Plate Tectonics Part III

The next “a-hah!” moment for me in understanding geophysics came in 1965 with a paper by J. Tuzo Wilson, “A new class of faults and their bearing on continental drift.” At the time it seemed a light had gone off in my head, even though by then I was deeply enmeshed in ice fog studies.

The red lines are spreading centers; the blue line is a transform fault which has its origin in the offset between portions of the spreading center. The part of the transform fault between the offset segments is active; the plates are sliding past each other. The parts to either side are "fossil"--although the offsets are still visible, there is no movement.

Up to that point, it was assumed that if a feature—such as a stream, a mountain range, or a magnetic stripe—was displaced by a fault, it was evidence that they had once been continuous, and movement along the fault had separated them. This paper suggested the existence of a new kind of fault, now called a transform fault, where the apparent displacement was due to an offset in a spreading center. Spreading centers were themselves new, though grabens (places where the crust on either side was moving apart, resulting in a downdropped block in the middle) had previously been recognized.

Suddenly the apparent faults in the Pacific Ocean floor, faults that stopped at the coast, made sense. The rocks on either side of the transform fault did not move relative to each other. The only motion was between the offsets on the spreading center.

We now know that plates are bounded by three kinds of faults:

Spreading centers, where plates move apart,

Converging boundaries, where plates collide,

Transform boundaries, which often connect the two, and allow plates to slide past each other.

The familiar faults such as the San Andreas are the active portions of transform faults, but the offset magnetic stripes in the Pacific are generally the “fossil” parts of transform faults. Looked at this way, the “end” of an active fault makes sense: it is where the transform fault joins another type of fault to make part of a plate boundary.

The full plate tectonics hypothesis had not yet been fully formulated, but the essential pieces had been found.

Plate Tectonics: Part II

My next step in understanding geophysics came when my father took me along to a lecture. At that point I was somewhat immunized against continental drift by the professor at Harvard, in spite of my unanswered questions. Since the topic of the talk was something to do with continental drift, I was prepared to be quite critical. Remember this was in the early ‘60’s, before the idea of plate tectonics. The notion that sea floor was the youngest, not the oldest, crust on Earth had not even entered anyone’s mind, and the lack of traces of the continents plowing through the sea floor seemed definitive.

That lecture totally changed my attitude.

The lecture was about paleomagnetism, the fact that when lava cools, it retains the signature of the terrestrial magnetic field present at the time. The horizontal part of the field gives the direction to the north pole; the vertical part gives how far the pole is from the site — the latitude. There were complications – sometimes two lava flows close enough in time and space that they should have pointed to the same pole had exactly opposite directions. But if the north and south poles were considered interchangeable it was found that rocks of the same age on the same continent pointed to a consistent pole location at any given time in the past.

(Why the magnetic signature seemed to reverse at times was a mystery at the time and is still not totally understood, though it now known to be a reversal of the magnetic field rather than a reversal of the magnetism of the rocks.)

The next step was to produce what are called apparent polar wander curves: plots of how the pole moved through time as seen from the site of the lava flow. Again, it was found that these curves were quite consistent for a given continent. (There are exceptions, but I’ll get to them in a later post.)

But the curves for different continents were quite different.

In particular, if the curves for north America, Africa and Europe were compared, and the continents were assumed to move in such a way that they “saw” the same pole, those continents must have been snuggled together back in the late Triassic.

I walked into that lecture convinced that the apparent fit of the continents (and the geology) of the continents across the Atlantic was a coincidence, and that Wegener’s continental drift hypothesis was wrong. Certainly his mechanisms were; there was no evidence that continents had ever plowed through seafloor. But I walked out convinced that while Wegener’s hypothesis was wrong in detail, the continents had indeed moved.

But how?

Formally, I shifted my studies for the next few years to ice fog. Informally, I kept trying to make sense of  solid-earth geophysics. Could there be some sort of underground erosion going on? What about those faults with hundreds of miles of displacement that disappeared when they reached continents?

Luckily, the major journal of my field was the Journal of Geophysical Research, so I was able to follow the steps people were making in the gradual emergence of plate tectonics. More of that later – but in the order I remember finding out, rather than in the order the discoveries were made.

How the Earth was Made, Season 1 (DVD Review)

This collection, containing 13 programs on 4 discs, looks at the geological history of specific places on the Earth. The series is grounded in plate tectonics and geological activity, with plate tectonics and glaciology being foremost.

In some ways it is a good introduction to how geological forces act, but as a geophysicist I do have some caveats.

