If you’ve been keeping even half an eye on any Earth-science-related social media this week, or even some of the mainstream news, you can’t have failed to notice that Sinabung, a volcano in Indonesia, erupted spectacularly early this week. Take a look on Twitter — #Sinabung will bring you some astonishing footage and images of the eruption.
Mount Sinabung: Part of a Volcanic Chain
The purpose of this digest, however, isn’t to repeat the news bulletins, but to dig a little deeper than the news headlines and their images, spectacular though they may be. With that in mind, I’m going to look at little more closely how Sinabung (or Agung Sinabung, as it’s more correctly called) fits into the theories of volcanism.
Indonesia has a lot of volcanoes (there are over 1100 entries on the Smithsonian/USGS volcano database for the country, although the majority of them are extinct or the entries are double-counted), but even looking at the numbers of those we would consider active is an eye-opener. There are 52 volcanoes which have recorded eruptions since 1699 (many repeatedly) and 39 have erupted since the beginning of this century.
Why so many? The interrelationship between earthquakes and volcanoes is at play here – one of the more obvious demonstrations as to how the Earth works as a system. Indonesia is highly seismically active, with a major subduction zone, the Java Trench, running along its western coast. There’s also tectonic activity elsewhere in the country.
Subduction zones are associated with earthquakes, but they’re strongly related to volcanoes, too. As the crust at the subduction zone descends, temperatures increase. The rock melts and, with molten rock being less dense that the cooler rock above it, it rises, reaching the surface and erupting. This is a feature of all subduction zones, which typically have a line of volcanoes — islands or mountain ranges lying around 100km (depending on the angle of descent) into the over-riding plate.
Take a look for yourself — you’ll see it in Alaska, in the Cascade range, the Andes or anywhere else where there’s a subduction zone. Sinabung is just one of a chain of frequently-erupting volcanoes in Indonesia and elsewhere, made newsworthy by the presence of news media. But in reality, this kind of volcanic activity is continuous and worldwide.
Recent Research: Eruption Forecasting
So, volcanoes are like earthquakes in the sense that we know that they’re going to erupt but pinning down the exact time at which they will do so — and, in consequence, managing the hazard that they produce — is a much more complicated business. There are many variables at play. Some volcanoes rumble and hiss for years before producing a major eruption, or never produce one at all. Others can produce cataclysmic explosive activity with very little warning.
As with earthquakes, the search for information that can help to warn of a common eruption is ongoing. This week, newly-published research based around Chile’s Villarica volcano revealed how volcanologists are seeking to use recordings of very low frequency sounds emitted by lava moving within a magma chamber to indicate the likelihood and timing of an eruption.
The study is based on the frequencies recorded at an eruption in 2015 and, as all similar studies do, comes with caveats based upon the number of different variables at play — not least that volcanoes are not the same and behave very differently. But the value of this kind of research is beyond dispute and that’s something clearly demonstrated by the fact that Sinabung’s enormous eruption this week is notable for the images it produced rather than for any deaths or injuries it caused. (For the record, I’ve seen none reported.)
To quote volcanologist Janine Krippner (via Twitter): “I keep looking at these #Sinabung eruption photos thinking “thank goodness this area was evacuated. Thank goodness the volcanologists & authorities are there.”
The Yellowstone Saga: A Cautionary Tale
A little knowledge, they say, is a dangerous thing. I’ve said above that volcanoes are complicated beasts and one of the more notorious is Yellowstone. It attracts attention because it’s picturesque, it’s mysterious and it’s active. And what we know of its history is that it has erupted, very far in the past, three times, on a monumental scale.
This is where it’s easy to lose perspective. Perhaps it’s because disaster sells newspapers/attracts ad clicks, or perhaps it’s just a human fascination with impending doom, but the idea that Yellowstone is about to erupt again is one that keeps coming up. It seems that every time there’s a minor tremor, or a herd of bison is spotted crossing a road, there are reports that a further catastrophic eruption is about to come upon is.
This week was no exception, and it was a swarm of earthquakes (which are sometimes, but not always) as a precursor to an eruption, that got the news media worked up. Yes, there were earthquakes — the USGS real time earthquake map shows 78 of them in seven days, the largest being M3.1. But while the newspapers report them with a degree of ghoulish anticipation, they aren’t as every volcanologist can tell you, at all unusual.
The resigned tone of the attached screenshot (from volcanologist Erik Klemetti) tells you everything you need to know.
So, a quick roundup from my guilty social media pleasure. Sinabung wasn’t even a contender in the #VolcanoCup (the Indonesian winner was the much more infamous Krakatoa) and as the competition reaches the end of the group stages, the biggest of the big beasts — Etna, Laki and Mount St Helen’s among them — are fighting it out.
I know I say this every week, but I really do urge anyone with any interest in volcanoes to pop over to Twitter and have a look. (Editor’s Note: There’s a link in the Resources section, below the article.) Wonderful images, fascinating facts and a very human passion for the Earth and its activity are all very much in evidence.