The Great Quake: How the Biggest Earthquake in North America Changed Our Understanding of the Planet

by Henry Fountain

  Some years before Hess’s fathometer work, another scientist had speculated—quite accurately, as it turned out—as to what might be going on. Arthur Holmes was a British geologist, born in 1890, who as a teenager had been inspired to study the subject by reading the works of Eduard Suess, the contraction theorist. Early in his career he had become interested in radioactivity, and he was a pioneer in the development of radioactive dating, using the rate of decay of isotopes in rocks to determine their age. At age twenty-three he had published a seminal work, The Age of the Earth, in which he estimated that the planet was 1.6 billion years old.

  On the question of the continents, Holmes at first had adopted Suess’s ideas about a cooling, contracting earth. But as the years went by and he learned more about radioactivity and heating, he eventually rejected contraction in favor of continental drift. Holmes thought a lot about Wegener’s theory, focusing on what most people considered its weakest link, the lack of a suitable mechanism by which the continents would plow across the oceanic crust.

  By the mid-1920s, scientists had some understanding of the earth’s interior, although it was still limited. There had been a series of discoveries based on the study of how waves produced by earthquakes were affected by traveling through the earth, starting with Richard Oldham, a British geologist who, in 1906, found evidence that the earth had a core. Three years later a Croatian, Andrija Mohorovičić, discovered a boundary between the planet’s top layer, the crust, and a region below it, called the mantle. This boundary varied in depth, from less than ten miles below the ocean floor to as much as sixty miles below the continents. Finally, in 1915, the German geologist Beno Gutenberg (who went on to develop the earthquake magnitude scale with Charles Richter) found what appeared to be a boundary between the core and the mantle, at a depth of about two thousand miles.

  One big question was whether this large mantle region was liquid, as recent work had suggested that at least part of the core was, or solid, like the crust. Holmes, through his knowledge of radioactive decay, knew that there was a lot of heat inside the earth. In The Age of the Earth he’d suggested that temperatures could reach 1,300 degrees Fahrenheit or higher not too far down. Perhaps, he thought, the mantle was basically an extremely thick liquid. Mostly it behaved like a solid, but under certain conditions it could slowly flow like a liquid. There was plenty of heat down there, and it had to go somewhere. Perhaps there could be convection within the mantle.

  Convection is all around us. It’s what makes water heat up in a pot on the stove, for example. As the water warms from the heat source below it, it expands, becomes less dense and rises. As it does so, it displaces colder water at the top, which descends because it is denser. Now this colder water is closer to the heat source, so it warms and rises, and the warmer water at the top, now farther from the heat source, cools somewhat and falls. A current is created as the water goes round and round, rising and falling as it heats and cools; the zone where all this is occurring is known as a convection cell. Since heat is continuously being added at the burner, eventually the entire pot of water is hot.

  Convection can occur in any liquid or gas. Hot air rises and colder air falls in the atmosphere, creating winds and, ultimately, weather. Cold water falls and warmer water rises in the ocean, and together with winds creates currents. And, Holmes suggested in a paper published in 1929 by the Geological Society of Glasgow, convection could set up currents in the mantle. Hot viscous rock would rise, spread out along the top of the mantle and then fall back down as it cooled. Most important for drift theory, Holmes argued that convection currents could be the mechanism driving it. The pressure of the rising mantle rock could cause a continent to break apart, with the pieces spreading to either side.

  The idea was intriguing, but it was also largely ignored. Holmes himself apparently did not spend a lot of time defending it. Much later, in writing about it, he described his idea as speculative and added that “purely speculative ideas of this kind, specifically invented to match the requirements, can have no scientific value until they acquire support from independent evidence.”

  By the late 1940s that independent evidence was starting to come in, as more scientists took up the study of the ocean floor. Bruce Heezen, of what was then known as the Lamont Geological Observatory at Columbia University in New York, led an effort to map the North Atlantic aboard a research ship, the Vema, which was equipped with a highly accurate deep-ocean fathometer. Back in New York, a Lamont geologist and cartographer, Marie Tharp, drew maps from Heezen’s data. (The observatory’s director, Maurice Ewing, had decreed that women were not allowed on the Vema.)

  Tharp produced her first map in 1952 and continued making maps for years as more data came in from the Atlantic and elsewhere. (She finally got to go on a research cruise, one run by Duke University, in 1965.) One thing the maps showed was that at the edges of the oceans there were often long trenches that were far deeper than the surrounding seafloor. But the biggest surprise was what the maps revealed about the middle of the oceans.

  It had been known since ships began laying telegraph cables between North America and Europe in the second half of the nineteenth century that there was a ridge of undersea mountains in the mid-Atlantic. Now Tharp’s detailed maps revealed that the ridge was actually two parallel ridges, with a valley between. What’s more, this double ridge extended from north to south for thousands of miles, like a giant surgical scar. And when Tharp mapped other oceans, it became apparent that the mid-Atlantic ridge was just a part of a system of connected midocean ridges that looped around the world.

