Geodesy – BLDGBLOG

Walker Lane

[Image: The shadow of the San Andreas Fault emerges near sunset at Wallace Creek; photo by BLDGBLOG].

All four long-term readers of BLDGBLOG will know that I am obsessed with the San Andreas Fault, teaching an entire class about it at Columbia and visiting it whenever possible as a hiking destination.

The San Andreas is often a naturally stunning landscape—particularly in places like Wallace Creek, Tomales Bay, or even the area near Devil’s Punchbowl—but the fault’s symbolism, as the grinding edge of two vast tectonic plates, where worlds slide past one another toward an unimaginable planetary future, adds a somewhat mystical element to each visit. It’s like hiking along a gap through which a new version of the world will emerge.

I was thus instantly fascinated several years ago when I read about something called the Walker Lane, a huge region of land stretching roughly the entire length of the Eastern Sierra, out near the California/Nevada border, which some geologists now believe is the actual future edge of the North American continent—not the San Andreas. It is an “incipient” continental margin, in the language of structural geology.

[Image: My own sketch of the Walker Lane, based on Google Maps imagery].

In fact, the Walker Lane idea suggests, the San Andreas is so dramatically torqued out of alignment at a place northwest of Los Angeles known as the “Big Bend” that the San Andreas might be doomed to go dormant over the course of several million years.

That’s good news for San Franciscans of the far future, but it means that a world-shattering amount of seismic strain will need to go somewhere, and that somewhere is a straight shot up the Eastern Sierra along the Walker Lane: a future mega-fault, like today’s San Andreas, that would stretch from the Gulf of California, up through the Mojave Desert, past Reno, and eventually back out again to the waters of the Pacific Ocean (most likely via southwest Oregon).

Much of this route, coincidentally, is followed closely by Route 395, which brings travelers past extinct volcanoes, over an active caldera, within a short drive of spectacular hot springs, and near the sites of several large earthquakes that have struck the region over the past 150 years.

That region—again, not the San Andreas—is where the true tectonic action is taking place, if the Walker Lane hypothesis is to be believed.

[Image: The gorgeous Hot Creek Geologic Site, along the Walker Lane; photo by BLDGBLOG].

In an absolute dream come true, I was able to turn this armchair obsession of mine into a new feature for Wired, and it went online this morning as part of their May 2019 issue.

For it, I spend some time out in the field with Nevada State Geologist James Faulds, a major proponent of the Walker Lane hypothesis. We visited a fault trench, we hiked along a growing rift southeast of Pyramid Lake, and we met several of his colleagues from the University of Nevada, Reno, including geodesist Bill Hammond and paleoseismologist Rich Koehler.

I also spoke with early advocates of the Walker Lane hypothesis, particularly Amos Nur and Tanya Atwater, both of whom have been suggesting, since at least the early 1990s, that something major might be in store for this under-studied region.

[Image: Coso Volcanic Field, near where the Eastern California Shear Zone meets the Walker Lane; photo by BLDGBLOG].

The Wired story is almost entirely focused on the science behind discovering the Walker Lane, from GPS geodesy to LiDAR, but there are also a few scattered thoughts on deep time and the vast imaginative horizon within which geologists operate. This comes mostly by way of Marcia Bjornerud’s new book Timefulness. There is also a brief look at indigenous seismic experience as allegedly recorded in Native American petroglyphs along the Walker Lane, via an interesting paper by Susan Hough.

But, on a more symbolic level, the Walker Lane totally captivates me, including how vertiginous and exciting it is to think about—let alone to hike along!—a new edge to the known world, a linear abyss emerging in the desert outside Los Angeles, slowly rifting north through hundreds of miles of dead volcanoes and disorganized fault lines, gradually pulling all of it together into one clear super-system, flooding with the waters of the Gulf of California, bringing a new version of the Earth’s surface into being in real-time.

In any case, check out the piece over at Wired if any of this sounds up your alley. The piece includes some great photos by Tabitha Soren.

International House of Wobbling

[Image: The Gaithersburg Latitude Observatory, via the U.S. Library of Congress].

The Gaithersburg Latitude Observatory was designed in 1899 as part of a ring of similar facilities around the world, all constructed at the same latitude.

[Images: The Gaithersburg Latitude Observatory, via the U.S. Library of Congress].

Each building was installed at its specific location in order to collaborate in watching a particular star, and—as revealed by any inconsistencies of measurement—to find evidence of the Earth’s “wobble.” This was part of the so-called “International Latitude Service.”

