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?

Calbuco Volcano - a beginner's guide to its hazards

I'm sure you all have read tons about Calbuco Volcano now, so I'm not going to bore you with the details. Hopefully you've seen some of the stunning photos that have emerged, e.g., the ones on the Flickr stream by the Chilean Geological Service.

I quickly want to talk about hazards though. This volcano has quite the selection of hazards for you to choose from. The explosive eruptions have sent ash more than 15 km high into the air (click on the orange links to learn more about each hazard). This ash is covering a lot of infrastructure, property, and destroying crops. Most of it is being blown to the North-East at this point. With eruptions this explosive there will also be big blocks of rock being thrown out of the volcano, sometimes landing several kilometers away!

If an ash cloud collapses it can produce a pyroclastic flow. The deposits from old eruptions at Calbuco show that pyroclastic flows in the past have reached as far as Puerto Montt, a city with around 200,000 inhabitants around 30 km away from the mountain. For now I would guess that these pyroclastic flows are more likely to go towards the North-East, following the direction of the wind, but there is no way to know for sure, especially if the weather conditions change.

In addition, if ash settles on the mountain and is mixed with water (for example from snow on the top, of if there is a bit more rain over the next few days or weeks), big lahars (mudflows, mixtures of ash, dirt, water, snow, and debris such as trees etc.) can happen and travel down the valleys of some of the many rivers flowing down the slopes of the mountains. These flows can be incredibly powerful and destructive. Lahars can also reach tens of kilometers, so the 20 km exclusion zone they've put up makes a lot of sense.

In addition, some lava fountaining has been seen at Calbuco after the initial, more explosive phase that sent the ash into the skies. This means that some small lava flows can occur on the mountain. And of course, the gases that accompany volcanic eruptions can be quite dangerous too, if you get too close. Better stay at a safe distance. That way it's also much easier to take photos of the entire ash cloud!

It currently looks like the activity is getting a bit weaker: Whereas the Chilean Geological Survey observed more than 1,500 earthquakes between April 22-23, this number went down to just over 1,000 between April 23-24, just over 500 one day later, and to around 300 today. Unfortunately it's very difficult to know whether this number is going to increase again, which could mean another pulse of eruptive activity. For now all we can do is to closely monitor and to keep away from the mountain as much as possible.

View image | gettyimages.com

View image | gettyimages.com

Volcanic whistles and more

We've been talking about science and being a scientist and girl power for a while, so I reckon it's time to get back to volcanoes. In August 2012 I went to Hawai`i for the AGU Chapman conference on Hawaiian volcanism. The lovely people at the Hawaiian Volcano Observatory (HVO) were nice enough to let me stay for a bit to get familiar with the volcano and to get some of their data to play with. It was also a good opportunity to catch up and collaborate with my friend and colleague Jess Johnson again. My supervisor Mark and I had decided that Kilauea would be a good volcano to study earthquake recordings.

What were we trying to achieve by studying Kilauea Volcano? The main question we had was 

"Do the continuous earthquake recordings look different for different types of eruptions?"

Intuitively one might say, of course there are differences (or at least that's what I would have said). But we wanted some real evidence. Kilauea tends to erupt most of the time, and the style of activity varies, so this was an ideal place for us to go and test our hypothesis. 

I got data from the continuous recordings of earthquake activity around Kilauea volcano for an eruption in the eastern section of the volcano (called the East Rift Zone, close to a crater called Pu'u `O`o) in 2007, and a similar eruption in 2011. These eruptions were related to magma breaking and pushing open a big crack a few kilometres underground. This is called a dike intrusion.

I also got data from a series of more explosive eruptions in the western part of the volcano, close to a crater called Halema`uma`u, in 2008. During the year 2008 these explosive eruptions slowly formed a connection between the magma supply at Kilauea and the surface. Now there is a lava lake that's something like 200 m across, and visitors can no longer access the crater like they used to. The explosions probably only moved magma around that was a few 100 metres below the surface, not kilometres like in 2007 and 2011.

