Early on the morning of May 18, 1980, Arlene Edwards, a freelance photographer from Portland, Ore., and her 19-year-old daughter, Jolene, drove across the Columbia River to a high outcropping of rock in southwestern Washington State. There they set up Arlene's camera and began to watch the Mount St. Helens volcano ten miles to their southeast. For the previous two months the volcano had been spitting out ash and steam, and the Edwardses were among dozens of observers on surrounding ridges who idea they were a safe altitude away. It was a gorgeous Sunday forenoon, the air warm and still below a cloudless sky, the volcano grand and terrible nether its ash-streaked glaciers.

All of a sudden, the unabridged n side of Mount St. Helens began to slide into the adjacent valley. An aroused, gray cloud of pulverized stone and hot gas leaped from the void that had been a mountainside seconds before. The cloud grew explosively, filling the eastern heaven and rushing toward Arlene and her daughter. When the deject hitting the viewpoint on which they stood, it blew Arlene ane,000 feet away; her trunk was later plant tangled in the branches of a hemlock tree below the ridge. Jolene, dead of ash asphyxiation, was institute almost her mother'southward pickup. Effectually the mountain, 55 other people lay dead or mortally wounded, victims of an eruption much larger than geologists anticipated.

More 3 and a one-half decades afterward and just a few hundred yards down the ridge from where the Edwardses were standing, University of Washington seismology graduate educatee Carl Ulberg kneels amongst the greenery of the regrowing forest. A large plastic cooler is half-buried in the ground in front end of him, its dirt-speckled lid like a hatch into the secret. He reaches into a tangle of electronics and wires and pulls out a wink memory card. In the altitude, Mount St. Helens glistens in the sun, cooled magma from the volcano's most recent 2004–2008 eruptions partly filling its crater. Ulberg slips the flash bill of fare, which contains six months of data on vibrations under the mountain, into a plastic carrying instance and inserts a fresh card into the recorder. "This is how we're going to figure out what'south going on down there," Ulberg says, looking across to the volcano.

For the past three years this seismic station and 69 others scattered around Mount St. Helens accept been recording the jolts of buried explosives, the trembling of earthquakes and even the faint susurration of oceanic waves on distant shorelines. They are part of a project known every bit Imaging Magma Nether St. Helens, or iMUSH, an initiative to trace the movement of molten stone from the earth's interior to its surface. It is ane of the near ambitious and comprehensive efforts ever undertaken to paradigm the plumbing system under a volcano, and it has revealed a subterranean globe hitherto not seen. The traditional view of volcanoes has been simple: a magma-containing chamber deep underground, with a strawlike duct leading to the surface. Just nether Mountain St. Helens, molten rock is traveling through several interconnected reservoirs, where it undergoes chemical changes that tin atomic number 82 to more than forceful eruptions. The magma feeding the volcano is moving horizontally likewise as vertically, making its way around obstacles and taking advantage of preexisting faults in the earth. As information technology moves around, the magma causes both deep and shallow earthquakes, presaging hereafter eruptions as the magma chamber under the volcano recharges.

These and other findings from iMUSH take implications not just for the millions of people living near this and other volcanoes in the Cascade Range—including areas almost Vancouver, Seattle, Portland, Reno and Sacramento—simply other volcanoes worldwide. More than 25,000 people have died from eruptions effectually the planet since 1980, then the need for better gamble forecasts is acute. Like Mount St. Helens, almost state volcanoes ascent to a higher place colliding plates of the earth'due south crust that enable heat from the interior to reach the surface. 1 goal of the project is to extend the findings from iMUSH to other volcanoes, even ones that announced to be quite different. "All volcanoes are individuals," says Michael Clynne, a geologist at the U.S. Geological Survey's location in Menlo Park, Calif. "But we need to thoroughly understand this one to know what'south going on at others."

Seeing through stone

The deepest holes ever drilled into our planet become downward simply about eight miles, but the roots of a volcano extend much further. Say you had a rig that could go down as far as y'all wanted and started drilling next to Mount St. Helens. Y'all would encounter typical continental rocks for the offset 45 miles or and then—but and so something astonishing would happen. The drill would striking oceanic rocks, waterlogged, nevertheless carrying fossilized sea life.

