LMU in München has a neat program called "IsViews", focused on imaging Icelandic volcanoes. They got, for example, this image right from the beginning, at an impressive 11 centimeters resolution.



(Credit: IsViews

(As always, right-click and view image to see in higher resolution)

But their latest radar picture is what I think all of us lava junkies have been waiting for. It's a couple days out of date, but I don't think anyone's going to be complaining ;) Bright colors = a rough surface.



(Credit: DLR / Fjarkönnun ehf / IsViews 10

Let's take a closer look at some key parts.

Here we can see the fissure row, now heavily dominated by the rapidly outpouring lava lake of Baugur. This forms a lava river to the northeast. To the south you can see sizeable fissures stretching all the way to Dyngjujökull and under the glacier.

The lava river disappears into a broad spreading area. A stark line separates the new lava tongue from the last. Broad patches of duller gray indicate a smoother surface than the majority of the "bright" lava in the image and might suggest still-flowing lava on the surface.

Note the "islands" in the picture. These are kīpukas, areas of elevated terrain left intact by the lava flow.

Here we see the Jökulsár á Fjöllum, which has been heavily modified by the lava flow. Note how the formerly broad, braided stream has been confined into one main channel (the side channel further to the east has not yet been reached). Furthermore, in several points it is pinched down to a narrow path, causing the water above it to back up into small reservoirs. Each of these are several kilometers long.

As one can see, the first tongue of lava went the furthest, almost 95% of the way to the waterfall Skínandi before the lava river diverted into other paths, giving him a last-minute reprieve (for the time being, at least). The lava river has diverted several times since, each time creating new tongues of lava. Each of them has widened the overall lava flow; the eruption is creating the very barriers to its lava's movement, dams of basalt up to 30 meters high. The edges of the older flows on the north and east are still creeping slowly forward according to the daily maps, and eventually new flows will ride over the top of old ones. Progress of the flows is inevitable... but only so long as the lava keeps coming. The ultimate fate of the plains, rivers, and waterfalls in the area thus depends heavily on how long the eruption carries on.

There are no signs of letup.

While the rate of quakes hasn't been as intense as during dike formation, it still has carried on at an abnormally high intensity, not only in terms of strength of the powerful caldera quakes, but also in sheer numbers. In the past two months the event has induced more quakes than are normally detected in all of Iceland in two years.

More on the caldera quakes at a later date, perhaps in my next article. There's a little curiosity on the map right now.

See it? Let's zoom in.

That's a surprisingly quake storm out of the blue north of Herðubreið. It is close enough to areas known to have been stressed by the dike intrusion that one would assume it's connected to the current event. Will it continue? I have no clue. Is there magma there? I have no clue. Does it have any significance? I don't know. I'm simply pointing out that a new chunk of land in the area decided to start rumbling.

Now, a quick word about mist, about sulfur dioxide, sulfur trioxide, sulfuric acid, sulfurous acid, sulfate ions, and so forth.

I've been getting some complaints recently in the comments about me referring to the sulfur component of the eruption as SO2 (sulfur dioxide) regardless of the form it's taken. There've also been some suggestions that what one is seeing isn't really a mist but particulate matter. So let's set the record straight.

Most of the sulfur as it leaves the vent - but not all - is in the form of SO2. Total sulfur emissions are usually listed as SO2 equivalent, or broken down into SO2 equivalent and HS (hydrogen sulfide), as any reading of scientific reports and peer-reviewed articles, either on this eruption or in general, make clear. It's very rare to see them break down SO2, sulphurous acid, sulphuric acid, and other such compounds unless there's some essential reason to do so.

There is little particulate matter associated with the mist in locations further from the eruption site, and there is no credible research indicating that past volcanic mist incidents are primarily due to particulate matter. The blue color comes from Rayleigh and Tyndall scattering, the same phenomena that make the sky appear blue. Particulate matter pollution is usually gray to amber colored, not blue. Nor are volcanic ash falls in general blue.

