Archive for the 'Carl Walrond' Category

Don Merton’s legacy

Old Blue, from whom all other black robins are descended

Old Blue, from whom all other black robins are descended

Ornithologist Don Merton died on Sunday 10 April 2011, some 27 years after the black robin dubbed ‘Old Blue‘. Don pioneered conservation techniques of intensively managing the last remaining individuals of a species to recover the population and also of transferring species from one island to another, where habitats were more favourable and predators absent.

In the 1960s active management of predators and manipulating breeding at an individual level was not the done thing. Managing threatened species was pretty much a case of preserving habitat and then leaving them alone. An experience on Big South Cape Island in 1964 changed that. Rats got onto the island and Don and his colleagues transferred the only known South Island saddlebacks and the tiny Stead’s bush wren to nearby rat-free islands. The Stewart Island snipe and the greater short-tailed bat were not transferred and they soon became extinct. While the wren was transferred, it did not breed on its new home and it too ceased to exist.

Don later recalled: ‘The tragedy of Big South Cape was a timely and valuable lesson for us. It convinced even the most sceptical that predators could induce ecological collapse and extinctions. But it also has a massive, enduring impact because it shaped the way we developed policies about conservation and put them into practice.’

His most startling achievement occurred in 1976, when the remaining seven black robins on Little Māngere Island, one of the Chatham Islands, were transferred to nearby Māngere Island, which had better forest. As a young boy Don had successfully placed goldfinch chicks in his grandmother’s canary’s nest, which the bird then raised as her own. Using this age-old cuckoo’s trick as a cue, he gave the eggs of the last surviving female, named old Old Blue, to tomtits, which they successfully incubated. Old Blue would then lay another clutch. Slowly the population grew and so the species was saved – from just five individuals and one breeding pair. When Old Blue died at age 13 her passing was announced in Parliament. All of the 250 or so surviving black robins are descended from her and her breeding partner Old Yellow.

Few people could lay claim to saving a species, yet Don, as well as having a major hand in saving multiple bird species, also developed approaches that could be adapted for other threatened species. The Department of Conservation’s current recovery plans for threatened species build upon the work of Don and other conservationists of the late 1970s. The continued existence of the kākāpō and black robin are his most visible legacy, yet the hands-on approaches he and his colleagues developed, and that many others have since built upon, continue to offer hope for retaining biodiversity both in New Zealand and overseas.

In conservation circles Don Merton was not only world famous in New Zealand, he was world famous worldwide. And rightly so.

New Zealand’s tsunami risk

Local-source tsunamis since the 1820s

Local-source tsunamis since the 1820s

Tsunami is one of the few Japanese words that have made it into the English language. The etymology of the word is from ‘tsu’ (harbour) and ‘nami’ (waves). Following the Japanese tsunami of 11 March 2011, generated by a massive earthquake of magnitude 9.0, many New Zealanders, especially those who live or work in low-lying coastal areas, will be interested in our tsunami history and level of risk.

Te Ara’s entry on tsunamis was written by Willem de Lange and Eileen McSaveney in 2005, not long after after the 2004 Boxing Day tsunami had devastated many places in the Indian Ocean. Since then, the 29 September 2009 tsunami off Samoa’s south coast, which killed 183, has further raised the profile of the hazard. After the Samoan tsunami Willem de Lange pointed out that while we were now much better prepared from a tsunami generated by a distant earthquake – which takes many hours to get here – we were about as well prepared for a tsunami generated close to our shores as Samoa was in 2009. In other words, there would be no warning.

A major problem is that there are many offshore earthquakes each year but almost all of them pose no tsunami threat, as most are small and do not cause large movements of the sea floor. Offshore quakes cause tsunamis when the sea floor suddenly drops or rises many metres – causing a pulse of energy that ripples outwards in the form of waves (it’s like what happens to the surface of a bucket of water if you drop it onto the ground). There would have to be a judgement call made after a large offshore earthquake as to whether a tsunami warning was issued (or not). This would need to be done in minutes – as the Japanese experience has shown that waves can move at the speed of a jet plane. If warnings were issued and no tsunami eventuated, there would be a danger of people ignoring future warnings. Currently, New Zealand does not have the capability to issue warnings based on science for local- and regional-generated tsunami within minutes.