  All this time, Harry Hess, now chairman of the Princeton geology department, had been continuing his own research and following closely the work of Heezen, Tharp and others. He looked at the evidence—the ridges, with their valleys, in the middle of the oceans, the trenches at their margins, and his own findings of guyots in the Pacific—and in a great example of scientific synthesis came up with a hypothesis to explain them. What if, he proposed in 1959, the midocean ridges were places where hot rock, or magma, was welling up from the mantle by convection, oozing out to become the seafloor and spreading apart. In his view, the valleys found between the twin ridges were evidence of this spreading, or rifting. At the ocean margins, the trenches were areas where the spreading seafloor, being denser than the continents, sank down again into the mantle, a process that came to be called subduction. The mantle thus contained convection cells that were like conveyor belts, bringing magma to the surface at the ridges (Hess referred to these as “ascending limbs”) and carrying it along to the edges of the oceans, where it went back down to the mantle (“descending limbs”) and eventually back to the ridges. In a way this was similar to what Holmes had proposed years before, but Holmes had suggested that the magma welled up under the continents, not at the ridges.

  Hess wrote that the process was extremely slow, with the seafloor moving about half an inch a year. But his idea, eventually known as seafloor spreading, explained a few other things. As he wrote later, it provided “a more acceptable mechanism” for continental drift, “whereby continents ride passively on convecting mantle instead of having to plow through oceanic crust.” But the sinking of the oceanic crust back into the mantle at the edges of the oceans could also help account for the mountains that are found all along the edges of the continents. The continents, he wrote, “are strongly deformed when they impinge upon the downward moving limbs of convecting mantle.”

  It was a strong hypothesis, but, as Hess himself acknowledged in a paper describing it in 1962, it was little more than an “essay in geopoetry.” More evidence was needed to confirm that the seafloor was really spreading, and in the way Hess described. That evidence would soon be forthcoming.

  The grizzly came rushing out of the alders on the other side of the river, headed straight for him.

  George Plafker had been working for the Alaska branch of the Geological Survey for a couple of years, and during that time had spent weeks in the bush. You can
’t spend as many days in the Alaskan wilderness as he had and not be familiar with bears. Plafker had come across both grizzlies and black bears before, on the trail and near his camps. His standard procedure in such cases was to speak up and back off at the same time. He’d shout or speak loudly, perhaps saying something like “Okay, I’m backing away as fast as I can.” Usually the sound of his voice was enough to set the bear scampering in the opposite direction. Occasionally he’d have to grab his gun and shoot in front of the bear’s feet—send some gravel up its butt, as he’d put it—to get it to hightail out of there.

  But this time, he didn’t have a chance to react. Plafker and an assistant were out working in the Samovar Hills—an isolated chain of short peaks in the southeast, on the edge of the Malaspina Glacier, one of the largest in Alaska. Plafker was wearing his usual khakis, and his head sported a bright red cap. Like everyone else in the Survey who did fieldwork, he made it a point to always wear something red. That way, if he was working by himself and keeled over or was otherwise incapacitated, his colleagues had half a chance of finding him.

  It was late in the evening, and dusk was coming on slowly, as it does in the Far North, where the sun sinks obliquely below the horizon. Plafker had been anxious to get back to camp before nightfall fully set in. He was hiking along what was obviously a bear trail—the only trail of any kind in this remote area—at a steady clip. His assistant, who was carrying Plafker’s .30-06 sawed-off rifle, was dragging a bit and was some distance behind. Plafker decided to wait up for him and take back the weapon. It was a good thing he did.

  Having resumed hiking and once again comfortably ahead, Plafker came upon a small stream, about fifty feet from bank to bank. The water coursed by in shallow rivulets, leaving plenty of gravel bars that would make crossing easy. The trail appeared to continue on the other side.

  Plafker started across, onto one of the bars, when he saw movement on the opposite bank. He wasn’t sure what it was, but he could hazard a guess. He stopped, then backed up a bit. That’s when the bear charged.

  Plafker didn’t have time to raise the rifle; he fired once from the hip. He didn’t appear to hit anything, but the noise and flame caught the grizzly’s attention. Startled, it stopped and turned sideways. By then Plafker had reloaded, put the rifle to his shoulder and fired another round. The bear dropped dead.

  A few moments later his assistant emerged from the trail, looking around. “What are you shooting at?” he asked.

  Afterward, Plafker considered that perhaps the animal hadn’t meant to be aggressive. Maybe it was just cornered, he thought—the terrain on the other side of the stream was steep, so perhaps the bear had had nowhere to go but across the water toward him. Perhaps if he hadn’t shot at it the grizzly would have raced right by him on the trail. But then again, if the bear had raced right by him and while doing so had happened to take a swipe at him with its claws, Plafker’s head would probably have been ripped off.

  This was an element of the Alaskan bush that Plafker hadn’t thought much about when he had sought a transfer to escape a desk job with the Geological Survey in Washington. But it added a certain amount of exhilaration and adrenaline to the work.

