Smart sensing tech to help scientists peer inside volcanoes

GNS Science lifted Mt Ruapehu's Alert Level to two after measuring temperatures of 43C in its Crater Lake, amid other signs of volcanic unrest. Photo / GeoNet

Technology first designed for the military could offer a crucial early look at the same volcanic rumblings that just prompted GNS Science to ramp up Mt Ruapehu's warning level.

A new study will draw on sophisticated remote-sensing equipment to peer inside volcanoes' hydrothermal systems, which could change over years - or even days.

As last year's eruption at Whakaari/White Island tragically illustrated, large blows following hydrothermal shifts can happen with few warning signs.

This month at Mt Ruapehu, scientists recorded a series of tremors, the largest amounts of carbon dioxide and sulphur gases measured in two decades, and Crater Lake temperatures as high as 43C.

Temperatures in the mountain-top lake each year typically cycle between 15C and 40C, and while it's crossed that threshold at times since Ruapehu's surprise 2007 bang, none of those episodes ended in eruption.

GNS Science said the current continued flow of these gases and heat through the lake signalled the vent underlying it was open, which triggered a shift to alert level 2 and its official flagging of "moderate to heightened volcanic unrest".

Massey University scientist Dr Gabor Kereszturi said gaining a clearer picture of hydrothermal systems like Ruapehu's was important as they could tell us much about hidden processes that came before bouts of volcanic unrest.

As was happening now, he said, hot fluids circulated within volcanoes, making rock weaker over time.

This sometimes led to landslides and larger flank collapses - seen here most recently during Mt Tongariro's 2012 blow, when a small lahar flow reached State Highway 46 - but also to "blue sky" snap eruptions like Whakaari's.

All of these hazards remained notoriously hard to predict - which was where Kereszturi's new study into hyperspectral technology came in.

Since Massey bought New Zealand's first operational hyperspectral sensor six years ago, he's been interested in using it as a window to our volcanoes.

Pioneered for military use back in the 1970s, hyperspectral imaging involves collecting data from across the electromagnetic spectrum - and then piecing it together to create high-definition, three-dimensional profiles.

"It is an extremely versatile sensing technology that can detect both physical and chemical properties of the surface of the Earth or any other objects," he said.

"It can also be used in the lab, or as mounted on low-flying aircraft; or now on satellites."
When it came to volcanoes, it could be used from safe distances to measure the properties of otherwise-inaccessible volcanic rocks.

Kereszturi's project, made possible through a just-awarded Rutherford Discovery Fellowship, would develop fresh applications for it to use in labs, or from aircraft and space.

Massey University scientist Dr Gabor Kereszturi said gaining a clearer picture of hydrothermal systems like Ruapehu's could help forecast volcanic hazards. Photo / Supplied

As it happened, the study's focus would be on Mt Ruapehu, as well as the nearby Tongariro Volcanic Complex.

Its goal was to combine airborne remote sensing with existing geophysical datasets to get an unprecedented look inside volcanic features.

The could help answer tricky questions such as how and when rock within those features had been hydrothermally changed - and how that related to volcanic "explosivity".

"Using ground measurements, we will also develop new models to map carbon-dioxide emissions and to understand their role in hydrothermal alteration."

To date, the tech has been used at few volcanoes worldwide - they include the Cascade Ranges, which has produced every eruption in the US over the last 200 years, and at Italy's famous Mt Etna.

Kereszturi ultimately hoped it'd become another tool to help New Zealand interpret critical early signs of unrest unfolding within its many volcanoes.

"Together with traditional monitoring techniques, hyperspectral technologies can help to detect departures from normal activity - which can provide a new angle to improve forecasting efforts in the future."