Tracking Changes in Yellowstone's Restless Volcanic System

Home , Yellowstone Caldera

U.S. GEOLOGICAL SURVEY and the NATIONAL PARK SERVICE—OUR VOLCANIC PUBLIC LANDS Tracking Changes in Yellowstone’s Restless Volcanic System

The world-famous Yellowstone geysers and hot springs are In the 1970s, a resurvey of benchmarks discovered the fueled by heat released from an unprecedented uplift of the enormous reservoir of magma Yellowstone Caldera of more (partially molten rock beneath than 28 inches (72 cm) over ﬁ ve decades. More recently, the ground). Since the 1970’s, new and revolutionary sat- scientists have tracked rapid ellite-based methods for tracking the Earth’s shifting uplift and subsidence of the ground motions have en- ground and signiﬁ cant changes abled University of Utah, U.S. Geological Survey, and other in hydrothermal (hot water) scientists to assemble a more features and earthquake activity. precise and detailed picture of Yellowstone’s ground In 2001, the Yellowstone Volcano movements. Global Position- Observatory was created by the ing System (GPS) stations like U.S. Geological Survey (USGS), this one in the Norris Geyser Basin can detect changes in the University of Utah, and elevation and horizontal shifts Yellowstone National Park to of 1 inch or less per year, helping scientists understand strengthen scientists’ ability to the processes that drive track activity that could result in Yellowstone’s active volcanic and earthquake systems. hazardous seismic, hydrothermal, (Photo courtesy of Christine or volcanic events in the region. Puskas, University of Utah.)

No actual volcanic eruption has occurred in this way, the water level of Yellowstone Lake lowstone Caldera, a shallow, oval depression, the Yellowstone National Park region of Wyo- would appear to rise at the south end. 53 miles long and 28 miles across (85 by 45 ming, Montana, and Idaho since a lava fl ow To test this idea, in 1975–77 scientists from km), in the middle of the park. This caldera poured out about 70,000 years ago. However, the University of Utah and the U.S. Geo- was formed 640,000 years ago during the the area’s many geysers and hot springs indi- logical Survey (USGS) resurveyed a series of most recent of Yellowstone’s great volcanic cate that the underlying volcanic system re- benchmarks along roads throughout Yellow- eruptions. In that eruption, 240 cubic miles mains active. In the early 1970’s, Earth scien- stone National Park. These benchmarks were (1,000 km3) of molten rock (magma) was tists found evidence that this system was more originally installed and their elevations and blasted into the atmosphere and scattered on active than even these spectacular hydrother- locations precisely determined in 1923. The the Earth’s surface—more than 1,000 times mal (hot water) features had suggested. results of the resurvey showed dramatically the volume erupted at Mount St. Helens in One important clue was found along the that the central part of the park had indeed 1980! The ground then collapsed into the south shore of Yellowstone Lake, where trees risen. The greatest uplift appeared to be in the partly emptied magma reservoir, forming an were dying because their trunks were partly area of Le Hardy Rapids on the Yellowstone enormous craterlike depression. below water and a boat dock had become River, a few miles downstream from the lake’s Later eruptions of many large lava fl ows, completely submerged. At the same time, the outlet. There the ground had risen 28.5 inches some as thick as 400 feet (120 m), buried the water level at the lake’s outlet on its north side (72 cm) since 1923, raising the nearby north original caldera fl oor and most of the caldera appeared little changed. end of Yellowstone Lake much more than the walls. Mount Washburn, a prominent land- Scientists reasoned that these observations south end. Scientists then focused their atten- mark in the park, is a section of the caldera could be explained by southward tilt of the tion on what could be causing the ground to rim that escaped burial. The most recent area around Yellowstone Lake, including the rise and whether the uplift was still going on. series of eruptions at Yellowstone, 160,000 to lake basin itself. If the entire area was being 70,000 years ago, covered much of the cal- pushed up, perhaps the ground at the north Yellowstone Caldera and its resurgent domes dera fl oor with more than 20 thick lava fl ows, end of the lake was rising more than the south The 1975–77 survey showed that the area including the Elephant Back fl ow, which can end, like a giant bathtub lifted at one end. In of recent uplift was located within the Yel- be seen west of Fishing Bridge.

