…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.
…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.
Hawaii lore is full of stories about trying to get lava flows to stop. The US Army Air Corps tried bombing flows, Princess Ruth was credited in 1881 with saving Hilo from a flow, the Mauna Loa observatory high on the volcano comes with levees built to deflect lava flows. Perhaps another chapter was written within the devastating eruption of 2018….
GG had the good fortune to visit Hawaii recently and of course had to check out the flows from the 2018 eruption. One spot visited was near the Puna Geothermal Venture (PGV), a geothermal energy plant run by global geothermal company Ormat Technologies that supplied about 25% of the Big Island’s electricity before being shut down as the 2018 eruption intensified. There were a few surprises.
First, though, what is remarkable is that there is a plant to discuss at all. The location of the plant was chosen for proximity to magma–indeed, one of the wells drilled actually tapped magma directly (not ideal for geothermal work). When the fissure system of the Lower Puna eruption began in May of 2018, the plant (placed on a 1955 flow adjacent to the cinder cone of Puu Honuaula) began capping wells and draining the fluid used in the closed-system geothermal heat exchangers. Initially it probably seemed as though this would prove unnecessary as the initial long flows starting on 19 May from the eruption headed south, away from the plant.
Those flows went south to the ocean, but late on May 25th flows began descending the north side of the East Rift Zone, emanating from fissure 8 and heading toward the geothermal plant. It seemed quite possible that the plant would be obliterated as lava encroached on the plant’s land. Soon thereafter a warehouse with a drilling rig and a substation were lost to the advancing lava; three of the production wells were covered.
But on May 29th the flows shifted to the north, cutting the access roads to the geothermal plant but bypassing the main facilities of the plant. With the main lava flow channel becoming well established on that north side, the plant looked like it might survive.
If you drive down to Lava Trees State Park and go past the turn a few hundred feet, you find the western corner of PGV’s land, from where you might think the plant doomed. Lava more that 60 feet thick lays across the roads that used to access the plant. Indeed, the top of the lava levees is about the same elevation as the main plant itself.
And yet, when all seemed to be said and done, although more than half the land of the Puna Geothermal Venture was under new lava, the main plant had survived. However, estimates in the media suggested it would be years before the plant could be reopened; indeed, it seemed possible that local opposition might shut the plant down permanently.
So GG was a bit surprised to first see ATVs and pickups going up and down over the flow and then hear from a local who stations himself near the road closures that the plant was about to fire up its generators again shortly–in latest March or April 2019, only a few months after molten rock blocked access to the plant. Indeed, those ATVs and pickups were traversing the initial access road that was cut in December 2018, well before the usual six month waiting period for cutting roads across new flows. And checking the local news, indeed it seemed that the geothermal plant was going to be back in operation sooner rather than later with the bonus that the water temperatures are now hotter than before; instead of 2-3 years as originally feared, the plant’s operators plan to produce electricity within 16 months of the end of the eruption.
When the geothermal plant west down, the island was forced to restart older diesel generators to cover for the power loss. The state is committed to renewable energy, so retreating to diesel was rather embarrassing, which generally strengthened the hands of alternative energy project advocates. But virtually all renewables generate their share of opposition; GG encountered flyers opposing a new wood-chip (biofuel) plant that touted solar and wind energy, but placement of wind turbines and solar farms have met opposition in some of those places. The geothermal plant, too, has faced opposition ranging from religious objections to the plant’s failure to control emissions of hydrogen sulfide from time to time. If there is to be power, somebody’s ox gets gored, it seems.
The 2018 eruption was close to the worst case scenario for PGV with active fissures of the East Rift Zone emerging only a few hundred meters from the plant. The choice of the elevated land near the old cinder cones was crucial in allowing the plant to survive, but certainly it was possible that Madame Pele could have opened the rift a bit to the north, swallowing up the power plant. So just maybe she approves of this use of her fires.
It is a rather rare thing when a rather pedestrian-seeming experimental geomorphology paper makes it to the New York Times, but that is the case with a recent study showing that waterfalls can be generated without any special events, like a change in climate or tectonic uplift. Quotes in the Times article indicate that this might require reevaluation of histories of areas that were defined by waterfalls.
Now GG is not a geomorphologist but he does pay some attention to that literature, and it isn’t so much waterfalls that have been dictating interpretations over the past few decades in places he cares about (western U.S.), but there is work that depends on the grade of rivers relative to drainage area (and rainfall and bedrock competence); are these impacted by this?
