Volcanoes in the United States

Between 1980 and 1990, volcanic activity killed at least 26,000 people and forced nearly 450,000 to flee from their homes (according to the U.S. Geological Survey (USGS)).
But that figure is for all around the world. It seems like volcanoes don’t really happen in the United States. Right?

Mount St. Helens
When you think of U.S. volcanoes, you can probably think of only one: Mount St. Helens, in Washington State, in the Pacific Northwest’s Cascade Mountain Range; it erupted in 1980, resulting in the deaths of 57 people. The USGS describes the event:

A magnitude 5.1 earthquake struck beneath the volcano at 08:32 on May 18, setting in motion the devastating eruption…. Within seconds of the earthquake, the volcano’s bulging north flank slid away in the largest landslide in recorded history, triggering a destructive, lethal lateral blast of hot gas, steam, and rock debris that swept across the landscape as fast as 1,100 kilometers per hour. Temperatures within the blast reached as high as 300 degrees Celsius. Snow and ice on the volcano melted, forming torrents of water and rock debris that swept down river valleys leading from the volcano. Within minutes, a massive plume of ash thrust 19 kilometers into the sky, where the prevailing wind carried about 540 million tons of ash across 57,000 square kilometers of the Western United States.

Studying the Mount St. Helens landslide has helped geologists to recognize about 200 similar past events around the world (including some in the same Cascades Mountain range as Mount St. Helens), and they’ve learned that “large landslides from volcanoes are far more common than previously thought”—they found 17 worldwide in the past 400 years.

Types of Volcanic Damage
When scientists assess volcanic dangers, they consider these types:

• Tephra: Volcanic rock and lava fragments that are exploded into the air by eruptions, or carried upward by hot erupting gases. These can be as small as ash particles or a yard across or more. The smaller tephra may be carried thousands of miles by the wind.

• Lahar: A mixture of water and rock pieces flowing down a slope; these look like wet concrete full of rocks (from gravel-size to 30 feet across), coming at you. Lahars are usually caused by heavy rain that accompanies an eruption and/or its aftermath. They can also be caused by quickly melting snow or the release of water from a lake.

• Landslide: Tons of rock and soil that “fall, slide, or flow very rapidly under the force of gravity.” These can be wet or dry, or both, and they usually start as rockslides or avalanches, which disintegrate into pieces. Add water and clay soil to get a lahar.
• Lava Flows: Stream of molten rock. These destroy everything in their path, but they move slowly enough you should be able to get away with no more effort than a “brisk walk.”

• Pyroclastic Surge: A moving mixture of hot rock fragments and gas, traveling at perhaps 100 kilometers an hour. Most pyroclastic surges have a base layer of coarse rock fragments flowing along the ground, with a cloud of ash rising above, dropping ash over a wide area downwind.

• Poisonous Gases: Volcanic eruptions, and even non-erupting volcanoes, may release gases into the atmosphere. Water vapor is the most prevalent; but you can also expect carbon dioxide and sulfur dioxide. According to Allstate Insurance’s FAQ on volcano dangers:

Sulfur dioxide gas can lead to acid rain downwind from a volcano. Large explosive eruptions that inject tremendous volumes of sulfur dioxide gas into the stratosphere can contribute to global cooling. Since carbon dioxide gas is heavier than air and collects in soil and low spots, people and animals walking into these low areas may suffocate and vegetation may die. Also, a few historic eruptions have released sufficient fluorine-compounds gas to deform or kill animals grazing in areas of ash fall; the fluorine compounds tend to be concentrated on fine-grained ash particles.

Other Cascade Mountain Range Volcanoes
Although Cascade Range volcanoes don’t erupt as frequently as, say, those in Hawaii, they are more dangerous because they explode violently when they go, and because they’re close to populated areas in Washington, Oregon, and California.

Mount Rainier: Although Mount Rainier, Washington, has not erupted in 500 years, it is one of the most hazardous volcanoes in the Cascades. Its 26 glaciers contain five times as much snow and ice as all the other Cascade volcanoes combined; if even a small percentage of this was melted by the volcano, huge lahars would result. Also, Mount Rainier is 3000 meters above the surrounding river valleys, and its internal structure has been weakened by volcanic activity that turned some of the volcano’s hard lava into soft clay. Thus, the USGS says, Mount Rainier is “extremely susceptible to large landslides that “quickly turned into lahars as they rushed down river valleys.” A huge landslide occurred as recently as 600 years ago.