U.S. Department of the Interior USGS Fact Sheet 100-03 U.S. Geological Survey 2004 111°W 110.5° 110° The uplift detected in the 1970’s was centered near Le Hardy Rapids, between two resurgent domes—sections of the caldera ﬂ oor that had earlier been pushed upward and faulted. Such resurgent domes form when magma rises to shallow levels beneath

45°N a caldera and slowly reinfl ates a previously depleted magma reservoir, pushing the overlying caldera fl oor upward to form a dome. The pressure of the infl ating magma reser-

Mount Washburn voir may even force some of the molten rock

M to emerge at the surface as lava. The fact that the uplift documented in t Y Sour Creek the 1970’s was centered within the caldera Dome LeHardyRapids near the resurgent domes seemed to indi- Fishing B cate that the magma reservoir was again

44.5° Mallard exerting pressure upward. What could be Lake Dome Yellowstone causing this? Was new magma entering Yel- Lake lowstone’s enormous reservoir from below? Perhaps volcanic gas was escaping from the magma reservoir, percolating upward and era causing the surface to bow upward? Perhaps some of Yellowstone’s hot water had become trapped beneath the surface, exerting pressure on the caldera ﬂ oor from below? New volcano-monitoring data soon forced scien-

44° tists to think again about what was occurring beneath Yellowstone’s active caldera.

