My Wonder List

There are things that puzzle GG and this is a partial list that will be updated from time to time.

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Mountains that Remade America

Jones_comp proof

For those who come hoping to see material related to the Grumpy Geophysicist’s trade book on the Sierra Nevada, The Mountains that Remade America, here are a few quick pointers. The paperback version came out in February 2020.

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“The Ministry for the Future” review

OK, well judging from the book’s cover, another review is utterly unnecessary, but here we are and GG can’t resist.

Kim Stanley Robinson’s science fiction writings have had an interesting trajectory. His Mars trilogy was in many ways treading a path through areas where much science fiction has roamed, though his view was not to take some moment from some terraforming of the planet as a setting for a story, his was the story of how the Red Planet might be made blue and green. You kind of wonder if Elon Musk read this (though the politics are wildly different). The next grand solar system level novel, 2312, saw humanity spread through the system, though in this case Robinson returned to a more traditional narrative framework. But Earth made something of an appearance here, hinting at books to come. Seemingly wanting to tamp down enthusiasm bred from the previous expansive books, especially the terraforming of Mars, came Aurora, whose interstellar journey ended with disaster. The optimism in Robinson’s works came through again, as rather than the more likely end of the mission in the deaths of all, he engineers the return of the craft with some of the crew’s descendants, allowing them to decry the decay of Earth and seek its restoration. The focus finally shifts to Earth in New York 2140, which seems quite bleak as global warming has wreaked havoc and New York City is partially flooded. And yet people persist in seeking solutions and making life better. In this novel, interludes from an omniscient observer of the general situation puncture the narrative, providing backdrop, context, and political commentary damning the authors of this calamity. We’ll pass over Red Moon, which in many ways is an investigation of how China works in some future, and come up to The Ministry for the Future, which carries Robinson into that most fraught time frame for science fiction: tomorrow’s headlines. This is perilously close to being a non-fiction book…

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Why so emotional?

GG’s spouse made an interesting observation the other day. She noted that a lot of problems in tectonics have a couple of features: they don’t seem to be getting solved, and they produce a lot of raised voices. In other words, lots of heat, little light. In contrast, she finds that the development of new techniques does not seem to produce the emotional outpourings seen in tectonics, so she has been more focused in that area. In pondering this, GG thinks it is in general about right. Why might this be?

Let’s start with the easier end, the development of new techniques. In seismology, for instance, we have seen the creation of ambient noise tomography. GG can still recall seeing one of the early posters at an AGU meeting and thinking, wow, pretty cool. In subsequent years different groups worked on improving and extending the technique. While they differed in some respects on the details of processing, these were never make-or-break disagreements. The technique has continued to be refined and applied widely.

Now some other fields might see a bit more controversy. The origination of U-Th/He dating of apatites had a lot of friction as there were disagreements about the physics of helium loss. And the use of clumped isotopes as a means of getting paleotemperatures and the oxygen isotope ratio of ancient waters has had a bumpy ride as the origin of the carbonates that are the source of measurements has proven to be a challenge. But in these cases too, while different groups emphasize different problems, they are seeking to overcome those problems and so these techniques are very much in the mainstream. No doubt somebody got hot under the collar once or twice about whether their carbonate was pedogenic or lacustrine, but that had a lot more to do with interpreting the measurement than making it.

Which brings us to tectonics. At times it just seems like tong wars erupt with regularity. In the 1980s there was the conflict between “pure shear” and “simple shear” interpretations of metamorphic core complexes that resulted in some fairly heated exchanges both in person and in print. The Baja-BC hypothesis has been around the block so many times it has worn a rut down so deep it isn’t clear anybody can escape it. It isn’t hard to find others (when did plate tectonics start? How high was the Sevier hinterland? Age of the uplift of the Rockies?). Why is this field so stalled out while producing so much controversy?

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Science and the GOP

GG would rather that there be no politics in science, but it is getting hard to see how we can view science as a nonpartisan field of work. Consider, for instance, this concluding paragraph on working with groups of Trump supporters from The Atlantic:

Now we are at the point where to be a Republican means to believe the Big Lie. And as long as Republicans leading the party keep promoting and indulging the Big Lie, that will continue to be the case. If I’ve learned anything from my focus groups, it’s that something doesn’t have to make sense for voters to believe it’s true.

Sarah Longwell, “Trump Supporters Explain Why They Believe the Big Lie”, The Atlantic, April 2022.

