According to Icelandic news there is little water in small streams that come from Hekla volcano. This lack of water in streams from Hekla volcano is often looked as indicators that a eruption is going to happen in coming months. This phenomenon has happened before a eruption took place in Hekla volcano, the last one that took place in the year 2000. But according to old news article (in Icelandic, pdf) (from the year 1995) this phenomenon was also observed before the big eruption in the year 1755. But I do not know if this happens always (it seems to do so. But I don’t have it confirmed) or just before some eruptions.
There has been drought in the area. But that might explain in part this lack of water in streams coming from Hekla volcano. But the rest of this lack of water might be related to changes in the area before Hekla volcano starts erupting. Far as I know there has not been any study into this phenomenon and why this happens to Hekla streams months before eruption takes place.
Hekla volcano does not give many long term signals on when it might start erupting. But far as this one goes, this might be the best signals we can get on the impending eruption in Hekla volcano. When the eruption might take place is impossible to know at current time.
Icelandic News.
Vatn er lítið í ám og lækjum nærri Heklu (Vísir.is, Icelandic)
Low Water Levels Indication of New Iceland Eruption? (English, Iceland Review) – Thanks to Erik at Eruption blog for this link!
Blog post updated at 04:19 UTC. A english news added.
Remember that it was a nano-strain event from the Hella strainmeter a few days ago when it dipped 150 nanometres negative. One wonders if that might have been related to this drying of the waters.
Seems like Hekla has had a phase of erupting every nine to ten years for quite some time now, and that the eruptions have been predominantly in the spring.
1980 aug 17 VEI 3
1981 apr 9 VEI 2
1991 jan 17 VEI 3
2000 feb 26 VEI 3
All of the eruptions where short ranging from 3 days to 2 months. Heklas average eruptive force is strong 3s and it is known to produce now and then strong 5s.
Interesting, my guess from a quick calculation would be an eruption around late february early march.
But then volcanos makes bad watches.
Warning! Humorous interpretation of the drying of waters at Hekla.
When the water goes Hekla becomes thirsty and borrows a few beers from Katla, and since Hekla is an alcoholic with stomach problems it vomits after the first one. Solution to all the eruptions would then be to haul a pipeline to Hekla so it never has to drink beer… 🙂
Ya, but this time, Katla is too drunk to pass anything as it is getting ready to heave. so they will have to share the same toilet…whata mess.
Interesting EQ 4km from Hekla in the last hour.
And that is Iceland for you!
Monday
29.11.2010 12:47:17 63.956 -19.640 11.2 km 1.6 30.34 4.2 km SSE of Hekla
A bit to small to start an eruption at Hekla I think.
Downgraded into an 0,6…
But might be an indicator for something volcano-tectonic, the deept looks interessting too : )
Yes it does, but it is still a small quake and it seems a bit off centre of the 5,5km fissure line ontop of the volcano.
Now I am almost getting a feeling of a conspiration here, the Hekluvöktun just went totally offline together with Vatnavöktun. We are now officially Nadjiwooned 🙂
And talking about that…
No full moon and no 2012 😉
Seems to be hard going for the conspiration theorists!
So true le Strange! But no worries, Scandinavians are level headed people who are fully aware that eruptions are the work of the jaevelen and his hordes of testy trolls.
Nah, we do not blame djävulen for it, we blame beer for it 🙂
Level-headed??? Take a look at me playing Nostradamus below…
Thanks Jon, this is fascinating. I shall be watching for any further Hekla developments with interest. Who knows, perhaps this blog will trigger off a study into this phenomenon.
Giggle-translator:
“Hekla has in recent years been told that Jack has come. This is food Hjartardóttur Driva in marriage…”
Even I am better in Icelandic than that. How does the english-only speakers survive with Giggle?
Well then Carl, try it in reverse: – “Jak to be your new Swedish teachers. What is it that creeping?”
To return to Iceland, the way things are going I think we’d better organise a sweepstake when it comes to which will be the next volcano to erupt.
Oh my in so many ways…
So I guess the most likely would be in this order. And warning, my imagination ran wild with me in the end… 🙂
1. Hekla (27 february based on mat-stat, VEI-3)
2. Grimsvötn (Central volcano). Nov 2011, VEI-2
3. Bardarbunga (Eldgja). Late december 2011, running throughout 2012 so the Nadjiwoons become happy, VEI-5.
4. Askja (Herdubreid). 2014, VEI-5+ Fissure eruptions spanning from Viti to Herdubreid where it opens up a southgoing fissure passing Herdubreidartögl and Upptyppingar.
