Featured in Kilauea: Mountain of Fire, Milton Garces records infrasound in order to better understand what’s happening in Kilauea’s underground lava tubes. NATURE spoke with him in March 2009.

Q: Tell us a bit about ISLA, the Infrasound Laboratory, and its mission.

A: We are located on the western tip of the Big Island of Hawaii. The lab’s main function is to operate listening stations as part of the International Monitoring System of the Comprehensive Nuclear-Test-Ban Treaty. Beyond that we conduct research on volcanoes, ocean waves, storms, and have recently deployed a hydroacoustic station.

Can you give a brief description of what causes infrasonic tremor and where the infrasound is physically emitting from?

Numerous sources at Kilauea could be producing the tremor. As the magma rises to the surface, pressurized gas comes out of the magma. The release of this gas causes pressure fluctuations, or infrasound. Anywhere pressurized gas is being released is a possible source of infrasound. Halemaumau is currently the loudest source of infrasonic tremor at Kilauea. Gas bubbles, both large and small, are involved in producing the sound at Kilauea. They can even excite large underground cavities into resonance, just like blowing over a beverage bottle or ringing a bell.

How long have you been listening to Kilauea?

ISLA’s first deployment was in 2002. Since then we have had continuous recordings using numerous stations since 2006.

Has anyone else done this before—recorded the infrasounds of lava flow?

Volcano infrasound research actually began with the eruption of Krakatoa in 1883. However, the past 20 years has seen the majority of volcano infrasound studies. Numerous volcanoes all over the world have been found to produce a significant amount of infrasound. Kilauea, however, has its own unique voice and we have captured a wide variety of signals from it, from tremor, explosions, lava skylights, fissure eruptions, and bench collapses.

Humans can’t hear the sounds coming from the volcano because they are at such a low frequency, but are there any organisms you know of that can detect Kilauea’s infrasound waves?

I know many animals communicate and hear infrasound (such as elephants), but am not aware of any organisms on Hawaii that would be able to hear infrasound from Kilauea. With that said, the higher frequency audible sounds would be heard by many.

Milton Garces listens to infrasonic recordings on a computer

What do you think the future applications of volcanic infrasound research may be?

I think the continued integration of infrasound with other technologies (such as seismic and satellite observations) will greatly help us understand and monitor volcanoes in the future. For example, we have a project in Ecuador right now where we are using infrasound and satellite observations to identify ash-rich volcanic eruptions, in hopes of providing early warning to aircraft operations in the region.

Can infrasound research be used to predict future eruptions?

Rather than focus on prediction, infrasound can tell us what is going on at the volcano right now and whether an eruption is occurring at that moment. Volcanoes are such complex systems that prediction is difficult. Gaining a more complete understanding of what is happening right now and what has happened before probably gives us the best chance for mitigating hazards.

What was your process of setting the microphones and what problems if any did you encounter as you did so?

First we had to select a good location — this is key to obtain good infrasound recordings. The dense jungle forest around Kilauea provides a great location as it shelters us from the wind. Then we needed to find a way to send our data back to our lab in Kona in real-time. From there the installation of the microphones is fairly simple, as we have a set design for our portable deployments. Luckily we have had no major equipment or data problems. Part of this can be attributed to the fact that we are able to record from long distances. Placing microphones next to active volcanoes often increases the likelihood of them being destroyed by the volcano, which is a main reason why we prefer to record from five to ten miles away.

What can infrasound measurements tell us that seismic data cannot?

Seismic data can tell us about magma moving underground, while infrasound is produced when there is pressure released at the surface. This way infrasound can help distinguish between subsurface and surface activity. Lots of seismic activity does not necessarily translate to lava or gas at the surface, but infrasound does. Also we often put out an array of microphones, kind of like an antenna, to determine what direction the sound is coming from.

Does Pele ever stop chanting? Will she ever?

Pele takes short breaks now and again, but she has remained active. Even if she were to take a break at Kilauea, it is likely that she would begin again in the relatively short future. Also, don’t forget Mauna Loa volcano is right next to Kilauea and has erupted numerous times in recent history, and when it does, we will be ready to record its unique voice.

AUDIO

Listen to the recordings (will open in a new browser window):

• Spattering Vent at Pu’u O’o in June 2007
• Collapse and Shutdown of Pu’u O’o in June 2007
• Opening of the Halemaumau Gas Vent in March 2008

Go to the ISLA Web site for more information.

Animals and Earthquakes
http://animalsandearthquakes.com
Learn more about scientific studies on animal behavior preceding earthquakes. Read interviews with James Berkland and Motoji Ikeya, both featured in the film.

Infrasound
http://en.wikipedia.org/wiki/Infrasound
Get the lowdown on low sounds from Wikipedia.

