How Do You Date a New Zealand Volcano?

Among impressive volcanic scenery in northern New Zealand lies the city of Auckland. The district is known for its volcanic cones. In fact, there are more than 50 recognised small volcanoes in the city and surround­ing areas. But the largest volcano by far in Auckland is also the youngest. It is called Rangitoto. How young is this youngest vol­cano? Now your problem starts.

Rangitoto is generally regarded as young for several reasons. Evid­ence based on botany and geo­morphology, and a hint from Maori legend that the name can mean 'red sky', contribute to a common acceptance that Rangitoto is youthful. Some of the lavas (scoria) have no vegetation, and seem to be no more than a few hundred years old.

Conflicting Dates

In the late 1960s, scientists from the Australian National University in Canberra dated numerous vol­canoes in Auckland using the potassium-argon method.1 Ten samples from both vegetated and unvegetated lava on Rangitoto were dated. Results seemed to show that Rangitoto was not a few hundred years old as it appeared to be. Ages from the 10 samples ranged from 146,000 years up to almost half a million years!

So how old is Rangitoto? A couple of hundred years? Or half a mil­lion?

The scientists took a sample of wood from beneath some Rangi­toto lava and dated it by the car­bon-14 method.2 The wood gave an age of only 225 years (plus or minus 110 years) - which poten­tially puts it in the lifetime of George Washington and German composer Johann Sebastian Bach. This is about the age all evidence points to except potassium-argon dating.

If lava which is little more than 200 years old can be wrongly dated at up to 465,000 years by the potas­sium-argon method, could potas­sium-argon dating always be wrong?

Wrong Every Time

The scientists who did the Rangi­toto tests dated 16 volcanoes in all. 11 of these were able to be compared with carbon-14 dates. In every case the potassium-argon dates were clearly wrong to a huge extent.

Similar conflict was found by researchers in Hawaii. A lava flow which is known to have taken place in 1800-1801 - less than 200 years ago - was dated by potas­sium-argon as being 2,960 million years old.3 If the real dates were not fairly well established by other means, who could have proved that the potassium-argon dates were so wrong?

So how do you date a volcano? The lesson seems to be that how ever you date it, don't count on the potassium-argon method.

by Robert Doolan

References

  1. Ian McDougall, H. A. Polach and J. J. Stipp, 'Excess radiogenic argon in young sub-aerial basalts form the Auckland volcanic field, New Zealand', Geochimica et Cosmochimica Acta, Vol. 33, 1969, pp.1485-1520.
  2. Carbon-14 dating is regarded by creationists as reasonably reliable for recent objects. For explanation see The Answers Book, pp.43-50.
  3. J. G. Funkhouser and J. J. Naughton, 'He and Ar in ultramatic inclusions', Journal of Geophysical Research, Vol. 73, 1968, pp.4601-4607.

Footnote

Many geological layers have actually been assigned vast radiometric ages on the basis of potassium-argon dating of volcanic intrusions into the layers. Well-known fossil hunter Richard Leakey's 1470 Skull was 'dated' by the same method used on surrounding volcanic material.

Source: 'Creation Ex-Nihilo', Vol.13, No.1, p.15