First, while the geological dangers are very real, the program has a tendency to emphasize the “this could happen tomorrow” aspect. There is very little emphasis on what we can do to minimize the effects of possible geological disasters. (All right, there’s not much we can do if Yellowstone blows again, but things like evacuation routes and plans for tsunamis and engineering for earthquakes are hardly touched on.)

Second, the programs do not distinguish among kinds of faults and plate boundaries. While mid-ocean ridges are recognized as divergent boundaries, the difference between transform boundaries such as the San Andreas Fault and convergent boundaries is never clearly described. Nor is the difference between ocean-continent convergence (which produces ocean trenches, volcanoes and massive earthquakes) and continent-continent collisions (responsible for the mountain belt extending from the Himalayas to the Alps.) The latter are capable of producing far greater earthquakes, as the potential area of breakage is far larger, and are also responsible for the “ring of fire” around the Pacific.

Third, the story of each region is told as if the scientists just had to find the missing pieces, and as if they knew what they were looking for. In many cases, the findings were a total surprise and the interpretation we accept today is quite different from what the researchers who found the information at first tried to make of it. I know — I was watching as plate tectonics gradually became the accepted framework of geology.

Overall the series is worth watching if you have any interest at all in how the world came to be as it is today. But take it with a grain of salt – the writers of the narration didn’t always know what they were talking about.

Individual programs are:
The San Adreas Fault
The Deepest Place on Earth (Challenger Deep)
Krakatoa
Loch Ness
New York
Driest Place on Earth (Atacama Desert)
Great Lakes
Yellowstone
Tsunami
Asteroids
Iceland
Hawaii
The Alps

Plate Tectonics: Part I

The important thing about science is that it has a built-in mechanism for corrections. It doesn’t always work as well as it should, because scientists are people and resist changing their beliefs. The fact remains that assumptions are always open to challenge.

I was reminded of this in watching a DVD on How the Earth was Made, which I’ll review soon. The point I want to make here is that the DVD presents examples as if the scientists involved were searching for pieces of a puzzle that they knew had missing pieces. More often the major breakthroughs – such as plate tectonics – are made when a gradually increasing number of people realize that the accepted theory just doesn’t explain something. Or many somethings. Essentially, that the puzzle pieces available have been put together wrongly, and the picture is in fact quite different.

This happened with plate tectonics.

I wasn’t involved directly, but I was at the Geophysical Institute when it happened, and had a chance to read many of the papers as they came out. And I was interested enough to do just that.

Even as early as grade school, I was unsatisfied with the encyclopedia’s explanation of mountain-building and geosynclines. What the encyclopedia said was that mountains were formed by the cooling and shrinking of the Earth, much as wrinkles are formed on the skin of a drying apple. Erosion wore the mountains down, depositing the sediments offshore, and the weight of those sediments pushed the ocean crust down so the mountains grew higher. It did not make sense to me, even then. These processes would have resulted in filling the oceans and leveling the mountains, not building them!

When I was a little older – high school age – I was given a book that gave some of the results of the International Geophysical Year – the IGY. The one that stuck in my mind as an unsolved mystery was the discovery of major east-west trending faults in the Pacific Ocean. Based on the offset of newly discovered magnetic stripes, these faults had large displacements – tens to hundreds of miles. But the displacements totally disappeared when the faults reached land! Not only could the east-west displacements not be found, in places such as the California coast there were well-known faults such as the San Andreas tending more nearly north-south.

At Harvard I took a basic geophysics class, hoping it would help me make sense of what seemed to be an increasingly frustrating puzzle. What I learned there – and it was the cutting-edge science of the early 60’s – left me as puzzled as ever.

Gravity measurements had proved that continents stood higher than oceans because continental rock was less dense than ocean rock. This was known as isostacy – the height of terrain essentially depended on how high it floated on the mantle.

Continental drift was nonsense – there was no way continents could plow through oceanic crust, and there were no traces of any such plowing through on the sea floor. The matching of rock formations on the opposite sides of the Atlantic was sheer coincidence.

Exchanges of plants and animals over  geological time were via land bridges.

The elephant in the room, from my point of view, was that isostacy did not allow sea floor to rise and form land bridges.

I went to the Geophysical Institute as a graduate student partly because of these mysteries, but I was sidetracked into atmospheric science and ice fog. Nevertheless, I stayed interested, and since many of the seminal papers in plate tectonics were published in the Journal of Geophysical Research (JGR) I watched the plate tectonics revolution happen. Next week I’ll talk about some of the breakthroughs that eventually led to the new paradigm of plate tectonics.