This is a small-scale tectonic plate, a piece of the northern Pacific seafloor that is angling into the world under the edge of North America. This procedure, known as subduction, is the major driver of volcanism worldwide. When slabs of oceanic chaff descend under continental plates, they rut upward and create magmas in the overlying crust that percolate toward the surface. The plate diving under Northward America has made non but the line of volcanoes extending from Mount Garibaldi in British Columbia to Lassen Superlative in northern California but besides thousands of lava fields and spatter cones that speckle the Cascade Range.

Simply Mount St. Helens has some odd differences from other volcanoes in this roughly north-s line. One is that it is about xxx miles to the west. Another is that seismic studies suggest that the rock directly beneath Mount St. Helens is besides common cold to produce magmas, so where does the volcano get its molten fuel? Despite its out-of-the-way location, Mountain St. Helens has been the most active volcano in the Cascades in contempo centuries. In the early 1800s it erupted almost continuously for decades and a blast around 1480 was several times the size of the 1980 behemoth.

Catastrophe: The major 1980 eruption of Mount St. Helens sent a towering ash cloud xv miles into the air (ane). People had to exist rescued by helicopter (2). The boom mowed down forests, and fallout blanketed towns (3). Credit: Getty Images (1); AP Photo (2); John BarrGetty Images (iii)

The iMUSH project has sought to explicate this strange behavior by tracing the path of the volcano's magmas "from slab to surface," the project's organizers say. "Nosotros're using all the tools we take available to endeavour to figure out what's going on," says Ken Creager, a geophysicist at the University of Washington and i of the project'due south leaders. "No one technique volition go us where we want to get. But by putting them together, we hope to come up with a coherent story about how magma is moving."

Last Dec a few dozen iMUSH researchers gathered around a long, rectangular table in San Francisco. All the people in the room would telephone call themselves geologists, just geology has many branches, and near of these researchers knew relatively little about the detailed piece of work others were doing. Ulberg, for example, is a seismologist who gathers and analyzes seismic signals, but the people effectually the table included chemists, traditional hard-rock geologists and experts on the earth's magnetic field. They were meeting for what Cornell University geophysicist Geoffrey Abers chosen the "stare and compare" phase of iMUSH: looking at one another's results to see how they fit together.

The seismologists at the tabular array had the most accessible story to tell—which is ironic, given that seismology is somewhat akin to tapping on a multilayered brawl with a hammer and deducing its composition by the sounds it makes. Since the 1980 eruption, permanently installed seismometers around Mount St. Helens accept been listening for earthquakes that occur anywhere most the volcano. The waves from earthquakes travel faster through dense, hard rock and slower through hot, partly liquid stone. Past comparing convulsion vibrations at different seismometers around the volcano, geophysicists had been able to piece together a rough picture of where magma resides under the mountain.

The iMUSH researchers temporarily gave this seismic network a huge upgrade by adding more and better instruments, including the seismometer Ulberg was servicing. "The instrumentation used in iMUSH was an order of magnitude better, and the resolution was too an guild of magnitude better," says Seth Moran, a geophysicist at the USGS's Cascades Volcano Observatory. The seismometers gathered data from natural vibrations and from shaking caused by two dozen one,000- and ii,000-pound explosives detonated in boreholes. The result has been a much more accurate and detailed picture of hotspots and conduits below the mountain.

Connected chambers

The first surprise lay directly beneath the crater's lava dome. Earlier results had pointed to a shallow reservoir of magma just a mile or two under the crater. New findings suggest that this surface area actually consists of a circuitous network of fractures that aqueduct magma from deeper in the globe.

Beneath this fracture zone, both older and newer data reveal a sizable reservoir of magma extending from nigh five to 11 miles under the crater. Merely here, too, the new images from iMUSH are more nuanced. The traditional movie of a volcano focused on big "chambers" of magma connected to the surface by narrow tubes. But "the more we have investigated, the more we have come to realize that it's quite rare for there to exist a high fraction of liquid in the upper crust," notes Brandon Schmandt, a seismologist at the University of New Mexico. "Maybe 1 to ten percent of the pore space in a rock might be filled with melt, but that's a very different epitome than a sleeping accommodation." In keeping with this idea, the magma reservoir under Mount St. Helens seems to be more of a mush than a melt. Chemical reactions can transform the magma into distinct compounds held in dissimilar parts of the reservoir.

