To Destroy, or Preserve? That is the Question on the Effects of Volcanism in Archaeology

By Brigid Gallagher 16/08/2012

In front of me a volcano is erupting. 

This is a slight exaggeration…but from my window last Friday, I could see a long low trail of ash from White Island spread above the horizon, and small billows of white changing form where another burst of steam spews forth.

I have been fighting the urge to go and buy a stronger set of binoculars in case I miss something. 

I have always been fascinated by volcanoes.  It started in earnest during 5th form geography when my teacher Sally Brodie (I really should thank her!) picked up the phone in her office and rang eminent geologist Sir Les Kermode.

The conversation went something like this…

“I am with a student who feels that she cannot fulfil the requirements of her project on the Tongariro Volcanic Field because she cannot adequately explain the difference between andesitic and rhyolitic volcanoes”.

Hmmm, maybe I was a little precious?!

And so I was given this lesson over the course of the next minutes, and I went away a well informed school girl who felt able to finish her assignment.

It was an invaluable lesson, and demonstrated early on that asking the right people the right questions was key to my understanding of science.  Especially when understanding physical sciences where I needed, and still do, need to visualise processes.

But back to volcanoes…and leap forward a few years…what on earth is an archaeological bod doing reminiscing about a desire to be a volcanologist?

Volcanoes have had, and continue to have a huge impact on archaeology in term of;

  1.  Site formation,
  2. Site damage and destruction,
  3. Site preservation and,
  4. Site dating.

…And as a conservation specialist, which is all about understanding the condition and decay mechanisms at play between materials and the environment, volcanic activity is also really exciting;

One single volcanic event can result in site formation, damage, destruction and preservation to different degrees, with long term implications and management needs. 

Assessing and understanding the complex behaviour between the negative and positive effects of one natural disaster, or moment in time, is for me is really interesting because the myriad of problems and solutions that are generated.

Archaeological Examples

Pompeii in Italy has probably made its fame by the effects caused on the Roman town by the eruption of Mt Vesuvius in AD79.  Whilst ash and molten rock formed a covering over the town, its quick cooling resulted in a protective layer to be created taking the form of the object, structure or person it covered.  In many cases this created an air tight capsule in which food stuffs, plaster and paint, human skin and bone, bricks and mortar could be preserved in a relatively pristine manner. Without the preserving qualities of the ash layer, Pompeii it could be argued, would have gone the way of so many other Roman towns, and now be another deteriorating archaeological site in Italy that relies on the tourist dollar, and requires huge amounts of money to help it stay in a state of semi restoration.  Though this has been the very subject of some recent media coverage.

…Luckily for the Romans they built in brick and stone.

New Zealand’s equivalent may well be Te Wairoa in Rotorua. However, buildings and structures of New Zealands prehistoric and historic past have been traditionally made of plant and tree materials such as raupo, punga, kauri and pine.  Placed under the pressures of dense volcanic ash layers, and in combination with the low ignition point of these materials, hot ash and molten rock in many instances has meant fire and destruction, not preservation.

…which has meant loss to the archaeological record.

Though in saying that…should you get a chance to visit The Buried Village at Te Wairoa you would be in for a very nice surprise with some whare that have been carefully excavated and restored, following preservation by volcanic ash. 

This a good example of how volcanic activity has both destroyed and served to keep a site in stasis until rediscovery or excavation. 

A form of time capsule was created.

One of New Zealand’s other big preservation stories as far as archaeology goes is the Sunde site on Motutapu Island. Located in the Hauraki Gulf and joined to Rangitoto Island (Auckland’s youngest volcano, dated at c. 1400) by a land bridge at low tide, Motutapu boasts preserved footprints due to the blanketing effect of Rangitoto’s last volcanic eruption and ash cloud.

Human and dog footprints found side by side are an evocative reminder of real people and animals living in New Zealand some 550 years ago.  Dated at c. 1450AD the foot prints show at least 8 people, 3 of which are children walking with their dogs.  Eruptions and ash fall from Rangitoto sealed the footprints, preserving them like the Laetoli footprints found by palaeontologist Mary Leakey’s team in Tanzania in 1976, and dated to 3.6 million years. 

Discovered in 1981 by archaeologist Reg Nicol, at that time from Auckland University, the ash had a preserving quality for the footprints, but archaeologists believe that it was also responsible for the destruction of settlements, gardens and forests on the Island.  Archaeologist Andy Dodd wrote in his Heritage Assessment “Motutapu Archaeological and Historic Landscapes” for the Department of Conservation (2008);

“The eruption smothered Motutapu in ash and caused widespread deforestation, but also produced friable soils suitable for gardening [and therefore aid regeneration]”.

Once again the destructive and preservative qualities of ash has been recorded by archaeological investigation. 

Its a strange balance that exists between materials and the environment. 

Depending on the perspective or the question there is different degrees of formation, damage, destruction and preservation contained within one volcanic event and ash dispersal.  

And the unfortunate aspect of volcanism is that often scientists don’t know what the ratio will be until the top has blown! Including near Pompeii, where a super volcano has recently been reported.

Never the less, next week we are going on long anticipated family holiday to the Central Plateau.  Hopefully there will be a quiet period of sun and snow… and I will only have to imagine the alternative.  But I think I will pick up a good pair of binoculars on the way…just in case!


Te Wairoa – The Buried Village

Motutapu archaeological and historic landscapes heritage assessment, DoC, 2008

The Motutapu Restoration Trust – Sunde Site

Pompeii online

 Note – this is a huge subject of which only a small portion has been considered here…and may be returned to in the future…