A favorite shortcut employed by many in trying to decide between hypotheses is to enlist Occam’s Razor–that the simplest explanation for something is most probably right. Now this has strength because humans are pretty good at rationalizing notions they put forward, adding in new ingredients to keep a favored explanation from collapse. But a theory that has probably passed its must-use-by date will have enough extra bells and whistles to discourage Rube Goldberg from trying to get it to work.
However, there is nothing that says Mother Nature had to be supremely parsimonious. In a complex system like Earth, there can be odd coincidences that are meaningless (like the Moon and Sun sharing the same apparent diameter from Earth’s surface) and outcomes that might be highly improbable (taking over 500 million years to get intelligence after making complex animals with hard parts seems like dawdling, especially when burning most of that time on dinosaurs). Even so, Occam can be a help if used with care.
But lots of times you can face competing hypotheses that lack Occam-style clues. For instance, which is simpler: that post-5 Ma erosion of the High Plains of the U.S. was caused by an eastward tilt, or that this was the product of a changing climate? Both are pretty easy to describe; both have issues. Yet many earth scientists feel pretty comfortable arguing that one is correct; what is the basis of such assurance?
Arguably the most common discriminator used by earth scientists is the principle of least astonishment. What surprises you least feels, in an Occam kind of way, like the interpretation that is most likely. The problem is, we all are astonished differently.
If you are a sedimentologist, you might look at the problem of the High Plains as one of depositing the Ogallala Group in the Miocene as crucial. Could you possibly deposit something like that on a slope like that we have today? This seems so astonishing that if can’t be right; the original slope had to be lower.
But maybe you are a geophysicist looking at the ways to create a tilt about 5 million years ago over something like 1000 km. That looks really hard to do, especially if dynamic topography from flow under the lithosphere is ruled out. It would be astonishing if that happened; it must be that the grade was already there much longer ago.
Skepticism from both geoscientists is warranted; either of these seems really hard to do. Data is gathered by both sets of experts. Margaret McMillan and colleagues measure paleogradients in the Ogallala using a widely applied approach and find there must have been a lot of tilting. Will Levandowski and colleagues (including GG) look at geophysical measurements and find support for the elevations comes from within the crust, where changes over the past 5 million years seem exceptionally implausible.
Could these be resolved? Well, you could posit that prior to 5 Ma there was dynamic subsidence holding the western end down and once that was released, the crustal buoyancy expressed itself. But now Occam detectors are flashing red–this feels ad hoc. Of course, there could be mistakes in the measurements of paleogradient, or in relating seismic wavespeeds to densities–each side has poison darts to shoot at the other side.
What makes this frustrating is what makes this interesting. After all, in the end somebody will be astonished–the earth did something they didn’t expect.
And a funny thing, shoes flip feet in the Sierra, where those studying the sediments argue for no tilting despite deposition at an even steeper grade than modern-day Ogallala, while geophysicists feel they have good evidence for a very recent change in the buoyancy structure of the region.
Are you astonished yet?
Well, it’s January and ski season is in high gear in North America, halfway between the Christmas and Presidents Weekend high water marks for ski areas. So many of you have seen lots of signs like those above. The irony is that these symbols, now so universal, were developed for a ski area that never was.
In 1964, the nascent National Ski Areas Association (NSAA) decided to try to make relatively uniform sign markers for skiers in North America. European ski areas had simply used colors; the new USA system would add shapes to the colors (which has obvious advantages for color blind skiers and for monochrome signage). But they committed a bit of a faux pas: the US intermediate color was used in Europe for out of bounds areas.
As this system was being promoted, Walt Disney Corp. was working on ski areas, largely because Walt had decided after the 1960 Olympics in Squaw Valley that he’d like his own ski area. Disney settled on Mineral King Valley, which set up a lengthy legal and political battle, but as part of the work being done for that development, Disney Corp. studied what would be the best signage to use. They were perhaps more sensitive to this given their experiences getting people around Disneyland. Their studies suggested that circles were the softest shape and most suitable for easy slopes, followed by the squares and then diamonds. The NSAA saw their work and adopted it, pitching their own system aside.
Disney was never able to use their system at their own resort.
As is discussed more thoroughly many other places (including GG’s own Mountains that Remade America), first the Park Service (that had to approve a realigned road) dragged its feet, and then the Sierra Club chose to oppose the development. Toss in the additional requirement of an Environmental Impact Statement, the death of Disney shortly after holding a news conference in Mineral King, a change in political representation and a general shift in the public from favoring development to favoring preservation¹ and the eventual death of the ski area proposal becomes clear.
Anyways, those signs (er, and the Country Bears Jamboree) are among the most lasting reminders of the Mineral King debacle. The influence of Disney’s work on skiing symbols even evolved into a warning system for something a bit more hazardous: volcanoes. Although the USGS was blocked for awhile after a volcano advisory in Mammoth Lakes misfired, because communication with local officials and, later, the public became necessary, the Long Valley USGS group used these now-familiar symbols for awhile (1997-2006):
So while Disney loyalists to this day pine for the ski area that never was, they can console themselves (a little) in seeing these reminders on any North American slope they care to visit.
