November 4, 2021 | David F. Coppedge

One-Eruption Volcanoes: On the Decline?

Monogenetic volcanoes pockmark the western United States
but their dates and causes are poorly understood

 

In southern California, drivers along old Route 66 can see the dark cones of extinct volcanoes. They appear to have erupted once and then stopped. At Pisgah Crater near Ludlow, California, large fields of rough lava with some 200 lava tubes bear testimony of a period of fiery violence in the past. A pristine volcanic cone appears farther east near Amboy, one of the motel-and-gas hangouts on old Route 66 that time forgot.

These volcanoes raise a host of questions. How long ago did the eruptions occur? Why did they occur here, within a continental plate instead of at the margins? How frequently do such monogenetic (“one-life”) volcanoes rise from the depths of the earth? Are we due for another one? This would be important to know, because an eruption under a major city could have devastating consequences.

Pisgah Crater (DFC)

Hundreds of monogenetic volcanoes and lava fields appear in west of the Rocky Mountains in California, Nevada, Arizona, Utah and New Mexico. Surprisingly, their dates and origins are not well understood, says Greg Valentine, geologist at the University of Buffalo, New York.  He decided to catalog all that is known about 2,229 monogenetic volcanoes and lava flows in the American southwest and northern Mexico as a step toward understanding them. He was assisted by Greg Ort, geologist at Northern Arizona University (NAU), who lives near some of the youngest of such volcanoes north of Flagstaff – the San Francisco Peaks.

A press release on from the University of Buffalo (Nov 3, 2021) introduces the mystery, saying, “Let’s talk about the 1,800-plus ‘young’ volcanoes in the U.S. Southwest.”

They’re born. They live once, erupting for a period that might last for days, years or decades. Then, they go dark and die.

This narrative describes the life of a monogenetic volcano, a type of volcanic hazard that can pose important dangers despite an ephemeral existence.

The landscape of the southwestern U.S. is heavily scarred by past eruptions of such volcanoes, and a new study marks a step toward understanding future risks for the region.

How Not to Date a Volcano

Geologists can come to very different conclusions about silent volcanoes. Back in 2006, CEH reported a case where the date and length of activity of a volcanic field in Nevada published in 1994 was radically revised downward in 2006, closing a time gap of tens of thousands to hundreds of thousands of years down to possibly a few months! (see “How Not to Date a Volcano” (13 Nov 2006). In 2012, the Ubehebe crater in Death Valley had its date revised 750% downward from 6,000 years ago to 800 years ago (23 Jan 2012). In another case, reported in CEH on 1 Nov 2012, geologists revised a date for a volcanic field near the Salton Sea from 30,000 years to 984 years – a correction of 3,000 percent! Readers are advised to take the dates in this current study with those mistakes in mind. These geologists, despite their moyboy beliefs, recognize some of the errors to which dating methods are prone.

Often both plateau and isochron ages are presented in original sources for 40Ar/39Ar age determinations; in such cases, we report the preferred age if that is stated by the original author or the plateau age if a preference is not given. Many volcanoes were dated by older K-Ar methods, and these ages are reported here if their source document is readily accessible, although that method is typically not as reliable as the 40Ar/39Ar method for young basalts. The low potassium content of the basalts and low radiogenic yield make the K-Ar method very sensitive to the composition of initial trapped Ar and to analytical procedures and corrections (see summary by Heizler et al., 1999), and often result in the production of dates with errors of the same magnitude as the age itself. Other dates reported here include U-series, surface exposure ages (36Cl, 10Be, 3He), 14C, optically stimulated luminescence, and magnetic secular variation. Because much of the Southwest is arid, suitable material for 14C dates is scarce, so this common dating technique is rarely used. Only ages that include some analytical information and error estimates are included in the compilation (with rare exception), which excludes relative geomorphic ages, for example. We stress the importance of readers studying the original sources before using the data in future analyses.

Regarding the frequency of eruptions, they say, “Our estimate of regional recurrence interval does not filter out these issues of volcano versus vent counts, and older versus newer geochronological methods, but is intended to provide a starting point from which decisions about further data collection could be made.” The dates should not be taken as gospel truth, in other words.

Vulcan’s Throne, part of the Uinkaret Volcanic Field. This cinder cone formed above all the Grand Canyon Layers; its lava is pouring into the canyon. Yet radiometric dates put it older than lava underneath all the Grand Canyon strata! (DFC)

Valentine and Ort collected their data primarily by literature searches on published data, not on field work. Their results are published open-access (PDF) in a research article in Geosphere, a publication of GeoScience World. Supplementary Materials are available including a spreadsheet of all 2,229 volcanoes, listing their names, locations, estimated ages, and published sources.