So we had data for two types of eruptions:

fissure eruptions in the east (i.e., lava fountains)

vs. explosive eruptions in the west

We used a technique called Fourier Transforms to find out what frequencies the earthquake waves were composed of at the different points in time (if you want an analogue explanation for what Fourier Transforms do check out this old post). That way we can make what's called a "spectrogram". You can learn a lot of things about the earthquake waves by doing that. For example, you can get an idea if the movement of the ground is from an earthquake that happened close by, or from an earthquake that was hundreds of kilometres away. The graphic below shows the seismic ground movement (the black wiggly thing) and the spectrogram (the rainbow coloured rectangle) for a few days in 2011. I've added some labels to explain in a bit more detail what we can see on it.

Seismic ground movement and "spectrogram" from Kilauea Volcano during an intrusion and fissure eruption. The coloured spectrogram shows how much of each frequency we have in the seismic wave at each point in time. Red means a lot of that frequency, blue means not a so much of that frequency. The red diagonal streaks across the graphic are the volcanic whistles, described below, where the frequency goes up (or down) over time. You can just hear the first one when you listen to the audio from the link in the text below.

So by doing that we learned three main things about eruptions at Kilauea:

1) Fissure eruptions and dike intrusions at Kilauea really do generate ground movement that is different from explosive eruptions.

2) These fissure eruptions and dike intrusions show two phases of ground movement:

Phase I (purple in the graphic above): The first phase is made up of lots of short earthquakes, close to the dike intrusion and the eruption. These earthquakes are probably related to breaking the rocks when the magma pushes open the crack. 

Phase II (blue in the graphic above): The second phase starts a few hours after the first phase. It doesn't have as many short earthquakes, but instead shows continuous (small) movement of the ground for a few days. This continuous movement is what we call "volcanic tremor". Phase II happens quite far away from the eruption and the dike. 

3) The second phase has something called "frequency gliding" (the diagonal streaks in the graphic above). It means that the frequencies of the waves slowly change over time, a bit like a kettle on the stove that starts whistling at a higher and higher tone when the water is boiling.

To give you an idea what I'm talking about I've taken some of the ground movement and sped it up by a lot. You can play the movement that happened over roughly 1 day in just over 1 minute. That way we can actually HEAR the ground move. Click here to listen to the earthquake activity during the 2011 eruption at Kilauea. At first you just hear some noise like the wind. That's before anything is happening. All of a sudden (around 7 seconds in) you start hearing a lot of clicking sounds, maybe like gun shots or like rain drops on a metal roof. Those are the little earthquakes during Phase I. Then it gets a bit quieter again, and then you start hearing something continuous, like a boiling kettle (around 45 seconds). That's the volcanic tremor from Phase II. If you listen really carefully you can even imagine that you're hearing the frequency gliding, i.e., the whistling getting higher and higher.

You may remember a study in 2013 from Redoubt Volcano up in Alaska. Redoubt was also whistling, for around 1-3 minutes before some of the explosions that happened there in 2009. They called it "screams". It turned out that the screams where actually little earthquakes getting closer and closer together in time, until you can't distinguish them anymore and they're just one continuous scream. 

The screaming or whistling at Kilauea is quite different: It's really slow and lasts for many hours. Nobody has seen gliding that lasts this long anywhere before. Also, the little earthquakes that you can hear in the beginning actually SLOW DOWN before the whistling starts, so the explanation from Redoubt doesn't work here. Many other models that explain this type of behaviour can't produce whistling that would last for several hours, so we spent some time exploring what could generate a signal like that. In the end we decided that the Kilauea tremor and whistling may be related to bubbles in the magma: We think that it's possible that gas bubbles in the magma reservoir beneath the western crater Halema`uma`u can form "bubble clouds", or areas where lots of bubbles collect in one place. These bubble clouds can start swinging, or oscillating, if there is magma flow or something else that can start the oscillation. This swinging is transferred into the ground. When the magma flow changes (for example when a crack breaks open somewhere else in the system, like the dikes in 2007 and 2011) the frequency of the bubble cloud tone can change, and produce the whistling that we observe. 

