THE Taupō supervolcano caldera, aka Lake Taupō, which volcanologists and geologists believe last erupted 232CE, producing the largest known eruption of the last 5000 years. Photo: Dougal Townsend/GNS Science.
TAUPŌ is a supervolcano – one of the planet’s volcanoes the eruptions of which wipe out large swathes of territory and affect weather world-wide from the sheer volume of ash ejected into the atmosphere.
Super eruptions are expected once every 20,000 years, and one could even be due as the last massive volcano to erupt did so 26,000 years ago, said Professor Stephen Sparks, vulcanologist from the University of Bristol.
“We’ve been studying the rates of these eruptions around the Earth and we find that roughly there’s one every 20,000 years. So they’re pretty unlikely to happen during any human’s lifespan,” he said.
The last big one was the Taupō Oruanui eruption. The Taupō Volcanic Zone also includes deposits from more than a dozen very large eruptions that happened within the past couple of million years.
Taupō’s alert level was raised to Volcanic Alert Level One on September 20, after some 700 earthquakes in the lake formed by the volcano’s caldera.
Then there was the 5.6 magnitude earthquake on November 30.
As recently as about 230 AD, the Taupō volcano ejected some 120 cubic kilometres of volcanic material into the atmosphere, the largest eruption in the past 5000 years, according to GeoNet.
Recent periods of volcanic unrest of the Taupō Volcano have been associated with earthquake swarms centred in the area of the Horomatangi Reef. From February to October 2022 during a period of volcanic unrest the reef had inflated upwards by a mean of 24 mm (0.94 in) relative to other reference points around Lake Taupō.
Since 1870, there have been 17 episodes of unrest in Taupō, including four that could have been classified as Alert Level Two, had the system existed, according to GeoNet. Although, none of those events caused an eruption.
Scientists consider there is a “very low” possibility of Taupō erupting, although they do not rule out an increase in activity.
How much warning would there be before an eruption? It varies from hundreds of thousands of years, to just one year.
The study suggesting only a year of advanced warning is based on the idea that before a super volcano erupts a huge amount of magma needs to build up. The build-up takes tens of thousands of years, said Guilherme Gualda, who authored the Nashville Tennessee Vanderbilt University study from July 2016.
“We have shown that the onset of the process of decompression, which releases the gas bubbles that power the eruption, starts less than a year before eruption,” he said.
The scientists studied microscopic quartz crystals in pumice taken from eastern California at the site of a super-eruption that formed the Long Valley Caldera 760,000 years ago.
The researchers analysed how long it took distinctive surface rims on the crystals to grow, a factor previous studies suggested were indicative of the lead time before a super volcano erupted. The new study determined more than 70% of the rim growth times were shorter than one year.
The study suggested intensifying signs of an impending supereruption would start to be felt within a year of eruption, but the scientists weren’t sure exactly what the signs at the surface would be.
Another study this time by the University of Illinois, suggested the trigger was tectonic stress.
“Traditionally, it is thought that eruptions occur when the pressure caused by hot magma overtakes the strength of a volcano’s roof rock,” said Professor Patricia Gregg said.
“But super volcanoes tend to occur in areas of significant tectonic stress, where plates are moving toward, past or away from each other. That plate motion will affect model calculations.”
She teamed up with graduate student Haley Cabaniss and fellow geology Professor Eric Grosfils to create a model of regional-scale tectonic stress based on the Taupō Volcanic Zone. They discovered that any type of tectonic stress impacts the stability of supervolcanoes.
“It does not matter if it is extensional, compressional or shear stress,” Haley Cabaniss said. “Any tectonic stress will help destabilise rock and trigger eruptions, just on slightly different timescales. The remarkable thing we found is that the timing seems to depend not only on tectonic stress, but also on whether magma is being actively supplied to the volcano.”
Even with different amounts of magma supply, stress, and tectonic plate movement – magma chambers remained stable for hundreds to thousands of years while new magma was being supplied to the reservoir.
“We were initially surprised by this very short timeframe of hundreds to thousands of years,” said Professor Gregg. “But it is important to realise supervolcanoes can lay dormant for a very long time, sometimes a million years or more. In other words, they may remain stable, doing almost nothing for 999,000 years, then start a period of rejuvenation leading to a large-scale eruption.
“When new magma starts to rejuvenate a supervolcano system, we can expect to see massive uplift, faulting and earthquake activity,” Patricia said. “Far greater than the meter-scale events we have seen in recent time. We are talking on the range of tens to hundreds of meters of uplift. Even then, our models predict that the system would inflate for hundreds to thousands of years before we witness catastrophic eruption.”
Whether New Zealanders get front row seats at the next Taupō eruption, the recent massive eruption of the Hunga Tonga–Hunga Ha‘apai volcano near Tonga in January 2022, is described as the volcanic equivalent of a ‘near miss’ asteroid whizzing by the Earth. The eruption was the largest since Mount Pinatubo in the Philippines in 1991, and the biggest explosion ever recorded by instruments.
Ash fell over hundreds of kilometres, affecting infrastructure, agriculture and fish stocks. The damage caused amounted to 18.5% of Tonga’s gross domestic product. Submarine cables were severed, cutting off Tonga’s communications with the outside world for several days; farther afield, the blast created a worldwide shockwave and tsunamis that reached Japanese and North and South American coastlines. The eruption lasted about 11 hours. Had it gone on for longer, released more ash and gas or occurred in more densely populated areas of southeast Asia, or near a high concentration of vital shipping lanes, electricity grids or other crucial global infrastructure, it would have had repercussions for supply chains, climate and food resources worldwide.
The Tongan eruption is regarded as a wake-up call.
Recent data from ice cores suggest that the probability of an eruption with a magnitude of 7 (10 or 100 times larger than Tonga) or greater this century is 1 in 62. Eruptions of this size have, in the past, caused abrupt climate change and the collapse of civilizations, and have been associated with the rise of pandemics.
Little investment has gone into limiting what an eruption of this magnitude could do. Impacts would cascade across transport, food, water, trade, energy, finance, and communication.
Using geological records and statistical techniques scientists found recurrence intervals of 1200 years for magnitude 7 and 17,000 years for magnitude 85 eruptions.
The last magnitude-7 event was in Tambora, Indonesia, in 1815. An estimated 100,000 people died as a result of volcanic flows, tsunamis, the deposition of heavy rocks and ash on crops and houses, and subsequent effects.
Global temperatures dropped about 1 °C on average, causing the ‘year without a summer’. The eastern United States and much of Europe endured mass crop failures, and the resulting famines led to violent uprisings and disease epidemics.
The global population is eight times larger now than in 1800, and the trade it relies on has grown more than 1000- fold since then. As the Covid pandemic and the war in Ukraine have shown, the modern world is highly dependent on global trade for food, fuel and resources; a disaster in one spot can cause price spikes and shortages far away.
