Volcano monitoring from a distance

In the past few weeks, there has been an eruption that keeps littering my inbox with emails: Bogoslof Volcano, on a tiny island of roughly 1 by 2 km out in the Bering Sea, west of the Alaska Peninsula.

View from a helicopter onto Bogoslof Island. Photo: Dan Leary, Maritime Helicopters

Despite the fact that it's effectively in the middle of nowhere (the nearest town is roughly 100 km away), Bogoslof is an interesting one. Being up in the Aleutian Chain, it sits along a very important corridor for international air traffic. If you remember the chaos all over Europe after the 2010 eruption of Eyjafjallajökull in Iceland, it's hardly surprising that monitoring volcanoes even in parts of the world as remote as Alaska is an important task. But how do you monitor a volcano that sits on an uninhabited, far away island?

An obvious answer would be to put a bunch of instruments onto the island. However, the island is so small, so far away from any population, in such a harsh environment, that the Alaska Volcano Observatory has to focus its limited resources elsewhere. In addition, the last eruption previous to this one had occurred in 1992, and it's been at least 40 years since the last eruption before that, so unsurprisingly the volcano was relatively low on the monitoring priority list.

This changed on 20th December 2016, when several pilots in the area reported an ash cloud that had risen up to over 10 km above sea level. Because there is so much air traffic going through the region, reports like that are an important part of monitoring volcanic activity in remote areas. Whereas the eruption had stopped within an hour or two, activity at the Alaska Volcano Observatory certainly wouldn't have.

Data had to be analysed, statements had to be published and scientists were looking for signs of any unrest that may have preceded the eruption. Indeed, looking back through the data, the volcanologists realised that Bogoslof had been showing signs of activity throughout the month of December, and the first explosion may have occurred as early as 16th December. So what kind of data can volcanologists use to monitor Bogoslof?

Even though there are no seismometers on the island itself, nearby Okmok and Makushin volcanoes have extensive monitoring networks. Because seismometers are very sensitive instruments, and volcanic eruptions make the ground shake with waves that can travel a long way, it is actually possible to look at seismic signals from Bogoslof on other islands.

Similarly, microphones recording "infrasound" (i.e. sound at frequencies much lower than the range we can detect with our ears) can detect pressure signals coming from far away, and volcanic eruptions often produce distinct infrasound.

Satellite image show the ash cloud at Bogoslof Volcano on 18th January 2017. Image: NASA Earth Observatory/Jeff Schmaltz

Satellites are also quite useful. A volcanic ash cloud can often be detected from space. Some satellites capture light of many different wavelengths, others can detect different types of gases in the atmosphere, some of which can be traced back to volcanoes. Visual observations by pilots, local residents or fishermen help to complement the picture we get from satellites.

Last but not least, volcanic lightning (i.e., lightning strikes in or around the ash cloud coming up in an eruption) has been an increasingly valuable tool to detect volcanic eruptions over the last few years. Volcanic lightning is still not fully understood and subject to active study by volcanologists around the world, but even without a complete understanding of the exact mechanism it is a spectacular sight and can be used for eruption detection. You can watch lightning happen all around the world through the World Wide Lightning Location Network if you're interested, almost in real time.

Spectacular eruption with volcanic lightning at Mt. Etna, Italy. Photo: Karl-Ludwig Poggemann

At the time of writing this post, Bogoslof continues to have explosions every few hours to days, and scientists are analysing these eruptions through all the different types of data mentioned above, even though there are no instrument directly on the volcano. Pretty amazing, isn't it?

Iceland vs. Japan - the art of eruption forecasting

Finally I'm getting around to writing a new post, after I've taken my summer break since the end of the last term.

Work is in full swing again, undergrads are back, and campus is as busy as ever. After some intense work over the summer I managed to finally submit my manuscript about Hawai`i tremor. Fingers crossed that it gets accepted!

In the meantime, lots of volcano-y things have been happening, so an update is well overdue. Everybody has heard about the eruption of Bárdabunga, of course. We know that a dike (a vertical crack in the rocks, filled with magma) pushed its way through the Earth's crust for quite some time, before it reached the surface and started a stunning fissure eruption. How do we know that? Because lots of earthquakes happened underground where the dike was breaking its way up! But all this is, of course, yesterday's news - and I'm sure many of you have read tons about this eruption and seen some of the spectacular videos and photos.

Another big event was the eruption of Ontake-san last weekend. Pretty much out of the blue this volcano started to erupt explosively - and in the process sadly took many lives. Volcano disaster wise in Japan, this is about as bad as the 1991 eruption of Unzen, which killed over 40 people. After the Ontake eruption some people claimed that the disaster could have been avoided. But the truth is, from what I've seen in terms of data it was very difficult, or maybe even impossible, to see this coming. Why is that?