Increased tidal disturbance around New Zealand after the March 2011 earthquake in Japan

Increased tidal disturbance around New Zealand after the March 2011 earthquake in Japan, recorded by GeoNet (http://www.geonet.org.nz/tsunami/)

Japan is the best-prepared country in the world for a tsunami, with computer systems taking into account 100 pre-computed models of distant-source tsunami, and 100,000 pre-computed models of local-source tsunami. Its system of seismic sensors compares earthquakes in real time with these models, and then generates earthquake and tsunami warnings. In theory, this enables it to produce warnings within three minutes. It is still too early to judge how well this system performed, but early reports suggest that Japan’s earthquake-warning system gave advanced warning of the quake to those in Tokyo.

In New Zealand, local and regional tsunami could be generated from earthquakes in Cook Strait, off Fiordland or off the east coast of the North Island and the Bay of Plenty. They can also be generated by above water and underwater volcanoes, and landslides such as the Ruatōria Giant Avalanche that occurred off the east coast of the North Island 135,000–155,000 years ago. A Kaikoura fisherman recalled a small tsunami caused by an underwater landslide in 1953. The major local and regional risks come from offshore earthquakes and landslides (which can be activated by earthquakes) or occur without warning. When the local-, regional- and distant-source risks are combined, return periods for large tsunami in New Zealand are short – for example in 2001 the return period for 5–10 metre tsunami affecting some part of the Wellington coastline was estimated at once every 84 years. Māori have tsunami in their oral traditions – a wave destroyed coastal settlements in the 1400s in Tasman Bay and deposits left by past tsunami have also been found.

We have a good warning system for distant-source tsunamis, but not for local- and regional-source tsunamis. At the moment, the best that can be said is that if you feel a strong earthquake near the coast get to high ground (35 metres above sea level) immediately. As the 22 February 2011 Christchurch earthquake has seen us scrabbling to inventory our at-risk buildings, it’s perhaps time to review our tsunami warning system for those waves generated closer to our shores. In the meantime, if you feel a quake near the shore, run for the hills.

Wellington and Christchurch’s earthquake risk

New Zealand regions at greatest likelihood of ground shaking

New Zealand regions with greatest likelihood of ground shaking

Following the devastating magnitude 6.3 earthquake in Christchurch, many will be assessing the risk of where they live. Over a long enough time frame pretty much anywhere in New Zealand, apart from Northland, is vulnerable to a large earthquake.

On the map above it is evident that Christchurch is among the lower ground-shaking hazard areas. These predictions were based on the distribution of active faults, how frequently faults have moved in the past, and the location of historic earthquakes. This illustrates that even lower-hazard areas are vulnerable – as previous ruptures on the Greendale Fault (the location of the 4 September 2010 magnitude 7.1 Darfield earthquake) do not seem to have occurred in the last 2,000 years.

Yet, hazard is not the same as risk. The highest-hazard area on this map is in the Southern Alps, where few people live. The highest-risk areas are where hazard intersects with population – our second and third largest cities: Christchurch and Wellington

There are three major known earthquake threat sources to Christchurch - and although all differ in their magnitude and distance from the city, all are expected to result in around the same amount of ground shaking. The rarest is from a major rupture of the Alpine Fault - around a magnitude 8 event. The return period is 1 in 100-300 years - the last was in 1717. Even though the fault is well over 100 kilometres away, the ground shaking from such a massive release of energy would still be considerable in Christchurch.

More frequent moderate-to-large earthquakes (6–7.5 magnitude) were expected from faults in the foothills of the mountains next to the Canterbury Plains, and in North Canterbury. Less frequent moderate earthquakes (5–6.5 magnitude) were expected from faults under the Canterbury Plains and Christchurch itself. The 4 September 2010 magnitude 7.1 Darfield earthquake and the 22 February 2011 magnitude 6.3 Lyttelton earthquake (thought by scientists to be an aftershock of the earlier earthquake) were in this later category. The strength and location of the Darfield earthquake surprised scientists and illustrates that our knowledge of the hazards we face is evolving.