Ice Ages and Alaska

I wrote this for the Alaska Science Forum in 1987, but it’s as true as ever. Besides, the Quaternary creatures of Alaska were a large part of the inspiration for my soon-to-be-released novel, Tourist Trap.

Imagine yourself in a spaceship approaching the earth, eighteen thousand years ago. The ice-covered Arctic Ocean is blindingly white in the early June sunlight, but not just the ocean — all of Scandinavia and parts of Europe and the British Isles lie under a glittering sheet of ice as well. Drift ice fills the northern Atlantic, and the warm blue waters of the Gulf Stream, which you expect to see swinging north of Norway, flow directly across to Spain. As you continue westward, Long Island and Cape Cod are mere piles of rubble at the edge of an ice sheet that rivals the one in Antarctica today. A massive lobe of ice pushes south of what will someday be the site of the Great Lakes, and Canada is an unbroken wasteland of ice, bounded on the south by rushing summer meltwaters that will someday become the Missouri and Ohio rivers.

The North Pacific and Alaska come into view — more ice? Yes, but not only ice. While the Coast and Alaska ranges are massive bastions of white, there are great lakes thawing under the summer sun in the Copper Basin and the inner part of Cook Inlet. And between the Alaska and Brooks Ranges there are wide sweeps of grassland, green with meltwater and the warmth of the sun, extending westward across what has been and will be the Bering Sea to Siberia, then sweeping onward thousands of miles to the back of the European ice sheets. Only an occasional mountain range carries an ice cap there, but areas of tan and gray are visible even from space — dust storms, sand dunes, and plains of silt and gravel dropped by the meltwaters from the glaciers. North of the ice-capped Brooks Range, the cracks that opened in the chill of last winter filled with drifting sand, rather than snow.

As you move into the Fairbanks area for a landing, you startle a small herd of shaggy ponies into headlong flight, and a few moments later a group of bison stampedes as well. Their small hooves, designed for speed on hard ground, are only slightly impeded by the moisture still oozing from the few remaining patches of snow. This is mineral soil, blooming with grasses, sedges, sagebrush and wildflowers in the spring flush of moisture, not muskeg.

The trumpet of a startled mammoth splits the air from the line of willows and taller grasses along the river, and a family of the huge, long-haired animals moves into view. They are edgy, and with good reason — a saber-toothed tiger has had its eye on the new calves for several days now.

Eighteen thousand years ago is an extreme case, near the height of the last ice age. But if you picked a random time in the last half million years, it would likely be closer to the icy picture I’ve just described than to the world we are familiar with today. Less than ten percent of this period has been as warm as the last few thousand years, or with as little ice on the land. Exact dating prior to about thirty-five thousand years ago (the limit of accurate radiocarbon dating) is still a problem, but many lines of evidence suggest a long series of ice ages, separated by relatively warm interglacials around ten thousand years long and close to a hundred thousand years apart. Our current interglacial has lasted a bit more than ten thousand years. Are we due for another ice age?

Since the glaciers of Antarctica, Greenland, the Canadian Arctic, and the mountain glaciers of modern Alaska together account for a third of the total area of the great ice sheets of the glacial maximum, we could argue that we are still in an ice age — that even what we think of as interglacials are in fact mere pauses in an ice age that has lasted for well over a million years.

Whether we label our era a minimal ice age or a true interglacial, our present civilizations are in balance with the climate. Consider: sea level rose over three hundred feet in the last twenty thousand years, drowning what was once dry land. Vast areas of the Bering and Chukchi seas, for instance, were steppes and cold deserts when the water that now covers them was locked up in glacial ice. Much of our concern about the onset of a “greenhouse” warming comes from the possibility that parts of the remaining land ice could melt, causing a further rise in sea level. If that should happen, shoreside cities — Homer and Honolulu, Nome and New York — might go the way of the Bering land bridge. Ice ages are by no means a problem only of the past.

Inside Planet Earth: DVD Review

This is an excellent DVD for getting across the idea that the inner workings of the earth, while at times disastrous, are essential for life.

The DVD actually has two programs, both originally shown on the Discovery channel: Inside Planet Earth and Amazing Earth. The graphics are intriguing, though some are repeated a bit too often. The actual camera work is excellent.

