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.

GG was supposed to give a talk at the Rocky Mountain Map Society on January 22, 2019, at the Denver Public Library, fifth floor, Gates Room, 5:30 pm and open to the public. This was postponed due to illness–we’ll try again later.

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A Go at Geoid (technical)

Consider for a moment the geoid, which is the difference in elevation between a reference spheroid and an equipotential.  The geoid has lots of neat properties, among them being directly related to the gravitational potential energy in the lithosphere. It is sensitive to density variations at great depths and so can give us insight into deep earth processes.  But there are some issues that casual readers of papers using geoid might want to be aware of.

Geoid has long been recognized as having a sensitivity to greater depths than gravity, but this is a mixed blessing as density variations far below the asthenosphere can affect the geoid, complicating a lithospheric interpretation. The most common approach is to filter the geoid to eliminate long wavelengths that are most sensitive to deep structure–but these same wavelengths are also sensitive to the difference between continents and oceans.  In the western U.S., the look you get from the geoid depends on how you filter it.  For instance, these are two images of the geoid, one as published in Jones et al., Nature, 1996, and the other with a different filter.


The clearest difference is at the right, where the solid zero line has moved a lot, but also note that the scale of the color bar has changed.  It can be a bit hard to compare these, so another way of looking at it is to plot some points from each against each other:


Geoid by province in the southwestern U.S.; error bars reflect scatter in the subset of points within each province used to make this plot (points were where seismic structures were located in Jones et al., 1996)

The diagonal line would be where points would plot if both filters yielded the same values. Clearly the southern Rockies (SRM) pick up a lot of power in the degree and order 7-10 range compared with, say, the Sierra Nevada (SN). If interpreting this for potential energy, at D&O >7 taper to 11 the western Great Plains (GP) would have a positive GPE and would be expected to have normal faulting, but at D&O >10 taper to 15 it would be quite negative and you would expect to have compressional stresses and possible reverse faulting.

(Beyond the issues with the edge of the filter is the nature of the taper–a brute force cutoff can produce some artifacts you might not want to interpret.)

Anyways, what is the appropriate filter?  There is no simple answer for three reasons.  One is that the maximum depth you might care about probably varies across the region so a filter that cuts off in the asthenosphere in one place might also cut off the lower lithosphere in another. Another is that there is significant shallow power in the longer wavelengths/lower orders: continent/ocean boundaries have some real power in low degrees and orders. So when you filter out the long wavelengths, you can be removing shallow signal as well as deep signal. The third is that the sensitivity with depth is gradational, so a filter won’t fully cut off greater depths unless there is reduction in power from shallower ones.

(If you are wondering, in the paper we chose D&O 7-11 as the most appropriate filter for our purposes).

So be cautious when a filtered geoid is presented as a purely lithospheric signal, for it could be contaminated with deep sources or cutting off shallow ones.

EarthScope and Tectonics

Recently NSF’s EarthScope program office put out a media announcement with the top ten discoveries they attributed to the soon-to-end program. (EarthScope, for those unfamiliar with the program, originally had three main legs: the Transportable Array (TA) + Flex Array collection of seismometers, the Plate Boundary Observatory (PBO) network of GPS stations, and the San Andreas Fault Observatory at Depth (SAFOD), a drill hole through the fault).  What struck GG about this collection was just how little we learned about tectonics, which was a selling point of sorts for the program prior to its start.

Now some of the “discoveries” are not discoveries at all–one listed is that there is a lot of open data.  Folks, that was a *design*, not a discovery. A couple are so vague as to be pointless–North America is “under pressure” and there are “ups and downs” in drought–stuff we knew well before EarthScope, so these bullets give little insight to what refinements arose from EarthScope. And then the use of LIDAR to look at displacements of the El Mayor-Cucapah earthquake was hardly a core EarthScope tool or goal even as the program might have contributed funds. So the more substantive stuff might amount to 5 or 6 points.

Arguably PBO has more than delivered and SAFOD disappointed, but GG would like to consider the TA’s accomplishments–or non-accomplishments. TA-related “discoveries” in this list are actually a single imaging result and two technique developments (ambient noise tomography, which emerged largely by happy coincidence, and source back projection for earthquake slip, which is largely a continued growth of preexisting techniques). So in terms of learning about the earth, we are really looking at one result worthy of inclusion.

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Football Spotlight

The New York Times has swung its spotlight on Boulder once again, but this time with the somewhat implausible notion that CU is leading the way to end college football. The motivation for the piece is a pair of votes by two regents against approving the contract for a new football coach–not because of any objection to the coach himself, but to protest supporting a game that damages the brains of its players.

This arguably is the third strike against football here at CU, but don’t expect any changes.  There was first a series of recruiting scandals that took out most of the university administration, then there continues to be an uproar over the amount of money collected and spent on football and how little goes to benefit players, and now we are recognizing the incongruity of higher education being the site for systematic brain damage leading to early death or suicide. Add them all up you’d think this would be the death knell for the sport at CU. Don’t hold your breath, (though it would probably end college admissions scams we’ve heard so much about recently)….

