In this article I’m looking at academic studies (and one actual event) in the week of 21-28 February, 2019 that look at the deep past, the present and — possibly — the near future.
The Earth system, as I never stop saying, is phenomenally complex, with cycles interlinked in time and space and on different scales. Understanding how it works is difficult enough in the present but much more so in the past — and yet because understanding the past can lead to understanding both the present and the future, it’s very important that we try.
Dating the Deccan Traps
One of the great debates in geoscience is the precise nature of the event, or combination of events, that hastened the end of the dinosaurs and a host of other plant and animal species in the great mass extinction at the end of the Cretaceous period, around 65 million years ago.
Scientific puzzles are solved slowly, albeit with the occasional major breakthrough. In the case of the dinosaurs that breakthrough was the discovery of a major meteorite impact crater in the Gulf of Mexico, but it’s widely thought not to have been the only factor. At the same time an immense eruption was taking place in what is now India — an eruption that produced vast quantities of material that is now the Deccan Trap scenery of the subcontinent.
To understand whether it was the eruption, or the impact, or a combination of the two, we need to refine the timings more closely. While the timing of the impact, a single event, is relatively easier to pinpoint, that of a continuous event is more problematic. Early studies suggested the eruption might have lasted 50 million years; later ones refined it to five million; and this week’s two studies have suggested a much narrower window.
The two research studies looked at the geochemistry of the lavas and used different dating techniques, both of which have their uncertainties. The results had certain similarities and key differences.
The main similarity was in terms of timing: both reduced the period of the eruption to a mere million years or so around the time of the impact. The differences related to the rates of eruption — one study (Renne et al) suggested that most of the volume was erupted after the meteorite impact while the other (Schoene et al) found that a significant volume was erupted beforehand.
These findings don’t solve the mystery as to whether these eruptions and the climate change associated with them (through the injection of vast quantities of gases into the atmosphere) — but they certainly don’t rule out the eruption as a factor in the death of the dinosaurs.
M7.5 Earthquake, Ecuador
I talk a lot about the average numbers of large earthquakes we can expect and here, almost a sixth of the way through the year, is the first big earthquake (I define that as at least M7.0) of 2019.
The earthquake occurred in association with the subduction of the Nazca tectonic plate below the South American continent, in the northern section of the Peru-Chile Trench. The two plates are converging at a rate of roughly 7cm per year.
The available data suggest that the mechanism was normal faulting rather than reverse faulting, implying that the earthquake was associated with deformation rather than movement at the plate interface — something which is supported by the depth (around 130km) and by the United States Geological Survey’s earthquake summary, which notes that: “the earthquake occurred as the result of normal faulting at an intermediate depth, approximately 130 km beneath western Ecuador within the lithosphere of the subducted Nazca plate”.
Tremors of this size are unusual but not unprecedented in Ecuador. In the past century the country has been the location of 11 of at least M7.0 and this week’s was the fifth largest (though of course the country can also experience the effects of earthquakes elsewhere). The largest of these have in the past been closer to the coast.
News reports on the earthquake have been relatively thin in the ground, but although there are indications of some structural damage there have been, as far as I can see, no indications of fatalities. In the past Ecuador hasn’t been so lucky, but this first major tremor of the year seems to have been relatively harmless.
Volcanic Warning For California
Generally speaking we think of California as being a state vulnerable to earthquakes rather than to volcanic eruptions. While it’s probably true that a major earthquake poses more potential problems for the state and its inhabitants than an eruption, it isn’t wise to neglect the potential risk from the eight volcanic areas identified as being moderate risk or greater.
The locations in question, from north to south, are Medicine Lake; Mount Shasta; Lassen; Clear Lake; Long Valley; Ubehebe; Coso; and Salton Buttes. Between them, they pose a risk to an estimated population of just under 200,000 and the report notes that: “Based on the record of volcanic activity over the last five millennia, the probability of another small- to moderate-sized eruption in California in the next 30 years is estimated to be about 16 percent. This is similar to the forecast for a magnitude 6.7 or greater earthquake specific to the San Andreas Fault in the San Francisco Bay region”.
The report is a detailed and fascinating read, not only assessing the extent of the threat but the nature of the various impacts and the agencies who might be involved in mitigating the risk. A key message is that: “volcanic hazards are likely to be more than a local problem, confined to a single county or region” and that they should not be overlooked.