Cascadia's Fault (17 page)

By the time his Alpine paper was in its final draft and being peer reviewed in the winter of 1979, Adams was already working in North America with a keen interest in the Cascadia Subduction Zone. The Alpine paper was published in a scientific journal called
Geology
only two months before the eruption of Mount St. Helens, and I suspect its
significance—especially the parallels to Cascadia—may have been lost in that spectacular volcanic dust cloud.

Unfazed, Adams continued to work on other evidence that Cascadia was an active threat. He had ongoing battles to fight against conventional wisdom and the principle of uniformitarianism. While at Cornell he had begun working with a researcher named Robert Reilinger on a study of how much the Coast Range mountains of Washington and Oregon were tilting to the east. Like the work of Ando and Balazs, which had come out in 1979, this Cornell project involved new data from highway survey crews that showed a significant upheaval: a change of elevation along the entire western side of the mountain range.

In 1982 Reilinger and Adams took the Washington highway data from the earlier study and extended it southward by adding new measurements from five more resurveyed east–west highways crossing through the mountains in Oregon. They showed that survey markers located near the coast had been lifted up a noticeable amount in the less than eighty years since the last set of surveys. Tide gauge data along the coast showed pretty much the same thing; the beaches had been lifted as well. Put it all together and you got a picture of a mountain range about 370 miles long and 37 miles wide (600 km by 60 km) being hoisted up along its western edge and tilted, en masse, toward the east.

In this new mountain-tilting paper Adams and Reilinger drew attention to another worrisome study published only six months earlier by Jim Savage and a team at the USGS that showed land in the Puget Sound lowlands around Seattle apparently being compressed: squished together in a northeasterly direction. That was the same direction the Juan de Fuca plate was supposed to be moving. If the ocean floor was actively sliding underneath the continent and
if
the two plates were locked together by friction, this kind of compression, or “crustal shortening,” near Seattle was exactly what you'd expect to find. It was also exactly contrary to what Robert Crosson and Ando and Balazs had said earlier.

When Ando looked at the vertical shift of outer coast survey markers and the eastward tilting of the Coast Range, he and Balazs reasoned that the long-term, apparently quake-free uplift meant the two tectonic plates were
not
locked. That's why Cascadia was seismically quiet. So how could one explain Savage's new compression data? How does the ground squeeze together if the plates are not locked?

A series of measurements of the distances between geodetic survey monuments on opposite sides of Puget Sound, spaced six to eighteen miles (10–30 km) apart across the sound, revealed a surprising and somewhat baffling trend. Between 1972 and 1979, Savage and his colleagues used a Geodolite, a powerful and precise distance-measuring instrument that fired a laser beam from a survey marker on one side of Puget Sound across to a similar marker on the other side. There, a bank of highly polished mirrors bounced the laser back to the Geodolite, which measured how long the beam took to make the round trip.

If it took less time in 1979 than it did in 1972 the two markers had to be closer together, and that's exactly what they found. They figured the accuracy of the Geodolite was within 0.2 inches (5 mm) and that the amount of squeezing of the valley floor was statistically significant. Savage and his coauthors (Mike Lisowski and Bill Prescott) recognized that their new data were “not easily reconciled” with Ando's aseismic subduction concept, but they published them anyway. They concluded that the laser measurements were evidence of strain building up, probably caused by the subduction of the Juan de Fuca plate underneath North America.

The significant point was that the two plates
had
to be locked together for this kind of strain to accumulate. Savage and his team were saying as politely as they could that Ando and Balazs must be wrong. “The implication is clearly that the Washington and Vancouver Island coasts are subject to great, shallow, thrust earthquakes,” they wrote in June 1981.

A year later, when John Adams was drafting his conclusions for the paper on Coast Range tilting based on highway survey data, he spoke to Savage on the phone and heard his idea about why the mountains might be tilting to the east. In Japan and several other places, subducting plates were bending the outer coast
downward.
Why would the Pacific Northwest coast be different? Why would it tilt eastward? Savage had a hunch that if the two tectonic plates were locked at a point only slightly inland from the coast—if the point of impact was nearly head on and close to the beach instead of deeper down and farther inland, beneath North America—then maybe the Juan de Fuca plate would push the mountains and beaches upward (like a crumpled fender) instead of dragging the coast down and curling it under, like in Japan.