Mt. Baker: This Washington State volcano was spitting out smoke and steam for at least 150 years or so before it cranked up in 1975, increasing its heat release tenfold during the year. A reservoir was closed to avoid a catastrophic wave, and public access to the surrounding recreation area was closed for a while. But since 1976, Mount Baker has not shown signs of activity.

Lassen Peak: This Northern California volcano exploded more than 150 times in 1914–15, sending ash clouds 3 kilometers in the air. Over the next few years, it developed a lava flow visible 34 kilometers away at nighttime. On May 19, 1915, hot rocks avalanching from the lava crater melted snow, causing a lahar more than 15 kilometers long. The most destructive explosion took place a couple of days later; it created a pyroclastic flow that destroyed forests 6.5 kilometers away and an ash plume 9 kilometers high, which the winds spread 500 kilometers east. Then, after a year or so of smaller eruptions, the volcano settled down.

Hawaiian Volcanoes
The volcanoes of the Hawaiian Island chain are among the largest on Earth. They stretch 2,500 km across the Pacific Ocean. The island of Hawaii is currently located over the “hot spot” of magma formation.
Mauna Loa: From its base (below the sea) to its top, Mauna Loa is 9000 meters, taller than Mount Everest. It is an active volcano that has erupted 15 times since 1900; eruptions lasted up to 145 days. The most recent was a 3-week eruption in 1984.

Kilauea: A Kilauea eruption began on January 3, 1983, and by June 1991 it had “covered 75 square kilometers of forest and grassland, added 120 hectares of new land to the island, and destroyed 179 homes.” This same kind of event had happened many times before; “about 90 percent of Kilauea’s surface is covered with lava flows that are less than 1,100 years old.” Most eruptions at Kilauea are non-explosive, but a 1790 eruption left footprints preserved in a layer of ash 30 kilometers away, probably those of Hawaiian warriors and their families. A third of the 250 people killed were suffocated by clouds from the pyroclastic surges. A smaller eruption in 1924 killed a photographer and “hurled rocks weighing as much as 8 tons as far as 1 kilometer.”

Alaskan Volcanoes
According to the USGS:

The Alaska Peninsula and the Aleutian Islands have about 80 major volcanic centers that consist of one or more volcanoes…. At least 20 catastrophic caldera-forming eruptions have occurred in the past 10,000 years…. Scientists are particularly concerned about the volcanoes whose eruptions can affect the Cook Inlet region, where 60 percent of Alaska’s population lives.

Redoubt Volcano: This volcano erupted for the fourth time in the 20th century in 1989, shutting down nearly all air travel to Alaska because of the clouds of ash. One Japanese airliner trying to land in Anchorage ran into an ash cloud and lost power in all four engines, falling 4000 meters before the pilots could restart the engines. It landed safely—but with $80 million in damage.

Augustine Volcano: Since Captain James Cook “discovered” and named this volcano in 1778, it has erupted in 1812, 1883, 1935, 1963–64, 1976 and 1986. In other words, “quiet times” between eruptions are rapidly shortening. In 1986, after 8 months of earthquakes under the volcano, a violent explosion took place, spewing plumes of ash 10 kilometers high, and flowing pyroclastic surges into the sea. A month later, lava began erupting near the summit; it added 25 meters to the top of the existing lava cone (A lava cone or lava dome is a steep-sided mound that forms when lava piles up near a volcanic vent.) Scientists have been concerned that this steep lava cone could fall into the sea, causing a tsunami. At least a dozen landslides have occurred there in the past; most recently, in 1883, part of the volcano’s summit fell into the sea, causing a 9-meter-high tsunami to hit the coast of the Kenai Peninsula, 80 kilometers away, within an hour. Fortunately, it hit at low tide, so there was no loss of life, and damage was minor. But subsequent eruptions have rebuilt the steep cone, similar to the situation just before the 1883 landslide.

