Arquivo da tag: Erupções vulcânicas

Opinion | Forty Years Later, Lessons for the Pandemic From Mount St. Helens (New York Times)

By Lawrence Roberts – May 17, 2020

The tensions we now face between science, politics and economics also arose before the country’s most destructive volcanic eruption.

Mr. Roberts is a former editor at ProPublica and The Washington Post.

Mount St. Helens erupted on May 18, 1980.
United Press International

When I met David A. Johnston, it was on a spring evening, about a month before he would be erased from existence by a gigantic cloud of volcanic ash boiling over him at 300 miles per hour. He was coming through the door of a makeshift command center in Vancouver, Wash., the closest city to the graceful snow-capped dome of Mount St. Helens, a volcano that had been dormant for 123 years. This was April 1980, and Mr. Johnston, a 30-year-old geologist, was one of the first scientists summoned to monitor new warning signs from the mountain — shallow earthquakes and periodic bursts of ash and steam.

As a young reporter I had talked my way into the command center. At first Mr. Johnston was wary; he wasn’t supposed to meet the press anymore. His supervisors had played down the chance that the smoking mountain was about to explode, and they had already reprimanded him for suggesting otherwise. But on this night he’d just been setting measuring equipment deep in the surrounding forest, and his runner-thin frame vibrated with excitement, his face flushed under his blond beard, and Mr. Johnston couldn’t help riffing on the likelihood of a cataclysmic event.

“My feeling is when it goes, it’s going to go just like that,” he told me, snapping his fingers. “Bang!” At best, he said, we’d have a couple of hours of warning.

Mr. Johnston was mostly right. Early on a Sunday morning several weeks later, the mountain did blow, in the most destructive eruption in U.S. history. But there was no warning. At his instrument outpost, on a ridge more than five miles from the summit, Mr. Johnston had only seconds to radio in a last message: “Vancouver! Vancouver! This is it!”

A photograph of David Johnston, who was killed when Mount St. Helens erupted.
Chris Sweda/Daily Southtown, via Associated Press

Monday, May 18, marks the 40th anniversary of the 1980 Mount St. Helens eruption, and as we now face our own struggle to gauge the uncertain risks presented by nature, to predict how bad things will get and how much and how long to protect ourselves, it may be useful to revisit the tension back then between science, politics and economics.

The drama played out on a much smaller stage — one region of one state, instead of the whole planet — but many of the same elements were present: Scientists provided a range of educated guesses, and public officials split on how to respond. Business owners and residents chafed at the restrictions put in place, many flouted them, and a few even threatened armed rebellion. In the end, the government mostly accepted the analyses of Mr. Johnston and his fellow geologists. As a result, while the eruption killed 57 people and flattened hundreds of square miles of dense Pacific Northwest forestland, the lives of hundreds, perhaps thousands, were spared.

At the first warning signs, state and federal officials moved to distance people from the mountain. They sought to block nonessential visitors from nearby Spirit Lake, ringed with scout camps and tourist lodges. Other than loggers, few people hung around the peak year-round, but the population surged in late spring and summer, when thousands hiked, camped and moved into vacation homes. Many regulars dismissed the risk. Slipping past roadblocks became a popular activity. Locals sold maps to sightseers and amateur photographers that showed how to take old logging roads up the mountain. The owner of a nearby general store shared a common opinion of the threat: “It’s just plain bull. I lived here 26 years, and nothing like this happened before.”

Like the probability of a pandemic, though, it was well-established that one of the dozen or so volcanoes in the 800-mile Cascade Range might soon turn active. Averaging two eruptions a century, they were overdue. A 1978 report by the U.S. Geological Survey, where Mr. Johnston worked, identified Mount St. Helens as most likely to blow next. Yet forecasting how big the event could be was a matter of art as well as science. Geologists could model only previous explosions and list the possible outcomes. (“That position was difficult for many to accept, because they believed we could and should make predictions,” a U.S.G.S. report said later.)

