Tsunami-like waves created by an earthquake may have triggered the world's largest known hydrothermal explosion some 13,000 years ago, a federal scientist says.
The explosion created the Mary Bay crater that stretches more than one mile across along the north edge of Yellowstone Lake. Debris from the explosion has been found miles away.
Lisa Morgan of the U.S. Geological Survey told a gathering of scientists over the weekend at Mammoth Hot Springs that an earthquake may have displaced more than 77 million cubic feet of water in Yellowstone Lake, creating huge waves that essentially unsealed a capped geothermal system.
Though much has been made in recent years of a possible eruption of Yellowstone's "super volcano," geologists studying the park have long said that the likelihood is greater for a large hydrothermal explosion.
Morgan said that over the last 14,000 years there have been 20 hydrothermal explosions in Yellowstone that mostly left craters bigger than football fields. They resulted in well-known Yellowstone landmarks such as Mary Bay, Turbid Lake and Indian Pond, all near the north edge of Yellowstone Lake.
The explosions happen when hot water just below the surface flashes into steam and breaks through the surface.
Smaller explosions in Yellowstone happen about once every two years but rarely when people are around or in danger, according to a 2007 hazard assessment produced by USGS.
In 1989, an explosion at Porkchop geyser at Norris Geyser Basin sent rocks and debris flying more than 200 feet.
But geologists are still trying to better understand the larger explosions that happen about once every 700 years in Yellowstone and have left behind the biggest hydrothermal explosion craters in the world.
At Mary Bay, Morgan said she thinks there were at least two big waves before the explosion. Evidence of those waves has been found more than 3 miles north of the lake's edge, she said.
The explosion's column may have reached more than a mile in the air and spread debris across some 18 square miles, she said.
"You would not want to be here when this occurred," Morgan said.
Predicting if or when another will happen remains difficult but it's worthy of continued study, scientists involved with Yellowstone's geology said.
"It's something we should take notice of," Morgan said.
A big blob of molten rock appears to pushing up remnants of an ancient volcano in Yellowstone National Park in Wyoming, scientists reported Friday.
They say no volcanic explosion is imminent â that already happened 642,000 years ago, creating the volcanic crater known as a caldera where part of Yellowstone Lake sits.
But satellite readings show just how volcanically active the area remains, the researchers reported in the journal Science.
From the middle of 2004 through 2006, the floor of the caldera rose 7 inches at a rate of 2.8 inches a year â the biggest rise ever measured, they reported.
âThere is no evidence of an imminent volcanic eruption or hydrothermal explosion. That's the bottom line,â University of Utah seismologist Robert Smith said in a statement.
âA lot of calderas worldwide go up and down over decades without erupting.â
Yellowstone is North America's largest volcanic field, produced by what is known as a hotspot, a plume of hot and molten rock squirting up from 400 miles beneath the planet's surface.
Monstrous eruptions took place there starting 2 million years ago but activity bubbles along much more calmly now â akin to similar volcanic fields such as the Campi Flegrei just outside Naples in Italy.
Beneath the field lies what is known as a magma chamber, which is actually similar to a wet sponge in structure.
âOur best evidence is that the crustal magma chamber is filling with molten rock,â Smith said. âBut we have no idea how long this process goes on before there either is an eruption or the inflow of molten rock stops and the caldera deflates again.â
Heat from the chamber warms the park's hundreds of hot springs and geysers, including âOld Faithful,â perhaps the world's best-known geyser.
Established in 1872 as the first U.S. national park, Yellowstone also stretches to parts of Montana and Idaho.
The Yellowstone "supervolcano" rose at a record rate since mid-2004, likely because a Los Angeles-sized, pancake-shaped blob of molten rock was injected 6 miles beneath the slumbering giant, University of Utah scientists report in the journal Science.
"There is no evidence of an imminent volcanic eruption or hydrothermal explosion. That's the bottom line," says seismologist Robert B. Smith, lead author of the study and professor of geophysics at the University of Utah. "A lot of calderas [giant volcanic craters] worldwide go up and down over decades without erupting."
The upward movement of the Yellowstone caldera floor -- almost 3 inches (7 centimeters) per year for the past three years -- is more than three times greater than ever observed since such measurements began in 1923, says the study in the Nov. 9 issue of Science by Smith, geophysics postdoctoral associate Wu-Lung Chang and colleagues.