Fauna Communications
http://www.animalvoice.com/
Learn more about Liz von Muggenthaler’s studies on animal commmunication.

Elephant Rumbles
http://www.pbs.org/saf/1308/segments/1308-2.htm
Caitlin O’Connell-Rodwell, featured in the film, tests an elephant’s ability to “hear” with her feet.

Four Ears to the Ground
http://www.findarticles.com/p/articles/mi_m1134/is_3_111/ai_84545901
Explore elephants’ abilities to “hear” and communicate with infrasound.

Hippos and Infrasound
http://acp.eugraph.com/elephetc/hippo.html
Learn how hippos communicate above and below water via infrasound.

Indonesian Tsunami Infrasound
http://www.aip.org/149th/garces.html
Listen to the infrasound generated by 2004’s Indian Ocean earthquake and tsunami.

Can Animals Sense Earthquakes?
http://news.nationalgeographic.com/news/2003/11/1111_031111_earthquakeanimals.html
The belief that animals can predict earthquakes has been around for centuries.

Shark’s Sixth Sense
http://www.findarticles.com/p/articles/mi_m0BQK/is_3_10/ai_n13778822
Find out more about shark behavior prior to Hurricane Charley in August 2004.

Books:

Hickman, Pamela. ANIMAL SENSES: HOW ANIMALS SEE, HEAR, TASTE, SMELL AND FEEL. Minneapolis: Kids Can Press, 1999.

Hough, Susan Elizabeth. EARTHSHAKING SCIENCE: WHAT WE KNOW (AND DON’T KNOW) ABOUT EARTHQUAKES. Princeton: Princeton University Press, 2004.

Ikeya, Motoji. EARTHQUAKES AND ANIMALS: FROM FOLK LEGENDS TO SCIENCE. Osaka: Osaka University, 2004.

Kaner, Etta. ANIMAL TALK: HOW ANIMALS COMMUNICATE THROUGH SIGHT, SOUND AND SMELL. Minneapolis: Kids Can Press, 2002.

O’Connell, Caitlin. THE ELEPHANT’S SECRET SENSE: THE HIDDEN LIFE OF THE WILD HERDS OF AFRICA. New York: Simon & Schuster, 2007.

Tibballs, Geoff. TSUNAMI: THE MOST TERRIFYING DISASTER. New York: Carlton Books, 2005.

Turner, Matt. ASIAN ELEPHANTS (ANIMALS UNDER THREAT). New York: Heinemann Library, 2005.

Sunrise, December 26, 2004.

Wit Aniwat, whose family runs an elephant camp for tourists in Thailand, was awakened by an unusual alarm clock: the trumpeting and wailing of elephants.

It was a bit out of the ordinary, but Wit thought nothing of it as the sun rose. There was work to do.

Five minutes later, another oddity. “The elephants became very agitated,” Wit recalls in NATURE’s Can Animals Predict Disaster? Astonished, he watched as the huge animals broke their chains and stampeded up a nearby hill. He and another trainer gave chase. But they hadn’t gotten very far when a terrifying sound overtook them: the sound of a towering wave of water crashing ashore and overwhelming everything in its path.

Luckily, Wit survived the tsunami. More than 200,000 other people around the Indian Ocean weren’t so lucky.

The elephants? They were fine too. Wit and many others believe it’s because they knew the wave was coming. And scientists say there’s a possibility that Wit is right. That’s because elephants are among a handful of animals known to be able to hear “infrasound,” the extremely low-frequency rumbles that are produced by natural phenomena from earthquakes and volcanoes to heavy winds and avalanches.

In fact, studies have shown that they use infrasound — which can travel vast distances through the ground, air, and water — to carry on long-distance conversations. Researchers have homed in on these “invisible” communications in just the last few decades, as sophisticated microphones and recording equipment allowed them to listen in.

Now, infrasound researchers wonder whether some animals can hear danger approaching. For instance, big storms such as hurricanes produce their own distinctive infrasonic signature. Similarly, earthquakes can produce several distinct infrasound pulses that can travel thousands of miles and much faster than water. Thus, tsunamis, also triggered by earthquakes, hit the shores only after infrasound.

In Thailand, it’s possible that Wit’s elephants picked up these signals before the wave hit, prompting them to trumpet their fear and then flee. But we may never know for sure. Elephants carrying radio tags in the region may have offered important insight. Unfortunately, researchers lost contact with the tagged elephants eight hours prior to the tsunami. When they regained transmission an hour after the tsunami hit, they found the elephants in the same vicinity as they were prior to the tsunami — just a few hundred feet from the shore. It is impossible to know exactly what happened while the transmitters were down.