Adams latched on to this as a possible explanation for the eastward tilting and thought he'd made a pretty convincing case. He was not completely successful, however, in exorcising the demon of aseismic subduction. At the request of his more senior coauthor, Robert Reilinger, he wrote a concluding paragraph that equivocated enough to dull the edge considerably. Taken as a whole, the tilting data and the lack of large quakes “suggests that subduction is occurring aseismically, although alternative interpretations are possible,” they wrote cautiously. Thinking about it more than thirty years later, Adams had to laugh. “That phrase was largely put in to—shall we say—to take the controversy out of the paper, to make sure it got through the peer-review process.”

But Adams was already hard at work on another study that would pull fewer punches. He was like a dog with a bone. He knew the mountains were tilting, he knew Puget Sound was getting squeezed, and he intended to follow up on those beaches that had been shoved up into marine terraces along the Oregon coast. He knew from his New Zealand studies that it took hundreds of years to build up enough strain for a giant subduction quake. And he knew about those turbidite mud
cores from offshore landslides that also were roughly five hundred years apart. Were the deep-sea landslides physical proof of Cascadia's violent past? He was determined to find out.

CHAPTER 10

The Whoops Factor: Cascadia's True Nature Revealed

While John Adams watched the Coast Range tilt and Jim Savage tracked the squeezing together of mountain peaks in Puget Sound, Mike Schmidt was learning about a new technology that could make the measurements far more precise. He would eventually join a team of researchers on Vancouver Island, where the distance between several mountain peaks was being resurveyed to find out whether continental drift was shoving them closer together as well.

My first impression of Schmidt was that he'd rather climb a big rock pile than stand there and look at it. He's a bearded bear of a guy who seems to have chosen the right career. In 1992 he led a team of Canadian scientists to the top of Mount Logan, Canada's highest peak and its fastest rising mountain. Fast in geologic terms, it grows by several fractions of an inch each year.

As a mountain climber, geophysicist, and surveying engineer, Schmidt wanted to establish new geodetic markers near the summit and try out some brand new and allegedly portable GPS technology, which was still in the experimental stage at the time, to trace the peak's constant movement. Logan, which occupies a big chunk of the
southwestern corner of the Yukon, is poking up and creeping horizontally for the same reason that mountains in Puget Sound near Seattle are getting squeezed together. In the case of Logan, the floor of the Pacific Ocean is jamming itself underneath North America from the Gulf of Alaska.

This is the same tectonic force that caused the 1964 Alaska earthquake. The Pacific plate is thrusting the entire St. Elias Range a tiny bit higher and shoving it slowly inland at the same time. Because 1992 was Canada's 125th birthday and the 150th anniversary of the Geological Survey, Schmidt came up with the idea of putting together an expedition to climb the mountain and settle a long-standing debate about how high Mount Logan really was. With sponsorship from the Royal Canadian Geographical Society, he and his team did exactly that.

They couldn't simply fly to the top because the summit was too high and the air too thin for ordinary helicopters. Plus the researchers themselves would need time to acclimatize to the altitude before starting the hardest part of their work. So instead of an easy ride in a chopper, they made nine trips over three days in a single-engine, ski-equipped Helio Courier airplane to airlift the fifteen members and all their gear to a base camp on the Quintino Sella Glacier, 9,055 feet (2,760 m) up the mountain. From there they had only another 10,495 feet (3,199 m) to go, Schmidt told me, slogging steeply uphill the hard way. It was the only “relatively safe” option.

For thirty days starting in early May they skied and climbed and packed loads of food, tents, sleeping bags, clothing, climbing gear, and heavy cases of the new high-tech survey equipment—satellite receivers, antennas, and heavy batteries—steadily upward through spectacular spring sunshine and howling late-winter snowstorms that nearly forced them back. Being so close to the Gulf of Alaska meant that nasty weather could blast across the slopes with almost no warning. And it did, several times.