Greg A. Valentine; Michael H. Ort; Joaquín A. Cortés, “Quaternary basaltic volcanic fields of the American Southwest.” Geosphere (2021) https://doi.org/10.1130/GES02405.1

Ample Wiggle Room

The authors recognize that volcano dating is not an exact science, even with modern radiometric methods. Some of their assumptions could be considered arbitrary. Their use of the “Quaternary Period” (supposedly 2.6 million Darwin Years to the present) depends on the consensus Geologic Column. Other assumptions trust modeling and simplification methods. Additionally, there are disagreements about volcano counts, because some vents may have been erupting at the same time.

We estimate the recurrence rate (new basaltic monogenetic volcanoes per year) based upon the compiled dates and upon the total volcano count over the Quaternary Period. The former is incomplete because only a fraction of volcanoes has been dated, while the latter provides an upper bound (but with uncertainty due to potential errors in the volcano count), assuming a constant Quaternary rate and using a simple Poisson model. An important conclusion of our work is that more detailed mapping, physical volcanology, and geochronology are needed to reduce uncertainties and to provide insights into non-homogeneous processes such as spatial and temporal clustering of volcano occurrences both at the regional scale and at the scale of individual volcanic fields.

Poisson models are only educated guesses in the absence of reliable knowledge, they note.

The Poisson model assumes a constant mean rate of eruptions, which is appropriate given insufficient data to suggest otherwise (realizing that within individual volcanic fields, and potentially at the regional scale, more data would likely indicate some degree of temporal clustering or episodicity) and that each eruption is independent.

Recurrence Rate Conclusions Arbitrary

If 2,229 volcanoes all emerged within 2.5 million years, that would imply one volcano every 1,200 years. The authors recognize, however, that such a belief is beset by uncertainties as large as 100%.

The recurrence rate based only upon dated volcanoes (<720 ka) is equivalent to one volcano on average every ~2700 years, while that based on the total volcano count is equivalent to one volcano every ~1200 years, or every ~960 years for the 52 volcanoes during the last 50 k.y. (Table 2). For comparison, the four youngest in the Southwest are: Sunset Crater (~900 yr, San Francisco field), Little Springs (~1300 yr and possibly as young as 1025 CE, Uinkaret field), McCartys flow (~3 ka, Zuni-Bandera field), and Dotsero in Colorado (~4150 yr). (Note: Cerro Colorado volcano in the Pinacate field has a magnetic secular variation age of ca. 3.9 ka, but this young age is contradicted by stratigraphic relations.) These four volcanoes all formed within about the last ~4150 years, which is equivalent to one volcano every ~1040 years. This timeframe is too short to be a statistically rigorous comparison for rates estimated over 2.58 m.y., but it is reasonably similar to the full count-based rate given all of the uncertainties. Much more geochronological and physical volcanological work is needed to test whether there are non-Poisson temporal and spatial trends on the regional scale as well as at the scale of individual fields.

In short, their primary goal to estimate how often monogenetic volcanoes emerge rests on moyboy beliefs, unreliable dating methods, and simplifying models chosen “given insufficient data to suggest otherwise.” It was a noble effort to collect and categorize published dates, but can be regarded as little more than a heuristic exercise, i.e., ‘let’s assume this as a starting method in the absence of something better.’

Use of a different heuristic, therefore, seems fair. Instead of assuming a “constant Quaternary rate” of volcano emergence using one model, why not consider a declining rate? As an analogy, consider what happens when turning the heat off on a stove that is cooking oatmeal. There would be furious bubbling while the heat is on, and some bubbling would continue when the heat is turned down slowly, declining over time until no new bubbles form. In another analogy, pubescent young people often have rapid onset of pimples while hormones are changing, but those fade over time in most, so that their skin is clear by adulthood. When the underlying cause is turned off, the effects decline over time.

Amboy Crater, standing alone and silent in the California desert. (DFC)

Most creation/flood models assume rapid plate movement at the onset of the Flood. Once the continental plates come to relative rest, that would lead to a declining rate of new volcano emergence. What we see now are relics of rapid plate tectonics that largely halted centuries after the Flood, although some motion is still measurable. If this is correct, then the threat of new volcanoes declines (but does not vanish) accordingly.

The Flood model may seem arbitrary to critics who prefer the standard Geologic Column. That old-earth preference, however, is not a help. If the earth is billions of Darwin Years old, why did over 2,000 volcanoes occur in just the last 2.6 million years? Why did they all pop up in one region, the American southwest? Why are they not seen in lower strata where exposed, as in the Grand Canyon? If the present is the key to the past, as uniformitarians believe, these volcanic cones stand as silent witnesses against billions of years. The scientific community should be open to any model that can explain the observations with causes appropriate to the evidence. Flood geology provides that.

At the very least, this story illustrates that scientists can look at the same evidence through different worldview lenses and come to different conclusions. Evidence does not interpret itself. Gathering evidence, however, is useful to everyone, and this team provided a service by collecting what is known (or assumed) for scientists to consider. Yes, we agree; “Let’s talk about the 1,800-plus ‘young’ volcanoes in the U.S. Southwest.”

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Categories: Dating Methods, Geology

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