Novarupta, Katmai National Monument: This eruption ejected about 30 times as much magma as the Mount St. Helens explosion, making it the largest eruption in the world during the 1900s. Over 15 cubic kilometers of magma was explosively ejected over a period of 60 hours. It caused Mount Katmai volcano 10 kilometers away to collapse, forming a 600-meter deep caldera. The pyroclastic flows went for 21 kilometers, with ash and pumice depsited to perhaps 200-meter depths. According to a National Geographic scientific expedition in 1916, four years after the eruption, the deposits were still hot enough to boil water.

Trident: This volcano erupted intermittently from 1953 to 1960, with lava flows up to 4.5 kilometers long, and producing a lot of ash.

Mount Veniaminof: This massive volcano—its caldera is 8 kilometers across—is filled with ice to at least 60 meters deep. In 1983¬¬–1984, a series of explosive eruptions occurred, melting a 1.5-kilometer pit in ice near the volcano’s base, and the melting ice formed a temporary lake.
Mount Spurr: This ancient volcano’s crater contains a lava cone called Crater Peak. Eruptions from this cone are responsible for at least 35 layers of ash found in the Cook Inlet area of Alaska (most populated), “all of which were erupted in the past 6,000 years.” The most recent eruptions were in 1992, generating ash plumes up to 14 kilometers tall, small pyroclastic surges, and small lahars.

“Restless Calderas”
When a huge amount of magma is erupted from beneath a volcano, the ground collapses into the now-empty space. This depression is a caldera. Calderas can be up to 25 kilometers across and several kilometers deep. According to the USGS, “calderas are among the most spectacular and active volcanic features on Earth.”

Earthquakes, ground cracks, uplift or subsidence of the ground, and thermal activity such as hot springs, geysers, and boiling mud pots are common at many calderas. Such activity is caused by complex interactions among magma stored beneath a caldera, ground water, and the regional buildup of stress in the large plates of the Earth’s crust.

Scientists have recently documented volcanic activity at two U.S. calderas—at Long Valley Caldera in California, and Yellowstone Caldera in Wyoming. According to the USGS, “Whether unrest at these calderas simply punctuates long periods of quiet or is the early warning sign of future eruptions is an important but still unanswered question.”

Long Valley: This caldera is about 300 kilometers east of San Francisco. It was formed by a huge eruption 700,000 years ago; pyroclastic surges flowed 65 kilometers and covered 1500 square kilometers. For the past 40,000 years, many eruptions have occurred, but only in a line of vents extending about 50 kilometers north of the caldera. Since 1980, four moderate earthquakes have occurred in the caldera area, and “swarms” of smaller earthquakes have occurred; the center of the caldera has risen more than 50 centimeters since 1975. The Earth’s crust is stretching, and the magma beneath it is rising.

Volcanic unrest in the area around Mammoth Lakes in the southern part of the Long Valley caldera has increased concern among scientists over the possibility of a future volcanic eruption. Again according to the USGS:

During a typical explosive eruption of a Mono-Inyo vent, tephra (volcanic ash and larger rock fragments) may accumulate near the vent to a thickness of 10 m. Areas downwind of an explosive eruption could be covered with a layer of volcanic ash and pumice more than 20 cm (8 in) thick at a distance of 35 km (22 mi) and 5 cm (2 in.) at 85 km (53 mi).

Areas as far as 15 km (10 mi) from an explosive eruption could be swept by hot, fast-moving pyroclastic flows and surges. This zone is based on the distance that pyroclastic flows are known to have traveled in the past few thousand years.

After a persistent swarm of earthquakes beneath Mammoth Mountain in 1989, geologists discovered that large volumes of carbon dioxide (CO2 ) gas were seeping from beneath this volcano. This gas is killing trees on the mountain and also can be a danger to people.

Yellowstone: Located under Yellowstone National Park, this is not a mere volcano, but a supervolcano, a term coined by The British Broadcasting Corporation in its 1995 docu-drama by that name. http://www.bbc.co.uk/sn/tvradio/programmes/supervolcano/

The BBC predicted the eruption of this “supervolcano” would take place before long, and would pretty much destroy the world; others disagree.