One way that scientists use to estimate a locality’s future earthquake pattern is to look at its past. Since 1869, 11 strong earthquakes felt in Christchurch have resulted in Modified Mercalli scale ground shaking of 5 or more in the city:

• 1869, Christchurch, magnitude 5, ground shaking intensity 7–8

• 1870, Lake Ellesmere, magnitude 5.5, ground shaking intensity 6–7

• 1881, Castle Hill, magnitude 6.0, ground shaking intensity 5–6

1888, Hope Fault, North Canterbury, magnitude 7–7.3, ground shaking intensity 5–7

•  1901, Cheviot, magnitude 6.9, ground shaking intensity 6

• 1922, Motunau, North Canterbury, magnitude 6.4, ground shaking intensity 6–7

1929, Arthur’s Pass, magnitude 7.01, ground shaking intensity 6

• 1929, Buller, magnitude 7.8, ground shaking intensity 5–6

• 1994, Arthur’s Pass, magnitude  6.7, ground shaking intensity 3–6

2010, Darfield, magnitude 7.1, ground shaking intensity 5

• 2011, Lyttelton, magnitude 6.3, ground shaking intensity 8.

The 1869 and 1870 quakes were in the category of quakes beneath the Canterbury Plains and Christchurch itself. The largest of the above quakes in terms of ground shaking in the past century, prior to the 2011 Lyttelton quake, was the 1922 Motunau magnitude 6.4 earthquake in North Canterbury, which caused ground shaking of 6–7 in the city, as measured on the modified Mercalli scale. The 2010 Darfield magnitude 7.1 quake caused ground shaking of 5 in the city, while the magnitude 6.3 Lyttelton quake caused ground shaking of 8, because it was both closer to the city and shallower. Only the 1869 quake (believed to have been centred beneath New Brighton) caused ground shaking approaching this at 7–8.

While Christchurch is considered to have a lower earthquake hazard than Wellington, the risk it faces from medium-sized quakes is similar – which, prior to the recent quakes, would have surprised many people. This is due in part to the underlying geology of unconsolidated silts and sands that Christchurch is built upon. While hazard maps of areas prone to liquefaction exist, they largely join the dots of information gained from drill cores, while underlying geology in these types of deposits can vary from metre to metre. The predicted areas of liquefaction in existing hazard maps proved to be poor predictors of liquefaction in the September 2010 earthquake. As the water table is quite near the surface, many of these sands are water-saturated and when shaken turn to a jelly-like consistency. Not only does this lead to water and silt bursting through the surface, the ground shaking intensity is much worse than for areas built on bedrock, and the ground can also subside unevenly – with subsequent building collapse. This underlying geology is what brings Christchurch’s earthquake risk close to that of Wellington’s – for medium-size ground shaking events that is. Wellington’s risk from a very large catastrophic earthquake is higher than Christchurch’s.

Wellington is built on a faultline. You only have to fly into the city to experience the city’s earthquake history, as the airport is built on land upraised in the Haowhenua earthquake, which probably occurred in the 15th century. New Zealand’s largest ever recorded earthquake (magnitude 8.2) occurred on the Wairarapa Fault in 1855. The main threats to Wellington are from earthquakes on the Wellington Fault or the Wairarapa Fault, along with faults under Cook Strait which would likely cause a tsunami. Reclaimed areas such as the CBD, Miramar and Petone are at high risk from liquefaction, higher ground shaking intensity and tsunami, while areas with steep slopes risk landslides.

A large, shallow daytime earthquake of around magnitude 7.4 along the Wellington fault would probably result in around 500 deaths, 4,000 injuries, and perhaps 1,800 people trapped and over 100,000 buildings damaged. The return period is 1 in 700 years, and for a larger event (magnitude 8.2) on the Wairarapa Fault, 1 in 1,000 years. Yet, due to the multitude of faults, the return period for a very strong quake causing extreme ground shaking in Wellington is just 150 years.