¹ for instance, during this time Denver went from seeking the 1976 Winter Olympics to refusing to host them, largely over financial concerns but also because of environmental objections.
It seems like the Fall AGU meeting brings some new wrinkle to the GPS measurements in the Sierra. In the past we’ve seen suggestions that the Sierra were going up tectonically, then that they were going up because of water removal from the Central Valley, then they were still going up even with water removal in the Central Valley, and now we have the Sierra going up because of water removal in the Sierra itself. This latest missive is from Don Argus and several colleagues at JPL deserves a look; their paper on this was published about at the same time in the Journal of Geophysical Research (though that paper doesn’t have the coda from the AGU talk about the loss of elevation in the wet winter of 2016-2017)
Basically they wrote that during the California drought from 2011 to 2015 that the Sierra lost 48 km³ of water and so rose at least 17 mm from that loss while also rising an additional 5 mm from water loss in the adjacent Central Valley and then might have risen no more than 2 mm from tectonics for a total elevation gain of 24 mm (or just about an inch). That is a lot of uplift for a few years. This interpretation means that the Sierra actually stores a lot more water within its granites than is typically thought to be the case, which aligns with earlier work by Argus and colleagues.
Lesson 4: There is always more to learn
While my influence on friends of a friend through my travels was unexpected, the one place we do look to be a guiding light is with our children. Having learned our lessons before parenthood, we hope to be that beacon of wisdom that can infuse our children with knowledge without the necessity of living through the same mistakes we made. While we all discover that our abilities in this vein are limited, it is usually because we aren’t heard or heeded. Even so, I don’t think things necessarily worked out the way I had planned when my younger daughter joined me for a llama-pack on the John Muir Trail…
I’ve spent months living in the backcountry, and while there are those who have had to deal with more severe situations (animal attack, major injury and the like), and there are those who’ve spent a lot more time in wilderness (rangers, packers, trail crews, some guidebook authors and some really serious aficionados), I’ve felt like after all that time and all those mistakes that I have reached a place where I am about as comfortable in the wilderness (well, at least the pretty dry wildernesses of the southwest) as anybody. And so on this trip I could show my youngest just how it is done.
Lesson 3: Connections
As both a scientist and educator, you hope to have an impact that ripples through a broader population. Your scientific insights help others to make new discoveries, your teaching to help students to improve their lives and that of others they in turn impact. Most of the time, you really don’t know how successful you’ve been. Science can lumber off in the wrong direction while you might have been on the right path (or, of course, vice versa). Former students might never be in touch, or worse, might tell you you failed (yes, I had this happen. Encountering a fellow working at a science museum, I learned he had taken my intro historical geology class. “Has that helped you in your job here?” I asked. The response was quick and blunt: “No.”).
I would never have thought that I might have affected others in any serious way through my pursuit of backpacking. And I would not have guessed I would have learned of such an impact through a murder. And yet, that is my tale to tell…
GG has pointed out here and in The Mountains that Remade America that the Sawyer decision that ended hydraulic mining in most of the Sierra Nevada is a very interesting precedent when you consider global warming and oil and gas companies. We’re getting closer to seeing if the comparison will withstand real scrutiny, as the City of New York has filed suit (joining a number of smaller jurisdictions, including Boulder) against the five largest oil companies. As with the plaintiff in Woodruff v. North Bloomfield, the New York City case alleges material damages, and as in the older case, this was a consequence of the action of several companies. And as in that case, the only way to mitigate damage would be to leave large economic reserves of a mineral (as legally defined) in the ground. Arguably the 1884 decision recognized that the damage to a growing economic sector (agriculture) outweighed damage to a stagnant sector (gold mining). We’ll see if any judge in the U.S. wants to walk in Judge Sawyer’s footsteps….
Lesson 2: Perseverance (part 2)
Well, after getting in position in the backcountry to do seismology and well on the way to recovering from the setbacks of losing helpers and the blocked trail, we now got to start doing what we had come here for: deploying these bulky old seismometers.
We decided that bedrock on the valley wall would be our best choice for this first station [we missed a much easier exposure of bedrock just north of the ranger station area]; this meant we pulled out our packframes, lashed the gear to the frames, and struggled up the scree at the base of the west wall of the canyon.
For the most part, things went reasonably well. We found a nice spot to dig in our seismometer (an L4-3D if you are wondering), the seismograph unpacked OK and would run. But then we finally ran up against a serious problem. We had to figure out what the time on the seismograph was. It had to be within about a hundredth of a second, or all our effort would be wasted as the experiment (seismic tomography) required accurate times.
[As a reminder, the seismometer is the instrument that actually detects and amplifies ground motion, in this case varying voltage in wires that go to the seismograph, which further amplifies the signal and records it, in this case on the reel-to-reel tapes.]