To know whether that is actually what was happening at Kilauea we would need some more info, for example a detailed study of where exactly the whistling was coming from on the volcano. However, it was still really interesting to see how by comparing the earthquake recordings from several different eruptions we were able to identify similarities and differences, and how that - in combination with other observations during those eruptions - made it quite tricky to come up with possible explanations for what we observed. Many studies focus on just one eruption, but we showed that we can learn a lot by looking at the bigger picture.

If you're still reading this you really must have a lot of spare time, so feel free to check out the journal article that we wrote about all this.

Mini series on volcano hazards - part III: More on flows

As we learned last time, if an ash cloud becomes to heavy it can collapse and generate a pyroclastic flow. Those flows are not the only ones that happen during or after volcanic eruptions.

An obvious one are lava flows. Depending on the type of volcano, lava can be sticky or runny. The sticky lava tends to be able to store more pressure, and erupt more violently when it finally does. That's what happened e.g. when Mount St. Helens erupted on May 18, 1980. More runny lava tends to erupt less explosively, instead we say the eruptions are "effusive". Of course, as always, there are exceptions to those rules, but it's a good big picture way to think about different styles of eruptions. During effusive eruptions, runny lava either just trickles out of a vent, or sometimes fountains out of fissures. That looks just like a fountain in the park, but with lava instead of water. Here's a video from Kilauea on Hawai`i, you can see lava fountaining out of a fissure, and then - curiously - disappearing into a crack in the ground.

Lava flows are a hazard, mainly because there's not that much that you can do when one shows up in your backyard, like in the photo below. Luckily, at least they're usually quite slow, so you should be able to run (or even walk) away and save yourself.

Lava flow in Kalapana, a now mostly abandoned village on the Big Island of Hawai`i (photo:USGS/Wikimedia Commons)

So that's lava flows. But did I mention mudflows, so-called lahars? Those guys can be quite dangerous too. But what are they? Imagine an explosive eruption with a pyroclastic flow. That kind of eruption often happens on steep, high volcanoes which in turn have snow and ice covering them, sometimes all year round. We learned that pyroclastic flows are really hot, right? What happens to some (or all) of the snow and ice when it gets hit by a pyroclastic flow? It melts. Sometimes a lot. So now we have a lahar - a hot mix of ash, lapilli, bombs, and meltwater rushing down the mountain, sometimes as fast as a car. During that process, lahars often take out trees and other "obstacles", and the more material they carry the more obstacles they can take out, like a tsunami on land. That's exactly what happened in 1985 at Nevado del Ruiz, Colombia. The lahar that was caused by a relatively small explosive eruption was so powerful rushing down into the country surrounding the volcano that it killed over 23,000 people, and left another 10,000 injured and/or homeless.

The same thing can happen long after an eruption has stopped. After the famous eruption of Mount Pinatubo in the Philippines in 1991, not snow and ice but heavy rain started to generate mudflows by mixing with ash on the slopes of the mountain. 

Below an image of a house buried by a lahar. Imagine how powerful the flow must have been!

House buried during lahar, Chaiten, Chile, Dec 2009 (photo: Photovolcanica/Richard Roscoe)

Let's keep in mind that these flows can happen a long time after a volcano has stopped erupting, as long as there is enough loose material on its slopes. Now we need to monitor not only the volcano, but also keep an eye on the weather to make sure we're covering all our bases. Luckily, some smart engineering can help us against this hazard. In some places, e.g. at Sakurajima in Japan, they constructed large, concrete flow channels and dams (sabos) to direct lahars away from villages. Even though sabos can't provide a guarantee that a lahar won't sweep away your house, they're a good start at reducing the risk linked to this particular type of volcanic hazard.

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!