That last sentence is spooky: something doesn’t have to make sense for voters to believe it’s true. Now the Big Lie referred to in the piece is that Trump didn’t legitimately lose the 2020 election, but frankly it could reflect a number of other things. Disputing that COVID-19 is a real disease, that vaccines work, that masks work, that ventilation works in reducing incidence of the disease. That climate change is real, that it is caused by human-generated emissions of carbon dioxide and methane. Hell, potentially even that the Earth is spherical. To the degree that anti-science beliefs join the Big Lie in the pantheon of GOP entrance requirements, we risk science as we know it.

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Quick Quake Notes

OK, not a current quake, but one 150 years ago (plus a few days; thanks to Craig Poole for reminding GG of this anniversary). This was the great Owens Valley Earthquake of 1872, which was possibly the largest quake in California history. Now GG wrote a fair bit about this in his book (feel free to go and buy a copy!), so just a few notes about this quake.

First up, as we just passed April Fools Day, one consequence of the quake was nearly the renaming of Mt. Whitney. The peak had been named a decade previously by members of the California Geological Survey for the head of their bureau (the Shoshone name of Tumanguya not apparently having been considered). Whitney came to survey the damage from the quake, and it is clear his arrogant ways offended the residents of Owens Valley enough that they spent quite a bit of effort getting the peak renamed Fisherman’s Peak. That effort was only derailed by the bill in the state assembly being modified on April 1st by a wag in the state senate, making a change the governor thought irreverent. He vetoed the bill. (More details here).

The quake was felt over a widespread area, including Yosemite Valley, where John Muir exulted in crashing boulders while standing behind a sturdy tree. A large landslide in the backcountry of Yosemite is sometimes thought to have been triggered by this quake (Slide Canyon)*; it certainly caused a large number of avalanches in the Sierra given the date. And the quake created scarps in the valley. In particular, the vertical throw across a branch of the fault just west of Lone Pine led most workers to assume that motions were dominantly vertical. In a way, this was true of G.K. Gilbert’s examination of the scarps about a decade later. When he combined his studies of scarps near Salt Lake City with the evidence that these were created suddenly in earthquakes, he wrote the first scientific earthquake forecast, published in the Salt Lake City papers in September of 1883.

Gilbert’s published work emphasized the vertical slip across the scarps and that role in creating mountains. But he had also observed things sliding side to side. Had Whitney and Gilbert’s observations of the lateral motions across faults been more widely shared, that quake might have spurred examination of the the concept of strike-slip motion of many kilometers (or tens, hundreds, or thousands of kilometers) well before the 1906 San Francisco earthquake. But confusion about the unpublished notes, questions about whether photographs were reversed and other such difficulties delayed recognition of the strike-slip motion of the quake until a century later. Really, the significance of the quake only became really apparent in the wake of the 1993 Landers earthquake. In fact, for the most part the quake was accommodating northward motion of the Sierra more than any upward motion (a recent study on this indicates a 6:1 ratio of horizontal to vertical motions). This had led to a period between the 1960s and 1990s when the Owens Valley quake seemed a curiosity detached from plate motions; the recognition of the strike-slip motion helped geoscientists recognize that these faults east of the Sierra are absorbing a fifth or quarter of relative plate motions.

Odds are good we won’t see that fault rupture again any time soon. Trenching of the fault suggests it fails roughly every 10,000 years. Not that residents of the region should relax; there are plenty of other faults, as the more recent M7.1 2019 Ridgecrest quake helps to remind us.

* OK, this is wrong, and GG leaves it as a warning to fading memory. Greg Stock, Yosemite Park geologist reminds GG about N King Huber’s Geological Ramblings in Yosemite, which had a chapter describing dendrochronology work on the slide, putting it at 1739-1740. Stock also notes there is ongoing work on the age of the slide using other techniques.

The 85 Ma Trainwreck: The Sevier Waistland

No, that isn’t a typo, as we’ll see. In essence, the question to be considered here is, what might the crustal structure of the backarc/foreland looked like c. 85 Ma?

A trick that igneous petrologists sometimes like to use is to look at rare earth element distributions and see if elements that like to go into garnet are relatively rare in a granitic rock. Such an absence is then ascribed to the melt having been generated at a sufficiently high pressure that garnet was stable. Thus the absence of such elements would require a crust thick enough to have the high pressures necessary for the garnet. Related tricks look for plagioclase feldspar crystalizing; this phase is only present at shallower levels.

One such analysis was published by Economos et al. (2021) for some of the younger plutonic rocks in the Mojave. In general, they found that there was not a signal of plagioclase but there was a signal from the rare earths that garnet was stable where melts were originated. For the most part, that puts the origin of the melts below 35 km depth. An empirical calibration suggested by Profeta et al. (2015) was applied by Economos et al to their measurements, yielding Moho depths of ~50-80 km. While the most consistent results were from the younger Cadiz Valley batholith, a consistent range of La/Yb ratios suggested that there was no large change in crustal thickness back to 83 Ma. It seems likely then that the crust at 85 Ma was already very thick.

