U.S. GEOLOGICAL SURVEY and the NATIONAL PARK SERVICE—OUR VOLCANIC PUBLIC LANDS Steam Explosions, Earthquakes, and Volcanic Eruptions— What’s in Yellowstone’s Future?
ellowstone, one of the world’s Ylargest active volcanic systems, has produced several giant volcanic eruptions in the past few million years, as well as many smaller erup- tions and steam explosions. Although no eruptions of lava or volcanic ash have occurred for many thousands of years, future eruptions are likely. In the next few hundred years, hazards will most probably be limited to on- going geyser and hot-spring activity, occasional steam explosions, and moderate to large earthquakes. To better understand Yellowstone’s volcano and earthquake hazards and to help protect the public, the U.S. Geological Survey, the University of Utah, and Yellowstone National Park formed the Yellowstone Volcano Ob- servatory, which continuously moni- Midway Geyser Basin in Yellowstone National Park appears otherworldly tors activity in the region. beneath stormy skies. In the background, steam vigorously rises from the hot waters of Grand Prismatic Spring, known for its rainbow colors produced by thermophilic (“heat loving”) or- ganisms. Grand Prismatic is the largest hot spring in Yellowstone and the third largest in the world. This and other hydrothermal (hot water) features are among the main attractions for visitors to the park (inset photo). Each year, millions of visitors come These features are fueled by heat from a large reservoir of partially molten rock (magma), just a few miles to admire the hot springs and geysers of beneath Yellowstone, that drives one of the world’s largest volcanic systems. (Photograph courtesy of Robert Fournier; inset courtesy of Susan Mayfi eld.) Yellowstone, the Nation’s fi rst national park. Few are aware that these wonders water carry huge quantities of thermal en- into the atmosphere as mixtures of red-hot are fueled by heat from a large reservoir ergy to the surface from the magma cham- pumice, volcanic ash (small, jagged frag- of partially molten rock (magma), just ber below. Continuing up-and-down ground ments of volcanic glass and rock), and gas a few miles beneath their feet. As this motions on the Yellowstone Plateau refl ect that spread as pyroclastic (“fi re-broken”) magma—which drives one of the world’s the migration of both hydrothermal fl uids fl ows in all directions. Rapid withdrawal largest volcanic systems—rises, it pushes and magma below the surface. of such large volumes of magma from the up the Earth’s crust beneath the Yellow- Ground motions, earthquakes, and hy- subsurface then caused the ground to col- stone Plateau. drothermal activity are all current manifes- lapse, swallowing overlying mountains and Stresses in the crust produce movements tations of volcanic activity at Yellowstone. creating broad cauldron-shaped volcanic on faults, causing earthquakes to occur. In the not-so-distant geologic past, Yellow- depressions called “calderas.” Thousands of small quakes are recorded stone has produced many major volcanic The fi rst of these caldera-forming each year by the seismographic network eruptions, which have repeatedly reshaped eruptions 2.1 million years ago created of the Yellowstone Volcano Observatory its natural wonders. a widespread volcanic deposit known as (YVO), a partnership of the U.S. Geologi- the Huckleberry Ridge Tuff, an outcrop of cal Survey (USGS), the University of Utah, Caldera-Forming Eruptions which can be viewed at Golden Gate, south and Yellowstone National Park. Faults and The Yellowstone region has produced of Mammoth Hot Springs. This titanic fractures also allow surface water to pen- three exceedingly large volcanic eruptions event, one of the fi ve largest individual etrate to depth and become heated, rising in the past 2.1 million years. In each of volcanic eruptions known anywhere on the again to produce hydrothermal (hot water) these cataclysmic events, enormous vol- Earth, formed a caldera more than 60 miles features, such as geysers. Steam and hot umes of magma erupted at the surface and (100 km) across.
