Volcanoes that appear to be benign can be much more violent than previously feared due to volatile magma hidden deep below the surface, a study shows.
Scientists studied volcanoes on remote islands in the Galápagos Archipelago in the Pacific Ocean off the coast of Ecuador.
Volcanoes that reliably produce small lava eruptions of basalt, an igneous rock, hide chemically diverse magmas in their underground plumbing systems, they found.
This includes some that have the potential to generate ‘explosive activity’ and could pose an unexpected safety risk for local authorities in the future.
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The 2015 eruption at Wolf volcano in the Galapagos Archipelago – an ideal location for studying monotonous volcanism
Researchers studied two Galápagos volcanoes – Wolf and Fernandina – which have erupted basaltic lava flows at the Earth’s surface for their entire lifetimes
‘This was really unexpected,’ said lead author of the study Dr Michael Stock of Trinity College Dublin.
‘We started the study wanting to know why these volcanoes were so boring and what process caused the erupted lava compositions to remain constant over long timescales.
‘Instead we found they aren’t boring at all – they just hide these secret magmas under the ground.’
Many volcanoes produce similar types of eruption over millions of years and aren’t known for life-threatening activity.
For example, volcanoes in Iceland, Hawaii and the Galápagos Islands consistently erupt lava flows – comprised of molten basaltic rock – which form long rivers of fire down their flanks.
a) Map of the Galápagos Archipelago showing the different volcanic centres. Boxes show the locations of maps (b) and (c). b) Detailed map of Wolf volcano showing the 2015 lava flow extent is in red. The sampling locations of the lavas and tephra analysed in this study are shown as green circles and blue diamonds, respectively. c) Detailed map of Fernandina showing the extent of the pyroclastic flow (dashed line) – a fast-moving current of hot gas and volcanic matter
Although these lava flows are potentially damaging to houses close to the volcano, they generally move at ‘a walking pace’, the team say.
Such magmatic systems show ‘monotonous volcanic behaviour’, erupting chemically homogeneous liquids over long timescales, spanning several decades to millennia.
They also do not pose the same risk to life as larger explosive eruptions, like those at Vesuvius in Italy, famous for the obliteration of the ancient city of Pompeii in AD 79, or Mount St. Helens in Washington State, US.
Pictured is a shot of Mount Vesuvius from 2008 as it lays dormant. Vesuvius in Italy is famous for the obliteration of the ancient city of Pompeii in AD 79
FATAL VOLCANIC ERUPTIONS
The worst volcanic tragedy on record happened in 1815 when Mount Tambora in Indonesia. It killed over 90,000 people.
Then came Mount Krakatoa in 1883, also in Indonesia. It claimed over 35,000 lives, mainly due to resulting tsunamis.
The worst of the 20th century is considered to be Mount Pelee in 1902 on Martinique in the Caribbean, killing around 30,000.
Mount Ruiz in Columbia erupted twice in 1985. A mixture of mud, ash and water raced down the volcano’s slope through river channels.
It almost totally buried a town 30 miles away – killing an estimated 25,000.
Mount Vesuvius in Italy devastated the nearby cities of Pompeii and Herculaneum when it erupted in AD 79. Thousands died, with some remains preserved by the ash.
A long-term consistency in a volcano’s eruptive behaviour informs hazard planning by local authorities and helps prepare residents for emergencies.
However, a solid safety record doesn’t completely rule out future dangerous activity, they found.
The western Galápagos Archipelago is an ideal location for studying monotonous volcanism, the researchers claim, because it hosts several volcanoes that have erupted near-homogeneous basaltic magmas for several thousands of years.
Researchers studied two Galápagos volcanoes – Wolf and Fernandina – which have erupted basaltic lava flows at the Earth’s surface for their entire lifetimes.
The samples used in this study include basaltic lava and tephra from an eruption of Wolf in 2015 and samples of an igneous rock called gabbro from the eruption of Fernandina in 1968.
By deciphering the compositions of microscopic crystals in the lavas, the team could reconstruct the chemical and physical characteristics of magmas stored underground beneath the volcanoes.
Records of deep volcanic processes preserved in the structure and chemistry of crystals erupted from the two volcanoes revealed more.
‘The most important aspect of this research is how detailed studies of even a few erupted crystals can reveal much greater complexity in the plumbing systems beneath active volcanoes than we would have otherwise imagined,’ said Dr David Neave at the University of Manchester.
‘[This means] some seemingly gentle volcanoes may be capable of more dramatic changes in behaviour than we previously thought.” said Dr Neave.
Magmas beneath the two volcanoes are ‘extremely diverse’ and include compositions similar to those erupted at Mount St. Helens, which notoriously killed nearly 60 people and destroyed 250 homes in 1980.
The team collects samples from solidified lava flows on Wolf volcano with assistance from a Galápagos National Park ranger
Usually, explosive volcanoes only erupt consistently due to enough magma flushing beneath the edifice.
This occurs when they are located close to a ‘hot spot’ – a plume of magma rising towards the surface from deep within the Earth.
However, chemically diverse magmas could become mobile and ascend towards the surface under certain circumstances.
In this case, volcanoes that have reliably produced basaltic lava eruptions for millennia might undergo unexpected changes to more explosive activity in the future.
‘Although there’s no sign that these Galápagos volcanoes will undergo a transition in eruption style any time soon, our results show why other volcanoes might have changed their eruptive behaviour in the past,’ said Dr Stock.
‘The study will also help us to better understand the risks posed by volcanoes in other parts of the world – just because they’ve always erupted a particular way in the past doesn’t mean you can rely on them to continue doing the same thing indefinitely into the future.’
The study has been published in Nature Communications.
HOW CAN RESEARCHERS PREDICT VOLCANIC ERUPTIONS?
According to Eric Dunham, an associate professor of Stanford University’s School of Earth, energy and Environmental Sciences, ‘Volcanoes are complicated and there is currently no universally applicable means of predicting eruption. In all likelihood, there never will be.’
However, there are indicators of increased volcanic activity, which researchers can use to help predict volcanic eruptions.
Researchers can track indicators such as:
- Volcanic infrasound: When the lava lake rises up in the crater of an open vent volcano, a sign of a potential eruption, the pitch or frequency of the sounds generated by the magma tends to increase.
- Seismic activity: Ahead of an eruption, seismic activity in the form of small earthquakes and tremors almost always increases as magma moves through the volcano’s ‘plumbing system’.
- Gas emissions: As magma nears the surface and pressure decreases, gases escape. Sulfur dioxide is one of the main components of volcanic gases, and increasing amounts of it are a sign of increasing amounts of magma near the surface of a volcano.
- Ground deformation: Changes to a volcano’s ground surface (volcano deformation) appear as swelling, sinking, or cracking, which can be caused by magma, gas, or other fluids (usually water) moving underground or by movements in the Earth’s crust due to motion along fault lines. Swelling of a volcano cans signal that magma has accumulated near the surface.
Source: United States Geological Survey