“Cataclysmic” super-eruptions did occur—2.0 million, 1.3 million, and 0.6 million years ago. The most recent explosion, 64,000 years ago, was a thousand times the size of the 1984 Mount St. Helen’s eruption. In an August 2009 article, National Geographic says:

Scientists calculate that the pillar of ash from the Yellowstone explosion rose some 100,000 feet, leaving a layer of debris across the West all the way to the Gulf of Mexico. Pyroclastic flows—dense, lethal fogs of ash, rocks, and gas, superheated to 1,470 degrees Fahrenheit—rolled across the landscape in towering gray clouds. The clouds filled entire valleys with hundreds of feet of material so hot and heavy that it welded itself like asphalt across the once verdant landscape. And this wasn’t even Yellowstone’s most violent moment. An eruption 2.1 million years ago was more than twice as strong, leaving a hole in the ground the size of Rhode Island. In between, 1.3 million years ago, was a smaller but still devastating eruption.

Each time, the whole planet would have felt the effects. Gases rising high into the stratosphere would have mixed with water vapor to create a thin haze of sulfate aerosols that dimmed sunlight, potentially plunging the Earth into years of “volcanic winter.” According to some researchers, the DNA of our own species may pay witness to such a catastrophe around 74,000 years ago, when a supervolcano called Toba erupted in Indonesia. The ensuing volcanic winter may have contributed to a period of global cooling that reduced the entire human population to a few thousand individuals—a close shave for the human race.

According to the USGS:

If another large caldera-forming eruption were to occur at Yellowstone, its effects would be worldwide. Thick ash deposits would bury vast areas of the United States, and injection of huge volumes of volcanic gases into the atmosphere could drastically affect global climate.

Fortunately, the Yellowstone volcanic system shows no signs that it is headed toward such an eruption. The probability of a large caldera-forming eruption within the next few thousand years is exceedingly low.

The USGS also says:

The Earth’s crust beneath Yellowstone National Park is still restless. Precise surveys have detected an area in the center of the caldera that rose by as much as 86 centimeters between 1923 and 1984 and then subsided slightly between 1985 and 1989. Scientists do not know the cause of these ups and downs but hypothesize that they are related to the addition or withdrawal of magma beneath the caldera, or to the changing pressure of the hot ground water system above Yellowstone’s large magma reservoir. Also, Yellowstone National Park and the area immediately west of the Park are historically among the most seismically active areas in the Rocky Mountains. Small-magnitude earthquakes are common beneath the entire caldera, but most are located along the Hebgen Lake fault zone that extends into the northwest part of the caldera. A magnitude 7.5 earthquake occurred along this zone in 1959.

None of the events—cataclysmic caldera-forming eruptions, lava flows, large earthquakes, or major hydrothermal explosions—are common in Yellowstone. Although visitors to Yellowstone National Park may never experience them, some hazardous events are certain to occur in the future.

This house fell into Hebgen Lake during the 1959 earthquake and floated along the shore until it came to rest here. The owner of the house, then-70-year-old Mrs. Grace Miller, escaped only after kicking out her front door and leaping a 5-foot-wide ground crack as her house dropped into the lake. (USGS photograph by J.B. Hadley.)

National Geographic finishes its recent article by asking, “Is it going to blow again?”

Some kind of eruption—perhaps a modest one like Mount Pinatubo’s in the Philippines, which killed 800 people in 1991—is highly likely at some point. The odds of a full, caldera-forming eruption—a cataclysm that could kill untold thousands of people and plunge the Earth into a volcanic winter—are anyone’s guess; it could happen in our lifetimes, or 100,000 years or more from now, or perhaps never.

Be Prepared: How Would a Volcanic Eruption Affect You?

Allstate Insurance has a website focused on keeping yourself, your home, and your possessions safe in the event of various natural disasters. Here’s what they say about volcanoes:

Volcanic eruptions are one of Earth’s most dramatic and violent agents of change. Not only can powerful explosive eruptions drastically alter land and water for miles around a volcano, but tiny liquid droplets of sulfuric acid erupted into the stratosphere can change our planet’s climate temporarily. Eruptions often force people living near volcanoes to abandon their land and homes, sometimes forever. Those living farther away are likely to avoid complete destruction, but their cities and towns, crops, industrial plants, transportation systems and electrical grids can still be damaged by volcanic debris (tephra, lahars) and flooding.

Take the volcano quiz at Survival-Quiz.com—learn what you need to know to survive.

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