"Our best evidence is that the crustal magma chamber is filling with molten rock," Smith says. "But we have no idea how long this process goes on before there either is an eruption or the inflow of molten rock stops and the caldera deflates again," he adds.
The magma chamber beneath Yellowstone National Park is a not a chamber of molten rock, but a sponge-like body with molten rock between areas of hot, solid rock.
Chang, the study's first author, says: "To say if there will be a magma [molten rock] eruption or hydrothermal [hot water] eruption, we need more independent data."
Calderas such as Yellowstone, California's Long Valley (site of the Mammoth Lakes ski area) and Italy's Campi Flegrei (near Naples) huff upward and puff downward repeatedly for decades to tens of thousands of years without catastrophic eruptions.
Smith and Chang conducted the study with University of Utah geophysics doctoral students Jamie M. Farrell and Christine Puskas, and with geophysicist Charles Wicks, of the U.S. Geological Survey in Menlo Park, Calif.
Yellowstone: A Gigantic Volcano Atop a Hotspot
Yellowstone is North America's largest volcanic field, produced by a "hotspot" -- a gigantic plume of hot and molten rock -- that begins at least 400 miles beneath Earth's surface and rises to 30 miles underground, where it widens to about 300 miles across. There, blobs of magma or molten rock occasionally break off from the top of the plume, and rise farther, resupplying the magma chamber beneath the Yellowstone caldera.
Previous research indicates the magma chamber begins about 5 miles beneath Yellowstone and extends down to a depth of at least 10 miles. Its heat powers Yellowstone's geysers and hot springs -- the world's largest hydrothermal field.
As Earth's crust moved southwest over the Yellowstone hotspot during the past 16.5 million years, it produced more than 140 cataclysmic explosions known as caldera eruptions, the largest but rarest volcanic eruptions known. Remnants of ancient calderas reveal the eruptions began at the Oregon-Idaho-Nevada border some 16.5 million years ago, then moved progressively northeast across what is now the Snake River Plain.
The hotspot arrived under the Yellowstone area sometime after about 4 million years ago, producing gargantuan eruptions there 2 million, 1.3 million and 642,000 years ago. These eruptions were 2,500, 280 and 1,000 times bigger, respectively, than the 1980 eruption of Mount St. Helens. The eruptions covered as much as half the continental United States with inches to feet of volcanic ash.
The most recent giant eruption created the 40-mile-by-25-mile oval-shaped Yellowstone caldera. The caldera walls have eroded away in many areas -- although they remain visible in the northwest portion of the park. Yellowstone Lake sits roughly half inside and half outside the eroded caldera. Many smaller volcanic eruptions occurred at Yellowstone between and since the three big blasts, most recently 70,000 years ago. Smaller steam and hot water explosions have been more frequent and more recent.
Measuring a Volcano Getting Pumped Up
In the new study, the scientists measured uplift of the Yellowstone caldera from July 2004 through the end of 2006 with two techniques:1. Twelve Global Positioning System (GPS) ground stations that receive timed signals from satellites, making it possible to measure ground uplift precisely.
2. The European Space Agency's Envisat satellite, which bounces radar waves off the Yellowstone caldera's floor, another way to measure elevation change.
The measurements showed that from mid-2004 through 2006, the Yellowstone caldera floor rose as fast as 2.8 inches (7 centimeters) per year -- and by a total of 7 inches (18 centimeters) during the 30-month period, Chang says.
"The uplift is still going on today but at a little slower rate," says Smith, adding there is no way to know when it will stop.
Smith says the fastest rate of uplift previously observed at Yellowstone was about 0.8 inch (2 centimeters) per year between 1976 and 1985.
He says that Yellowstone's recent upward motion may seem small, but is twice as fast as the average rate of horizontal movement along California's San Andreas fault.
The current uplift is faster than ever observed at Yellowstone, but may not be the fastest ever, since humans weren't around for its three supervolcano eruptions.
Chang, Smith and colleagues conducted computer simulations to determine what changes in shape of the underground magma chamber best explained the recent uplift.
The simulations or "modeling" suggested the molten rock injected since mid-2004 is a nearly horizontal slab -- known to geologists as a sill -- that rests about 6 miles (10 kilometers) beneath Yellowstone National Park. The slab sits within and near the top of the pre-existing magma chamber, which resembles two anvil-shaped blobs expanding upward from a common base.
