I shall begin (of course) with the Moon.
This is an Earth science article, but the Moon is a part of the Earth system just as the Earth itself is part of the solar system. Current theories indicate that the Moon was born of a collision between an extra-terrestrial body and the young Earth, which means that the two will have some geological similarities (though the Earth, being dynamic, has evolved a lot since then).
The Moon is integral to our society. It affects our tides (though, as we discovered last week, not our earthquakes) and it’s ingrained in our culture. We sing songs to it and sigh to it, we respond to its rhythms and it is rooted in our deepest myths and nightmares (think werewolves and lunacy). And that’s why this week’s triple lunar event — supermoon, blue moon, lunar eclipse, all on one night — made so many headlines.
I admit to a little wobble about the terminology. The media are calling it a ‘Super Blue Blood Moon’ which packs quite a punch. But was it actually a supermoon? Was it actually a blue moon? Was it even a blood moon? But it didn’t take long to lay my fears to rest.
You can spend a lot of time on the internet trying to find a scientific description of a supermoon, but there doesn’t appear to be one (I stand corrected if there is). The best explanation, and the one that I take as gospel, comes from NASA, which notes that it is considered to be: “a full moon occurring near or at the time when the Moon is at its closest point in its orbit around Earth”. It may not technically have been a supermoon, but it was in the sense that it looked significantly larger than a normal moon to the naked eye.
And a blood moon? That term originates from the reddish shadow that is cast across the moon during the process of a lunar eclipse (when the Earth blocks the Sun’s light). So yes, a blood moon — but only where the lunar eclipse was visible (not, alas, for me).
The term blue moon is a little less scientific, generally taken as a layman’s phrase for something that happens rarely. In fact it refers to the second full moon of a calendar month. The first in January occurred on the second of the month. Blue moons are rare, but perhaps not that rare. If you missed this one, as I did, there’s another one coming our way in March.
Earthquakes, Cascadia and the Orphan Tsunami
Even though I’m no longer writing a detailed earthquake digest, I do like to keep an eye on the United States Geological Survey’s earthquake map. This week there were three earthquakes at some distance off the Pacific coasts of Oregon/California. They weren’t large — the largest was M5.6 — and they weren’t damaging. They occurred at the western edge of the Juan de Fuca tectonic plate, a fragment of a much larger plate, the eastern edge of which is being subducted under the US along the Cascadia subduction zone.
The earthquakes at the western edge of the plate are strike-slip, caused by parts of the crust sliding past one another. That’s why they’re harmless. At subduction zones the movement is compressional, tending to produce larger and more damaging earthquakes, whose vertical component has the capability to generate major tsunamis.
In contrast to other major subduction zones worldwide, Cascadia is — perhaps ominously — quiet, with no significant earthquake activity recorded along it. Seismologist Robert Yeats points out that for years it was considered to be aseismic, posing no earthquake risk.
As it happens this week marks the anniversary — 218 years on 26 January — of a devastating tsunami which struck Japan and which had no obvious source. It wasn’t until the mid 1990s that the source of this disaster was traced. It came from somewhere along the Cascadia subduction zone. What that tells us is that Cascadia is capable of producing very large earthquakes indeed, much larger than the ‘Big One’ so often talked about for California. And although it may not do so very often, it would be wise for those living on the north west coast of the US — and on the far side of the Pacific — to be prepared for when it does.
Cascadia may be quiet, but it’s a sleeping giant.
Fireworks: The Best Volcano
In the first of these Earth Science roundups, I mentioned the trend for Twitter cups, where you vote for your favourite whatever and the vote proceeds to a knockout round. These things are terrific as a means of science communication, because those who are interested tweet their votes and their reasons for it.
February 1 sees voting opening in the latest of these, the #volcanocup. I confess that I’m not quite sure how the group stages have been arrived at (if you look at the picture, you’ll see what I mean), but there are a few groups of death in there, with some of the planet’s biggest, most beautiful and most notorious volcanoes pitted against one another in the opening round.
Some big beasts are going to go out early. Vesuvius up against Etna? Toba against Krakatoa (now that really is a big one)? And in the battle of the Icelandic tongue twisters, will my personal favourite, Eyjafjallajökull, win out over Bárðarbunga, or will Katla slip through by virtue of being easy to pronounce?
It’s a bit of fun, but if you follow the hashtag you’ll not only learn a few facts, but you’ll be exposed to dozens of volcanologists showing their love for the subject. And that’s no bad thing. I shall keep you updated.