Viewpoint

National Museum Siting Madness

The debate over the proposed National Museum of New Zealand is now concentrated on the aesthetics of an appropriate design -- the site for the new museum seems to have been settled. Clearly, lessons that could be learnt from the past have gone unheeded.

I am referring, of course, to the effects of New Zealand's largest known earthquake, of about magnitude 8, that occurred at 9:15 pm on the 23rd of January, 1855.

It is instructive to review eyewitness accounts from those early Wellington inhabitants for information as to what happened, because undoubtably the same thing will happen again during an earthquake of similar magnitude. Damage to the Wellington area will be widespread and incalculable. While the geology of Wellington City remains the same, extensive reclamation has taken place since the 1855 earthquake and this material has yet to stand the test of a magnitude 8 shake.

The first great shock of the 1885 earthquake lasted nearly 50 seconds, followed almost immediately by another. Shortly afterwards, the sea rose in the harbour between two and three metres, and receded about three metres lower than at spring tides. This cycle repeated every 20 minutes throughout the night for eight hours.

All the shops and houses along the foreshore were inundated and extensively damaged as a result. One ship anchored in Lambton Harbour grounded four times during the rapid rise and fall of the tide. Shocks of variable intensity continued throughout the night and the "trembling motion of the ground was continuous".

In the Te Aro and Thorndon areas, the first earthquake shock floored most people, levelled every brickwork chimney and opened up numerous fissures through which sand and mud were ejected, particularly in the area of the formed road along the foreshore. Uplift around the harbour amounted to between one and two metres, but was somewhat less in the Lambton Harbour area because of seaward movement of unconsolidated tidal and shoal sediment. A new shoreline created by the lift extended out into Lambton Harbour 20-40 metres from its pre-earthquake position.

Reclamation into the harbour began after the earthquake. Debris was initially taken from weathered greywacke rock in the cliffs behind Lambton Quay and Wellington Terrace. Later, fill was obtained from other areas and also dredged from the sea bed. The reclamation material therefore consists of variably consolidated porous sediments of different composition, density, hardness, grain size, permeability, etc. Nearly all of the fill has been dumped on the sand, mud and gravel of the shoal that originally extended out into Lambton Harbour. Relatively solid basement rock lies at a depth of about 160m.

Significant amplification of earthquake vibrations, at least in the upper part of the reclamation area, is to be expected. For an earthquake with a magnitude similar to that of 1855, many parts of the reclaimed area are likely to liquefy and flow outwards into the harbour. During the 1942 earth-quakes of magnitude 7 and the 5.5 magnitude quake of November 1968, the most significant concentration of damage was to buildings sited on reclaimed land.

It is a sobering thought that the amplitude of the surface vibration during an earthquake of magnitude 8 is ten times more than that of a magnitude 7 earthquake.

In short, the reclaimed land around Lambton Harbour provides one of the worst areas for the construction of a large and important building that is to house the "treasures of the Nation". Taken in conjunction with the tidal phenomenon that occurred during the 1855 earthquake, and now compounded by the presence of relatively unconsolidated fill, the shoreline area around Lambton Harbour would not be the place that I want to be during a large earthquake.

Public officials responsible for spending large amounts of money on the new museum should look closely -- if they haven't already done so -- at lessons from the past before committing the rate-payer to yet another think-big project with a positively disastrous future.

What, may I ask, is wrong with development going ahead on the present museum site -- a prominent hill within the city and with plenty of building space?

Rodney Grapes is an Associate Professor in the Research School of Earth Sciences, Victoria University of Wellington.