Our recent earthquake history has not been an accurate gauge for our risk and hazard, and in that respect we have been lucky. Up until 22 February 2011 there had not been a large on-land earthquake close enough to a major city to cause very strong ground shaking since Napier in 1931. It is unlikely that it will be another 80 years before another large quake occurs close to one of our cities or towns. So get ready.


End times

At a dawn ceremony on Sunday at Waitangi Māori elder Kerei Tia Toa told those listening that he had a vision of Wellington devastated by an earthquake and tsunami. As is common with all who hold themselves up as prophets, he was remarkably short on detail, apart from his belief that it would be in June. This gives him a one-in twelve chance of being right as it is only a matter of time before a major quake causes widespread damage and loss of life in the capital. That is no prophecy – rather telling us what we already know – which is not always a bad thing as Civil Defence are keen to get the message across that we must be prepared to look after ourselves and our own after the big one.

'This is what happened in Napier in 1931; could worse be in store for Wellington?

This is what happened in Napier in 1931; could worse be in store for Wellington?

Kerei Tia Toa’s speech livened things up, but it’s unlikely to place him among the pantheon of Māori prophets such as Te Whiti, Te Mahuki and others. They all had pretty poor track records in their predictions. Te Mahuki prophesied in October 1890 that the second coming would occur on 2 November 1890. In anticipation, his followers took over Te Kuiti stores. For this he served a year in jail.

Some elements of Christianity had commonality with pre-European Māori society in which tohunga and matakite (seers) had acted as visionaries. Māori were especially taken with the Old Testament. Nineteenth-century prophets saw themselves as leaders of the persecuted, their lands dispossessed, and found resonance with stories of a landless forsaken people wandering the desert. Māori Zionism may at first seem curious, yet ultimately it was a response to what was happening at the time. Te Mahuki and Te Whiti’s status, and those of other Māori prophets, rests more on their actions of resistance (passive or active) to colonial land grabs and concerns for the wellbeing for their people, rather than any ability to see into the future.

The prophets have been very influential spawning the Rātana and Ringatū faiths, and showing that Māori movements could successfully cut across iwi divisions. Politically they have also had a legacy – in recent years the prime minister and leader of the opposition have headed to Rātana pā in January to commemorate the birth of the founder of the movement, Tahupōtiki Rātana.

All this and more is detailed in Judith Binney’s soon-to-be-published entry on Māori prophetic movements. My prediction, nay my prophecy, is that when it is published in April it will become one of the most popular Te Ara entries. I think I’ve got a greater than one-in-twelve chance of being right on that. And I won’t be leaving Wellington every June.

Blood moon on the rise

Lunar eclipse, taken by Geoff Trotter in Christchurch

Lunar eclipse, taken by Geoff Trotter in Christchurch

It was cloudy in Wellington two nights ago, so the lunar eclipse was not visible here. But a Christchurch member of our Flickr group added the photo above to our pool, so at least I’ve been able to see what it was like.

Lunar eclipses occur when the sun, earth and moon all line up, and the moon passes through the earth’s shadow. In Geoff Trotter’s image the moon is shaded, but it can also appear reddish due to refracted light from the earth’s atmosphere falling onto it.

Contrary to scenarios popular in stories such as Prisoners of the sun, where Tin Tin foretells an eclipse to escape from the Inca, indigenous people did know about eclipses (but couldn’t predict them). The story’s roots are from when Christopher Columbus foretold a lunar eclipse in 1504 in Jamaica so getting the natives to reinstate his ships’ food supplies, which they had withheld due to sailors cheating them.

Rona is snatched up by the moon

Rona is snatched up by the moon

Ethnographer Elsdon Best documented Māori knowledge of the sun and moon. Māori termed an eclipse of the sun ‘rā kūtia’ and thought that it was caused by demons devouring it – but they knew it eventually recovered.

In Māori mythology, Rona was snatched up by the moon after she had cursed it, because it had gone behind a cloud causing her to stumble. The feature that Europeans call ‘the man in the moon’ Māori saw as Rona, a tree and her water gourds. During an eclipse of the moon Rona is said to be fighting the moon. Don’t worry if you missed it this time, as Rona gives the moon the bash again in 2011.