Reykjanes Ridge and Eldey-Geirfuglasker Volcanic Belt
A year and a half ago I wrote what I thought would be the end of writing about Icelandic volcanoes for quite some time. Reality obviously caught up with me, and I had to write quite a few more articles.
The Woolly Mammoth was not intended to be left alone, my idea back then was to revamp it on an annual basis as new scientific data came to light, and also due to the not so small fact that Icelandic volcanoes tend to do interesting new things quite often.
So, not only had the Woolly Mammoth grown stale, it also needed to be redone. I was never quite satisfied with how it had turned out. To put it mildly, it was too much of a mammoth and contained too little wool. Or in other words, it was too long and could quite honestly do with a bit of fleshing out for the more interesting volcanoes.
So, in the 2018 version I will cut it up into far more manageable chapters. The chapter part comes out of my idea to slowly flesh the entire thing out into a proper book sometime in the future. And books do quite nicely with chapters.
Instead of doing it in alphabetical order, or a chapter per volcano, I will this time do it a chapter per main volcanic belt.
In the 2018 Woolly Mammoth there will be a few new volcanoes, and some volcanoes will have additional information, and for others the risk estimation system I developed for the 2016 edition will be changed.
Icelandic Eruption Risk Value
Below I have assigned a risk value for every volcano to erupt, ranging from 1 to 5. This risk level is of my own device and is based on historical eruption frequency and current level of activity. The risk is purely based on how likely the volcano in question is to erupt in the next ten years, the risk number is not to be viewed as a sign of how dangerous an eruption might be.
The risk numbers are percentage based and grouped, so for any volcano the number would be anything in between the given numbers. The reader would also be well advised to remember that sometimes a volcano may change its pattern and behaviour radically.
1 = Between 0 and 1 percent (pretty much a dormant volcano that has erupted since the last ice age)
2 = Between 1 and 10 percent (this would be a dormant volcano that has given signs of awakening)
3 = Between 10 and 25 percent (active volcano with moderate eruption frequency or with a low eruption frequency that is giving signs of increased activity)
4 = Between 25 and 50 percent (active volcano with a high eruption frequency giving off signs of activity on a continued basis)
5 = Between 50 and 80 percent (very active volcano with a high recurrence rate of eruptions and giving off signs of being on the road to an eruption)
See these numbers as a handy way of discerning between the volcanic deadbeats and the volcanoes that are likely to blast off soon.
The foundation for the total of the numbers adds up to the eruption frequency of Iceland. And that is between 3 to 7 years on average. During heightened activity as the Icelandic Mantle Plume goes into overdrive that frequency is 1 eruption every 3 years, and during slower times it is 1 eruption per every 7 years. So, the individual volcanoes might be off somewhat off, but the value for all of Iceland should be accurate.
The volcanic belts
Some of you may notice that I have added two more volcanic belts in the Woolly Mammoth Guide to Icelandic Volcanism. The Eldey – Geirfuglasker Volcanic Belt and the Vestmannaeyjar Volcanic Belt are not normally used in the literature. The reason that I think it is warranted, is due to that the areas express volcanism that is sufficiently different to separate them from the mainstream volcanic belts and zones.
Traditionally the Eldey – Geirfuglasker volcanic systems are counted as either part of the Reykjanes Volcanic Belt or the Reykjanes Ridge, part of the Mid Atlantic Rift, but the eruption styles and frequency are so different that it warrants to be set apart in my view.
The Vestmannaeyjar volcanic system is traditionally seen as the southernmost part of the Eastern Volcanic Zone, but it is sufficiently different from a tectonic standpoint to differentiate it. After all, the Eastern Volcanic Zone is not a nascent new rift and the Vestmannaeyjar are.
I am feeling quite confident that in the future science will incorporate these different naming practices, after all they mirror reality.
Surprisingly little is known about the Reykjanes Ridge beyond Geirfuglasker and Eldey. What we do know is that it is the part of the Mid Atlantic Ridge where it connects to Iceland. The lavas are predominantly unaltered MORB (Mid Ocean Ridge Basalt), unaffected by the mantle derived basalts of central Iceland.
The eruptions are also closer related to normal ridge spreading types in that they are driven solely by the force of plate tectonism. Or in other words, as the plates are pulled apart magma will rise into the cracks and faults, and sometimes this magma will overflow and erupt as lava.
This in turn creates a localized upwelling of warmer upper mantle material lifting the spread centre causing a distinct ridge to form. In the case of Reykjanes Ridge it is erupting more than the rest of the Mid Atlantic Ridge, so a broader and less deep part of the ridge has formed. It is unclear why this is happening, but it is most likely related to the larger volcanic presence of Iceland itself.
The Reykjanes Ridge tapers off to the SSW and broadens as it continues towards the NNE until it reaches the Eldey-Geirfuglasker Volcanic Belt (EGVB).
What little data there is suggests that eruptions occur frequently along the Reykjanes Ridge, but that it almost never causes any concern to human life. It may though affect ships passing over an active eruption, and potentially an eruption may cause a ship to sink due to loss of buoyancy from actively degassing vents during eruptions.
There seems to be evidence that the Reykjanes Ridge is yesterday’s news. The Mid Atlantic Ridge is now slowly moving to a new spread centre that will connect the MAR to Iceland. We will return to this when we come to the chapter about The Vestmannaeyjar Volcanic Belt (VVB).
Risk level = 2
Eldey & Geirfuglasker
Eldey and Geirfuglasker are two NW-trending fissure swarm volcanoes that form a larger double system that is separated in behaviour from the Reykjanes volcanism and the Reykjanes Ridge volcanism.
What sets them apart is that they are the intersection between the Reykjanes Ridge part of the Mid Atlantic Ridge (MAR) and the Reykjanes Volcanic Belt (RVB). As such they are not true MAR-volcanoes, and not true Icelandic volcanoes either, but instead form an intermediary type of volcanism.
But, compared to the Reykjanes Ridge volcanism we can here clearly see and talk about two discrete volcanic features that anyone will recognize as a volcano.
These two volcanoes have had six known historical eruptions with four of them forming ephemeral islands. It is likely that there have been further eruptions, but that these have been too small to be noticed. The last eruption occurred in 1926 and did not produce an island.
There are no central volcanoes associated with them; instead they form two short volcanic fissures with shallow elongated flat topped subaqueous banks. The eruptions are predominantly of the Surtseyan type.
These two volcanoes are intensely seismically active with frequent intense earthquake swarms. At least Eldey has a high temperature thermal field.
Risk level = 3
In the next chapter we will deal with the Reykjanes Peninsula volcanism as we finally are ready to step unto the shores of Iceland.