U.S. Department of the Interior USGS Fact Sheet 2005-3024 U.S. Geological Survey 2005 A similar, smaller but still huge erup- charged with dissolved gas, then moved tion of a lava fl ow, which would be far less tion occurred 1.3 million years ago. This upward, stressing the crust and generating devastating. Since Yellowstone’s last caldera- eruption formed the Henrys Fork Caldera, earthquakes. As the magma neared the sur- forming eruption 640,000 years ago, about located in the area of Island Park, west of face and pressure decreased, the expanding 30 eruptions of rhyolitic lava fl ows have Yellowstone National Park, and produced gas caused violent explosions. Eruptions of nearly fi lled the Yellowstone Caldera. Other another widespread volcanic deposit called rhyolite have been responsible for forming fl ows of rhyolite and basalt (a more fl uid va- the Mesa Falls Tuff. many of the world’s calderas, such as those riety of lava) also have been extruded outside The region’s most recent caldera-form- at Katmai National Park, Alaska, which the caldera. Each day, visitors to the park ing eruption 640,000 years ago created the formed in an eruption in 1912, and at Long drive and hike across the lavas that fi ll the 35-mile-wide, 50-mile-long (55 by 80 km) Valley, California. caldera, most of which were erupted since Yellowstone Caldera. Pyroclastic fl ows from If another large caldera-forming eruption 160,000 years ago, some as recently as about this eruption left thick volcanic deposits were to occur at Yellowstone, its effects 70,000 years ago. These extensive rhyolite known as the Lava Creek Tuff, which can would be worldwide. Thick ash deposits lavas are very large and thick, and some cov- be seen in the south-facing cliffs east of would bury vast areas of the United States, er as much as 130 square miles (340 km2), Madison, where they form the north wall and injection of huge volumes of volcanic twice the area of Washington, D.C. During of the caldera. Huge volumes of volcanic gases into the atmosphere could drastically eruption, these fl ows oozed slowly over the ash were blasted high into the atmosphere, affect global climate. Fortunately, the Yel- surface, moving at most a few hundred feet and deposits of this ash can still be found in lowstone volcanic system shows no signs per day for several months to several years, places as distant from Yellowstone as Iowa, that it is headed toward such an eruption. destroying everything in their paths. Louisiana, and California. The probability of a large caldera-forming Today, most of the landforms within the Each of Yellowstone’s explosive caldera- eruption within the next few thousand years Yellowstone Caldera refl ect the shapes of forming eruptions occurred when large is exceedingly low. these young lava fl ows. Cliffs surrounding volumes of “rhyolitic” magma accumulated the Upper Geyser Basin near Old Faithful at shallow levels in the Earth’s crust, as little Lava Flows Geyser are the cooled steep fl ow fronts of as 3 miles (5 km) below the surface. This More likely in Yellowstone than a large highly viscous (thick and sticky) magma, explosive caldera-forming eruption is erup-
-/.4!.! VOLCANIC HISTORY AND RECENT SEISMIC ACTIVITY IN THE YELLOWSTONE REGION
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2 once-slow-moving rhyolite lavas. Some Earthquakes (equivalent to $70 million in 2005 dollars) narrow ridges and valleys on the Canyon- From 1,000 to 3,000 earthquakes typi- and killed 28 people, most of them in a Norris road are corrugations on the surface cally occur each year within Yellowstone landslide that was triggered by the quake. of a 110,000-year-old rhyolite fl ow. These National Park and its immediate surround- Geologists conclude that large earth- roughly concentric ridges formed as the ings. Although most are too small to be felt, quakes like the Hebgen Lake event are un- thick, pasty lava slowly oozed northeast- these quakes refl ect the active nature of the likely within the Yellowstone Caldera itself, ward, wrinkling its surface. Within the cal- Yellowstone region, one of the most seismi- because subsurface temperatures there are dera, rivers and streams commonly occupy cally active areas in the United States. Each high, weakening the bedrock and making it the gaps between individual lava fl ows, and year, several quakes of magnitude 3 to 4 are less able to rupture. However, quakes within springs