There is a hint near the end of the Nature article suggesting that the answer could be yes:
In the Big Tujunga Creek catchment, California, USA, many tributaries, such as Fox Creek (Fig. 1c), have a knickzone that has been linked to an increase in uplift rate3. Each knickzone is composed of numerous waterfalls that lack known origins, are consistent with autogenic formation, and have probably changed erosion rates of the broader knickzone in a manner that is inconsistent with fluvial incision models. [GG bolding]
Now if all that was happening was that rivers of a certain grade developed a sort of ramp-flat (waterfall-flat) geometry without changing the overall grade, current styles of interpretation probably would remain robust. But if the development of this style of “self-formed” waterfalls messes with that, then all bets are off for streams with such features. And that includes virtually all of the rivers and streams in the Sierra…
GG kind of wonders how this compares with Clyde Wahrhaftig’s old hypothesis of stepped topography originating from variable bedrock erosion of granite. By stepped topography, he meant the repetition of steep bare granite slopes alternating with vegetated flats as one moved up the west side of the Sierra Nevada. In that hypothesis, the lip of the steep slopes (where the waterfalls are) should have a low erosion rate while the flats near the base of falls should have higher rates. In essence, the exposed bedrock created local knick points that did not move downward much while the upstream areas were eroding to match that elevation. But recent work from Jessup et al (2011), who measured erosion rates with cosmogenic isotopes, found “the pattern of erosion rates is one in which steps erode more quickly than treads, in direct contradiction to Wahrhaftig’s (1965) hypothesis.” But this is precisely the pattern seen in the new experimental work: the flats at the base of the waterfalls stop eroding once a plunge pool gets deep enough that the falling water doesn’t have any erosive power, while the lip of the waterfall gradually erodes down, eventually erasing the waterfall over some thousands of years. The flat acts as the knickpoint, not the top of the fall.
While an interesting speculation, at this moment the notion that autogenic waterfalls explains the stepped topography of the Sierra deserves a shaker full of salt. First, the scale of stepped topography is about an order of magnitude larger than the kinds of self-generating waterfalls discussed in the latest work. Second, stepped topography extends well away from the modern stream courses, something the new experimental work does not explore at all. Thus there are serious issues that would need to be solved before this could move beyond speculation. But while the new waterfall work might complicate the current style of landscape evolution analysis, it might also hold a clue to solving a more cryptic landscape puzzle.
Spent many hours in November sitting in on sessions and perusing posters at the Geological Society of America annual meeting; one goal was to see what’s up with the evolution of elevation of the U.S. Cordillera.
First a quick recap. There are two camps, more or less, on each side of the Cordillera. The old mountains camp on both sides points mainly to oxygen and hydrogen isotope variations in proxies for precipitation. There are also attempts to retrodeform the lithosphere resulting in thick crust and high elevations. The dominant counterargument is that the paleometeorology used to interpret the isotopic values is flawed. On the young mountain side, classical geologic observations are invoked, including apparent tilting of river channels and the recent incision events in many places. The counterargument to this is that the appearance of a tilted channel may be biased by the depositional environment and that changes in climate can drive incision as easily as uplift. In between in some ways are geophysical observations of the lithosphere; recent changes in the lithosphere seem likely in much of the region, supporting younger mountains, but seem older east of the Southern Rockies.
Well, a meeting in Indianapolis isn’t one to bring out all the western geologists (next year’s meeting in Phoenix is a whole different matter), but a couple of things popped up. Did anything look to change the landscape, either by opening up new vistas or overturning old results? Not that GG discerned. Below are some notes probably only of interest to the most interested….
GG has been piddling along though the Sierra (ostensibly to give a campfire talk in Mineral King) and in doing so stared a bit longer at a recent paper on the age of a pediment in the Sierran foothills by Sousa et al. in Geosphere in 2017. In a way this is a callback to concepts from far back in the geologic literature, namely the significance of an “Eocene erosion surface.”
Here, to be brief, low-temperature thermochronology from a low-elevation pediment in the western foothills of the Sierra yields very old ages–in fact, overlapping with the emplacement of plutons in the Sierran crest [this was not a unique observation; Cecil et al., 2006, had a pretty old point in their collection]. Sousa and coauthors model these data and get a cooling to surface conditions by about 40 Ma. Because these pediments abut noticeable topography, this means there was at least that much local relief in the ancient Sierra. While the pediments had been noticed by others, many suspected a far more recent age.
In some ways, this is old news. The Eocene sediments in the northern Sierra have long made clear the presence of significant local relief, and many workers had inferred that such relief was probably higher in the southern Sierra (e.g., Wakabayashi and Sawyer, 2001). But the southern Sierra lacked the Eocene sediments necessary to know what the Eocene landscape might have looked like, so this paper opens up a new window for us.
Where does this lead us? Kind of down a rabbit hole only to come up with no strong and useful statement–though perhaps future work could nail things down. This is more a personal attempt to try and grasp what is going on, so profound errors might exist and insights are few. So, proceed at your own risk….
How should one read a scientific paper? As presenting conclusions one should take as our best estimate of truth? Or as information one can use to test competing hypotheses? You might think it must be one or the other, but that is rarely the case.
Consider the just-published paper by Bahadori, Holt and Rasbury entitled “Reconstruction modeling of crustal thickness and paleotopography of western North America since 36 Ma”. From the abstract you might be tempted to say that this paper is solving a problem, in this case the Late Cenozoic paleoelevation history of the western U.S.:
Our final integrated topography model shows a Nevadaplano of ∼3.95 ± 0.3 km average elevation in central, eastern, and southern Nevada, western Utah, and parts of easternmost California. A belt of high topography also trends through northwestern, central, and southeastern Arizona at 36 Ma (Mogollon Highlands). Our model shows little to no elevation change for the Colorado Plateau and the northern Sierra Nevada (north of 36°N) since at least 36 Ma, and that between 36 and 5 Ma, the Sierra Nevada was located at the Pacific Ocean margin, with a shoreline on the eastern edge of the present-day Great Valley.
There is one key word in that paragraph that should make you careful in accepting the results: “model”. What is the model, and how reliable is it?