Smith describes the slab's computer-simulated shape as "kind of like a mattress" about 38 miles long and 12 miles wide, but only tens or hundreds of yards thick.
In reality, he believes the slab resembles a large, spongy pancake formed as molten rock injected from below spread out near the top of the magma chamber.
The pancake of molten rock has an area of about 463 square miles, compared with 469 square miles of land for the City of Los Angeles.
Smith and colleagues believe steam and hot water contribute to uplift of the Yellowstone caldera, particularly during some previous episodes, but evidence indicates molten rock is responsible for most of the current uplift.
Chang says that when rising molten rock reaches the top of the magma chamber, it starts to crystallize and solidify, releasing hot water and gases, pressuring the magma chamber. But gases and steam compress more easily than molten rock, so much greater volumes would be required to explain the volcano's inflation, the researchers say.
Also, large volumes of steam and hot water usually are no deeper than 2 miles, so they are unlikely to be inflating the magma chamber 6 miles underground, Smith adds.
Ups and Downs at Yellowstone
Conventional surveying of Yellowstone began in 1923. Measurements showed the caldera floor rose 40 inches during 1923-1984, and then fell 8 inches during 1985-1995.
GPS data showed the Yellowstone caldera floor sank 4.4 inches during 1987-1995. From 1995 to 2000, the caldera rose again, but the uplift was greatest -- 3 inches -- at Norris Geyser Basin, just outside the caldera's northwest rim.
During 2000-2003, the northwest area rose another 1.4 inches, but the caldera floor itself sank about 1.1 inches. The trend continued during the first half of 2004. Then, in July 2004, the caldera floor began its rapid rate of uplift, followed three months later by sinking of the Norris area that continued until mid-2006.
Smith believes that uplift of the middle of the caldera decreased pressure within rocks along the edges of the giant crater, "so it allowed fluids to flow into the area of increased porosity." That, in turn, triggered small earthquakes along the edge of the "pancake" of magma. The amount of hot water flowing out of the deflated Norris area is much smaller than the volume of magma injected beneath the caldera, Smith says.
The research was funded by the National Science Foundation, the U.S. Geological Survey and the Brinson Foundation.
Adapted from materials provided by University of Utah.
The orange shapes in this image represent the magma chamber -- a chamber of molten and partly molten rock -- beneath the giant volcanic crater known as the Yellowstone caldera, which is represented by the rusty-colored outline at the top. The red rectangular slab-like feature is a computer-generated representation of molten rock injected into the magma chamber since mid-2004, causing the caldera to rise at an unprecedented rate of almost 3 inches a year, according to a new University of Utah study. In reality, the injected magma probably is shaped more like a pancake than a slab. The two rusty circles within the caldera outline represent the resurgent volcanic domes above the magma chamber.
(Credit: Wu-Lung Chang, University of Utah)
According to the National Geographic, the Yellowstone caldera has been rising at a rate of approximately 3 inches every year since the middle of 2004, three times faster than any previous measurements.
Although the Supervolcano hasnât produced any eruption for at least 70,000 years, it is still very active and most experts believe that it will erupt at some time in the future. Whether this will be a moderate eruption (comparable to Mount St. Helens), or something much larger and potentially more catastrophic globally, is impossible to predict.
The last major eruption at Yellowstone was 640,000 years ago, which created a caldera some 40 miles in width, but these have happened on a fairly regular basis over the last two million years, and it could be said that the next is overdue.
The current changes at Yellowstone were detected by global positioning system stations and radar instruments on an orbiting satellite, but Kenneth Pierce of the U.S. Geological Survey in Bozeman, Montana said â..the Yellowstone caldera has inflated and deflated about six to eight times without a volcanic eruptionâ during the last 14,000 years. Robert Smith, a geophysics professor at the University of Utah who co-authored the recent study agreed âCalderas go up and downâ but âoccasionally they burpâ.
A large "burp", as Robert Smith puts it, could produce catastrophic effects for the world population and a similar eruption of the Supervolcano in Toba (Indonesia) 75,000 years ago is believed to have wiped out 60% of the human population. On that occasion the Toba Supervolcano ejected almost three times as much material as the Yellowstone eruption did 640,000 years ago. However, the Yellowstone caldera can do much worse and this occurred 2.2 million years ago.