emerge at the edges of fl ows. felt by people in the park. the caldera can be as large as magnitude Any renewed volcanic activity at Yellow- Although some quakes are caused by 6.5. A quake of about this size that occurred stone would most likely take the form of such rising magma and hot-ground-water move- in 1975 near Norris Geyser Basin was felt mainly nonexplosive lava eruptions. An erup- ment, many emanate from regional faults throughout the region. tion of lava could cause widespread havoc in related to crustal stretching and mountain Even distant earthquakes can affect the park, including fi res and the loss of roads building. For example, major faults along Yellowstone. In November 2002, the mag- and facilities, but more distant areas would the Teton, Madison, and Gallatin Ranges nitude 7.9 Denali Fault earthquake struck probably remain largely unaffected. pass through the park and likely existed central Alaska, 1,900 miles (3,100 km) long before the beginning of volcanism northwest of Yellowstone. Because this there. Movements along many of these quake’s energy was focused toward the ac- faults are capable of producing signifi cant tive Yellowstone volcanic and hydrother- earthquakes. mal system, it triggered hundreds of small The most notable earthquake in Yellow- earthquakes there. The region’s hydrother- stone’s recent history occurred in 1959. mal system is highly sensitive to quakes Centered near Hebgen Lake, just west and undergoes signifi cant changes in their of the park, it had a magnitude of 7.5. wake. Earthquakes may have the potential This quake caused $11 million in damage to cause Yellowstone’s hot-water system to destabilize and produce explosive hy- drothermal eruptions. Since its last cataclysmic volcanic eruption 640,000 years ago, the Yellowstone region has had about 40 Hydrothermal Explosions eruptions of slow-moving lava fl ows of rhyolite (a variety of molten rock that is thick and sticky). Some The large magma reservoir beneath Yel- of these fl ows cover more than 100 square miles, and lowstone may have temperatures higher many are very thick, like this approximately 180,000- than 1,475°F (800°C), and the surrounding year-old rhyolite fl ow exposed at Obsidian Cliff. rocks are heated by it. Because of this, the Although no lava has been erupted at Yellowstone for 70,000 years, future such eruptions are likely to average heat fl ow from the Earth’s interior occur. (USGS photograph by Robert Christiansen.) at Yellowstone is about 30 times greater
EARTHQUAKES IN THE YELLOWSTONE REGION
-/.4!.! The Yellowstone National Park region produces about 2,000 earthquakes each year. Most of these quakes are %PICENTER OF too small to be felt, but they refl ect the active nature of (EBGEN ,AKE the region, one of the most seismically active areas in - QUAKE the United States. )$!(/ 9ELLOWSTONE The most powerful earthquake in Yellowstone’s recent .ATIONAL history occurred in 1959. This quake was centered near 0ARK Hebgen Lake, just west of the park, and had a magnitude 79/-).' (M) of 7.5. The Hebgen Lake earthquake killed 28 peo- ple—26 in a huge landslide triggered by the quake—and caused $11 million in damage (about $70 million in 2005 dollars). Numerous structures and roads in the region were severely damaged when hillsides collapsed, gaping cracks opened in the ground, and large blocks of rock were displaced. The Hebgen Lake quake caused widespread changes in Yellowstone—roads were closed throughout the area, some geysers stopped erupting, and others were newly formed or came back to life after years of dormancy. Also, the Old Faithful This house fell into Hebgen Lake during the 1959 earthquake and Inn was strongly shaken—pipes broke, a chimney collapsed, and the inn had to fl oated along the shore until it came to rest here. The owner of the be evacuated. house, then-70-year-old Mrs. Grace Miller, escaped only after kick- Although quakes of this magnitude are rare in the Yellowstone region, they are ing out her front door and leaping a 5-foot-wide ground crack as her certain to occur in the future. To better understand this hazard and help protect the house dropped into the lake. (USGS photograph by J.B. Hadley.) public, scientists of the Yellowstone Volcano Observatory (YVO) continually monitor the region’s seismic activity.
Seismogram of the 1959 magnitude 7.5 Hebgen Lake earthquake recorded at Butte, Montana, about 100 miles from the epicenter.