Further beneath this magma storage area, some other surprise: the seismic data have revealed a large mass of rock that is too cold and dumbo for magma to get through. Seismic waves sweep through the region at high velocity, an indication of exceptionally dense material. Blocked past this mass, ascent magma appears to exist detouring around the rock to the southeast. "Magma will come up the easiest mode it tin," says seismologist Alan Levander of Rice University. "What we think is that rock is moving up the sides of these high-velocity regions, collecting at the top and so moving into the upper magma reservoirs."

Knowing the complete pathway for the movement of magma could help predict future eruptions. Afterwards the 1980 eruption of Mount St. Helens, seismologists detected deep and unusually protracted earthquakes along presumed magma conduits, and comparable earthquakes have occurred before and after eruptions elsewhere in the earth. "The full general concept is that magma is moving on the way to an eruption or to refill a reservoir after an eruption," observes John Vidale, a seismologist at the University of Washington. These so-called deep, long-period earthquakes do not always presage an eruption, and sometimes they occur only subsequently a magma reservoir has emptied. But "when they're firing off, something is moving, and a volcano may be more than dangerous than usual," he says.

Ghost plate

Seismic waves are not the only fashion to encounter inside the earth. High in a higher place our heads, charged particles from the sun batter the globe's magnetic field and create electric currents inside the planet. With arrays of electromagnetic detectors on the earth's surface, geophysicists tin can measure out changes in these currents over time—and these changes reflect the presence of liquids. The method is chosen magnetotellurics. "Once you lot start to melt a rock, it lights upwardly similar a Christmas tree," says Paul Bedrosian of the USGS.

The magnetotelluric data from iMUSH have been eagerly predictable because of the hope that they volition resolve a long-standing controversy. Previous and sketchier information hinted at the presence of a huge reservoir of liquid underneath Mount St. Helens, Mount Adams to the eastward and Mount Rainier to the north. Some geologists proposed that all three volcanoes might exist sitting atop a vast, interconnected sea of magma.

Credit: Bryan Christie Design; Sources: Carl Ulberg and Ken Creager University of Washington; Paul Bedrosian U.S. Geological Survey (historic panels); Maren Wanke and Olivier Bachmann Swiss Federal Constitute of Applied science Zurich (reservoir schematic)

The much more detailed iMUSH information take non shown whatsoever such sea, only they signal to another intriguing possibility. The loftier conductivity under the volcanoes appears to be coming from a large region of h2o-bearing sedimentary rocks cached by plate tectonics. These rocks announced to mark the edge of the last major piece of North America to be tectonically plastered onto the Pacific Northwest: a ghost plate, once function of a region known as Siletzia that now lies buried, mostly to the west of Interstate 5, in Washington and Oregon. The suture zone between Siletzia and the balance of North America could exist an area of weakness through which fluids from below can travel. Sure enough, Mount St. Helens appears to sit down higher up or very near to that zone.

A preexisting weakness in the crust also could explicate the blobs of dense rock underlying Mountain St. Helens. Continual injections of magma into the suture zone could gradually cool, requiring future injections to make their way around these solidified intrusions. Like the seismic information, the magnetotelluric data reveal dense stone beneath Mount St. Helens around which magmas must exist migrating, although the two methods identify the rock in slightly different places. Reconciling these differences to create more detailed subterranean maps "is the juiciest part of the process," says Adam Schultz, who does magnetotelluric research at Oregon State Academy.

Many makes of magma

The about complex data, however, are neither seismic nor magnetotelluric. They are the data generated past walking around, picking upwards rocks on the mount and analyzing their components. A great diversity of lavas have erupted from Mount St. Helens, which seems counterintuitive given that they all came from the same volcano. Only even a glance at the multihued and multitextured walls of the volcano's crater suggests how hard information technology will exist to explain the petrology—the origins, limerick and distribution—of all the rocks information technology has emitted. Every bit magma ascends, it "differentiates, ascends again, crystallizes, picks upwardly some stuff, assimilates and finally reaches the surface," notes Olivier Bachmann, a petrologist now working in Switzerland, who was instrumental in getting iMUSH upward and running. The move of rock within the globe "is like a big washing motorcar," he says.

One kind of rock is both ubiquitous and telling. All around the volcano, hikers can achieve down and selection upward pieces of pumice, a calorie-free-colored, frothy stone so filled with bubbles that it floats. Nether a hand lens, the rock looks tortured. The air bubbles are stretched into long tendrils, equally if the lava were being torn autonomously as it solidified.