Some scientists suggested a much larger evacuation, but uncertainty, a hallmark of their discipline, can be difficult for those making real-time public policy. The guidelines from federal and state representatives camped out in Vancouver, and from Washington’s governor, Dixy Lee Ray, often seemed in conflict. Moreover, the Weyerhaeuser Company, which owned tens of thousands of acres of timber, opposed logging restrictions, even as some crews got nervous about working near the rumbling dome.

By mid-April, a bulge grew on the north flank, a clue that highly pressurized magma was trapped and expanding. If it burst, a landslide might bury Spirit Lake. The governor, a conservative Democrat who was a biologist by training, finally agreed to stronger measures. She ordered an inner “red zone” where only scientists and law enforcement personnel could enter, and a “blue zone” open to loggers and property owners with day passes. If the zones didn’t extend as far as many geologists hoped, they were certainly an improvement.

Then the mountain got deceptively quiet. The curve of seismic activity flattened and turned downward. Many grew complacent, and restless. On Saturday, May 17, people with property inside the red zone massed in cars and pickup trucks at the roadblock on State Highway 504. Hearing rumors that some carried rifles, the governor relented, allowing them through, with a police escort, to check on their homes and leave again. The state patrol chief, Robert Landon, told them, “We hope the good Lord will keep that mountain from giving us any trouble.” The property owners vowed to return the next day.

The next day was Sunday. At 8:32 a.m., a powerful quake shook loose the snow-covered north face of Mount St. Helens, releasing the superheated magma, which roared out of the mountain in a lateral blast faster than a bullet train, over the spot where Mr. Johnston stood, mowing down 230 square miles of trees, hurling trunks into the air like twigs. It rained down a suffocating storm of thick gray ash, “a burning sky-river wind of searing lava droplet hail,” as the poet Gary Snyder described it. Mudflows clogged the river valleys, setting off deadly floods. A column of ash soared 15 miles high and bloomed into a mushroom cloud 35 miles wide. Over two weeks, ash would circle the globe. Among the 57 dead were three aspiring geologists besides Mr. Johnston, as well as loggers, sightseers and photographers.

About a week later, the Forest Service took reporters up in a helicopter. I had seen the mountain from the air before the eruption. Now the sprawling green wilderness that appeared endless and permanent had disappeared in a blink. We flew for an hour over nothing but moonscape. The scientists had done their best, but nature flexed a power far more deadly than even they had imagined.

Lawrence Roberts, a former editor at ProPublica and The Washington Post, is the author of the forthcoming “Mayday 1971: A White House at War, a Revolt in the Streets, and the Untold History of America’s Biggest Mass Arrest.”

Small volcanic eruptions could be slowing global warming (Science Daily)

Date: November 18, 2014

Source: American Geophysical Union

Summary: Small volcanic eruptions might eject more of an atmosphere-cooling gas into Earth’s upper atmosphere than previously thought, potentially contributing to the recent slowdown in global warming, according to a new study.

The Sarychev Peak Volcano, on Matua Island, erupted on June 12, 2009. New research shows that eruptions of this size may contribute more to the recent lull in global temperature increases than previously thought. Credit: NASA

Small volcanic eruptions might eject more of an atmosphere-cooling gas into Earth’s upper atmosphere than previously thought, potentially contributing to the recent slowdown in global warming, according to a new study.

Scientists have long known that volcanoes can cool the atmosphere, mainly by means of sulfur dioxide gas that eruptions expel. Droplets of sulfuric acid that form when the gas combines with oxygen in the upper atmosphere can remain for many months, reflecting sunlight away from Earth and lowering temperatures. However, previous research had suggested that relatively minor eruptions — those in the lower half of a scale used to rate volcano “explosivity” — do not contribute much to this cooling phenomenon.

Now, new ground-, air- and satellite measurements show that small volcanic eruptions that occurred between 2000 and 2013 have deflected almost double the amount of solar radiation previously estimated. By knocking incoming solar energy back out into space, sulfuric acid particles from these recent eruptions could be responsible for decreasing global temperatures by 0.05 to 0.12 degrees Celsius (0.09 to 0.22 degrees Fahrenheit) since 2000, according to the new study accepted to Geophysical Research Letters, a journal of the American Geophysical Union.