The region of Yellowstone National Park in Wyoming, Montana, and Idaho is famous for its spectacular geysers and extensive hot springs, indications that an underlying volcanic system remains The ups and downs of the caldera’s movements active. The central part of the park is occupied by the great, partly fi lled depression of the Yellow- To learn more about the changing ground stone Caldera, formed in a giant volcanic eruption 640,000 years ago that blasted 240 cubic miles levels in the Yellowstone area, scientists con- (1,000 km3) of molten rock (magma) into the atmosphere—more than 1,000 times the volume erupted at Mount St. Helens in 1980. Later eruptions largely fi lled the caldera and pushed up two resurgent ducted additional surveys across the eastern domes within it—the Sour Creek and Mallard Lake Domes. No actual volcanic eruption has oc- part of the caldera nearly every year from curred in the Yellowstone region for about 70,000 years. However, since the 1970’s, scientists have 1983 to 1998. In the 1990’s, new and revolu- detected signifi cant changes in this remarkable volcanic and hydrothermal (hot water) system, including rapid ground uplift and subsidence and bursts of earthquake activity. tionary satellite-based methods for tracking the Earth’s changing ground surface—the Global Positioning System (GPS) and In- -111.5° -111° -110.5° -110° terferometric Synthetic Aperture Radar (In- SAR)—were applied by University of Utah, A new satellite-based tech- USGS, and other scientists to assemble a more 45° nique known as Interferomet- ric Synthetic Aperture Radar detailed picture of how and when the ground (InSAR) allows direct and moves above Yellowstone’s magma reservoir. precise measurement of the These new data reveal that Yellowstone is vertical changes in ground level. This InSAR image of the in nearly continuous but frequently changing area around the Yellowstone movement—the fl oor of the caldera contin- Caldera (dotted line) shows ued to rise until 1984, stopped rising during vertical changes during the 4-year period 1996–2000. 1984–85, and then subsided for the next 10 ° 44.5 The ringed pattern centered years. Parts of the central caldera began rising northwest of Yellowstone again in 1995, but a more complex pattern Lake is a prominent area of dome-shaped uplift. Each of uplift and subsidence has prevailed since complete cycle of colors in 2000. InSAR data show that between 1995 the color bands represents a and 1997 a large area along the northwest little more than one inch (28.3 mm) of vertical change. Yellow rim of the Yellowstone Caldera, centered near triangles are continuous GPS Norris Geyser Basin, started to rise. The pic- 0 28.3 mm 44° 01020MILES stations; white dots are loca- ture that emerges from all these data is of a Range Change tions of earthquakes in the 01020KILOMETERS period 1996–2000. dynamic system in which the caldera fl oor is in almost constant motion—episodes of uplift Earthquakes atYellowstone ov and subsidenceoccuratvarious locationsand on thenortheastshoreof Yellowstone Lake: in 1872,whenhissurvey partywas camped earthquakes was given byFerdinandHayden Norris Geyser BasinonJune30,1975. shock insidethe Yellowstone Calderanear recent large earthquake was amagnitude 6.1 lent to$70millionin2003dollars). The most and causeddamageof$11million(equiva- 18, 1959. That earthquake killed28people west ofthe Yellowstone Calderaon August which struckabout15miles(24km)north- the magnitude7.5HebgenLake earthquake, occurred inhistoricaltime. The largest was eight magnitude6orgreaterquakes have Y tive areasinNorth America. Y frequency anddistribution ofearthquakes at remains anactive volcanic system,isthe tery, andafurtherindicationthattheregion such shorttimeintervals? A cluetothismys- around thecalderatogoupanddown over ellowstone region eachyear, and atleast ellowstone, oneofthemostseismicallyac- er different timescales. quake shocksareofvery commonoccurrence. observations made,itwillbefoundthatearth- the countryshouldever besettledandcareful the country. Ihave nodoubtthatifthispartof reason whythey never visitthatportionof and thisfact isgiven bythe Indiansasthe and atsomeseasonsoftheyearvery severe, these earthquake shocksarenotuncommon, An earlywrittenaccountof Yellowstone’s Thousands ofsmallearthquakes rattlethe What couldcausedifferent areasinand The Yellowstone area is one of the most seismically active parts of the United States, but the frequency of of frequency the but States, United the of parts active seismically most the of one is area Yellowstone The earthquakes varies dramatically and is related to other events in this active volcanic system. Precise mea- Precise system. volcanic active this in events other to related is and dramatically varies earthquakes surements of elevation made regularly since the 1970’s document the rise and fall (shown diagrammatical- (shown fall and rise the document 1970’s the since regularly made elevation of surements ly here) of the ground surface in the Yellowstone Caldera, thought to be caused by movements of magma magma of movements by caused be to thought Caldera, Yellowstone the in surface ground the of here) ly (molten rock) or hydrothermal (hot, watery) fl watery) (hot, hydrothermal or rock) (molten We of late 1985 may have been caused by the escape of hydrothermal fl hydrothermal of escape the by caused been have may 1985 late of layer above the magma reservoir, which also initiated an episode of subsidence in the caldera. the in subsidence of episode an initiated also which reservoir, magma the above layer NUMBER OF EARTHQUAKES PER QUARTER wereinformedbymountain-menthat 1000 100 200 300 400 500 600 700 800 900 0 9518 9519 952000 1995 1990 1985 1980 1975

Diagrammatic caldera uplift

(a v erage 22 mm/yr) seismic data No uun18 swarm 1985 Autumn

uids beneath the surface. The spectacular earthquake swarm swarm earthquake spectacular The surface. the beneath uids igamtccleasubsidence caldera Diagrammatic