For the most part, this seems in reasonable agreement with the deformational story we’ve already looked at.

This might seem unexceptional. The Coney and Harms (1984) reconstruction of crustal thicknesses, while deeply flawed (it is a rather circular argument, which we could discuss some other time), does provide some context regionally and crustal thicknesses approaching 60 km were inferred from restoring Cenozoic deformation. More recent work by Long (2019) and Bahadori et al. (2018) tends to confirm pre-extensional crustal thicknesses in the Great Basin to be ~55 km, though these are mainly along the Sevier belt, much as Coney and Harms envisioned. These all tend to have some issues with magmatic additions and flow in the lower crust, so some caution is warranted.

Consider this cartoon of the situation c. 80 Ma:

Elements of the Cordillera c. 80 Ma, with restoration of post 36 Ma deformation (so 80-36 Ma deformation not accounted for)

Here is where the “waistland” business comes in. Something like 200 km of shortening was seen across the Sevier belt in northern Utah prior to 80 Ma (e.g., DeCelles, 2004). With the ending width of the fold and thrust belt being about 400 km (from the map above), that would be a thickening of about 50%, so if the average thickness was 55 km afterwards, it was about 37 km before.

Now there is not much reason to suspect a different shortening in the Mojave (DeCelles and Coogan, 2006, had over 300 km of total shortening in central Utah, and Levy and Christie-Blick, 1989, while having smaller shortening numbers, saw little variation from SE Idaho to southern Nevada). The hinterland in the Mojave can’t get too wide as the Colorado Plateau restores pretty closely to the arc; this is the “waist” of the Sevier belt alluded to before. If this hinterland was maybe 150 km after shortening (and quite plausibly after considerable early Cenozoic extension), then if it started with a 37 km thick crust, it could have reached thicknesses over 80 km with 200 km of shortening, in the ballpark from the Economos et al. analysis.

Farther to the southeast, we encounter an area that was thinned significantly in the Jurassic, with the effects of that still evident into the Cretaceous, when strata broadly correlative with the Mesa Verde group capped Paleozoic rocks along the Mogollon Rim. So while that hinterland could have been very thin, too, the crust was pretty thin to start with.

What this suggests is that the Mojave was a special place before the POR schists were emplaced, and before a putative oceanic plateau was thrust under the area. It was unusual because of the preexisting structure of the North American plate. What is more, this unusually thick crust is a potent driver for a lot of the peculiarities we’ve already been examining.

Is there other evidence that might support this inference of a peculiarly thick crust? Well, maybe; for that, we’ll want to look at the sedimentary history of the region…which hopefully GG will finally get around to finishing up…

85 Ma Trainwreck pages

The 85 Ma Trainwreck: Crustal Architecture

At some point GG is going to actually have to commit to assembling all these thoughts into a real paper (or admit defeat in trying to understand this area). But for now, time to resume exploring some of the issues in the Mojave.

We’ll look over the details of sedimentation later on. Here the focus is briefly on just what sits under the region where schists are seen in fensters. Consider this map that we’ve used before:

Palinspastic location of POR-type schist exposures using McQuarrie and Wernicke (2005) reconstruction. Dates are range between maximum depositional age and oldest metamorphic age (usually hornblende Ar-Ar) from A. Chapman (2017), except for Salinian Schist (Ducea et al.), Plomosa Mountains (Seymour et al., 2018) and Cemetery Ridge (Jacobson et al., 2017). Red dots are intrusive rocks dated with U-Pb with ~2 m.y. of 75 Ma. Heavy line is trench position c. 36 Ma. Queried numbers reflect overlap of maximum depositional age and some metamorphic ages.

There are two main areas where these schists are exposed: the Rand Schist in the northern swath somewhere in the 77-85 Ma range, and the Pelona/Orocopia swath to the south that is younger. As the boundaries between these schists and overlying rocks are taken to be old megathrust zones (usually reactivated), the common interpretation is that the area under these belts is made up entirely of these POR schists. If you dig around a bit, you will find cross sections drawn to show that nearly the whole crust is made up of POR schists. So let’s ask a few questions: was there enough of this stuff to fill out these regions? And what can we say about what is there now?

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Too much sun…

GG enjoys the occasional “huh, that seems wrong” moment. So the fact that the earliest sunset is well before the winter solstice is always good for a chuckle. Or watching where the moon rises through a month and how that sort of recaps the sun’s trip over the year. We’re coming up on another of these moments: the spring equinox and why it isn’t quite as equi- as the name suggests.

