Exploring the big! volcano

Print Friendly

One of these days…

A field of volcanoes you have never heard of will wake up, and if it fulfills its geologic potential, the consequences will be heard around the world.


Calm curving water body surrounded by rocky, gravelly landscape.

The Why Files.
Placid, beautiful, mysterious: The Laguna del Maule caldera is all of these today. When will it wake up and reveal the molten rock that is driving one of the most active volcanoes on the planet?

Curiously, Laguna del Maule, situated along the spine of the Andes, doesn’t even look like a volcano. No towering peak, no plume of smoke or steam, no stench of sulfur. But 36 times in the past 20,000 years, volcanic vents surrounding the lake basin have created monster fields of lava — with huge deposits of volcanic glass, pumice and ash.

Once, almost a million years ago, this volcano field had an eruption that, if repeated, could change history by affecting air travel, agriculture and climate. Tantalizing scraps of lava indicate other enormous eruptions 1.5 million and 336,000 years ago.


Long, thin land mass protrudes from water, backdrop is mountainous and tan.

The Why Files
This peninsula, formed during a lava flow 24,000 years ago, is near the center of uplift today — and therefore likely a marker for a growing chamber of magma.

It’s a maxim of geology: What happened before can happen again.

The volcanic field is 20 kilometers in diameter, and the recent surge in attention is largely due to a widespread, 1.5 meter rise since 2007. “That’s phenomenal,” says Brad Singer, a professor of geoscience at the University of Wisconsin-Madison, who began studying this part of the Andes 20 years ago. “There is no other volcano in the world that is going up at this rate.”

The Why Files
Brad Singer explains the role of rock samples in understanding the volcanoes at Laguna del Maule.

Other causes for concern include swarms of earthquakes, horizontal spreading, spreading faults, and new detections of carbon dioxide gas that likely signal the enlargement of the underground magma pool that powers the volcano.

Eruptions can be ranked by estimating the volume of volcanic ash (mainly tiny shards of glass) they release. In 1980, Mt. St. Helens released about one cubic kilometer. In 1991, Pinatubo in the Philippines sent more than 10 cubic kilometers; its ash and sulfur gas injected into the upper atmosphere cooled the planet for two years.

About 950,000 years ago, an eruption at Laguna del Maule spewed dozens of cubic kilometers — perhaps more than 100. The eruption blanketed Argentina, downwind, with ash.

Based on data from Geological Society of London, 2005 and Gunder and Mahood, 1988. Graphs by The Why Files
The bigger the eruption, the less common it is. Laguna del Maule could go back to sleep, or (rollover) enter the history books as the largest eruption in recorded history.

Past is prologue

A 100 cubic-kilometer eruption could cause global cooling, and intense damage to agriculture could affect the entire globe.

Because the only people around Laguna del Maule are the horsemen who drive cattle in the summer, the immediate human impacts will be limited — unless giant flows of hot rock or debris reach Chilean cities. But dense ash-fall during the growing season could devastate agriculture in Argentina, to the east.

Just 50 kilometers north of Laguna del Maule, a similar volcanic field, called Calabozos, has had three super-eruptions in the past million years, spewing about 1,000 cubic kilometers of ash in total.

Those eruptions rank among the largest in a million years.

map of Satellite image of Chile with a zoomed portion show site of Laguna del Maule.

The Why Files
Laguna del Maule, a massive volcanic complex in Chile, could change the planet, with an eruption like three giants at nearby Calabozos. Maule could be returning to life. How dangerous is that?

The immediate cause of concern at Laguna del Maule comes from radar satellites and the global positioning system, which show that 1.5-meter rise in six years. The accelerating uplift is almost certainly due to new magma entering a pool located five kilometers underground.


cross-section of earth showing ocean tectonic plate sliding beneath continental plate, with eruptions further inland.

Volcano diagram from Shutterstock
Volcanoes are fed by molten rock, or magma, located deep underground. A weak spot in the crust allows magma to reach the surface, where the rocky products are called lava. In places like Laguna del Maule, silica-rich lava holds vast amounts of water. When pressure drops, this water flashes to steam; the rapid expansion of volume drives explosive eruptions.

In 2013, with support from the National Science Foundation, UW-Madison geoscientists began a field campaign to gather more basic data on Laguna del Maule.

“Our aim is to try to figure out if magma is actively intruding in the crust below the volcanic field,” says Singer, who worked at the site with U.S. Geological Survey expert Wes Hildreth, who started the first systematic mapping of the area in the 1980s. “We hypothesize that this is what is inflating the crust,” Singer says. “It’s like a balloon blowing up the surface.”

History, says Singer, is usually a good guide to the future. Laguna del Maule has “had at least three million years of pretty constant igneous [molten-rock] activity, and about every half million years it looks like a fairly substantial, caldera-forming eruption. Are we overdue for another?”