By Schmidt's account, though, the expedition was a complete success.
They nailed a new brass survey marker at 18,044 feet (5,500 m), on the edge of the Logan plateau; when they finally reached the summit, the portable GPS system worked perfectly and the official height of the mountain was confirmed at 19,550 feet (5,959 m). But they also proved under extremely harsh field conditions that this new, extremely precise technology could be used to help figure out what was really happening along Cascadia's fault.

Measuring mountains and the drift of continents using satellites, sophisticated antennas, and software to track the warping and bending and horizontal migration of land caused by plate tectonics would become the focus of Mike Schmidt's working life. At the Pacific Geoscience Centre on southern Vancouver Island, he helped develop the technology and methodology for tracking the minute and ongoing deformation of the earth's crust. But before GPS, there were lasers and Geodolites and each step along the way was a huge improvement.

I heard the story of how it all began from Schmidt's senior colleague, Herb Dragert, who was there at PGC when the study of migrating mountains began in 1976. Apparently a burning desire to prove that Tuzo Wilson at the University of Toronto was right all along about plate tectonics had been Dragert's personal motivation. As an eager young student, his imagination had been fired by Wilson and those big ideas about drifting continents. “He kind of said to us, ‘Okay—we do get plate convergence on the west coast and we should be able to measure the actual motions of the earth's surface,'” Dragert recalled with gusto. “These mountains should be squeezed!” Which is precisely what he, Schmidt, and a team of others from the Geological Survey would try to confirm.

On Vancouver Island the idea was to locate the original stone cairns and brass markers on mountain tops that had been surveyed back in the late 1930s to remeasure the distances and the angles between the peaks and thus find out whether—or indeed, how much—they had moved by the late '70s. Decades later I wanted to see how the work had been
done. In 2007 I needed a way to illustrate the process for a television documentary, so Schmidt was going to show me by doing it again.

Thus I found myself in a helicopter once more, flying this time toward the lumpy shoulder of Mount Landalt, a few miles north of Lake Cowichan on southern Vancouver Island. The skids of the JetRanger touched down gently on a bed of gray lichens and green moss sprinkled with tiny, bright fuchsia-colored flowers. Schmidt pulled out the first of two steel cases, each a little larger than your standard, full-size suitcase. Then he carried a set of heavy-duty tripod legs to the summit and set them up directly above the control point, the brass marker that had been established by the original survey crew back in 1937.

The instrument he hauled out of its foam-padded metal case was about twice the size of that old breadbox your grandmother used to have. It was a Rangemaster III, with a bright orange housing, knurled brass knobs, a black instrument panel, and a self-contained digital computer that flashed the distance calculation to an LED readout. State of the art in 1976, it still appeared in perfect working order after many years in a storage locker. The helicopter pilot then flew across to Mount Whymper, the next nearest mountain in the hazy distance, where he landed and set up a reflector box on a tripod directly above the survey marker on that peak.

Back on Mount Landalt, Schmidt peered through his viewfinder on the Rangemaster and used a portable radio to call the pilot, who then tilted the bank of mirrors on Mount Whymper until Schmidt got a return signal—a reflection of the laser beam—on Mount Landalt. Scintillating shafts of cherry-red light bounced off a dozen mirrored prisms in the reflector box. The Rangemaster then performed its magic: a quick calculation of the time it had taken the beam to shoot across the valley from one peak to the other and bounce back. With laser gear like this they could measure the distance between peaks up to twenty-five miles (40 km) apart and be accurate within fractions of an inch. A significant improvement, but there was still another problem to solve.

With nothing more sophisticated than pack horses, climbing gear, and transits (telescopic instruments mounted on tripods for measuring precise, horizontal angles between objects that are far away) the British Columbia survey crew back in 1937 could accurately plot the geometry between a series of peaks. But computing the exact distances between mountains was extremely difficult. In those days most surveyors still used sixty-six-foot chains (eighty chains to the mile, or about fifty to the kilometer) to establish a baseline measurement. If you know the angles and the length of one side of a triangle (the baseline), you can calculate the lengths of the other two sides. But because of jagged mountain terrain and dense bush, the distances calculated and printed on the old maps of Vancouver Island were too imprecise to work as reference points in a modern-day study of minute tectonic creep along a fault. The new laser equipment that became available in the 1970s changed everything.