( m averag The migratingearthquakeswarmof1985 entists ofthe1985 swarm shows thatduring 4.9 and4.3)struckonNovember 9. 20, andthetwo largest events (magnitudes ev ing the1985swarm, asmany as100to200 epicenters hadbeenlocatedinthisarea.Dur- Previously, onlyabout100totalearthquake were feltnear West Yellowstone, Montana. Madison Valley area—morethan100ofthem than 3,000earthquakes struck theupper 1985. Over thenext several months,more west ofthecalderabeginning inOctober Ye stone region. sites ofearthquake swarms inthe Yellow- the arearemainsoneofmostcommon “Earthquake Camp,” anaptname because lowstone Lake thatHaydennamedthiscamp v with known active faults orformersitesof Although many earthquakes areassociated Hebgen Lake earthquake tothenorthwest. tween thecalderaandrupturezoneof been locatedbothwithinthecalderaandbe- ing daystoweeksorlonger. Swarms have quakes thatsometimesoccurinswarms last- are small(magnitudelessthan3),shallow earthquakes inthe Yellowstone region. Most pinpointed thelocationsofthousands of UtahandUSGSscientistshave since network ofinstrumentsin1973.University activity, theUSGSinstalledapermanent

u olcanic eruptions(vents), somearenot. l a ents perdayoccurredfromOctober 16to A new analysisbyUniversity ofUtahsci- The largest earthquake swarm recordedat To So commonweretheseshocksat Yel-

llowstone since1973occurredjustnorth- t i e

v e mm/yr) 19

documentandmonitorthisseismic e a r th q u a

uids through the impermeable rock rock impermeable the through uids

r l

u t p o l i f t 0 2,000 4,000 6,000 8,000 10,000 12,000 14,000

CUMULATIVE NUMBER OF EARTHQUAKES Y to trackandrespondchangesin strengthen thecapabilitiesofscientists canic depressions)intheworld. To at many otherlarge calderas(vol- similar tohistoricalchangesobserved va detected unmistakablechangesinits Y Y cal Survey, theUniversity ofUtah,and supported jointlybytheU.S.Geologi- stone Volcano Observatory (YVO) is Long Valley,The California. Yellow- for Hawaii, Alaska, theCascades,and 2001, complementingexisting ones v VOLCANO OBSERVATORY THE YELLOWSTONE • Communicatenew scientifi • • Assess thelong-termpotentialhaz- • Strengthenthemonitoringsystemfor olcano observatory was createdin ellowstone’s activity, afi ellowstone inthepast30yearshas ellowstone NationalPark. Enhance scientifi st underground volcanic system, of theEarth’s crust;and stone andinthesurroundingregion processes occurringbeneath Yellow- of active geologicandhydrologic Ye ex ards ofvolcanism, earthquakes, and hydrothermal (hotwater) system; and subsidence,changesinthe tracking earthquake activity, uplift The principalgoalsof YVO include: Increased scientifi State, andFederaloffi tional Park staff, thepublic,andlocal, vo hazardous hydrothermalexplosions or activity, andforecastsofpotential the currentstatusof Yellowstone’s plosive hydrothermalactivity inthe lcanic eruptionsto Yellowstone Na- llowstone region;

c understanding

c surveillance of

cials.

fth U.S.

c results, NW SE Yellowstone Caldera Volcanic and hydrothermal activity in the Yellowstone area is fueled by a large res- Geysers 0 ervoir of magma (partially molten rock) be- Swarm earthquakes neath a caldera (volcanic depression) that formed in a cataclysmic eruption 640,000 years ago. The magma reservoir includes 5 both rhyolitic magma, rich in silica (SiO2), Rhyolite and basaltic magma, which contains less (partial melt) R elati SiO2 and is denser. Capping the magma 10 Brittle vely im permea reservoir is a zone of hot, ductile rock that Basaltic magma ble layer Ductile can slowly fl ow to close any fractures and is therefore relatively impermeable (mean- 15 ing that fl uids cannot easily pass through). Basalt magma The cooler rock above behaves in a more intrusion brittle manner and can be readily fractured. 20 zone Sometimes the impermeable rock can be ruptured, allowing hot, salty fl uids to es- Pre-swarm seismicity 1973–1985 cape upward and laterally, moving through cracks in brittle rock. As shown in this dia-

APPROXIMATE DEPTH, IN KILOMETERS 25 1985 earthquake swarm (first part) Rising basaltic magma gram, such a ﬂ uid release in 1985 is thought to have triggered a large swarm of earth- 30 quakes just northwest of the caldera.