A caldera is a ring-shaped structure formed when by collapse when a giant pool of magma is vented to the surface.

Stupendous super-eruptions

Humans have seen the aftermath of super-eruptions, but never the eruption itself, which may disgorge a million tons of rock every second. If the past is a reliable guide, super-eruptions can change the planet.


Terraced fields drop down to a lake surrounded by mountains.

The caldera at Lake Toba, in Sumatra, Indonesia, formed during a stupendous super-eruption about 70,000 years ago. In its last eruption (so far!) the volcano released about 2,800 cubic kilometers of lava and ash!

The effects of “Rare but extremely large explosive supereruptions …will be felt globally or at least by a whole hemisphere,” wrote two scientists in 20081. The most widespread effects are likely to derive from the volcanic gases released, particularly sulfur gases that are converted into sulfuric acid aerosols in the stratosphere. These will remain for several years, promoting changes in atmospheric circulation and causing surface temperatures to fall dramatically in many regions, bringing about temporary reductions in light levels and producing severe and unseasonable weather (‘volcanic winter’). Major disruptions to global societal infrastructure can be expected for periods of months to years.”

The questions we ask

“Volcano” and “prediction” are not words that geologists like to join together, but the essential goal at Laguna del Maule is to understand the situation well enough to answer a simple question: How likely is an eruption that would be large enough to affect the region or the planet?

How much do we need to worry?

Singer hopes that the 2013 exploration of Laguna del Maule will soon be augmented with a wider variety of analytic techniques:

Dating techniques can tell when magma cooled at the surface, revealing the “pulse” of eruptions.

Mineral analysis can assess the physical conditions before previous eruptions, and suggest how changes in the magma trigger eruptions.

Seismology uses earthquakes and explosions to define the shape of underground structures.

Gas measurements offer clues about the type and volume of magma under the volcanic field.

Electrical and magnetic measurements outline the shape of a magma chamber.

Gravity meters can detect changes in the volume of magma at depth.

Eyeballs, a venerable tool of geology, can see faults, uplift and lava from past eruptions.

These techniques gain precision if their data are merged, Singer says. Many methods “can give a fuzzy picture of what’s down there, but the more techniques you can bring to bear, the more you can tighten up the boundaries between different materials” and so get a better picture of the magma and its potential routes to the surface.


Man holding camera touches black, glassy rock in younger woman’s hand; a man looks on.

The Why Files
Brad Singer (left) advises UW-Madison graduate students Nathan Andersen and Erin Birsic, as they hunt for rocks of a certain age for Birsic’s master’s thesis. She is focusing on remnants of a massive eruption from 950,000 years ago, but after millennia of erosion those rocks are scarce.

Need a date?

If you need a date, Singer is a good guy to know, at least if you want to date rocks. A specialist in geochronology, Singer uses sensitive instruments to squeeze out a date of formation for igneous rock, meaning when the rock solidified from cooling magma.

The overall goal at Maule is to tease out the timing of the many lava flows in the basin.

One dating technique relies on the radioactive decay of potassium into the gas argon, which follows a schedule set by the half-life of the isotope potassium-40.

Magma is hot, and any argon present will diffuse into the crust, but argon is trapped after magma cools into lava at earth’s surface. “Once it cools past a certain point, then argon stops diffusing, allowing argon produced from radioactive decay to build up,” says Nathan Andersen, a Ph.D. student in geoscience at Wisconsin who is dating recent lava flows at Maule.

Potassium-40 decays into argon-40, and so counting each isotope becomes the foundation for calculating the date of cooling.

However, potassium decays slowly, and this system has yet to date recent flows at Laguna del Maule, which are apparently younger than 2,000 years.

The eyeball on the highball

High-tech is eye-catching, but once you know what you are looking for, eyesight offers insight. Look at the large granite intrusions underneath Tatara San Pedro, a nearby volcano. The granite is apparently the remains of a magma chamber which cooled about 6 million years ago.

“It looks like a frozen magma body that is analogous to the magma body we think is active beneath Laguna del Maule today,” Singer says. Similar bodies of frozen magma have risen over 80 million years in California’s Sierra Nevadas. “But here, it’s now 2,500 meters above sea level. That’s 7,500 meters of uplift in 6 million years!”

The express elevator that is raising Laguna del Maule can be seen with the naked eye. White streaks on certain parts of the shoreline contain diatoms and ash that were deposited in the lake. “These are a sign that the uplift has been going on for many centuries,” Singer says.


Low mountain reflects in a glassy lake, with natural line visible across the slope.

The Why Files
Laguna del Maule was much larger 19,000 years ago; then the lake level dropped after a lava dam broke. Black arrows show traces of the old shoreline; blue arrows show a landslide that occurred since the sudden drop in lake level.

