Sunday, February 16, 2020

Studying an Active Volcano

Under the Volcano

Photography by Sallie G. Sprague
Text by Sallie Sprague and Stuart J. Shiffman

Ten days in the shadow of an active volcano give volunteer researchers a lens of nature's awesome power and its ultimate fragility.

Deadwood frames two researchers
below the Arenal Volcano. The daily
"ash trail" followed the gully up to
the south lava flow seen in the
Imagine going to a foreign country and spending ten days hiking in humid rain forests and baking deserts, in the shadow of an active volcano. Back at camp at the end of each day, you take an icy shower to rid yourself of the volcanic ash and insects cemented to your skin under a layer of sunscreen and bug repellent. At three in the morning, you get out of bed and stumble in the dark to an observation platform, from which, with luck, you might be able to see the volcano. There, listening to howler monkeys, coatimundi and dozens of varieties of birds, you wait for the volcano to erupt.

This is fun. Trust us.

Arenal at rest, showing the
current and former craters.
Near the village of La Fortuna in Costa Rica, 75 miles from the capital city of San Jose, there is a macadamia nut plantation that hosts an observatory facing the slopes of the Arenal volcano. This remote outpost is operated by the Smithsonian Institution as a base from which scientists and volunteers work, collecting samples of what the volcano spews out, recording data on eruptions, and studying the effects of the volcano on the delicate ecology of the rain forest.

A huge plume of ash
and smoke mark a
daytime eruptions of
Arenal is one of very few active, explosive volcanoes in the world, and has been more or less continuously active for the past 25 years. Until 1968, Arenal was a popular tourist attraction in Costa Rica. Troops of Boy Scouts, and packs of howler monkeys, held picnics on its slopes. It supported a lush, fertile pre-montane dry forest for 800 years, and was generally thought to be extinct.

But that year, after several days of largely-ignored earthquakes, Arenal exploded in a Plinean eruption (so named after the explosion of Vesuvius that destroyed the ancient Roman city of Pompeii, as described by the historian Pliny the Elder). The eruption created a new crater several hundred meters below the peak, and killed about 70 farmers and rescue workers who were caught in the deluge of rocks, ash and hot mud. Within days, a scientific team from the Smithsonian and the Universidad de Costa Rica arrived at the site to study the eruption and its impact on the countryside, and, perhaps more importantly, to help determine the likelihood of continued explosive activity.

Daily collection of
ash samples in the
devastated zone took
researchers from
tropical forest to near
barren areas struggling
under acid rain.
Since then, under the guidance of volcanologist William Melson and botanist Victoria Funk, both of whom are staff scientists with the National Museum of Natural History, the Smithsonian has been sending research teams, recruited from the ranks of Smithsonian Associates, to observe the volcano. The research teams are diverse in their backgrounds and training, but share a fascination with volcanoes.

Standing at a remote observation post in the middle of the zone devastated by the 1968 eruption (and several major events in the 1970's), you feel you might as well be on Mars. The area is strewn with rocks the size of small houses, thrown out by the force of the major eruptions. Fumaroles, or volcanic vents, belch hot gases from the rocks several hundred feet above you. Broad gullies run down to the shore of a nearby lake, formed by 20 years of heavy rainfall and erosion after the death of the forest. It is clearly inadvisable, not to mention extremely difficult, to climb the glass-sharp boulders and loose lava to the active crater looming only a couple of thousand feet above the observation post. And in fact, climbing the mountain was prohibited several years ago, when a visiting college student actually succeeded in reaching the rim of the crater just in time for the next eruption to kill him.

The sandy soil below the volcano has minimal nutrients, and is extremely acidic due to the acid rain that results from the hydrogen sulfide and halide gases issuing from the crater. Little grows here only island of sparse vegetation supported by decaying hulks of trees toppled in the initial eruption. Tough grasses and short, scrubby blueberry bushes present a vivid contrast to the lush green tropical forests that cover the surrounding hillsides. Indeed the climate in the devastated zone is more like that of southern California than that of the nearby forests. Except that in southern California there are cactus and sagebrush to invade the empty land. Here, there is nothing in the local ecosystem that will tolerate such harsh conditions, and so nothing to colonize or re-vegetate the devastated area.

Nearby is Lake Arenal, a reservoir created during the '70's by the construction of an earthworks dam. The dam supplies a major portion of the power used in the capital city. The shores of the lake are worn away by the erosive action of the years of wind and rains, and their exposed layers of soil attest to eight earlier Plinean eruptions of Arenal, over the course of about 3,700 years. Lying embedded in the beach, in muddy soil laid down 2,000 years ago, are fragments of colorful pre-Columbian pottery.

Both the old and new craters of Arenal are part of a line of volcanic activity moving slowly westward toward the Pacific Ocean. The tectonic movements of three plates colliding in the Earth's crust are believed to cause this activity. As one plate moves under another, bending an edge down into the Earth's magma layer, magma forces its way up through the two overlapping layers. The magma scours chunks of rock from the walls of the shaft, which are churned and partially melted into lava.

Until 1968, Arenal had only a single peak. But the eruption that year blew a gaping hole in the western flank of the mountain. In the next few years, the active crater moved up the flank of the old mountain so that now Arenal has two adjacent craters, joined by a saddle. The old crater sits belching gases sedately into the atmosphere. The new crater to the west is the one still sending boulders and gases high into the air. In 10,000 years, scientists predict, the line of volcanic activity will move westward and open a new shaft under the dam that forms the lake. But for the time being, the lake is safe.