That stone provides a clue to the ferocity of the 1980 eruption. It consists of a substance known as dacite, which contains a relatively high per centum of silica. Silica makes magma mucilaginous, so that it clogs up the vents of volcanoes and traps the gases it contains. That is one reason why the 1980 eruption was so powerful: the glutinous dacite remained trapped nether the mount, building up pressure, until the plummet of the volcano'due south due north flank gave the pressure a way to escape.

Merely Mount St. Helens has erupted many other kinds of lava over its history. On its south side, lava caves burrow through runny basalts similar those seen in Hawaiian volcanoes. The pre-1980 cone, which took shape in only the past 2,500 years, consisted in part of mountain-edifice andesite rocks. How can a single volcano produce such unlike kinds of lava?

A abode run for iMUSH would be bookkeeping for the dacitic magmas that fabricated the 1980 eruption and then deadly while explaining the origins of the volcano's other magma types. Dawnika L. Blatter, Thomas West. Sisson and Westward. Ben Hankins, who are all USGS scientists, recently published a new caption, drawing both on the iMUSH results and on previous findings. Their hypothesis hinges on earlier work done by a joint Vanderbilt University–USGS team on the dating of zircons, which are crystals that tend to class in high-silica magmas. Zircons in lava from Mount St. Helens have undergone repeated cycles of heating and cooling, "like kneading a dough," Sisson says. Over many thousands of years injections of molten stone from beneath announced to take repeatedly heated areas of mush. Equally information technology thermally cycles, the magma picks upwardly silica from the surrounding crustal rocks, giving Mount St. Helens' lavas their characteristic stickiness. When plenty free energy enters the system, the transformed magma forces its way to the surface.

Mount Doom: Before the 1980 outburst blew off its pinnacle, Mount St. Helens towered nigh ten,000 anxiety in the air. Credit: Getty Images

But sometimes the injections of magma from below are powerful plenty to shoot right through the middle of the storage region with footling modification. Every bit geophysicist Weston Thelen of Cascades Volcano Observatory says, fresh magma from deep in the earth can "race out of the drape, largely skip storage and be erupted immediately," bookkeeping for the runny basalts that Mountain St. Helens sometimes emits.

If this model bears out, it could have implications around the earth. Many infamously fierce volcanoes erupt mostly dacitic magmas, including Mountain Pinatubo in the Philippines, Thíra in Greece and Krakatau in Indonesia. If earthquakes, gas emissions or other signals could be linked to the processing of magmas underground, volcanologists could take another way of predicting dangerous eruptions. "1 of our shortcomings in studying hazardous volcanoes," Sisson says, "is we generally don't know they're getting prepare to erupt until magma makes it to the upper crust, where information technology generates earthquakes and footing deformation." Understanding how magma is beingness cooked deep underground—how it is separating chemically, how it is interacting with the surrounding rock—could indicate what information technology is getting ready to do.

Preparing for the inevitable

Today Mount St. Helens is placidity. Tourists viewing the crater and scientists working on its flanks have no need to worry well-nigh an unexpected eruption. Simply the mountain's repose will not concluding. Several times since the 1980 eruption—most recently in 2016—flurries of relatively shallow earthquakes below the crater have pointed to the movement of magma. The earthquakes practice not hateful that an eruption is imminent, only "the system is recharging," says the University of Washington's Creager. "The volcano has begun building up to its next eruption."

Geologists and emergency planners in the Pacific Northwest learned a hard lesson from the 1980 eruption. When a dangerously unpredictable volcano is rumbling, they will never once again let people within just a few miles. Merely volcanoes pose many dangers other than explosive eruptions. If ashfalls similar those from previous Cascades eruptions were to occur today, they would devastate big downwind communities. Volcanic mudflows can roar down river valleys with little warning. At nowadays, Mount Rainier, which looms but to the southeast of Seattle and Tacoma, is considered much more dangerous than Mount St. Helens because of its size and the number of people living nearby. More than than 150,000 Washingtonians live and work on top of mudflows from Rainier that have occurred within the by few g years.

The iMUSH results have given geologists a more detailed, though more complicated, picture show of what is happening under Mount St. Helens. That picture is producing a new perspective on subterranean signals that mean something is happening, signals that not been well understood. When the adjacent eruption occurs—either at Mount St. Helens or elsewhere—a amend grasp of those details could mean the deviation between life and death.