Centuries-old eruptions could help predict future lava flows

Geology researcher Dr Paul Ashwell

A look into how some of New Zealand's biggest volcanoes erupted hundreds of years ago could help predict lava flows for future eruptions.

A University of Canterbury geology researcher has found a host of factors play a part in how lava domes erupt.

Understanding these factors and how they affect the eruption of lava is critical to predicting if it will produce block and ash flows, Dr Paul Ashwell said today.

With supervision from volcanologist Dr Ben Kennedy, Dr Ashwell's thesis investigated lava domes at Mt Tarawera and Mt Ngongotaha, near Rotorua.

He wanted to look at how each dome erupted and what impact it would have had on the surrounding areas.

Mt Tarawera erupted about 700 years ago and rates as the largest eruption in New Zealand since Taupo erupted 1800 years ago. Tarawera formed three large lava domes at the top of the volcano.

"This eruption was studied by another of my supervisors, Professor Jim Cole, and was an important site for understanding early concepts of volcanology in the 1960s and 1970s," Dr Ashwell said.

"I built on this work by looking at one of the lava domes, Ruawahia, which is at the summit of Mt Tarawera, in detail and mapped very small structures such as bubbles and crystals to get an idea as to how each part of the dome erupted.

"I found that Ruawahia may be made up of several smaller domes or flows of lava that together form the dome, but each forming at a different time. I also found out that the underlying ground surface was a very important feature, as it dictated how far the lava could move."

With help from honours student Matt Edwards, they mapped the edge of Ruawahia, and performed experiments to try to recreate how the Tarawera lava behaved as it flowed.

They found that popcorn-like rock on the edges of Tarawera was evidence large chunks had fallen off during eruptions, producing clouds of hot gas, ash and rocks that incinerated the land beneath the volcano.

"These events pose a significant hazard at lava domes in New Zealand and around the world," Dr Ashwell said.

Dr Kennedy says the research results are significant because it revealed that Mt Tarawera was not plugged by a single lava dome before the 1886 eruption as previously thought.