It was once believed that "volcanic winter" was caused by particulate matter, such as fine ash. It is now known that particulate matter takes a distant second place to SO2.

SO2 creates a mist via oxidation in the prescence of water to sulfuric acid. Sulfuric acid (H2SO4) nucleates a mist because it is highly hygroscopic and draws out atmospheric moisture to dilute itself down to around 10%, thus creating tiny acid droplets that are extremely good at scattering light. While chemical that directly causes the condensation is H2SO4, the source of the H2SO4 is SO2. And the reactions, of course, do not stop at H2SO4.

No, dissolved SO2 is not sulfurous acid. Dissolved SO2 is aqueous (dissolved) SO2. It can also form sulfurous acid, but that only dominates in weak solutions. In anything but very weak solutions, most dissolved SO2 remains SO2, aqueous. And even if this wasn't the case, it'd be picking at straws to say the least; you don't see people complaining about dissolved salt no longer being salt, despite the fact that it dissociates.

Also as per the same paper, SO2 dissolves surprisingly well in water - at the sort of temperatures we're getting, over 3% by mass. Hence any mist can be expected to contain not just H2SO4 and other sulfates, but also aqueous SO2.

But really, what's my main reason for simply saying SO2? Because that's what volcanologists do. Volcanic sulfur emissions are simply referred to in general - unless there's a specific reason not to - as SO2 emissions. The lists of volcanoes are by "SO2 emissions". The pages for monitoring volcanic gases group them all together under "SO2", including using SO2 in the webpage titles and project names - even though they're also registering other forms of oxidized sulfur. Basically, nobody is going around calling the sulfur components of plumes "SO2 gas / aqueous SO2 / sulfurous acid / sulfuric acid / miscellaneous sulfate emissions". And so I'm not about to start doing so either.



(Credit: Vilhelm Gunnarsson)

But all this raises a good question... why exactly is the mist - and the sky itself - blue? And why are sunsets yellow to red, with those through the mist even moreso?

(For all of you science nerds out there who already know the answer, you can skip this part!)

The real question to ask yourselves is, why should the sky have any color at all? Why should sunlight of any color be coming from directly over you? The sun's not there, so why is its light coming from there?

The answer is the aforementioned scattering.

Rayleigh scattering is the scattering of light by very tiny particles. Tyndall scattering involves scattering by particles that are also very tiny, but not as tiny as in Rayleigh scattering. In terms of the sky color, Rayleigh scattering is the dominant mechanism. Light passing overhead from the sun that normally wouldn't hit you becomes scattered, changes direction, and if you're lucky, ends up heading in your direction.

So why blue?

Both of the two types of scattering work better on shorter wavelengths of light, like blue, than longer ones. You can think of it like how long waves like radio waves can pass through the walls of your house but short waves like light get scattered when they hit the walls. The more easily scattered blue light is far more common than reds and oranges.

So why are the sunsets yellow to red in color?

Light from the setting sun is heading straight toward you, but it's going through a lot of atmosphere to reach you. As a consequence, most of the blue light has been scattered away before it reaches you, leaving only the longer wavelength colors.

The mist itself follows these same rules, but to an even greater extent. The scattering is so intense that even mist flowing through a valley is enough to scatter most of the light passing through it. And it scatters away all but the deep reds at sunrise / sunset.

Now, most explanations of sky color stop at that point. But there's a smartass followup question one can add:

"So why is the sky blue and not purple? Purple's even shorter wavelength than blue, right?"

This is actually an even more complicated question than the former. But the short of it is, true, purple light is scattered even more than blue. But human eyes aren't as sensitive to purple light as they are to blue, especally without a strong red component, and your body interprets the net color of all of the total spectrum reaching it - lots of purple, lots of blue, a moderate bit of yellow, and so on down the line - as blue. It's a biology question, not a physics one.

And this, my friends, is where this blog jumped the shark.