Indonesia has also seen some recent volcanic activity, and scientists are concerned that Mount Kelud might be on the verge of a devastating eruption. A number of volcanoes in the region have been spewing out hot ash, molten rock and dark smoke, including Anak Krakatao (Child of Krakatoa). Kelud killed more than 5,000 people following an eruption in 1919.
A large eruption could easily plunge the Earth into a âvolcanic winterâ and worsen the present climatic changes we are experiencing. Some have suggested that these âchangesâ might even be connected with Global Warming, and if the cause is originating from space, this may well be true.
Earthside Comments: We've been particularly interested in this subject for some time. What follows is some of the information upon which the Discovery Channel movie is based.
Over the past two million years, the Yellowstone supervolcano has erupted every 600,000 years. It was 640,000 years ago when it last exploded. Another eruption, geologically speaking, is therefore, threatening.
Five miles beneath Yellowstone, lies an immense pool of red hot magma. Fed from the Earth's mantle, it has been growing. This reservoir of magma and gas is now 31 miles long, 19 miles wide, and six miles deep. The building pressures must be enormous.
The Yellowstone "hot spot" is considered the foundation of a rare "supervolcano." It is estimated that a supervolcano would erupt with the power at least 1000 times greater than that of an 'ordinary' volcano.
The eruption 640,000 years ago created an extremely large crater - the caldera - that today comprises a major portion of the center of the park.
Signs of increased volcanic activity have recently been observed in and around Yellowstone National Park. The north part of Yellowstone Lake has bulged by nearly 170 feet over the past 50 years. The lake has spread into forest on one side of the lake as the surface beneath the water has inflated.
A massive eruption of the Yelowstone supervolcano would be catastophic for North America and would also result in years of freezing temperatures for the rest of the planet as volcanic dust and ash obscured the warmth of the sun.
Molten rock flowing beneath Yellowstone has been causing the national park to rise and fall, scientists say. Periodic uplifting and settling has occurred here over the last 15,000 years. A new model helps explain the latest episode of rapid surface rise and increased geyser activity—from 1997 to 2003—in the volcanically active region in the western United States.
The Yellowstone caldera has been classified a high threat for volcanic eruption, according to a report from the U.S. Geological Survey. Yellowstone ranks 21st most dangerous of the 169 volcano centers in the United States, according to the Geological Survey's first-ever comprehensive review of the nation's volcanoes. Kilauea in Hawaii received the highest overall threat score followed by Mount St. Helens and Mount Rainer in Washington, Mount Hood in Oregon and Mount Shasta in California.
YELLOWSTONE NATIONAL PARK, Wyo. -- Scientists say the odds of another catastrophic volcanic eruption in Yellowstone within anyone's lifetime are extraordinarily remote, but that's exactly what happens in a made-for-television movie that will air this Sunday. The docudrama, "Supervolcano,'' will be shown on the Discovery Channel. The middle of Yellowstone is a huge caldera that last erupted 640,000 years ago. Other huge eruptions occurred 1.3 million and 2.1 million years ago. "It's actually quite a well-done movie,'' said Bob Christiansen, former U.S. Geological Survey scientist-in-charge for the Yellowstone Volcano Observatory. The producers consulted with Christiansen, and he said they worked hard to get the science behind the eruption right. "It depicts the worst possible scenario that could conceivably happen,'' he said, "and it should be viewed in that light.''
Yellowstone's biggest event occurred 2 million years ago, ejecting 1,500 cubic miles (2,500 cubic kilometers) of rock into the air. Waist-high layers of volcanic ash or tuff from that eruption have been found in Iowa, nearly a thousand miles away. Here is the bad news: the last eruption occurred about 700,000 years ago -- and the two before that likewise were separated by 700,000 years. "The current thinking has not changed for several years," said John Valley, professor of geology at the University of Wisconsin-Madison. "There has historically been a clear recurrence interval at the Yellowstone hotspot." It is not unreasonable to think another gigantic eruption may happen within the next 100,000 years, and perhaps sooner, he said. "That's the blink of an eye geologically, but it's not going affect anyone's decision to buy a house," Valley said. Perhaps as time passes, these eruptions get less intense? "No," he said. Based on past experience, the consequences to humanity from such an eruption could be serious in the extreme.