The lake bench, 200 meters above the existing lake, shows an old shoreline that, when formed, was as horizontal as the lake itself. Singer suspects that the profile of the bench carries a long-term record of uplift.

Faults, which show how adjacent sections of rock have moved against each other, are another eye-catcher. Last year, the Wisconsin scientists found new evidence of horizontal spreading and faults; these structures show earth movement, and could facilitate the rise of magma and an eruption.

Thou shalt know thy rocks


Laguna del Maule landscape.

The Why Files
The Laguna del Maule landscape is steadily changing. The white scrap of cooled magma (foreground) is the eroded remains of a massive lava flow. The rock originated as a pyroclastic flow; a fast-moving, red-hot material that cooled after being deposited, probably about 19,000 years ago.

If you know what you are looking at, small outcrops can play a large role in understanding the geologic history at Laguna del Maule. Analysis of the chemistry, minerals and texture of rocks can show that remote outcrops are remnants from a single eruption, or a single magma body. “When you start to see rhyolite on one side of the lake,” Singer adds, “and identical rhyolite on the other side, and you try to imagine how big the system must have been to produce both of those eruptions, that really grabs your attention.”

(Rhyolite, an uncommon type of magma that is rich in water and silica, and resistant to flow, is the most explosive and dangerous magma on the planet.)

Finding chemically similar lava over such a large area indicates that a large eruption is possible in the future.

Measuring the ground shaking

When the earth moves, the resulting vibrations convey clues about the planet’s internal structure. Both earthquakes and deliberate explosions can produce a “CAT scan of the crust,” based on how waves are transmitted, reflected, absorbed or converted into different waves, says Clifford Thurber, a seismologist at UW-Madison.

Earthquakes radiate P and S waves:

P, or “primary,” waves resemble sound waves, with zones of compression and decompression.

S, or “secondary,” waves, are a bit slower, and travel rather like a slithering snake.

In the first months of this year, seismographs at Laguna del Maule were “detecting repeated swarms of earthquakes, clusters that happen close together in time and space,” Thurber says. “Those are hallmarks of magmatically active volcanic systems, but they do not prove anything. On the other hand, if it were seismically silent, one would have to wonder if anything is going on.”


Building surrounded by fence has large crack in upper façade.

2013 photo, The Why Files
This building in Talca, Chile, was destroyed by the magnitude 8.8 Maule earthquake in 2010. This, the sixth-largest quake ever measured, killed 525 people.

After a swarm of earthquakes in March, 2013, scientists at the Chile’s Southern Andes volcano observatory issued a yellow alert, indicating that an eruption was possible in weeks or months.

Stronger and longer earthquake swarms and tremors are danger signs, Thurber says. “If we get sustained tremor, a low-level shaking that continues for hours to days, then we would get nervous. If we start to get very large earthquakes, 6 magnitude, it’s time to go.”

Thurber is introducing state-of-the-art computer analysis of seismic waves that will pinpoint arrival times more precisely. With improved earthquake locations, “We can do a better job of clarifying the structures that produce the earthquake,” Thurber says.

With a seismic expert on the line, we had to ask why the giant 2010 Maule earthquake did not trigger an eruption at nearby Laguna del Maule, just a few hundred kilometers the east of the epicenter. “It’s odd,” says Thurber. “This happens around the world. Sometimes a large earthquake triggers activity, and sometimes it does not. The volcano has to be ready.”

The Why Files
Glyn Williams-Jones explains the significance of carbon dioxide measurements at Laguna del Maule.

Gas attack!

Volcanoes can release staggering amounts of gas: Mt. Pinatubo coughed up an estimated 20 million tons of sulfur dioxide.

Carbon dioxide, a hallmark of basalt, is the big concern at Laguna del Maule, and
despite difficulties with two brand-new carbon dioxide meters, Glyn Williams-Jones, a volcanologist at Simon Fraser University in British Columbia, did find some elevated levels along the lakeshore in 2013.

“That means there is basalt entering the magma chamber from below,” says Williams-Jones.

Newly arrived, extremely hot basalt could interact with the existing rhyolite magma and boost the odds of eruption.

Woman bends over boxy white device with one eye hovering over eyepiece and other eye closed.

The Why Files
Helene Le Mevel, a graduate student, adjusts a meter that measures the local gravity field with astonishing precision. If significant amounts of magma are rising underground, gravity should be weaker in next year’s measurements — if the measurements are precise and accounts for the ongoing uplift of the area.

Electrical currents

To get a better sense of what’s happening under ground, geophysicists can measure electrical currents and magnetic fields inside Earth. “The surface is bathed by electromagnetic radiation from the sun, and there is an electrical response at depth,” says Singer.

The technique, called magnetotellurics, is used in geothermal energy exploration, and an energy company has already used it to find a shallow steam field just west of the caldera that could power a geothermal electric generator.