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Fear of Every Geology Prof…

…is death on a class trip.  Going to places with unstable footing and exposure is often part of seeing geology that clarifies understanding, but it carries real risks. For GG, the most terrifying site is Toroweap Point in Grand Canyon National Park where, every time he visits, he breathes a sign of relief when the same number of students pile back into vehicles that had piled out of them. That site has 3000′ of vertical cliff to punish the unwary, but it doesn’t take that much for a fatality, as an environmental studies class from Briar Cliff University found out when they lost a classmate to a 100′ fall.

While family and friends grieve, another discussion is probably going on, if not now then soon. Should the school curtail field expeditions? Given the growing number of deaths by selfie, what is the role (and responsibility) of the instructor who takes students to places with hazards? Should the school dictate what is and is not an acceptable risk? Should students sign waivers, and if so, are they really enforceable?

Geoscience education benefits immensely from seeing what you are studying in the field. And the greatest hazard in field trips is generally the drive to the field or working on roadcuts near highways. But the drama of a fatal fall is more damning in some ways.  GG hopes that future students will get to experience the field safely, hopefully mainly by recognizing and avoiding hazardous situations on their own and with the guidance of an instructor rather than by being blocked from accessing important or memorable sites by fearful administrators.

Dunning-Kruger Dog Owners

Seems that a lot of pundits are having fun with evaluating various political figures as suffering from the Dunning-Kruger effect, which is often summarized as being unaware of how ignorant you are and so thinking you are quite competent (it is rather the flip side of the imposter syndrome, where people think they are less competent than they objectively are). Something similar to the Dunning-Kruger effect seems to affect many dog owners, who are seemingly unaware of just how stupid their dogs are.

Now stupid in this context isn’t really dog stupidity (though it can include that), it is more dog misbehavior according to human standards. And in a dog-centric place like Boulder, demonstrations of dog owner obliviousness are widespread.

For instance, Boulder has rules for dogs allowed off leash on many trails.  Dogs are supposed to respond immediately when the owner calls; owners (well, guardians–you don’t own dogs in Boulder, but we’ll use owner for the broader non-Boulder public) are to keep the dog under close visual observation.  Dogs are supposed to leave other dogs and wildlife alone.

Frankly, it amazes GG that there are quite a number of dogs that behave extremely well under this program. And there are quite a few dog owners (like GG) fully aware that they and/or their dogs are unsuited to this and so keep their dogs leashed (GG’s golden would chase any wildlife to the ends of the earth if off leash). And then there are the Dunning-Kruger-ish dogs and their owners.

This third class of dog owners think their dogs are well behaved, a surmise not demonstrated by their canine companions. These owners are often found calling out to their dogs from hundreds of feet as the dog happily does whatever he or she finds interesting. And after about 5 or 10 or 20 calls, the dog bounces back to the owner, who greets the wayward pup as “such a good dog.” Such owners are offended if their utter inability to control their dog is pointed out: an open space ranger some years ago saw a dog run off, eat the eggs of a ground-nesting bird and then return to the owner, whom the ranger confronted. “Oh no, not my dog, he was right here with me the whole time.”

These folks are the reason there are dog feces scattered about in open space areas, and why there is less wildlife in many areas than there might be [though lets not let feral and outdoor cats off the hook]. (Boulder does try to protect more sensitive areas by requiring a leash on some trails and banning dogs altogether on others).

GG can look out over a small patch of open space behind his house and sees the off leash dogs wandering all over the place, some behaving OK and then others not so much. A woman running on a trail ran a good 100 yards past her large white dog, who, after sniffing around a bit, deposited some stool by the trail before rushing off to be greeted by his oblivious owner.

Occasionally the karma gods intervene. She ran a second time down the trail (ignoring the fresh stool) and the dog sprinted farther than she went this time.  She turned back and was calling from nearly the full length of the field, perhaps 200 yards. And after a bit her dog was sprinting back towards her–except the dog was now two-toned, white on top and black on the bottom. Hopefully he greeted her with open, wet, muddy paws…

Reaping Restraint

GG has written a few times about the state of oil and gas regulations here in Colorado. A lot of that is now changing as Senate Bill 181 has passed the Colorado Legislature and heading for the governor’s desk, where it is expected to be signed.

As is typical these days, the public debate was overheated.  Claims that passing this legislation would end petroleum development and cripple the Colorado economy were broadcast in commercials, while some advocates felt that the bill didn’t go far enough and were upset when amendments loosened some of the language of the original bill. Others felt that this was overturning the voters’ rejection of proposition 112 last fall (e.g., comments here). Votes in the legislature were along party lines.

So is this the death knell of oil and gas in Colorado? Best to see what passed rather than rely on public pronouncements. So let’s look at what is in here.

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Spring is Here…

…and while in other places flowers are blooming and trees are leafing out, in the Rockies it is fall.

Falling rocks, that is:


This is a spot on the road between Boulder and Nederland a little above Boulder Falls that GG has always been very wary of.  Fortunately it appears nobody got hit by a rock, though once you start having rockfalls in a spot there is an increased risk of more.  Probably the state highway department will have a close look in the near future.

Springtime is a big time for rockfalls as solid freezes of the winter give way to freeze-thaw and bigger temperature swings on canyon walls. Occasionally cars get crushed, usually cars parked under steep rocky slopes. More hazardous are rockfalls into dwellings.