3 than that typical for areas elsewhere in the as the water is converted to steam. Such Much larger hydrothermal explosions northern Rocky Mountains. As snowmelt activity drives the eruptions of geysers, like have occurred at Yellowstone in the recent and rainfall seep deep into the ground, they Old Faithful, which are repetitive releases geologic past. More than a dozen large can absorb enough of this heat to raise the of plumes of steam and water. Rarely, hydrothermal-explosion craters formed temperature of the ground water close to steam explosions are more violent and can between about 14,000 and 3,000 years ago, the boiling point. Geyser basins and other hurl water and rock thousands of feet. In triggered by sudden changes in pressure of thermal areas in Yellowstone National Park Yellowstone’s geologic past, such violent the hydrothermal system. Most of these cra- are places where hot ground water has events, called “hydrothermal explosions,” ters are within the Yellowstone Caldera or risen close to the surface. Research drill- have occurred countless times, creating new along a north-south-trending zone between ing at Yellowstone in the 1960s confi rmed landscapes of hills and craters. Norris and Mammoth Hot Springs. that the ground water beneath many of the A recent and notable hydrothermal explo- The largest hydrothermal-explosion park’s thermal areas is very hot. At Norris sion occurred in 1989 at Porkchop Geyser crater documented in the world is along Geyser Basin, water temperatures as high in Norris Geyser Basin. The remains of this the north edge of Yellowstone Lake in an as 460°F (238°C) were recorded at depths explosion are still clearly visible today as embayment known as Mary Bay. This 1.5- of only 1,090 feet (332 m). an apron of rock debris 15 feet (5 m) across mile (2.6 km)-diameter crater formed about Because the boiling point of water in- surrounding Porkchop’s central spring. 13,800 years ago and may have had several creases with increasing pressure and pres- In the 1880s and early 1890s, a series of separate explosions in a short time inter- sure increases with depth, deep water can powerful hydrothermal explosions and val. What specifi cally triggered these very be hotter than boiling water near the sur- geyser eruptions occurred at Excelsior large events is not fi rmly established, but face. If the pressure that confi nes this deep Geyser in the Midway Geyser Basin. Some earthquakes or a pressure release caused by water is reduced quickly, pockets of water of the explosions hurled large rocks as far melting glaciers or rapid changes in lake may suddenly boil, causing an explosion as 50 feet (15 m). level may have been a signifi cant factor.
HYDROTHERMAL (STEAM) EXPLOSIONS AT YELLOWSTONE
Geysers and hot springs are com- mon expressions of a hydrothermal Excelsior Geyser (hot water) system, but sometimes erupted in a series changes in “plumbing” result in large of violent hydro- volumes of water suddenly fl ashing thermal explosions into steam, causing violent hydrother- in the 1880s and mal explosions. A large hydrothermal early 1890s; one explosion can hurl water and rock of these eruptions thousands of feet and create new is shown in this landscapes of hills and craters. In colorized postcard Yellowstone’s geologic past, hydro- made from a photo- thermal explosions have occurred graph. These were countless times. the largest such In 1881, Colonel Philetus W. Norris, events to occur in Yellowstone National Park’s second the Yellowstone superintendent, witnessed a spec- region in historical tacular hydrothermal explosion at times. (Original Excelsior Geyser in the Midway Geyser photograph by Basin. He described the aftermath as F. Jay Haynes, follows: “The pool was considerably 1888; date on post- enlarged, its immediate borders swept card is incorrect.) entirely clear of all movable rock, enough of which had been hurled or forced back to form a ridge from knee to breast high at a distance of from 20 to 50 feet [ 6 to 15 m] from the ragged edge of the yawning chasm.” After a series of such explosions that ended in the early 1890s, Excelsior, once the Colonel Philetus W. Norris world’s largest active geyser, became was Yellowstone National a quietly boiling hot spring. Except for Park’s second superin- several geyser eruptions in 1985, it has tendent (1877 to 1882). A remained so ever since. decorated Civil War Union A more recent hydrothermal explo- veteran, Norris enjoyed sion occurred in 1989 at Porkchop challenges, and his efforts Geyser in Norris Geyser Basin. The re- were essential in putting mains of this explosion are still clearly the park’s management visible today as a 15-foot (5 m)-diam- on a sound footing. (Pho- eter apron of rock debris surrounding tograph courtesy of the Porkchop’s central spring. National Park Service.) Yellowstone National Park research geologist Rick Much larger hydrothermal explo- Hutchinson examines rock debris thrown out in a 1989 sions have occurred at Yellowstone in the recent geologic past. The hydrothermal explosion at Porkchop Geyser. [In March greatest concentration of hydrothermal-explosion craters lies around 1997, Hutchinson was killed in a snow avalanche while on the north end of Yellowstone Lake. These craters owe their origins duty inspecting thermal features in the park.] (Photograph to spectacular explosions thousands of years ago. courtesy of Robert Smith, University of Utah.)