My only objection was that at times the narration could be misleading. True, we have been in an ice age for the last 40 million years. But most of the evolution of mammals – and certainly of humans – has taken place during that period. We are adapted to an ice age in the broad sense. My concern is that many people will take “ice age” to mean the periods like 20 thousand years ago, when ice sheets covered much of North America and Europe.

Over all, I found this a good program if a bit sensationalist – and this is my field, so I am aware of shortcomings.

Before Computers

There was a time when digital data recorders did not exist. Data was recorded on strips of paper with grids on them, generally wound around a slowly turning drum while a pen marked them. Trying to do anything with data of this sort required digitizing it.

My first job as a research assistant at the Geophysical Institute involved doing just that.

The process was called scaling, and involved a device that was moved along the paper, lined up with the ink trace at specified intervals, and a button pushed. The eventual result was a string of numbers for one component of the magnetic field. This was done for both horizontal components.

I then had to plot these numbers on an x-y graph, connecting the dots in time order for a number of stations and events. Plotting in those days used millimeter graph paper, with points entered and connected by hand.

Today, it would take five minutes on a computer — but this was 1963. It took a small army of graduate students (SAGS was actually used as an acronym) just to get the data in a form in which it could be analyzed. (SAGS are still used, but these days it is generally in collecting the data, not in doing things a computer can do better.)

All of this was carried out in the basement of what is now the Chapman Building, which looked then very much as it does today, except that it had a dome on the roof. Eventually, we found that the disturbance in the magnetic field during a sudden impulse was elliptically polarized at high latitudes, and my first paper was actually written on the results of that study.

It may sound like a silly thing to do, but that discovery provided a small boost toward our understanding of the effect of the solar wind on the magnetic field of the earth — a subject not to be ignored in the design of long-distance power lines. But I’m very glad for computers!

The Fairbanks Flood of 1967

Floods in Interior Alaska occur at two times of year. The first, which is expected by anyone who lives near a river in Alaska, is breakup floods. April is our direst month, but the melting snow is dumping tons of water into the rivers, and ice jams can form temporary dams, never in the same place twice, which lead to major flooding in the villages. A couple of weeks ago a public service announcement included a story of a small boy who was frustrated when the local teacher refused to put things up high during flood season in spite of warnings from his pupils. “You should have listened to us old-timers,” the children told him after he and his family had to be evacuated in a boat.

But one of the greatest floods in Fairbanks history occurred during the second flood season, in late August.

If April is our driest month, August is the wettest. During the summer of 1967, the rains started in earnest in July, and the Tanana river began rising from more than melting glaciers. At that time the only road into Fairbanks was the Richardson Highway, which runs along the north bank of the Tanana. That river is just south of Fairbanks, and the road had already been washed out in places by early August. The nearest upstream bridge was 100 miles east; there was at that time no highway bridge downstream that connected to anything. Fairbanks itself is built where the Chena, a smaller, meandering river, flows into the Tanana.

In mid-august the southwesterly flow from the Bering Sea, augmented by the remains of a typhoon, began dumping unprecedented amounts of rain in the headwaters of the Chena River. By Monday, August 14, it was apparent that flooding would affect Fairbanks, which is on a double flood plain. The university is located on a hill and Al George, the civil defense coordinator, announced that the 300 extra beds in the dorms would be available for refugees.

The next morning the radio sounded totally confused as to what was going on. I looked across the street, saw that water was pouring into an excavation and beginning to flood a trailer park, and stuck the cats, their food and whatever was in the powerless refrigerator in the car when I went to work. Luckily! By that time the 300 beds had been expanded to wherever people could be put, which included everywhere except the power plant—on lower ground and itself in danger of flooding. (The city and Borough power plants had already been flooded out.) For most of the next week, I was the room clerk at the Geophysical Inn or helping distribute supplies for the Salvation Army. The intersection I’d driven through at 10 am was deep enough to float trucks by noon, and it was several days before I could get home. I did have luxury quarters—the floor of the office I normally shared with my Thesis advisor. Other offices often housed several families.

I was also able to reassure my family almost at once. The Geophysical Institute at that time was heavily radio-oriented, and a number of ham radio operators were our main contact with the lower 48 states. By the time the flood was a day or two old, the operators were overwhelmed and the messages were pretty limited. I recall an old, crank-operated phone that was our link with Outside.

One of my jobs was to try to locate and check off Institute employees. Among the missing for the first couple of days was Dan Crevenston, the Assistant Director (I think — need to check.) Not until the army managed to get its high-wheeled vehicles running between the campus and the airport (which stayed inches above the flood water) did we find that Dan was helping run things at the airport – which had become another refugee center.

