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News Article

Volcanoes and tree rings


Could tree rings be an early warning system for impending volcanic eruptions?

Early detection of possible volcanic activity is crucial for reducing the risk to populations and damage to infrastructure.  With the use of modern technology, once an eruption has begun, scientists are able to describe the seismic activity and surface deformation.  However, during the pre-eruptive phase, very little is known about how the magma moves under the Earth’s surface. A study, recently published in Scientific Reports, has found that tree rings could be considered as an early warning system for an impending eruption.

Geophysicist Nicolas Houlié, from ETH Zurich, first identified tree rings as a possible indicator of a volcanic eruption back in 2001.  He was looking at a satellite image of Mount Etna, when he noticed a long green line, three kilometres in length, on the north-eastern side of the volcano.  The line reflects the Normalised Difference Vegetation Index (NDVI).  The higher the value, the more vegetation is present and thriving in the area.  But what was remarkable about the discovery, was that the volcano erupted along that same line just one year later.

It is widely accepted by dendrochronologists that NDVI values are connected to tree growth and are also reflected in tree ring width.  Houlié teamed up with Ruedi Seiler, a geographer and PhD student at the Swiss Federal Institute for Forest, Snow and Landscape Research WSL and dendrologist Paolo Cherubini, Head of Dendrochonology at WSL, to conduct a cross-disciplinary research project that examined the information provided by tree rings, about volcanic processes prior to their eruption.

Tree rings provide valuable environmental information as the ring width reflects the growth conditions of the tree and is based on a combination of nutrient conditions, precipitation and temperature during a growing season. Regarding the relationship between tree rings and volcanic eruptions, Seiler predicts that “the ring width may also be influenced by volcanic activity on Mount Etna and in other volcanic regions.”

The team conducted their research alongside the lava flows that had ran down Mount Etna’s western flank in January 1974.  This was the site where Italian researchers also spotted an anomaly on satellite images in 1973, prior to the eruption.

Over fifty tree samples were collected, to identify any pre-eruptive signals in the tree rings.  However, they found that there were neither exceptionally wide nor exceptionally narrow tree rings for summer 1973.

“If volcanic activity does influence tree rings, then the pre-eruptive phase of the 1974 eruption can only have begun when the trees had already ceased their seasonal growth,” said Seiler.  However, the duration of the pre-eruptive period, which in this instance is just a few months, is consistent with the results of earlier geochemical and geophysical studies.

While there were no changes to the trees growth before the 1974 eruption, the study suggests that the trees grew less over the two summers after the eruption than in other years.

“I see great potential in this observation: we may be able to use tree rings to reliably date minor flank eruptions,” said Houlié.  This is significant because the past behaviour of a volcano can provide information about its activities in future and therefore contribute to improving measures to protect the population.

Volcanic eruptions from the last 20 years have been well-documented using real-time monitoring with GPS, seismometers and gas monitoring devices.  However, volcanic events that occurred in the 2,000 years before that cannot be dated reliably, while even older eruptions can be dated fairly accurately using the C14 method.  Houlié states that “tree ring data could help to close the information gap for the period stretching from 20 to 2,000 years ago.”

The researchers are hoping to continue their investigations to better understand how tree rings may be used for predicting volcanic eruptions.

Further information on tree rings and volcanoes is available to subscribers of the Forest Science database.  For example, by using the search string “growth rings” AND volcanoes yields 41 results, while trees AND "volcanic activity" returns 148 records. 

Journal reference

Ruedi Seiler, Nicolas Houlié, Paolo Cherubini. Tree-ring width reveals the preparation of the 1974 Mt. Etna eruptionScientific Reports, 2017; 7: 44019 DOI: 10.1038/srep44019

Article details

  • Author(s)
  • Stephanie Cole
  • Date
  • 12 April 2017
  • Source
  • Swiss Federal Institute for Forest, Snow and Lands
  • Subject(s)
  • Dendrochronology