To learn about how Jonathan Potthast used sources to support his own ideas, turn to “A Writer at Work” later in this chapter: How did he contextualize sources to show their relevance? How did he combine summary and quotation to integrate source material into his essay and avoid simply stringing quotations together?

Basic Features

A Focused Explanation

A Clear, Logical Organization

Appropriate Explanatory Strategies

Smooth Integration of Sources

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Possibly the most destructive natural disaster, short of a large asteroid impact, would be the eruption of a supervolcano. Supervolcanoes are volcanoes that produce eruptions thousands of times the size of ordinary volcanoes. Like hurricanes, the power of volcanoes is measured using an exponential scale, the Volcanic Explosivity Index, or VEI (fig. 1).

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A brief synopsis of the effects of regular volcanoes can provide clues as to how destructive the eruption of a supervolcano would be. Volcanic eruptions feature several dangerous physical effects, including pyroclastic flows, pyroclastic surges, lahars, tephra falls, and massive amounts of fine ash particles in the air. Pyroclastic flows, which are dense superheated mixtures of ash, rock, and gas, are the most deadly feature of volcanoes. They are often as hot as 1,400 degrees Fahrenheit and flow at rates of hundreds of miles per hour, making prior evacuation the only possible means of escape. Driven by gravity, pyroclastic flows destroy everything in their path, and “they pose lethal hazard from incineration, asphyxiation, burial, and impact” (United States, “Pyroclastic”). In the wake of the May 18, 1980, Mt. St. Helens eruption, a pyroclastic flow “swept down the mountain, flattening forests, overtaking escaping vehicles and killing several people who stood absolutely no chance of moving out of its path” (“Lahars”).

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3

In addition, by rapidly heating phreatic (underground) water, volcanic eruptions can trigger violent steam-driven explosions. The water from these phreatic eruptions can then combine with lava from pyroclastic flows to create devastating mudslides called lahars. (Rainwater or melting snow can also combine with lava flows to form lahars.) Lahars flow with enough force to uproot trees, carry away cars, and flatten buildings (“Lahars”). They flow much faster than humans can run, and can kill people instantly. When cooled, they solidify into a sort of concrete. For example, the eruption of Mt. Vesuvius in 79 A.D. produced lahars large enough to bury the entire city of Pompeii in what quickly became solid volcanic rock (“Lahars”). The most dangerous aspect of lahars, however, lies in their ability to form long after a volcanic eruption has apparently ceased, even after evacuated inhabitants have returned to their homes.

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Pyroclastic surges, another devastating feature of many volcanoes, are composed of gas and particles of volcanic ash which move as quickly as pyroclastic flows but are less dense. P. J. Baxter, a physician specializing in occupational and environmental medicine at Cambridge University and a consultant to the World Health Organization on volcanoes, notes that humans exposed even briefly to pyroclastic surges face serious burns as well as risks of asphyxia (suffocation) and hypoxia (oxygen deprivation to body tissue). The extreme heat of the surges, if not hot enough to kill a person instantly, can kill a person by burning their lungs, throat, and windpipes so severely that those organs swell to the point of preventing any air from getting in.

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Tephra falls, or showers of pieces of volcanic rock ejected from a volcano, can also be deadly to those nearby. The sheer force of a tephra “rain” can cause roofs to collapse and people without shelter to be battered to death (Horwell and Baxter). While tephra presents an immediate and short-lived danger, however, fine ash particles in the air cause more lasting damage. Heavy ash deposits can destroy vegetation, causing widespread famine and suffering to animals that depend on those plants for food. Inhaling fine volcanic ash can cause silicosis, an irreversible lung disease (Horwell and Baxter). Ash particles also cause damage to moving parts in machinery and vehicles.

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Aside from the obvious immediate destruction of these physical effects, a volcanic eruption can also have a surprising aftermath.For example, following the 1996 Soufreire Hills volcano, hydrogen sulfide and sulfur dioxide (gases produced in the eruption) combined to form sulfuric acid; this, mixed with the rainwater, destroyed acres of cloud forest (Brosnan). Coral reefs could be destroyed in a similar manner.

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Even more astounding, ash in the air after a volcano can temporarily cause dramatic changes to the climate. For instance, in the years following the eruption of Tambora in Indonesia on April 5, 1815, fine particles of volcanic ash and aerosols created a fog-like layer in the atmosphere that blocked some of the sun’s rays and led to temporary global cooling of about five and a half degrees Fahrenheit (“Mount Tambora”). In Europe and North America, 1816 became known as “the year without a summer”; the New England states, for example, experienced a “killing frost through June, July, and August” (“Mount Tambora”). Although “enough grains, wheat, and potatoes were harvested to prevent a famine,” crops such as corn, beans, and squash were destroyed before they could be harvested, hay crops were meager, and “there were reports of people eating raccoons, pigeons, and mackerel” (Foster). Other recent major volcanoes, such as Krakatoa in 1883, have produced similar cooling effects: “On the average, temperature dropped by as much as 1.2ºC in the succeeding year. In the years that followed, global climates were very erratic, stabilizing only 4 years after” (Villanueva).

