As we approach the festive season and the year’s end, it’s always interesting to look back over some of the major events of the year. What constitutes a significant event is, of course, open to definition. If yours is the only home destroyed in a minor earthquake, for example, you’re naturally going to regard it as a more significant event than a larger earthquake elsewhere.
The personal impact aside, there are many other variables. Do you judge an earthquake as significant on its magnitude or on its impacts? How do you compare an earthquake that lasts minutes to a volcanic eruption that lasts for months? Such comparisons require a lot of time and will no doubt generate a lot of argument. So this week I’m going to spare myself the effort needed and allow myself a little pre-Christmas indulgence.
This week I’m going to give you a round-up of the major earthquakes and an overview of what I suspect few people would argue was the most significant volcanic eruption of the year. And for the rest of the digest I hope you’ll allow me a little indulgence as I push the boundaries of Earth system science towards, and possibly beyond, their limits.
The Major Earthquakes of 2018
2018 has a fortnight still to run, and a lot can happen in that time. In the New Year I plan to give a more detailed look at the year’s earthquakes but I did think it worth looking at the major tremors so far this year.
According to the United States Geological Survey: “It is estimated that there are 500,000 detectable earthquakes in the world each year. 100,000 of those can be felt, and 100 of them cause damage.” Typically we would expect to see one event of at least magnitude 8 each year and the number of tremors of at least M7 will be in the high teens.
There is enormous variation to this. The USGS statistics show that in 2008 and 2016 there were no M8.0 earthquakes, while in 2007 there were four. Similarly, in 2006 there were just nine earthquakes of M7 or more and 2010 produced 23 of them. A quick look at the major earthquakes of 2018, then, shows nothing out of the ordinary — a solitary, very deep earthquake of M8.2 off Fiji, and a further 14 of M7.0-M7.9.
The map shows that the distribution is also what we’d expect. A round dozen of them were associated with the Pacific Ring of Fire, the seismic belt which surrounds the Pacific Ocean and whose activity has alerted the attentions of some of the more excitable tabloid headline writers. But the Ring of Fire is named because of its regular and large and long term activity. There has been no increase this year.
The other three earthquakes were all on the eastern side of the Americas. One will have passed almost completely unnoticed — an M7.1 in the remote South Sandwich Islands, in the South Atlantic. The other two, an M7.3 in Venezuela and and M7.1 in Honduras, were associated with the Caribbean plate, trapped between North America, South America and the Pacific.
At the macro level there’s nothing much to see here, nothing out of the ordinary with this series of earthquakes, though each of them will have had its individual contribution to earthquake science.
Kīlauea: A Round-Up
I’ve been reporting over a lot of the year on the eruption in the Lower East Rift Zone of Kīlauea volcano in Hawaii, which was active from 30 April to 6 September and which was officially declared at an end on 6 December, after three months without any eruptive activity.
Kīlauea is defined as America’s most hazardous volcano (in the USGS’s National Volcano Threat Assessment, not just the newspapers), something which doesn’t necessarily mean that it’s the most dangerous. My reports on the eruption were essentially regular updates, but now that the eruption has concluded there’s scope for scientists and civil authorities to produce more detailed examinations of what happened and the lessons which can be learned from them.
For an easily-readable summary I recommend and article in the New York Times (see resources section, below) not least because it contains extensive links to various online resources. It also links to an academic report, which isn’t too long and which is well worth a read if you want to understand the detail.
In short, what happened at Kīlauea was another episode in the creation of the Hawaiian chain, part of an ongoing cycle of land creation which has been going on for millions of years and will continue for millions more. Magma inflates the volcano, drains out along subterranean “plumbing” to erupt at a distance of tens of kilometres. The magma chamber enters, the eruption ceases and when the chamber refills the whole cycle starts again.
The Kīlauea eruption was slow and long-lasting but it was also large. Although, as the report notes, other eruptions have produced larger volumes of lava: “the high effusion rate of the LERZ vents was sustained longer than that of any observed Kīlauea eruption.”
What’s also interesting is that the LERZ activity was the last phase in a volcanic eruption which has been ongoing for a very long time. As the Global Volcanism Program notes in its weekly update: “the end of the LERZ eruption also marks the end of the over-arching, on-going eruption at Kilauea that began at the East Rift Zone (ERZ) in 1983.”
The Boundaries of the Earth System
Earth system science is about the notion that everything within the Earth system is linked and that one action will have implications elsewhere. This includes human activity, at the macro scale (e.g. global climate change) and the micro scale (e.g. culverting a stream or river which subsequently floods in previously safe locations)
This week my eye was caught by an academic article which took this a step further, with an investigation into the extent to which cultural heritage and geoheritage (the heritage associated it hate natural environment) are interlinked and, perhaps more interestingly, to what extent they should be.
It’s an interesting idea and its thrust is that by understanding human cultural ideas and activity associated with geoheritage sites, in this case volcanoes, can improve management of risk. The conclusion is that cultural and geoheritage aren’t currently linked, but that they should be. “In concluding, we encourage heritage workers to be more fully interdisciplinary, to read more widely outside their own fields, and to disseminate their research more broadly for mutual benefits of preservation, risk reduction and valorisation”.
Santa Tracker: Santa’s On His Way
And finally, a festive footnote. Every Christmas Eve I sit down with my mince pies and look up North American Aerospace Defense Command’s (NORAD) Santa Tracker to see where the big man is, where he’s going next and how many presents he’s delivered. Give it a try.