Earthquakes Rattle Jackson
Four earthquakes shook Jackson Hole in the early morning hours Wednesday. The first temblor at 12:57 a.m. measured 5.0 on the Richter scale, the largest recorded in Teton County history, according to the Wyoming State Geological Society. It was followed by four aftershocks, all centered about 7 miles east of Kelly in the Gros Ventre Range. ... an expert on seismic activity in Yellowstone, said it is unclear how activity in one area might affect seismic activity on other nearby faults. But he said it does not appear that increased heat and geothermal activity in the Norris Basin this summer is related to tectonic or magma activity, but may instead be due to the drought and dropping water tables.
Casper Star Tribune - January 8, 2004
Yellowstone Geyser Puzzles Scientists
YELLOWSTONE N.P., WYO. - Call it Yellowstone's unfaithful geyser. Steamboat geyser has erupted five times since May 2000, shooting scalding water and rock as high as 300 feet into the air, and roaring 24 hours afterward. But Steamboat has not always been that dynamic; before the recent events, it had not erupted since 1991, and it has gone 50 years between know eruptions. Although park officials are unsure of what is happening at Steamboat, they note that the region around the Norris basin has risen about five inches in the past few years, and that water temperatures there increased before an April 2002 eruption. Water flows have increased as well, possibly exerting pressure on Steamboat, and steam vents and springs have multiplied. These and some other shifts to the Norris basin's underground plumbing help to explain why Steamboat seems to have awakened.
National Parks Conservation Association - October/November 2003
In Yellowstone, a Subterranean Volcano Exerts Its Influence
Thermal Activity in Yellowstone Sparks Increased Monitoring
New York Times - October 7, 2003 (full story below)
Norris Geyser Basin of Yellowstone National Park has long been recognized as the hottest and most changeable of Yellowstone's famous hydrothermal wonders. This summer, Norris lived up to its hot, unstable reputation as scientists and visitors alike have seen significant changes in many geysers and increased ground temperatures in the western part of the basin. Porkchop Geyser, which sprang to life from a small hot spring in 1971, erupted in July for the first time since 1989. ... On July 23, the park superintendent closed access to the western part of Norris Geyser Basin, known as the Back Basin, for public safety (other parts of Norris remain open to the public).
U.S. Geological Survey's Hawaiian Volcano Observatory - September 15, 2003
Lake-Bottom Feature Fascinates Scientists
CODY, Wyo. The dark depths of Yellowstone Lake, with recently discovered thermal vents and explosion craters, hold some of the most tantalizing mysteries in Yellowstone National Park. The most intriguing may be a bulge on the lake floor that stretches seven city blocks and rises as a tall as a 10-story building.
Billings Gazette - September 13, 2003
A Monster Awakens?
In the heart of America lies a monster that could destroy life on earth.
This worrying situation was confirmed on September 8th. by Dr. Bruce Cornet, a geologist and paleobotanist with the USGS, who explained: "Steam pressure is apparently building again in Yellowstone, and hydrothermal fluids and steam are working their way up through fractures and vents. If more steam vents appear, that means a continuous pathway for pressure release has been established to the magma chamber. If that happens, the pressure in the magma chamber will continue to drop until it reaches a critical stage when the superheated water within the magma explodes. Unfortunately, as the steam venting subsides, was just another cyclical event, and the danger is over. But that will be the farthest from the truth. It will be the quiet before the storm." Initially this should be of little or no consequence to anyone apart from those planning to visit Yellowstone .... except for one thing. Lurking beneath Yellowstone National Park is one of the most destructive natural phenomena in the world - a massive supervolcano.
Daily Express - September 10, 2003
Earthquake Felt in Yellowstone National Park
A magnitude 4.4 earthquake occurred near Yellowstone National Park in Wyoming Thursday and was felt in the park, the University of Utah Seismograph Stations said. No injuries or damage was reported or expected, seismologist Jim Pechmann said. The epicenter of the earthquake at 1:46 a.m. MDT was Huckleberry Mountain, Wyo., eight miles southeast of the south entrance to the park. Pechmann said the quake was felt in the park at the south entrance and at Grant Village, a tourist service area.
