use of more distant readings, and this is done by collaboration with USGS and other geological organisations. In return, data from New Zealand seismometers is made available for study by seismologists in other countries.

The NEIC has also revamped its website, meaning that many old links will no longer work. Earthquake reports have been enhanced, and page layouts have changed.

The NEIC can be reached via the link on this website.