4 PREHISTORIC CALDERA-FORMING ERUPTIONS OF YELLOWSTONE
Eruptions of the Yellowstone volcanic system have included the two largest -OUNT -OUNT Volcanic Ash Fall from Yellowstone Eruptions volcanic eruptions in North America 3T (ELENS 3T (ELENS in the past few million years; the third ASH ASH #!.!$! 5.)4 largest was at Long Valley in California %$ 34!4%3 and produced the Bishop ash bed. The -OUNT 9ELLOWSTONE biggest of the Yellowstone eruptions oc- 3T (ELENS 0LATEAU curred 2.1 million years ago, depositing the Huckleberry Ridge ash bed. These
eruptions left behind huge volcanic
depressions called “calderas” and ,ONG ,ONG - E spread volcanic ash over large parts 6ALLEY6ALLEY S A of North America (see map). If another #ALDERA#ALDERA & A L large caldera-forming eruption were to LS A occur at Yellowstone, its effects would SH D BED E be worldwide. Thick ash deposits would B "ISHOP SH bury vast areas of the United States, and A ASH BED 5. E )4% G injection of huge volumes of volcanic $ 3 ID 4!4 Y 2 gases into the atmosphere could drasti- %3 ERR - CKLEB cally affect global climate. Fortunately, %8) (U #/ the Yellowstone volcanic system shows ,AVA # no signs that it is headed toward such an REEK ASH BED eruption in the near future. In fact, the -),%3 probability of any such event occurring at Yellowstone within the next few thou- +),/-%4%23 sand years is exceedingly low.
Volcanic ash, like this ash from the 1980 eruption of Mount St. Helens, is made up of tiny jagged particles of rock and glass (see inset, magnifi ed about 200 times). Even a light dusting of volcanic ash can pose a health hazard to people and animals and damage crops, electronics, and machinery. Heavy ash fall, such as that from a large caldera- forming eruption, would devastate the surrounding area and affected areas downwind. (USGS photographs.)
MI KM MI MI KM KM MI KM 9ELLOWSTONE -ESA &ALLS ,ONG 6ALLEY MI MI MI 9ELLOWSTONE ASH MI #ALIFORNIA KM KM MI (UCKLEBERRY 2IDGE ASH -A 9ELLOWSTONE KM KM "ISHOP ASH KM ,AVA #REEK 4AMBORA +RAKATAU -OUNT -A .OVARUPTA 0INATUBO 02%()34/2)# -A )NDONESIA )NDONESIA 3T (ELENS %2504)/.3 ASH !LASKA 0HILIPPINES 7ASH -A How Big Were the Yellowstone Eruptions? 4( #%.4529 %2504)/.3 Explosive eruptions are best compared by recalculating the volume of erupted volcanic ash and 4( #%.4529 pumice (see photos) in terms of the original volume of molten rock (magma) released (shown %2504)/.3 in this diagram by orange spheres). On this basis, the 585 cubic miles (mi3) of magma that was erupted from Yellowstone 2.1 million years ago (Ma) was nearly 6,000 times greater than the volume released in the 1980 eruption of Mount St. Helens, Washington, which killed 57 people and caused damage exceeding $1 billion. Even the 1815 Tambora, Indonesia, eruption—the largest on Earth in the past two centuries—was more than fi ve times smaller than the smallest of Yellowstone’s three great prehistoric eruptions at 1.3 Ma.