1. The eruption appears to have been a so-called "phreatic" eruption. That means that instead of magma pushing upwards through the crust, water was seeping into the volcano. This (cold) water probably reached a hotter region underground, where it immediately turned into steam. This steam wanted to rise and expand - it increased the pressure underground which then lead to the explosive eruption. A very similar thing happens in your kitchen: Have you ever heated up a pan or pot without anything in it, and then poured water onto the hot surface? You immediately get a big sizzle and lots of steam.

When scientists analyze the ash from this eruption, they will probably find mostly fragments from old rock that was broken into ash, and probably not many fresh magma pieces. Because no (or very little) fresh magma pushes upwards during these kinds of eruptions usually there aren't many precursors. No large numbers of earthquakes like we had in Iceland just a few weeks earlier, no big changes of the shape of the volcano like there was before the eruption of Mount St. Helens in 1980.

2. That "nothing" was happening on the volcano before the eruption is not 100% true. Since mid September there had been some more earthquakes than usual. However, the highest numbers were recorded on Sep 10 and 11, and they went down again afterwards. Furthermore, these "seismic crises" aren't unusual on volcanoes. Ontake had very similar periods with increased earthquake activity for example in the mid 90s, without eruptions following. Other volcanoes such as Long Valley caldera in California frequently have earthquake swarms - the latest one just a week ago, yet it hasn't erupted in the last 10,000 years or longer. Based on what we know about volcanoes, earthquake swarms CAN mean an eruption is coming, but they don't mean that an eruption HAS to happen. Often other warning signs accompany or follow earthquake swarms, in which cases eruptions become easier to forecast. These other warning signs could be a change on the volcano shape because of magma pushing rock out of the way, or more gases coming out of the volcano. Whereas in Iceland we had some idea what was gonna happen, in Japan we just couldn't see it coming. Despite all our research and efforts, unfortunately we aren't at a point where we can completely understand and forecast the processes happening below our feet in volcanically active areas.

In the case of Ontake, around 10 minutes before the eruption started another earthquake-like signal showed up on the instruments: Volcanic tremor. I've talked about tremor in one of my very early posts, but it might be time for a little update.

Volcanic tremor is a little bit like an earthquake, but with two main differences:

• Tremor ground oscillations are usually a little bit "slower" than earthquake ground oscillations: Whereas earthquake oscillations go back and forth anywhere between say 1 and 25 or more times per second, tremor oscillations only make it up to 5 or 10 times per second for one full cycle of back and forth.
• Tremor can go on for a really long time: Whereas earthquakes are usually over after a seconds, tremor can last for minutes, or hours, or days.

Luckily tremor usually only happens very close to the volcano, and the shaking is very small, so people don't usually feel it - otherwise shaking going on for several days or longer might be quite annoying. Yet, we can record these oscillations on our seismometers and usually when we see them we keep a good eye on the volcano to make sure we don't miss any eruption warning signs. Something like 2/3 of all tremor cases happen just before or during eruptions - but that also means that 1/3 of tremor cases don't appear to have anything to do with eruptions. That's why tremor isn't a very reliable warning sign - certainly worth to keep an eye out for but not a unique sign that something is about to happen. Lots of people have had ideas about what causes this tremor signal, but unfortunately many of these studies don't agree with each other, or only work for one specific volcano. In my research I study tremor from volcanoes in lots of different places: Hawai`i, Alaska, Latin America, ... I am trying to find out whether there are different tremor "types", that can tell us more about what causes tremor in different places. That way, maybe one day it will be easier for us to know whether the tremor that we record on our instruments is just harmless, or whether it tells us to get the hell out - and maybe disasters like the Ontake one can be avoided in the future!

What happened at Ontake is certainly worrying - after all there are lots of other volcanoes in the world and other "blue sky eruptions" (i.e. without clear warning signs) might happen elsewhere. Some people here in the Pacific Northwest started to worry a bit, and a radio station got in touch with Mark and me to check whether they could ask some questions in a radio interview. Of course I said yes, after all I love talking about volcanoes and I thought it could be fun. I expected that they would ask me some questions and then cut it and broadcast it at some later point in time. Instead, the whole thing was a 30 minute live interview - which I only realized as we started the interview! Whoops... That made it of course slightly terrifying, after all I hadn't ever given a radio interview. I also felt a little bit weird, sitting alone on the phone in one of our meeting rooms at work and yet talking to anybody who was listening to the radio station at the time. In my surprised state I probably sounded like a complete fool, and most likely made something like 80 out of "100 mistakes scientists make when talking to the media". But what the heck, everybody has to start somewhere, after all! If you're interested you can listen to or download the podcast here - don't judge me too harshly though! Thanks to Cfax 1070 and Terry Moore for hosting me - it was definitely a fun experience :)