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Luckily, no supervolcano has erupted in recorded history. Several supervolcanoes exist today, but most are under the ocean, and all are considered dormant or extinct. According to National Parks Service geologists, a catastrophic eruption would probably provide a good deal—maybe even years—of advance warning, and other geologic events (“a serious increase in earthquakess, ground deformation, and geyser basin temperature”) would occur within days or weeks of the eruption (United States, “Yellowstone’s” 00:02:27-52).

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A dormant supervolcano close to home is in Yellowstone National Park. According to Joel Achenbach, a reporter on science and politics for magazines and newspapers such as National Geographic, Slate, and the Washington Post, three super-eruptions have occurred there, with one just 640,000 years ago (a blink of an eye in geologic terms). Even more powerful was a super-eruption 2.1 million years ago that “[left] a hole in the ground the size of Rhode Island” (Achenbach 1). The caldera, or crater, of the Yellowstone supervolcano is about 45 miles across, and over time, has been eroded and covered by glaciers and forests; part of the caldera’s rim is invisible, hidden beneath the surface of Lake Butte.

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It was thought that the volcano was extinct, but activity is making scientists rethink that view (Achenbach 2). A huge magma chamber lies deep under the volcano’s caldera. When shifted by earthquakes and pressed by hot rock, the land above it rises and falls. An earthquake swarm in the mid-1980s made Yellowstone drop, so that it was about eight inches lower ten years later (Achenbach 2). More recently, “portions of the caldera have surged upward at a rate of nearly three inches a year, much faster than any uplift since close observations began in the 1970’s” (Achenbach 3). Such activity indicates a live volcano.

11

Although a catastrophic eruption is far from imminent, one is possible. If a super-eruption were to occur here, the results would be devastating: A Yellowstone eruption, for example, could deposit a 10-foot layer of ash that would destroy vegetation 1,000 miles away. Toxic gases would sweep across much of the nation, making “two-thirds of the U.S. . . . uninhabitable . . . forcing millions to leave their homes” (Bates). Burning plants would generate vast amounts of carbon dioxide that would increase the greenhouse effect and ultimately contribute to global warming, but the immediate effect of a supervolcanic eruption would be dramatic global cooling. While Tambora created a “year without summer,” a supervolcanic eruption would “potentially plunge the Earth into years of ‘volcanic winter’” (Achenbach 2). According to science writer Charles Choi, a supervolcanic eruption would have an impact comparable to that of a mile-wide asteroid, killing many millions of people and changing the entire global landscape.

Works Cited

Achenbach, Joel. “When Yellowstone Explodes.” National Geographic Magazine, Aug. 2009, pp. 1-3.

Bates, Daniel. “Is the World’s Largest Super-Volcano Set to Erupt for the First Time in 600,000 Years, Wiping Out Two-Thirds of the U.S.?” Daily Mail, Associated Newspapers, 25 Jan. 2011, www.dailymail.co.uk/sciencetech/article-1350123/Worlds-largest-volcano-Yellowstone-National-Park-wipe-thirds-US.html.

Baxter, P. J. “Blast, Burns, Asphyxia and Hypoxia: How Do Pyroclastic Surges Damage Humans?” Montserrat Volcano Observatory, Michigan Technical U, Department of Geology, www.montserratvolcano.org/humans.htm. Accessed 6 May 2014.

Brosnan, Deborah M. “Ecological Impacts of the Montserrat Volcano: A Pictorial Account of Its Effects on Land and Sea Life.” Sustainable Ecosystems Institute, 21 Oct. 2005, www.mona.uwi.edu/cardin/virtual_library/docs/1007/1007.pdf.

Choi, Charles Q. “Supervolcano Not to Blame for Humanity’s Near-Extinction.” LiveScience, Purch, 29 Apr. 2013, www.livescience.com/29130-toba-supervolcano-effects.html.

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Foster, Lee. “1816—The Year Without Summer.” Climate Corner. United States, Department of Commerce, National Oceanic and Atmospheric Administration, www.erh.noaa.gov/car/Newsletter/htm_format_articles/climate_corner/yearwithoutsummer_lf.htm.

Horwell, Claire J., and Peter J. Baxter. “The Respiratory Health Hazards of Volcanic Ash: A Review for Volcanic Risk Mitigation.” Bulletin of Volcanology, vol. 69, no. 1, 2006, pp. 1-24. Springer Link, doi:10.1007/s00445-006-0052-y.

“Lahars and Pyroclastic Flows.” The Geography Site, 16 May 2006, www.geography-site.co.uk/pages/physical/earth/volcanoes/pyroclastic%20flows.html.

“Mount Tambora.” Encyclopaedia Britannica, 2016, www.britannica.com/place/Mount-Tambora.

United States, Department of the Interior, Geological Survey. “Pyroclastic Flow Hazards at Mount St. Helens.” Volcano Hazards Program, 22 Jan. 2013, volcanoes.usgs.gov/volcanoes/st_helens/st_helens_hazard_77.html.

---, ---, National Parks Service. “Yellowstone’s Restless Giant.” Yellowstone National Park, 27 Apr. 2007, www.nps.gov/media/video/view.htm?id=FEF54BF6-155D-451F-6725EBD604F1CD16.

Villanueva, John Carl. “Mount Krakatoa.” Universe Today, 18 Sept. 2009, www.universetoday.com/40601/mount-krakatoa/.