San Fransisco Chronicle/Associated Press - August 21, 2003
Mystery Bulge in Yellowstone Lake
Park Lake Hints at Buildup to Huge Blast
YELLOWSTONE NATIONAL PARK, Wyo. - The mystery of the deep at picturesque Yellowstone Lake is a bulge that rises 100 feet from the lake floor, stretches the length of seven football fields, and has the potential to explode at any time. Of all the life-threatening events that could happen at Yellowstone - from volcanic eruptions to massive earthquakes - this type of hydrothermal explosion is likely the most immediate, serious hazard in the park. So, scientists are trying to better understand possible warning signs.
Denver Post - August 10, 2003
Steamboat geyser erupted for the fourth time in just over a year, prompting new questions about increased activity for the world`s biggest geyser. Intervals between eruptions at Steamboat, a famously unpredictable and spectacular geyser, historically range from about four days to 50 years.
KTWO-TV - April 29, 2003
Yellowstone Volcano Observatory
Monitoring the Largest Volcanic System in North America
United States Geologocal Survey
It Is Time To Cast a Worried Eye Towards Yellowstone
Larry Park and Marshall Masters - August 22, 2003
Dr. Robert Smith, University of Utah
Yellowstone National Park Region Seismicity Maps
University of Utah Seismograph Stations
Yellowstone: Restless Volcanic Giant
Daniel Dzurisin, Robert L. Christiansen, and Kenneth L. Pierce,
VOLCANO HAZARDS FACT SHEET: USGS Open-File Report
Supervolcanoes Could Trigger Global Freeze
BBC- February 3, 2003
Hidden deep beneath the Earth's surface lie one of the most destructive and yet least-understood natural phenomena in the world - supervolcanoes. Only a handful exist in the world but when one erupts it will be unlike any volcano we have ever witnessed. The explosion will be heard around the world. The sky will darken, black rain will fall, and the Earth will be plunged into the equivalent of a nuclear winter.
First shown: Thursday, February 3, 2000 - BBC2
NARRATOR: Yellowstone is America's first and most famous National Park. Every year over three million tourists visit this stunning wilderness, but beneath its hot springs and lush forests lies a monster of which the public is ignorant.
PROF ROBERT CHRISTIANSEN (US Geological Survey): Millions of people come to Yellowstone every year to see the marvellous scenery and the wildlife and all and yet it's clear that, that very few of them really understand that they're here on a sleeping giant.
NARRATOR: If this giant were to stir, the United States would be devastated and the world would be plunged into a catastrophe which could push humanity to the brink of extinction.
PROF ROBERT SMITH (University of Utah): It would be extremely devastating on a scale that we've probably never even thought about.
PROF BILL McGUIRE (Benfield Greig Centre, UCL): It would mean absolute catastrophe for North America and the problem is we know so little about these phenomena.
Mount Washburn Web Cam
New York Times - October 7, 2003
In Yellowstone, a Subterranean Volcano Exerts Its Influence
By JIM ROBBINS
YELLOWSTONE NATIONAL PARK, Wyo. - The rolling pine forests, snowcapped mountains and crisp fall evenings here tend to make people forget the fact that the park sits atop a huge simmering underground volcano. But new geologic events have served up reminders.
In a few days in July, acidic ground water dissolved parts of the unpaved trails in the Norris Geyser Basin, and the ground temperature of the trails shot up to 200 degrees from the usual maximum of 80. Park officials closed nearly half of the basin's trails, and they remain shut.
On Aug. 21, a magnitude 4.4 earthquake shook the southern boundary of the park and startled residents. Yellowstone is one of the most seismically active places on the planet, with hundreds of shakes and shimmers throughout the year. They reach magnitude 4 usually only every other year.
In the park, such events are no great surprise. "Change is what we expect in Yellowstone," said the park geologist, Hank Heasler.
Although there is no indication that any of the changes suggest an impending eruption, even that would not be so surprising.
Over last 630,000 years, Yellowstone has experienced 29 eruptions the size of the one on Mount Pinatubo in the Philippines in 1991. The average interval here has been 20,000 years, and 70,000 have passed since its last eruption.
But the volcano, with a caldera 45 by 28 miles, has the potential for far more catastrophic explosions. The last major eruption, estimated at a magnitude 1,000 times as great as the Mount St. Helens explosion of 1980, was 627,000 years ago. The ancient blast blew up miles of mountain range, and ash from it has been uncovered in 22 Western states. It was so thick 1,000 miles away in Kansas that it was mined in the 1930's and used to make a cleanser.