Magnetotellurics has already revealed that the crust around Laguna del Maule is about 40 kilometers thick, and that the magma body is about 5 kilometers below ground, Singer says. In the future, the technique could help define the size and location of melted crust near the magma chamber.

Gravely measuring gravity

Accurate measurements of gravity are another telltale about changes in the hot, molten magma. Because matter expands as it warms, magma is 10 percent less dense than surrounding rock, explains Basil Tikoff, a UW-Madison specialist in large-scale structure of the Earth, such as faults, old mountain belts and tectonic plates.

Gravity “does not have the resolution of other techniques, and it requires an enormous amount of fieldwork,” Tikoff says. “It’s a kind of geophysics that very few geophysicists do now.”

The Why Files
Basil Tikoff of UW-Madison explains the role of the gravity meter.

In March, Tikoff, graduate student Helene Le Mevel, and Williams-Jones installed 38 gravity stations on two lines crossing the center of uplift. The gravimeters are built around an ultra-precise spring that allows a suspended weight to respond to gravity. Although the meters are more than one-h century old, they are accurate to one part in 100 million. “If there is an earthquake, we have to turn the gravimeter off and wait,” says Tikoff. “If the land is going up and down, the gravimeter can see that, even if we can’t feel it.”

The pull of gravity decreases as  the instrument gets farther from the center of the Earth. “This instrument is so sensitive that if we went up a few stairs, you could tell,” Tikoff says. Therefore, Laguna del Maule’s pervasive uplift must be mathematically removed from subsequent measurements.

Baseline measurements taken in March and April will serve as reference points for subsequent surveys early in 2014. Located at the crest of the Andes, Laguna del Maule will be impassable until then due to its astonishing snowfall.

What comes next?

Laguna del Maule is a contradiction. To people who would be affected by a large eruption (which could include all of humanity in a super-eruption) it’s a threat.

But to geologists, it’s an opportunity to see how Earth is changing, and that is what draws Singer back. “The processes of deep Earth history are abstract,” Singer says. “I am more attracted to things that happen to the planet on a rapid time scale, such as glaciers and volcanoes. These take place on a human time scale.”

Three people on a tan beach with dark black rocks using tall yellow instrument, lake and mountains in background.

March, 2013, The Why Files
Gravimeters must be protected from vibration due to wind. Graduate student Tor Stetson-Lee blocks wind as Basil Tikoff measures gravity on the east shore of Laguna del Maule. That flying-saucer-on-a-stick is a GPS receiver able to measure altitude in millimeters.

The explanation for the new activity is pretty clear, Singer says. “There is no reason other than new magma to explain uplift of that size.”

The rapid uplift, combined with swarms of small earthquakes, apparent releases of carbon dioxide, and spreading of faults cannot go on forever. If they continue, the magma’s upward pressure will eventually exceed Earth’s ability to contain it.

Then Laguna del Maule erupts.

Until then, geoscientists see a chance to observe in real-time processes whose results can be seen all over the planet, and there is lots to be learned before the eruption, says Singer, who normally looks, forensic-style, after the eruption. “I try to reconstruct the history of magmas that feed the volcano, and how the processes inside the magma affect the way the volcano erupts, whether it’s explosive or passive. I try to stay away from them when they are erupting.”

Volcanoes usually emit a sequence of warnings, including a critical change in seismic signals, but nobody knows if Laguna del Maule will break the mold or follow it, adds Thurber, the seismologist. “We don’t have perspective. Studies that have been done on systems like this have exclusively been done after they have blown their top.”

Volcanoes are inherently unpredictable, especially the bizarre giants like Laguna del Maule, Thurber says. “We have no idea what the timeframe is to go from the rapid inflation we see now to an eruption. It could stop inflating and say ‘I’m done for now.’ It’s completely unpredictable; it could erupt tomorrow, next week, next year, next decade, next century. We don’t know for sure it is going to blow, but it sure as heck looks like it. If it erupts, the fact that a study had been done beforehand would be phenomenal, and unique in the world.”

— David J. Tenenbaum


Terry Devitt, editor; Emily Eggleston, project assistant; S.V. Medaris, designer/illustrator; David J. Tenenbaum, feature writer; Amy Toburen, content development executive


  1. Consequences of Explosive Supereruptions, Stephen Self and Stephen Blake, Elements, Vol. 4, 41–46
  2. Supervolcanoes and their explosive supereruptions, Calvin F. Miller and David A. Wark, Elements, Vol. 4, pp 11–16.
  3. Explore the United States volcanoes
  4. Oregon State University’s everything-you-want-to-know resource: Volcano World
  5. Keep an eye on volcanic activity in Hawaii
  6. National Geographic’s Volcanoes 101
  7. Laguna del Maule pops up on Wired’s science blog, Eruptions
  8. A Mexican volcano is waking up, too!