So if you got to one of the calculators showing you sunrise and sunset times, over much of the northern hemisphere you’ll see sunrise and sunset at the same time on 17 March, several days before the equinox. So what gives?

There are two main elements here, neither the same as what controlled that too-early sunrise or the lunar recap of the motions of sunrise. One is that we usually define sunrise and sunset by when the edge of the sun peeks over the horizon. But the sun has a finite size, about half a degree. At the equator, with the sun zooming straight up, that means sunrise is about 1/1440th of a day before the center of the sun comes up, which is exactly one minute. Add on the same extra minute at sunset and you can see that on the equinox that you’d expect the time from sunrise to sunset to be 12 hours and 2 minutes. At other latitudes, where the sun comes up at an angle (pretty close to 90°-latitude), the extra time is longer; here in Denver and Boulder, it buys us about another minute. So we should get three minutes more on the equinox.

But on March 20th this year, we get nine minutes of extra sun, not just three. Where are those other six minutes coming from? Well, if you’ve ever been fortunate enough to see a total lunar eclipse at the same time as the Sun was rising or setting, you’ve experienced the answer. Or if you’ve looked up from within a swimming pool. When you look up from within a pool, everything appears to be higher than what you see just above the water. Light gets bent as it enters the water, so objects appear closer to the zenith. Earth’s atmosphere bends light; the rays of light from the sun would be passing far over our heads except that as they hit the atmosphere, they get bent down towards the surface. So we actually can see a bit more than half a hemisphere when we are standing on a totally flat area. This buys us several more minutes of sunshine than we’d get on the Moon (were it rotating as fast).

It turns out that refraction in the atmosphere can be complicated by vertical variations of temperature and humidity, which can lead to the occasional misshapen moon:

Moonrise from near summit of Mt. Washington. CH Jones photo.

In addition, those of us at higher altitude have less atmosphere to play with, so the effect here in Boulder is probably a bit less than for folks on the seashore. So these numbers are closer to suggestions than rigidly precise times.

So there you go. Another little treat to enjoy as the northern hemisphere days get longer. If you want another discussion of this with some pictures, has a decent exposition.

Is parsimony really a guiding principle of science?

Make things simple, but not simpler. Occam’s razor. Reductionist science lives on finding an underlying structure that accounts for the important differences in observations. If you can explain a bunch of observations with one rule, that beats having a special rule for each observation. But is this really a (or the) guiding principle of science?

Well, arguably the most parsimonious explanation for stuff is “God made it that way.” Why did we abandon such a universal explanation for everything? While today we look to science for explanations about why something happens (auroras, shooting stars, earthquakes, tsunamis), it feels like the origin of science was the more prosaic “what will happen if I do this?” Flinging things at enemies was a popular option in warfare for a long time, but the trial-and-error approach isn’t so wonderful if your enemy, seeing where you are firing from, is quicker to lob a shell at you more precisely. Recognizing that there are rules that are quite predictable gives you an edge–you can get things done more efficiently or even do things you previously couldn’t do at all. You don’t need to answer “why is there gravity” to be able to use a theory for it to do things like go to the moon.

So maybe science is being parsimonious while being able to predict things. Yet some theories look less than optimally parsimonious. The Standard Model for physics looks like something Rube Goldberg might have come up with. Is string theory really parsimonious? You get the feeling Occam’s Razor will draw blood on some pretty well established theories.

Earth science really slams into these problems. Say, you want a theory in how mountain ranges are created. You look today and see the Himalaya rising as India hits Asia. OK, maybe mountain ranges are made as two continents collide. Oh, but we have the Andes, too, and mountains in Alaska. Um, OK, well, mountains are made where two plates collide. OK, great. A fairly simple explanation that allows us to look for mountains. (We’ll put aside where plates collide and all we get are a few volcanoes).

That explain all mountains? It does seem helpful for the Appalachians and Urals and Alps. How about the Sierra Nevada? Assuming the young Sierra story holds water (it is argued), the range has largely risen up with plates not colliding. Seems trouble for our universal mountain-building theory. Or the ranges of the Basin and Range; why is all that going on? Sure seems distant from the plate boundary.

But then we have the Rockies about 1000km from the edge of a plate. Why are the Rockies there instead of where the plates were apparently colliding? Maybe a plate was scraping the bottom of North America. Maybe the Colorado Plateau was really strong. Maybe there was dynamic flow in the mantle. Maybe the Ancestral Rockies had set things up. How universal and parsimonious is our plates-colliding theory if we keep finding troublesome mountains?