Whether the caldera erupts or not, the stew of partly molten rock 5 to 10 miles below the park exerts a powerful and constant influence.
"The whole of the Yellowstone Plateau is going up and down from the magma," averaging one and a half centimeters a year, said Dr. Robert B. Smith, a professor of geophysics at the University of Utah and a member of the Yellowstone Volcano Observatory. "It's like a living, breathing thing."
In light of the new activity, safety is a growing concern, and officials are writing a hazard plan in case the region grows more active. The ground warming could mean that heat is increasing water pressure, a possible cause of eruptions.
In 1989, Porkchop Geyser in Norris Basin became clogged with silica. It exploded and created a 12-foot-wide crater now called Porkchop Hot Spring.
A hydrothermal explosion at Mary Bay in Yellowstone Lake some 13,000 years ago blew out a crater more than three miles across.
Serious earthquakes are always a possibility. Even though the temblor on Aug. 21 caused no damage, it was widely felt.
The largest quake recorded in the West, 7.5 on the old Richter scale, was centered just outside the park in 1959. It dislodged a huge slice of a mountain west of the park, buried 25 campers as they slept in a national forest campground and dammed the Madison River to create Quake Lake.
One question that occupies geologists is how the caldera affects fault lines and vice versa. Five major faults terminate in the molten caldera, and even far-flung events can shake the earth here. In November 2002, a magnitude 7.9 quake in Denali National Park in Alaska rippled through the region, leading to more than 500 other quakes that Dr. Smith watched simultaneously on a computer in Utah.
"The whole of Yellowstone lit up like a Christmas tree," he said. "It was exciting. I had a ranger call me and say, `I've called you before about earthquakes, but these are coming at us from all directions.' "
Except for the quake two months ago, Yellowstone has had far fewer quakes in recent years. "Seismically, its been deathly quiet," Dr. Smith said. "We average a half-dozen to 20 quakes" a day. "The last two years, we see a couple a day."
The energy of the quakes has been harnessed to shed light on the volcano. A measuring method, seismic tomography, which is similar to C.T. scanning, uses the shock waves that the quakes generate to map structures deep in the earth. Figures from 12,000 quakes gave Dr. Smith a picture of the size and shape of the magma chamber.
The magma also fuels geothermal features. All the geyser basins are similar, in that they sit over porous channelized rock layers that contain water under pressure. The water seeps toward the magma zone, where it is superheated. As the water is forced back toward the surface, the pressure is relieved and volume expands, causing geysers to erupt.
Even among the steaming, hissing and bubbling landscapes here, Norris Basin stands out. Steamboat Geyser is the tallest one in the park, at 380 feet, more than twice as high as Old Faithful. Test drilling in 1929 measured water temperatures 265 feet down at 400 degrees, and drilling equipment had to be withdrawn.
"The geothermal features of Norris are equally amazing to scientists who have been here for 30 years or someone on their first visit," said Mr. Heasler, the geologist.
Each year, a disturbance at Norris alters features and muddies the water. This year, the disturbance, on July 11, was more severe than usual. Because the "plumbing" is underground, the more precise mechanics of geyser basins are not well understood, and why Norris Basin has changed so markedly and suddenly is guesswork.
"The most common hypothesis is that snowmelt wanes and the water table lowers and weight on the system decreases and, as a result, the water boils more aggressively," said Dr. Jake Lowenstern, a geologist at the United States Geological Survey in Menlo Park, Calif., who is in charge of the Yellowstone Volcano Observatory.
Many features took longer than usual to return to base line, although some have not returned. Echinus Geyser once erupted frequently, every 35 to 75 minutes. In 1998 it switched to an irregular pattern. It had been erupting every two to nine hours before this season's disturbance, which somehow made it blow on a schedule again, every 3 hours 30 minutes to 3 hours 40 minutes. The geyser has now reverted to irregularity.
Pearl Geyser, an erupting pool named for its opalescent blue color, usually has two-meter eruptions. After the disturbance, it changed color to crystal clear, then became a steam vent and later returned to an opalescent pool with one-meter eruptions.
At the northern end of the basin, a series of vents, or fumaroles, appeared and mud pots cropped up on the trail, splattering hot acidic mud, though it later disappeared.
"Norris," Mr. Heasler said, "is showing us something, and whether we can figure it out, we'll see."