These new data could help to explain why increases in global temperatures have slowed over the past 15 years, a period dubbed the ‘global warming hiatus,’ according to the study’s authors.

The warmest year on record is 1998. After that, the steep climb in global temperatures observed over the 20th century appeared to level off. Scientists previously suggested that weak solar activity or heat uptake by the oceans could be responsible for this lull in temperature increases, but only recently have they thought minor volcanic eruptions might be a factor.

Climate projections typically don’t include the effect of volcanic eruptions, as these events are nearly impossible to predict, according to Alan Robock, a climatologist at Rutgers University in New Brunswick, N.J., who was not involved in the study. Only large eruptions on the scale of the cataclysmic 1991 Mount Pinatubo eruption in the Philippines, which ejected an estimated 20 million metric tons (44 billion pounds) of sulfur, were thought to impact global climate. But according to David Ridley, an atmospheric scientist at the Massachusetts Institute of Technology in Cambridge and lead author of the new study, classic climate models weren’t adding up.

“The prediction of global temperature from the [latest] models indicated continuing strong warming post-2000, when in reality the rate of warming has slowed,” said Ridley. That meant to him that a piece of the puzzle was missing, and he found it at the intersection of two atmospheric layers, the stratosphere and the troposphere- the lowest layer of the atmosphere, where all weather takes place. Those layers meet between 10 and 15 kilometers (six to nine miles) above the Earth.

Traditionally, scientists have used satellites to measure sulfuric acid droplets and other fine, suspended particles, or aerosols, that erupting volcanoes spew into the stratosphere. But ordinary water-vapor clouds in the troposphere can foil data collection below 15 km, Ridley said. “The satellite data does a great job of monitoring the particles above 15 km, which is fine in the tropics. However, towards the poles we are missing more and more of the particles residing in the lower stratosphere that can reach down to 10 km.”

To get around this, the new study combined observations from ground-, air- and space-based instruments to better observe aerosols in the lower portion of the stratosphere.

Four lidar systems measured laser light bouncing off aerosols to estimate the particles’ stratospheric concentrations, while a balloon-borne particle counter and satellite datasets provided cross-checks on the lidar measurements. A global network of ground-based sun-photometers, called AERONET, also detected aerosols by measuring the intensity of sunlight reaching the instruments. Together, these observing systems provided a more complete picture of the total amount of aerosols in the stratosphere, according to the study authors.

Including these new observations in a simple climate model, the researchers found that volcanic eruptions reduced the incoming solar power by -0.19 ± 0.09 watts of sunlight per square meter of the Earth’s surface during the ‘global warming hiatus’, enough to lower global surface temperatures by 0.05 to 0.12 degrees Celsius (0.09 to 0.22 degrees Fahrenheit). By contrast, other studies have shown that the 1991 Mount Pinatubo eruption warded off about three to five watts per square meter at its peak, but tapered off to background levels in the years following the eruption. The shading from Pinatubo corresponded to a global temperature drop of 0.5 degrees Celsius (0.9 degrees Fahrenheit).

Robock said the new research provides evidence that there may be more aerosols in the atmosphere than previously thought. “This is part of the story about what has been driving climate change for the past 15 years,” he said. “It’s the best analysis we’ve had of the effects of a lot of small volcanic eruptions on climate.”

Ridley said he hopes the new data will make their way into climate models and help explain some of the inconsistencies that climate scientists have noted between the models and what is being observed.

Robock cautioned, however, that the ground-based AERONET instruments that the researchers used were developed to measure aerosols in the troposphere, not the stratosphere. To build the best climate models, he said, a more robust monitoring system for stratospheric aerosols will need to be developed.

Journal Reference:

  1. D. A Ridley, S. Solomon, J. E. Barnes, V.D. Burlakov, T. Deshler, S.I. Dolgii, A.B. Herber, T. Nagai, R. R. Neely, A.V. Nevzorov, C. Ritter, T. Sakai, B. D. Santer, M. Sato, A. Schmidt, O. Uchino, J. P. Vernier. Total volcanic stratospheric aerosol optical depths and implications for global climate changeGeophysical Research Letters, 2014; DOI: 10.1002/2014GL061541