In a weird way, earth science almost moves in the opposite direction of, say, particle physics. The physicists are looking for the one equation to rule them all; earth scientists are teasing out all the different ways Earth can do something. Parsimony in earth science is almost backwards from the way a lot of folks regard Occam’s Razor. We will hone an explanation to its bare essentials and then compare with all the examples we have. The ones it explains we can set aside. The ones it cannot we go on to investigate. There are two possibilities: our original explanation was wrong and focused on immaterial aspects, or there is more than one way to achieve some outcome. The great challenge in all this is to somehow sidestep the features that are not important while really nailing the ones that matter.

Consider the Rockies again. A fairly likely candidate for the same process is in South America, the Sierras Pampeanas. A paper some time ago pointed out that the geometry of these ranges (length and width) looked to be about the same as in the Rockies, and the bounding faults are reverse or thrust faults in both places. Is this then the key element that provides the insight into the origin of the Rockies? Some think so, but GG (and some others) have argued this is simply what happens when you squish an area in a continental interior with a thin cover of sedimentary rocks. Kind of like that you can’t really tell if a nail was driven by a hammer or a nailgun; the different tools can make the same outcome. GG argues that it is the source of the compressional stress that we care about and that important differences between the Sierras Pampeanas and the Rockies cannot be dismissed. Which is really right? With so few possible candidates, it is hard to tell. Occam’s Razor has little effect when your choices are so few and potential confounding features are so widespread.

Parsimony is an important tool, but not really the be-all and end-all some make it out to be. There is a temptation to force discrepant cases into a theory’s box when you value parsimony over all. Sometimes it is the right call, sometimes not. Relying on Occam to answer the question can be a big mistake.

Not So Big State U?

Here in the foothills of the Rockies, there has been conflict between the flagship state university and the community. The conflict revolves around size. Now in Colorado the university has a lot of independence from local laws, but in this case they want some property annexed by the city so that city services can come in and allow for a fairly dense development. This gives the city some leverage.

Now Boulder has a wealth problem. Those that have wealth have a roof over their heads; those that don’t are on the street or commuting from somewhere else. So the city has had a goal of increasing affordable housing. And a big part of that discussion concerns CU students, who absorb a lot of housing in the city, presumably crowding out others who might want to live in town.

So the university is saying that their property will be largely used for making housing for students and staff and faculty. You might think this would find a lot of support in the area. Well, think again. One branch of opposition likes the open space that the university inadvertently has been preserving and doesn’t want to see it built over (to be fair, though, the site is mostly an old gravel mine with severely damaged soils). Another branch (mainly people who live downstream) don’t want to see development so that larger flood control structures can be built on the land. It is the third branch worth pointing out today. This group wants to limit the size of the university, arguing that there are plans for nearly doubling the size of the school, and blocking this development would align with their goals.

Now that wish of a smaller school seemed pretty pipe-dreamish…until a similar group in Berkeley managed to get their flagship school in court, where they were ordered to freeze enrollment, which will result in a fall class a third smaller than planned. A line from the story could easily come from Boulder: “Many neighbors are upset by the impact of enrollment growth on traffic, noise, housing prices and the natural environment.” And that is the basis for the lawsuit. The university is looking at a big hole in their budget if this order stays in place.

Could CU be blocked from growing by something similar here? Hard to say; Colorado laws are not as strict as California laws. Should CU cap its growth? That is a worthwhile question. It might be wise for the powers that be to consider how vulnerable the school is to something like the Berkeley situation.

Too Much Attribution?

NB: Added a pp on wester US drought story, 2/14/22

Pick a natural disaster, any natural disaster, and these days, odds are good you’ll also find a story or two or twenty saying “this is a manifestation of climate change.” This is quite the sea change from not that long ago when the role of climate change was not brought up, not even by climate researchers. While the consideration of climate change is welcome, the broad-brush assumption that it is behind every disaster is getting to be questionable. This runs the risk of overlooking other contributors that can be very important if not dominant in some situations.

The problems most easily attributed to climate change, with very little argument, are heat waves and droughts. Attribution studies often approach this by running climate simulations with and without the extra CO2 we’ve put in the air and heat in the ocean and seen how often a given heat wave or drought emerges. Lots of times they are really rare in the pre-industrial climate but common in modern conditions. From this you can get relative odds: a heat wave that might show up in 1 of 1000 pre-industrial simulations but shows up in 20 of 1000 modern simulations would suggest that heat wave was 20 times more likely because of climate change.

Precipitation is a lot chancier.

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