5. Katla (Godabunga). 2016, VEI-7 that blows away the entire top of Godabunga in one piece, it lands in the ocean close to the Faeroes where it becomes a new island. After 4 years of continues explosive eruptions the entire Katla volcano colapses into the now empty magma-chamber, the now formed crater is below sea-level and the inrushing water causes a final VEI-8 eruption on christmas eve 2020. Civilisation as we know it ends.
But I guess it will be the only volcano no one has guessed at erupting next, and that it will be week. Tindfjallajökull or something coughing up a VEI-1.
Ah, forgot…
6. Trap-formation starting at Esjufjöll, Öraefajökull going up to Snaefell in the year 2025. 4,2 million kubic kilometres of lava pouring out into the sea constructing a land-bridge to Norway before the eruption ends in 1,1 million years.
Cockroach scientists find remnants of an earlier civilisation under the lava.
Anyone who can beat that?
Eldgja canyon belongs to Katla volcanic system, sorry mate. 😀
Ah…
I of course meant Thjorsarhraun/Veidivötn fissure:)
Eldgja vill of course rupture during the Katla eruption.
I’ve got an idea, can you rig that vibrating volcano chair of your’s to the top of Katla? Because it would be a heck of a lot more amusing to watch you spinning through the Icelandic skies than the seals on the spinning ice disk.
And a question, could we possibly see a tsunami hit southern Norway if something big blows in Iceland?
http://www.metalsucks.net/wp-content/uploads/2010/11/surfmetal.jpg
Nah, I built that chair so I wouldn’t have to sit ontop of Katla 🙂
I would definitly say no to a tsunami originating from Iceland due to tectonic quakes. Would take M7,6 in the ocean for that. And that is a minimum number.
A fault slip would of course do it, and with that I mean the side of a subemerged mountain falling off. A cataclysmic under-water volcano could in principle also produce a tsunami. But all of these are unlikely to happen.
How about a part of Vatnajokull glacier breaking off during the eruptions at Esjufjoll and falling into Jokulsarlon, creating a massive tsunami? Oh ofcourse Reykjanes peninsula wakes up after 700 years of dormancy, completely destroying Reykjavik and all of the suburbs by a massive fissure eruption from Krysuvik, Hengill and Brenninsteinsfjoll.
Don’t forget all of the 80 craters at Raudholar just north of Reykjavik erupting at the same time.
Nah, Jokulsarlon is a large lava canyon that will have an eruption during the trap-formation.
Silly volcano forecasting season in full swing here 🙂
Oh, you’re such a volcano-babe magnet le Strange!. If possible, be a dear and cam it up so we have something exciting to watch until Hekla heats up a bit more.
Could I have some of that “müsli” you’re quaffing? Makes for an interesting read… 🙂
Well… I can’t read the flipping thing. I know it’s about re-vegetation / re-forestation of a volcanically affected area.
But it does have an impressive image of the 1991 Hekla eruption… a night time shot.
http://www.hekluskogar.is/Skjol/Hekluskogar%20Skoven%201-09.pdf
@Carl le Strange
I have a bottle of mead waiting for Yule time. Made it myself. (specifically to find out what the real deal was… no store bought stuff) It metered out at around 10 – 12% ABV. I also made up about 3 liters of lemmenjuoma… but I am a bit fearful of it. I need to make sure I have about 2 days of nothing in my schedule before I try it out.
[OT] Selfmade mead…. wow. I’m very interested to hear how that turned out ( and of course the recipe wenn it is drinkable).
@ Carl: your plan for the eruptions had me laughing out loud. May be you shpuld inform the volcanoes what is expected of them.
It’s actually quite simple. I took 3 lbs of raw (strained) local honey and diluted it to about 24% sugar concentration. Using standard brewers yeast, but a much smaller quantity… say just a few grains that were started in pure water with a bit of sugar, and about 1 teaspoon of lemon juice to create a slightly acidic evironment, started the fermentation process. I used as little yeast as possible since a culture can carry the flavor of what it grew up in. After about four months (it’s a really slow ferment) I racked off the mead and let it go for another month. Then I added 1 ounce of bentonite clay dissolved in water and racked it again after a week. That clarifies the mix and removes the last of the yeast.
Yeast doesn’t grow well in honey-water, so you might need to add nutrient. Since the nutrient is essentially ultrasonically blasted dead yeast cells, I took the slow route because of the flavor issue.