Looting was official, and wasn’t really looting. As I recall, local grocery stores donated whatever they had above water to the flood relief effort, and the army’s high-wheeled trucks moved it to the campus.

One sidelight if you’ve looked at the University’s official story. There is a photograph of the old Geophysical Institute in Part 3 of that story. The peculiar t-shaped structure at one end? Some of the stacked trailers we had offices in as we outgrew the building, prior to moving into the new building in 1970. (I’m probably somewhere it that picture.)

Early History of the Geophysical Institute

The Geophysical Institute was authorized by Congress in 1946 and funded in 1948. I won’t even try to detail all of the infighting between the Institute and the University here; Neil Davis does a much better job in his book, The College Hill Chronicles. I will just mention a few highlights.

The Chapman building, built to house the Geophysical Institute, as it appears today.

The original focus of the Geophysical Institute was on aurora and radio transmission, specifically on the upper atmosphere. Sydney Chapman became the advisory scientific director on his retirement from Oxford around 1950, and he was still teaching occasional classes when I arrived in 1963. C. T. Elvey became the director shortly after Chapman arrived, but he left in the early ’60’s. The first GI building, now called the Chapman Building, was also built about 1950.

East wing of the Elvey Building as it appears today.

Between Chapman and Elvey, the Geophysical Institute played a large role in the International Geophysical Year, which is largely what got me interested in geophysics back in high school.

One version of the all-sky camera used to study the aurora was developed at the Geophysical Institute, pretty much cobbled together by students.

At one point the Geophysical Institute made the front page of the New York Times by being the first in the US to track Sputnik and calculate its orbit. GI scientists may not have been the first in the United States to see it, though!

The main tower of the Elvey Building. It's 8 stories high and (while you can't see it at this angle) has a huge satellite dish on the roof.

The Institute directors had always emphasized primary research, and by the early ’60’s, when I arrived as a graduate student, they were beginning to move down into glaciology, the atmosphere and seismology, and up towards the sun. Today there are research programs in atmospheric sciences, remote sensing, seismology, snow, ice and permafrost, space physics and aeronomy, tectonics and sedimentation and volcanology. Public outreach includes volcanic activity, earthquake information, aurora forecasts, an online webcam on the roof and the Alaska Science Forum, which I was writing 20-some years ago. Facilities include the Alaska Climate Research Center, the Alaska Earthquake Info Center, The Alaska Satellite Facility, the Alaska Volcano Observatory, Chaparral Physics (Infrasound), the College International Geophysical Observatory, the Mather Library and the Poker Flat Research Range.

The first building was outgrown shortly after I arrived, and while the new building was being planned and completed on West Ridge, the existing building was extended with trailers. The new building (now called the C.T. Elvey building) was completed in 1970. It, too, was outgrown, or rather overgrown. Toward the end of the last century the International Arctic Research Center was built partly as an extension of the Elvey building, with help from Japan. The library (which was especially cramped in the Elvey Building) and the Atmospheric Science program moved into IARC (now officially called the Akasofu Building.)

I’ll be blogging about individual research programs and facilities over the next few weeks. (Or months, most likely.)

The Geophysical Institute

“From the center of the Earth to the center of the sun.” The Geophysical Institute at the University of Alaska Fairbanks covers a lot of territory, and a lot of subjects. It started out with space physics and aeronomy, but has expanded its interests to include atmospheric sciences, seismology, remote sensing, snow, ice and permafrost, tectonics and sedimentation, and volcanology.

The building to the right is actually the International Arctic Research Center, but this is the building that now houses the GI's climate and atmospheric science program.

A large part of its work is cutting-edge research, but it also provides aurora forecasts, earthquake information, the Alaska Science Forum (a popular science feature distributed to media outlets throughout Alaska, which I once wrote) and volcano alerts. It maintains the world’s only scientific rocket launching facility owned by a university.

If you’ve read the bio on my website, you know that I spent more that 30 years  at the Geophysical Institute as a student, researcher and teacher. But what’s the Geophysical institute all about? What problems does it address? And what on earth does it have to do with writing science fiction?

I certainly can’t cover everything the Geophysical Institute does in a single article, but why not use this as my new article series for Sundays? As to what it has to do with writing science fiction, not much with the plots, but a tremendous amount with the planet building.

Next week I’ll try to give a little of the early history of the GI (as it is mostly called by those who work there.)