0 10 20 MILES

01020KILOMETERS the fi rst month the locations of earthquakes ence but rather by the latest period of caldera • How can the underground migration of moved to the northwest, away from the rim uplift, it has led scientists to ponder other liquids and gases be detected? What of the Yellowstone Caldera, along a narrow possible models that link magma intrusion, changes does such activity produce in the zone at an average rate of 500 feet (150 m) hydrothermal fl uid migration, and uplift of hydrothermal fl uids that emerge at the per day. For the rest of the swarm, into the the caldera. surface? following year, the earthquake locations grew systematically deeper, from less than 2 miles Monitoring future activity Coordination of scientists’ efforts by the (3 km) to more than 5 miles (8 km) deep, at The Yellowstone Volcano Observatory Yellowstone Volcanic Observatory will lead an average rate of about 80 feet (25 m) per (YVO), by facilitating collaboration among to better understanding of the region’s re- day. This intense earthquake swarm generally Earth scientists and focusing scientifi c at- markable volcanic and hydrothermal system coincided in time with the 1985–86 reversal tention on the active geologic processes in and ultimately to a greater ability to predict of ground movement in the central part of the Yellowstone, aims to increase our ability potentially hazardous events. This work at caldera—from uplift to subsidence. Was there to forecast potential consequences of these Yellowstone is only part of the ongoing ef- a common trigger for both sets of events? processes. Those future consequences could forts by the USGS Volcano Hazards Program A likely cause of the 1985 earthquake be large destructive earthquakes, hydro- to protect people’s lives and property in all swarm, according to scientists, was the thermal explosions, or volcanic eruptions. of the volcanic regions of the United States, rupture of a widespread layer of imperme- Forecasting whether hot pressurized fl uids including the Pacifi c Northwest, California, able rock (through which fl uids cannot pass) or even molten rock moving beneath Yel- Alaska, and Hawaii. above the magma reservoir. The rupture of lowstone will erupt at the surface depends this rock layer allowed pressurized hydro- on the ability of scientists to detect the Steven R. Brantley, Jacob B. Lowenstern, thermal fl uids (hot watery solutions) to move changing activity by real-time monitoring Robert L. Christiansen, Robert B. Smith, Henry Heasler, Greg Waite, and Charles Wicks upward and laterally out of the caldera and and on understanding how the vast Yel- into an adjacent network of fractures over a lowstone volcanic system, and other similar Edited by Peter H. Stauffer period of many weeks. As the fl uids pushed systems, work and behave. An ever-improv- Graphic design by Sara Boore and Susan Mayfi eld Banner design by Bobbie Myers through this network, cracks were opened ing monitoring system will undoubtedly and adjacent rocks were broken, resulting in contribute to this understanding and reveal COOPERATING ORGANIZATIONS several thousand small quakes. At the same new aspects of Yellowstone’s underground Yellowstone National Park time, according to this model, the lateral es- volcanic system. University of Utah cape of fl uids through the impermeable layer Future monitoring at Yellowstone will For more information contact: dramatically decreased the upward pressure seek answers to questions such as these: U.S. Geological Survey normally exerted by the hydrothermal sys- • Is ground deformation caused by rising (650) 329–5227 http://volcanoes.usgs.gov/yvo tem beneath the caldera, resulting in subsid- magma or by increased fl uid pressure or ence there. within the hydrothermal system? Yellowstone National Park http://www.nps.gov/yell/home.htm Another earthquake swarm occurred at • How are changes to the magma reservoir Yellowstone in 1995. Because this swarm linked to and refl ected in the overlying hy- This Fact Sheet and any updates to it are available online at http://pubs.usgs.gov/fs/fs100-03/ was not accompanied by caldera subsid- drothermal system?

Printed on recycled paper