  Not that he needed much more exhilaration. It had taken only a brief time working in Alaska for him to realize that he’d made the right decision to come here.

  He and Ruth and their infant daughter, Linda, had headed back to the West from suburban Washington in the spring of 1952. They’d settled first in an apartment and later, with $500 from her parents, had bought a house south of San Francisco. Shortly after he arrived at the Survey, it was fieldwork season in Alaska. So he left Ruth and the baby and headed north.

  At the time, the primary job of the Alaska branch was to learn enough about the geology of the state that its resources could be exploited. Some of those resources were metals like gold, copper, nickel and platinum. And increasingly, some were coal and oil.

  The USGS had plenty of topographic maps of Alaska, with their familiar whorls showing elevation contours and details like roads, streams and mountain summits. Since the 1930s, these had been made using aerial photography. But to determine the kinds of rocks that make up a given piece of land, how those rocks came to be there and what minerals or other valuable resources they might contain, most of the work has to be done on the ground. Those doing it need to have expertise. They need to be geologists.

  Geologic mapping is old-school science, about the most basic work that a geologist can do. You hike across terrain—preferably in a systematic way—looking for exposed rock formations. When you find one, you note its location and what kind of rock it contains—an old igneous rock like granite, say, or younger shales or sandstones or other sedimentary rocks. If you find something that’s particularly intriguing—embedded minerals that you aren’t sure about, or some fossils—you take out your rock hammer and chip off some samples to take back to the office.

  You examine the rock formation to see what has happened to it over time—signs that it has been pushed up, folded over or broken apart. If the formation is tilted, you measure its angle of incline (called “dip”) and the dip’s compass direction (called “strike”). You note its precise location in your field notebook and on your topo map—as precise as can be determined—and sketch its extent, if possible. Then you keep hiking in the same direction until you come upon more rock, and do the same thing. Later, back in the office, you map all of this, using your expertise to fill in the blank areas between the formations you saw.

  Plafker loved the work, and like most geologists he got better at it the more he did it. He learned that creeks were often the best place to explore because over time the water had cut through the landscape, exposing layers of rock on either side. Alaska had no shortage of creeks, and by hiking up one and noting the formations, then hiking across to the next creek and back down it, he could fairly easily construct a geological map of an area.

  At first Plafker had worked as an assistant, learning from Survey geologists with more experience and expertise. There were some characters among them, men like Darwin Rossman, whom everyone called Hardrock because of his penchant for studying granites and other rocks that had been a product of heat and pressure within the earth, rather than softer sandstones and the like that resulted from the buildup of sediments. Another was Don J. Miller, who had been mapping in the Chugach Mountains and elsewhere in southern Alaska for years. He became a mentor of sorts to Plafker, initiating him in the ways of the field.

  —

  Miller, ten years older, had been obsessively interested in rocks since his childhood growing up on a farm outside Akron, Ohio. He’d joined the Alaska branch in 1942 straight out of the University of Illinois, where he’d earned a master’s degree. After a couple of years of investigating copper and nickel deposits, he’d been assigned to the group looking for signs of oil.

  A geologist who studies rocks for their potential to contain oil reserves is of necessity looking at sedimentary formations. These rocks begin as deposits of sediment washed down over time from the weathering or erosion of other rocks, or as layers of dead organisms or other organic matter that settles out of a body of water. The sediments eventually become compacted and hard, and trapped organic matter decays to oil or gas. Petroleum geologists are also interested in how sedimentary rocks are folded or otherwise deformed. Pressure could cause them to wrinkle, like a tablecloth pushed from one end. The tops of these wrinkles—called “anticlines”—can trap oil and gas.

  Some anticlines are easy to see. It’s been said that when petroleum geologists were first exploring for reserves in Saudi Arabia, they could spot promising anticlines in the desert landscape from far away. But in most cases, anticlines or other oil-trapping features are located deep underground, and the surface topography doesn’t necessarily provide clues. So scientists like Miller had gotten good at studying the layers of sedimentary rocks—analyzing the stratigraphy—and how their folding might suggest the presence of oil.

/>   Plafker did a lot of different things in those early years in Alaska. For one thing, he surveyed four potential sites in the south-central part of the state for hydroelectric dams. But he also found himself exploring the sedimentary rocks of southern Alaska with Miller.

  The work would begin earlier in the year in the office in Menlo Park, studying topo maps and any mapping that had already been done in a given area. The goal was to identify places to study and map those that were potentially interesting and logistically possible to reach. Once in Alaska for the field season they would use Cordova or another town as a base and make forays into the field for up to a week at a time—“spiking out,” they called it.

  Plafker came to greatly appreciate the bush pilots who took him into the backcountry. They were an unusual breed. Some people might say they were crazy and, at times, reckless, but Plafker saw them as being good at problem solving and improvisation. It just so happened that they did much of their problem solving and improvisation when taking off or landing in places where most people would not think it was possible to put a plane.