5 HAZARDOUS EVENTS AT YELLOWSTONE THE YELLOWSTONE VOLCANO Scientists evaluate natural-hazard lev- OBSERVATORY els by combining their knowledge of the 3-!,, Smaller events are more likely frequency and the severity of hazard- (9$2/4(%2-!, Increased scientifi c surveillance of ous events. In the Yellowstone region, %80,/3)/.3 Yellowstone in the past 30 years has 3EVERAL TO 342/.' damaging hydrothermal explosions MANY PER %!24(15!+%3 detected unmistakable changes in its and earthquakes can occur several CENTURY /NE TO SEVERAL times a century. Lava fl ows and small PER CENTURY ,!6! &,/73 vast underground volcanic system, volcanic eruptions occur only ^ PER similar to historical changes observed rarely—none in the past 70,000 years. MILLION YEARS #!,$%2! at many other large calderas (vol- Massive caldera-forming eruptions, &/2-).' though the most potentially devastating %2504)/.3 canic depressions) in the world. To of Yellowstone’s hazards, are extremely OR PER strengthen the capabilities of scientists MILLION YEARS rare—only three have occurred in the -/2% &2%15%.4 to track and respond to changes in past several million years. U.S. Geo- logical Survey, University of Utah, and Yellowstone’s activity, a fi fth U.S. National Park Service scientists with volcano observatory was created in the Yellowstone Volcano Observatory 2001, complementing existing ones (YVO) see no evidence that another such cataclysmic eruption will occur at Catastrophic events are rare for Hawaii, Alaska, the Cascades, and Yellowstone in the foreseeable future. Long Valley, California. The Yellow- Recurrence intervals of these events stone Volcano Observatory (YVO) is are neither regular nor predictable. -/2% $%3425#4)6% supported jointly by the U.S. Geologi- cal Survey, the University of Utah, and These very large and violent hydrother- ably predict large quakes or hydrothermal Yellowstone National Park. mal explosions are independent of associ- explosions, events more likely than a vol- ated volcanism. None of the large hydro- canic eruption, remains a challenge. How- The principal goals of YVO include: thermal events of the past 16,000 years has ever, changes in the patterns of ongoing • Strengthening the monitoring system been followed by an eruption of magma. seismicity or other indicators of possible for tracking earthquake activity, uplift The deeper magma system appears to be geologic unrest are quickly reported to of- and subsidence, and changes in the unaffected even by spectacular steam ex- fi cials responsible for public safety in the hydrothermal (hot water) system; plosions and crater excavations within the National Park Service and other agencies. overlying hydrothermal system. Through continuous monitoring and • Assessing the long-term potential haz- Although large hydrothermal explosions research, YVO is greatly improving un- ards of volcanism, earthquakes, and are a feature of Yellowstone’s recent geo- derstanding of Yellowstone’s volcanic, explosive hydrothermal activity in the logic history, most explosions in historical earthquake, and hydrothermal hazards. Yellowstone region; times have been relatively small and have The work of USGS scientists with YVO • Enhancing scientifi c understanding left craters at most a few yards across. For is only part of the USGS Volcano Haz- of active geologic and hydrologic example, in early 2003, a long linear fi ssure ards Program’s ongoing efforts to protect processes occurring beneath Yellow- appeared on a hillside above Nymph Lake, people’s lives and property in all of the stone and in the surrounding region north of Norris Geyser Basin, venting volcanic regions of the United States, in- of the Earth’s crust; and steam and throwing bits of rock onto the cluding California, Hawaii, Alaska, and surrounding hillside. Although most hydro- the Pacifi c Northwest. • Communicating new scientifi c results, thermal explosions in the park are small, the current status of Yellowstone’s activity, and forecasts of potential their remains can be noticed by observant Jacob B. Lowenstern, Robert L. Christiansen, visitors and attest to the nearly continuous Robert B. Smith, Lisa A. Morgan, and Henry Heasler hazardous hydrothermal explosions geologic activity at Yellowstone. Edited by Peter H. Stauffer and James W. Hendley II or volcanic eruptions to Yellowstone Graphic design by Susan Mayfi eld and Sara Boore National Park staff, the public, and How Dangerous Is Yellowstone? Banner design by Bobbie Myers local, State, and Federal offi cials. None of the events described above— Current real-time-monitoring data are cataclysmic caldera-forming eruptions, COOPERATING ORGANIZATIONS Yellowstone National Park online at http://volcanoes.usgs.gov/ lava fl ows, large earthquakes, or major University of Utah hydrothermal explosions—are common yvo/monitoring.html . in Yellowstone. Although visitors to Yel- For more information contact: lowstone National Park may never expe- Yellowstone National Park rience them, some hazardous events are http://www.nps.gov/yell/home.htm certain to occur in the future. Fortunately, or U.S. Geological Survey systematic monitoring of Yellowstone’s (650) 329-5227 active volcanic and hydrothermal systems, http://volcanoes.usgs.gov/yvo/ including monitoring of earthquakes and See also Tracking Changes in Yellowstone’s Restless ground deformation, is now carried out Volcanic System (USGS Fact Sheet 100-03) routinely by YVO scientists. This moni- and other USGS volcano Fact Sheets toring will allow YVO to alert the public http://volcanoes.usgs.gov/Products/sproducts.html well in advance of any future volcanic This Fact Sheet and any updates to it are available online eruptions. Currently the ability to reli- at http://pubs.usgs.gov/fs/2005/3024/
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