[Image: The Gaithersburg Latitude Observatory, via the U.S. Library of Congress].

The building seen here basically operated like a machine, with a sliding-panel roof controlled by a rope and pulley, and a solid concrete foundation, isolated from the building itself, on which stood a high-power telescope.

[Image: The Gaithersburg Latitude Observatory, via the U.S. Library of Congress].

This pillar gives the building a vaguely gyroscopic feel, or perhaps something more like the spindle of a hard drive: a central axis that grounds the building and allows it to perform its celestial mission.

[Image: The Gaithersburg Latitude Observatory, via the U.S. Library of Congress].

What’s interesting, however, is that this absolutely heroic building program—a structure for measuring heavenly discrepancies and, thus, the wobble of the Earth—is hidden inside such an unremarkable, everyday appearance.

[Image: A photo of the Gaithersburg Latitude Observatory, via NOAA].

It’s a kind of normcore beach hut that wouldn’t be out of place on Cape Cod, with one eye fixed on the stars, a geodetic device revealing our planet’s wobbly imperfections, masquerading as vernacular architecture.

Global Positioning Shift

[Image: Australia, rendered by Neema Mostafavi for NASA].

Australia, it turns out, is not quite where maps think it is. Thanks to plate tectonics, the island nation is moving north by 1.5 centimeters a year, which means that the entire country is now nearly five feet further north than existing cartography suggests it should be.

As a result, Australia’s lat/long coordinates are going “to shift,” the BBC reports.

Interestingly, “the body responsible for the change said it would help the development of self-driving cars, which need accurate location data to navigate.” In other words, the navigational capabilities of autonomous vehicles and other self-driving robots are, at least indirectly, affected by plate tectonics—by the ground literally moving beneath their wheels.

“If the lines [of latitude and longitude] are fixed, you can put a mark in the ground, measure its co-ordinate, and it will be the same co-ordinate in 20 years,” explained Dan Jaksa of Geoscience Australia. “It’s the classical way of doing it.”
Because of the movement of the Earth’s tectonic plates, these local co-ordinates drift apart from the Earth’s global co-ordinates over time.
“If you want to start using driverless cars, accurate map information is fundamental,” said Mr Jaksa.
“We have tractors in Australia starting to go around farms without a driver, and if the information about the farm doesn’t line up with the co-ordinates coming out of the navigation system there will be problems.”

Put another way, gaps have been opening up between the world of robotic navigation and the actual, physical barriers those machines seek to navigate.

You could perhaps argue that there is our Australia—that is, a human Australia of streets, walls, and buildings—and then there is the machines’ Australia, a parallel yet intersecting world of skewed reference points and offset walls, a kind of ghost nation, inhabited only by robots, departing further and further from the limits of human geographic experience every day.

aussie
[Image: Via the Australian Intergovernmental Committee on Surveying and Mapping].

Of course, this would not be the first time that the accuracy of geographic information has a measurable effect on precision agriculture. However, it is also not the first time that geographers have realized that they don’t know precisely where a country really is.

In his recent book about GPS, Pinpoint, author Greg Milner writes about “the geopolitical importance of geodesy,” or the study of the Earth’s exact geometric shape (it is an “oblate spheroid”).

“The geopolitical significance of geodesy increased with the onset of the Cold War,” Milner writes. “In a very real sense, the West did not know the exact location of the USSR”—and, thus, did not know exactly how or where to target its missiles. “‘Missiles were the big drivers in getting the datums tied down,’ Gaylord Green remembers. ‘If I wanted to hit a target in Russia, I couldn’t hit squat if I didn’t have their datum tied down to mine.’”

Briefly, it’s worth pointing out a fascinating side-note from Milner’s book: “The trajectory a missile follows is influenced by the gravity field where it is launched, and its aim can be disrupted by the gravity at the target, so countries often kept their gravity data classified.” I love the John le Carré-like implications of classified gravity data, including what it might take to smuggle such info out of an enemy nation.

But let’s go back to the missile thing: in addition to the question of how farm equipment and other self-driving vehicles can successfully navigate the landscape when they don’t, in fact, have the correct terrestrial coordinates, Australia’s strange misplacement on global maps implies that every potential military target in the country would also have been roughly five feet away from where existing charts say they are.

An old, uncorrected missile system in a decaying military base somewhere mistakenly fires sixty years from now, rockets off toward Australia… and plummets into the sea, missing its coastal target by several feet. Plate tectonics as a slow national defense mechanism.