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 :)

Mini series on volcano hazards - part II: From blows to flows...

So last time we talked about the ash the comes out of the volcano when it blows its top. We said that volcanic bombs can be unpleasant when they hit you - to put it mildly. We also discovered that the ash goes up in the air and eventually (slowly) falls back down and creates some serious problems.

Now unfortunately the ash doesn't always slowly come back down to the ground. An ash cloud is a mixture of broken up pieces of magma of different sizes (remember? Ash, lapilli, and bombs), and a bunch of hot gases. The volcano spits out that mixture, and when there is a lot of the hot gases and not quite as much ash the mixture rises up into the air. It can go quite high, and then get transported with the wind and create a big mess for air travel (which we saw happening all the way from Iceland to Europe 4 years ago). Why does the ash cloud rise up so high? In very simple terms it's the same principle as a hot air balloon: The mixture of hot gases and ash is less dense than the surrounding air, so it rises. Sometimes, the amount of ash in the ash cloud is too much though - so the mixture can't rise. Instead it does what every heavy object does when you throw it up into the air: It comes back down, sometimes really really quickly. When this happens we call it a "pyroclastic flow" (from the Greek words for fire and broken in pieces). Check out the video from Earth Uncut TV below to see what a pyroclastic flow looks like.

As you can see in the video, these pyroclastic flows can get quite fast. With speeds of several 100 km/h, they're too fast to drive away from in a car. They're also quite hot: The mixture is almost as hot as the lava that comes of the volcano, something like 600-800˚ C. That's over 3 times hotter than the temperature in your oven when you make pizza. So imagine something that hot hits you at speeds faster than a race car. You can imagine what the outcome would be... In 1991, the Japanese volcano Unzen erupted and created a pyroclastic flow that (in)famously killed over 40 people, including Katia and Maurice Krafft, a couple of volcanologists. 

Has anybody seen the movie Pompeii that came out a few weeks ago (at least in North America, some places in Europe etc might have to wait a bit longer...)? It's based on a true story of a volcanic eruption and a pyroclastic flow of Mount Vesuvius in 79 AD. The pyroclastic flow from that eruption covered the city of Pompeii and everybody in there in several meters of ash. People's bodies were preserved in that ash, and at the historic site in Italy we can still see their casts in the positions they took in the last seconds of their lives that ended so abruptly almost 2000 years ago - a stark reminder of the power of volcanic eruptions.

Below another video (timelapse, by Photovolcanica) of a pyroclastic flow from Sinabung in Indonesia earlier this year. This particular one had a different trigger mechanism - the collapse of part of the volcanic edifice during the eruption. The outcome, however, can be as devastating as the pyroclastic flows generated by ash clouds. In fact, e.g. the Japanese example above was a pyroclastic flow created by a collapse of a part of the volcano.

As we will see next time, pyroclastic flows aren't the only flowing hazards on volcanoes. Water, ash, dirt, and bigger particles can create lahars, and of course lava itself can flow down the slopes of a volcano. But we'll save these topics for another time.

Mini series on volcano hazards: Ash and more

Since I was talking about eruption forecasting in the last post I think it's time to talk a bit about why we even care. Ok, we all know that volcanic eruptions can be dangerous, and that people like me are trying to understand them better, but what specifically can be a hazard during or after an eruption?

This is going to be a mini series - each post will cover a new hazard. So let's start with a very obvious one: Volcanic ash, lapilli, and bombs. What do these terms mean?

Explosive eruptions usually send pieces of rock into the air. All of the pieces smaller than 2 mm diameter are called ash. Everything between 2 mm and 6.4 cm is called lapilli, and everything larger than that is called volcanic bombs. Look at the photo below to see an explosion with a bunch of ash and some really large bombs.

The smaller the piece the further it can get away from the volcano - either because of the explosive power of the eruption, or because it gets carried away by wind in the atmosphere. Bombs are really dangerous when you're close to volcanic eruptions - it's probably not very healthy to get hit in the head with a 10 cm or so potentially hot rock that comes flying through the air. 

Explosive eruption at Sakurajima Volcano, Japan, Jul 2013. You can see an ash cloud rising. Can you spot the bombs at the bottom right of the ash cloud? Look at the size of the trees and the mountain, and estimate how large the bombs must be. Definitely wouldn't wanna get too close! Photo: K.Unglert

Ash is obviously also a problem close to the volcano: Imagine a huge sandstorm, but in addition particles in the ash are often also hot, and covered with acids from the gases in the eruption. Getting that in your eyes is inconvenient at best, and once you get the fine particles in your nose or lungs it only goes downhill. If you're exposed to ash from volcanic eruptions for a long time (e.g. many years living close to an erupting volcano) it can cause significant health issues. One way to make it at least a little bit better is to wear a mask that covers your face.

Unfortunately that's not the end of it. Even small layers of fine ash on e.g. air conditioning or air plane turbines cause the parts to corrode really fast - that's why airspace usually gets closed off around volcanic eruptions. Remember the eruption of Eyjafjallajökull in Iceland in 2010? Very fine ash particles got blown towards Europe and a lot of people were stranded in airports for days. 

Now imagine ash fall onto the roof of your house: Even a small layer, say 5 cm, can be really dangerous. Why? Well, ash - just like sand - is just tiny pieces of rock. If your roof is 10 m x10 m and has a 5 cm layer of ash on it that's a total volume of 5 cubic meters. Rock has a density of approximately 2600 kg per 1 cubic meter, so 2600 times 5 is? That's right, really really heavy! Even if the ash isn't as dense (and thus heavy) as solid rock, thin layers of ash add up to a heavy weight quite quickly. That makes building collapse a big danger.

Last but not least, there can be impacts on the economy. Ash fall covering crops can cause entire seasons to be without harvest, and animals don't find plants to feed from. Below is a photo of flowers covered in ash at Sakurajima Volcano, Japan, to give you an idea of what the ash can do. Now imagine thicker layers of ash from a bigger eruption!

Flowers covered in ash after a small explosive eruption at Sakurajima Volcano, Japan, Jul 2013. This was only a small eruption, so imagine what it must be like after a large explosive eruption! Photo: K.Unglert

Now we've learned about the main dangers of ash, lapilli, and bombs being thrown out of volcanic vents during an eruption. When the ash is a bit too heavy too rise, or when the ash and the bigger pieces build up over time, they can cause more hazards (pyroclastic flows and lahars), but we're gonna hear about those another time!