Studies in zoos show that even animals known to hear infrasound don’t necessarily become agitated when they hear the signals. But researchers also note that the animals in zoos are so frequently subjected to infrasound, from their urban setting, that they may be desensitized. Scientists say carrying out experiments in the wild that might settle the matter once and for all would be very difficult and expensive.

But researchers are learning more about infrasound through other kinds of studies. Alligator researchers, for instance, are cracking the code that these huge reptiles use to signal their mates. Among other things, they’ve learned that alligators can produce an array of infrasonic signals by vibrating air inside special sound-producing sacs in their chins.

Other researchers are studying the idea that infrasonic sound can produce emotions in people. To test this, they asked people at a concert to rate their emotional responses to several pieces of music, some of which had been secretly “spiced” with infrasonic noises. More than a quarter of the listeners reported that the infrasonic melodies produced “ghostly” feelings of anxiety, uneasiness, sorrow, fear, and chills down the spine. Infrasonic sound can also make people nauseous and sick.

Those physical and emotional reactions may explain why horror movies used to feature scary, low-pitched organ music, the researchers say. And perhaps why animals too get scared when they hear a mysterious, infrasonic pulse.

For centuries, biologists believed giraffes were the mute giants of Africa’s plains and forests — silent sentinels gazing to the horizon. In recent years, however, new techniques and technologies have allowed scientists to listen more carefully — and realize that giraffes may be talking after all. Just not in a way that we can hear.

Over the last few decades, biologists using special microphones, recording equipment, and computer analysis programs have realized that whales, elephants, and some other animals were using extremely low-frequency sounds — far below the range of human ears — to communicate.

These low-pitched sounds are known as “infrasound,” and they have at least one remarkable property: they can travel farther than higher-pitched noises through the air and earth. Such long-distance communication is a must for animals, such as giraffes or elephants, that can be spread over vast territories. Elephants, for instance, may be able to communicate with other animals up to several miles away.

Studying infrasound, however, is difficult. In part, that’s because so many things produce infrasound, from rumbling earthquakes and thunder storms to trains and cars. Sorting out wild sounds from the background noise can be nearly impossible. But by doing studies in zoos, where researchers can partly control experiments, scientists have been able to document the existence of infrasound and show that animals appear to be using it to communicate.

TALL BLONDES documents the work of one of these sound scientists. In 1998, Elizabeth von Muggenthaler of the Fauna Communications Research Institute in North Carolina and a group of colleagues announced that they had found evidence that giraffes use infrasound to communicate. In part, Muggenthaler had taken on the study — done on 11 giraffes at 2 zoos in North and South Carolina — because she had studied the use of infrasound by the Okapi, a relative of the giraffe. It would be natural, she thought, for the giraffe, which shares many behaviors with the Okapi, to also share the use of low sounds.

In their zoo study, the researchers noticed that the low sounds picked up by their microphones seemed to coincide with two behaviors: the “neck stretch,” where giraffes throw their head and necks back over their bodies; and the “head throw,” in which the animals lower and then quickly raise their chins. How exactly giraffes make the low, huffing noises is unclear, however. The researchers think the answer lies in studying how air moves through the giraffe’s long neck.

In a recent interview, Muggenthaler discussed her work trying to listen to the unhearable:

NATURE: Sounds like you’ve got a tough job.

Elizabeth von Muggenthaler: It is a such a hard thing to do. You can’t hear infrasound, so you are relying totally on your microphones and computerized analysis systems to detect it. Then, there are so many other things that create infrasound — from water and wind to cars and trains — that you have to be able to eliminate what you don’t want. The environment has to be very good where you are recording. It’s hard to do in the field.

NATURE: What tipped you off that giraffes might be using infrasound?

EVM: Well, here is an animal that is very social, they hide in forests [making visual communication difficult], and they hide their young during the day while foraging. They are hunted by other animals. But they were considered mute. Right there is your clue — there are no animals [that have such behaviors] that are mute. They wouldn’t survive if they couldn’t communicate.

Also, if you look at giraffes’ ears, you know something is going on. Their ears are like parabolas and they have [features] that suggest they can tune in on sounds.

NATURE: What would it take to study the giraffe’s use of infrasound in the wild?

EVM: Well, you would really need an array of microphones, so you’d be able to detect if it’s the giraffe or not. It would be a very expensive study.

NATURE: How did you get interested in infrasound?

EVM: It’s just that we humans are so limited. I knew I wanted to study animal communication [in college] and I liked the elephant [infrasound] studies [that other scientists had done]. So I tried to replicate that and ended up at NASA, renting equipment. It was while I was recording the elephants that I got the rhinos. [Editor's note: In 1992, Muggenthaler documented the use of infrasound by rhinos.] It’s just that there is this world of crazy stuff going on with sound. There is this unseen world out there, and I want people to know it exists.