There were all sorts of things going on in the week of 23-29 August 2018, but I found myself returning to a couple of old favourites — earthquakes and volcanoes. Volcanoes, at least aren’t directly affected by human activity and to date anthropogenic earthquakes have been of relatively small magnitude, so we can reasonably say that these are truly natural hazards.
There comes a point, though, where human activity can intensify the frequency of, or damage caused by, certain natural hazards, and I’ll be having a look at a couple of examples of this, too.
The Week’s Earthquakes
So many things about the Earth are cyclical. Continents break up and reform. Oceans open and close. Mountain ranges are uplifted and worn down. Ice ages come and go. It should come as no real surprise, therefore, that the patterns of earthquake activity fluctuate around an average.
I talked about this last week, and how a period of quiet has been followed by a (statistically normal) period of activity. This week the activity continues. The United States Geological Survey’s real time earthquake map for the week shows ten tremors in excess of M6.0, two of them of M7.1. The two larger ones aren’t associated with any of the previous ones, either, so can’t be accounted for as part of an aftershock sequence.
The more recent of them occurred along the complicated and congested section of plate margin between the Pacific and Australian plates, along the South New Hebrides Trench. Here, the Australian plate descends beneath the Pacific and the shallow earthquake was the direct result of subduction.
The second occurred at a depth of 609km beneath the Andes and is associated with the descent of the Nazca plate beneath South America. In this case the cause is less clear-cut and the USGS summary notes that the cause was normal faulting within the Nazca plate.
As a footnote, I learned something mind-boggling about this earthquake. The USGS summary notes that: “The deep part of the Nazca plate, in which the August 24th, 2018, earthquakes occurred, took 10 Myr or more to descend from the point at which it initially thrust under the South America plate.” (That’s 10 million years.)
California Burning — and There May be Worse to Come
There’s been a lot of media coverage of wildfires in California and elsewhere this year. Wildfires themselves are a natural phenomenon, although some of the fires experienced in the current age are the product of human activity, either careless or malicious.
The publication this week of California’s Fourth Climate Change Assessment sets alarm bells ringing for the future. The Earth is a system and change in one area leads to change elsewhere and the major change — a warming climate — will, according to the report, “make forests more susceptible to extreme wildfires”.
If we needed an example of how disastrous that might be, the report provides it: “By 2100, if greenhouse gas emissions continue to rise, one study found that the frequency of extreme wildfires burning over approximately 25,000 acres would increase by nearly 50 percent, and that average area burned statewide would increase by 77 percent by the end of the century.”
I picked out fire because it’s been in the news, but the rest of the report makes equally sobering reading, picking out other implications of climate change and how it is predicted to have a negative impact upon California. Sea level rise is another element, as is potential change to topography (with possible impacts on flooding).
There are other aspects, too, such as energy consumption and public health, which don’t fit directly with the theme of this digest but are certainly tied in to the issue of changing climate and associated changes to the Earth system.
Human-Induced Landslides on the Rise
At the beginning of the earthquake item I talked about how some things are cyclical. We can see from the wildfire example that it isn’t always the case, and that a change in the cycle can tip a particular element over into what is effectively a ‘new normal’.
Landslides are a hazard that is often overlooked. In the past I’ve commented on annual roundups, and this week my eye was caught by a longer-term assessment, including available data on fatal landslides (excluding those caused by earthquakes) from 2004-2016.
The analysis recognises some cyclical patterns, both geographically and temporally — for example, with increasing periods of rain leading to more landslides — but there are other factors which lead to a linear, rather than a cyclical, variation.
Specifically, human activity is significant. The report’s conclusion states that: “Our analyses have demonstrated that fatal landslide occurrence triggered by human activity is increasing, driven by construction, illegal mining and illegal hill cutting”. Other factors, such as loss of land ice (attributable to climate change) might also increase slope instability and, in consequence, landslides.
Kilauea and Volcanoes
It isn’t official, and Nature may yet surprise us, but it’s beginning to look as if the current phase of the Kilauea eruption is over. The most exciting activity reported in the Hawaiian Volcano Observatory update was that: “A single small lava dribble was oozing lava into the ocean.”
But, as I know I’ve said before, there’s plenty of other activity. One volcano steals the headlines, but plenty others are quietly fuming away around the world, unnoticed by anyone other than volcanologists or those who might be directly threatened by them.
Currently, there are 41 volcanoes erupting around the world, four of which — Alaid, Merapi, Kuchinoerabujima and Telica — are newly active. It’s a reasonable guess that most people won’t have heard of any of them, which just goes to show, once again, that the significance of a natural event, and the hazard it generates, are related to how they are perceived by humans.