Our research team was composed of a mother of two teenage boys, a retired Bell Telephone Company employee, a jeweler, a physician, a mathematician/computer programmer, an electronics technician, a freehand photographer and a civil servant. All were volunteers, willing to contribute their time and energy to a project aimed at someday, perhaps, being able to predict something about volcanic eruptions. We were also something else: students of the world around us, observing, concerned with the fate of our planet.

We gathered on a sweltering evening at a hotel in San Jose, not knowing which of the other guests were also going on this venture. At breakfast we picked out the not-very-discrete yellow and blue Smithsonian name tags and sized up our companions. In a flurry of hellos and tossed luggage, we left the city in the early morning. It was Sunday, April Fool's Day, 1990, and we were headed north, toward Nicaragua. Several hours of driving on tortuous roads brought us over the Continental Divide, where the heat and humidity of the city vanished for a time, like a dream. Several more hours brought us back down to the hot and humid plantation country, and finally to the observatory, nestled in a forest of long-needle pines. (The pines were imported for the local timber industry. This confused most of us because Costa Rica's forests, and tropical rain forests in general, are home to an immense variety of hardwoods, highly prized in the United States. In Costa Rica, mahogany makes the roughest furniture, or firewood, or rots in scrap heaps by the road. And the timber industry wants softwoods.)

Like a flock of kids in a new playground, we all had to inspect every aspect of our new locale. The observatory platform was high on our lists and soon had drawn most members of the group. We had our first, brief instructions in monitoring methods - instructions which were promptly interrupted by a large eruption. Huge clouds of ash billowed skyward as the "Kaboom!" reached us. (There was about a seven-second delay because we were two miles from the crater.) We had seen our first eruption; we hadn't traveled all this way to be disappointed by ten days of silence from Arenal.

After this auspicious beginning, we settled down to a pattern of three-hour shifts on the observatory deck, stop watches in hand, waiting. The eruptions were graded on the basis of size of plume, the amount of debris falling on the cone, and by a subjective assessment of the sound level, on a scale from 1-10. (Ten was strictly forbidden as by definition an eruption of that magnitude would have destroyed the observatory. A five made you jump. Seven and up rattled the roof, and the glass in the windows. We had several eights during our stay.)

Ash collection vials
were attached to tree
branches where the
tropical forest met the
devastated zone.
Surveyor's flagging
tape on nearby
branches, deadwood
or rocks enabled the
researchers to find the
vials each day.
This schedule continued for ten days, each day seeming like the one before. Time faded; offices and the calendar were forgotten. All that existed was the volcano. Each morning a four-member team would go out into the devastated zone. Two people would follow a trail through the rain forest and the desert, collecting samples of ash and acid rain from small bottles left out the previous day. The other two would go to a tiny shack on the slope of the volcano itself, amid giant boulders thrown out over the past 20 years, and wait for an eruption to send a cloud of ash overhead. They would collect all the ash that fell on a square meter of plastic which was spread out each day in anticipation.

We were lucky with the weather. Except for a few ominous-looking clouds that rolled in sporadically and that once dumped in an hour what seemed like the combined contents of the world's oceans, the sky was clear and blue, offering a superb view of the cone. Eruptions, and the time between them, varied widely, from a nervous and anticipatory several hours before a major explosion (which is scientifically referred to at the outpost as a "kaboom"), to scant minutes between minor rock slides or motions of the hot lava flow. We were fortunate enough to observe the formation of a new lava flow one clear night. Other events included tiny almost soundless whispers preceded by great gray clouds of ash, and a loud, chugging noise, like the passing of an ancient freight train, unheralded by any plume.

Pre-dawn eruption of the Arenal
volcano viewed from the
observation platform.
In the course of our stay at Arenal, we not only learned about volcanoes and geologic history, but also about ourselves. Limits were tested: Walking six to eight miles in the hot sun is not an everyday pastime for most of us; neither is sharing a 15-foot by 12-foot bunk room with several others; and neither is maintaining a sense of humor when you're either going to bed or getting up at 3 a.m. ... or one of your roommates is. We all stretched to adapt to the intense living situation, the stress of a volcano in the front yard, and the challenge of living in a new culture. Only two of the group had any facility with Spanish. The rest of us struggled, asking for extra blankets or milk for our coffee with all the eloquence of two-year-olds. (The experience made more real for us the difficulties that must be faced - and overcome - by people who come to live in the United States without being able to speak English.) By the time we left, a small eruption would elicit, "Oh, it's only a three" (in reference to the sound scale). We could also laugh knowingly at the folly of the "novice" tourists (as opposed to the several-day veterans we had now become) who thought they could climb to the crater in a few hours, clad only in shorts, T-shirts and tennis shoes.

The April, 1990, research
team on the observation deck.
The volcano is shrouded in
clouds behind them.
We also learned about parallels between the area surrounding the volcano and our own "civilized" world. The acid rain that results from Arenal's gaseous emissions wreak havoc on the delicate rain forest ecology. Acid rain in North America, resulting from the emissions of factories, power plants and automobiles, is different only in degree: It's not as intense yet. Our own pine forests are not as sterile yet as the devastated zone near Arenal, but at the present rate of deterioration, they could soon come to resemble the broad, dying tracts of forested land in eastern and central Europe. As we continue to put stress on our own forests, we increase the risk that they will someday take on the wasted lunar-landscape appearance of what we saw, under the Arenal volcano.


Originally published in Middlebury Magazine, Vol. 66, No. 1, 1992. For more information about the magazine contact the editor at or visit their web site at
Photos and text © Sallie G Sprague and Stuart J Shiffman. All rights reserved.