BTW, use an air trap to cap the bottle. It lets out the CO2 and keeps the air off the mead as it ferments.
For all, the same process works for hard cider. But it only takes about 2 weeks to get a good batch of that.
Since I’m OT, here is a link to a paper about “Postglacial lava production in Iceland” that covers some of the fissure eruptions and shield volcanoes that I did not know about.
www-old.isor.is/~ah/dr/AH6_eruptions.pdf
Hmmmm… Talk a bit more about lemmenjuoma.
The homemade mead is much better than the store-bought if you have a good recipé.
Just remember that the old norse/icelandic naval law stated that if the captain of a viking vessel didn’t carry 12 litres of mead per day and deckhand than he would either pay the ship as a fine if cought by inspectors, or it would be okay for the crew to behead him 🙂
Might explain the fearsome reputation of vikings… especially if you count in their eating of fly agaric mushrooms.
Well… After all these scenarios a bunch of real data: GRF has lifted up 30-40 mm in just two months. Check the general trend without points affected by ice. GOD has lifted up 10-30 mm in 1-2 months.
Where do you find this info?
The info is here!
http://hraun.vedur.is/ja/englishweb/gps/cts/vat.html
And that was not for GOD, that was for GFUM/Grimsfjöll. I was to quick on the button. But notice the 50mm north movement on GFUM, that is not good. Normal movement is allways to the south of that station.
Here is for Godaland/GOD (Katla) and other stations:
http://hraun.vedur.is/ja/englishweb/gps/cts/emyrfr2004.html
Jon, why didnt the microquake near Hekla show up at your helicorder?
There is a very small event at this timepoint. Barely visible but we see only a low resolution chart of the data I guess. Jón can zoom in much further.
It did show up on my geophone. But it was too small to show up on the internet graph. This happens often with really small earthquakes if they are more then 10km away from my geophone.
I have noticed some odd tremor patterns at Vatnasfell http://hraun.vedur.is/ja/oroi/vat.gif – For my general education, what, (if anything) does this show us? Many thanks
It looks just like a noise on the tremor plot.
Might be anything, but it is to weak to have any real significance. If it was a volcano in pre-eruption it would show on more tremor-stations and would be closing in on 6000-8000 units.
Some intermittent noise, my guess is a drill-rig due to shape and duration.
Looking at GPs timeseries here
http://notendur.hi.is/runa/eyja_gps.html
Inflation at the AUST is continous and building rather high???
Looking at corrected Grimsfall data it is also building??
http://strokkur.raunvis.hi.is/~sigrun/GFUM.html
Jon…would like your thoughts on these??
It is clear that Austmannsbunga is inflating (it is a part of the Katla volcano caldera). I have heard about it few months ago. But scientists in Iceland do not know how to properly interpret the data that they are getting.
But this is a worrying signs however and I am going to add them soon to my watch list if this trend continues.
“… Using the displacement vectors in a forward grid search for the best-fitting Mogi point source, suggests a centre of inflation in the northern part of the caldera at 4.9 km depth … The rate of uplift at the Austmannsbunga GPS point increased markedly between the 1993-2000 measurements and the 2000-2003 measurements, from a few mm per year to about 2 cm per year. Back-tracing… …suggests a start of the inflation in the early spring of 1999… … The cumulative uplift of the Austmannsbunga point since 1993 is 7.2 cm. With the location of the Mogi point fixed at 4.9 km depth, this corresponds to an uplift of 12 cm directly above it. A sub-surface magma volume increase of 0.019 km is implied…
Note: 122 words of a 1342 word page is less than 10%. I claim fair use.
Original link: http://eurekamag.com/keyword/g/113/godabunga.php
It’s worth the read.
So that gives that during the last six months the Austmannsbunga has lifted as much as it did from 1993? Total uplift would then be 15 cm since 1993.
Time to use the most scary word known to man…
Oops…
This is a running competition. Runners are Hekla, Katla, Grimsvotn, Esjufjoll and Askja. In which year will each of them finish the race?
My bets would be for something like this:
Hekla and Grimsvotn ~2011 VEI2
Katla ~2013 VEI5
Esjufjoll ~2020 VEI4
Askja ~2020 VEI2
My volcano wish list is as follows: 🙂
Grimsvötn december 2010 VEI4
Hekla january 2011 VEI4
Esjufjöll january 2011 VEI5
Askja february 2011 VEI5
Katla march 2011 VEI6
Edlgja april 2011 with 15-20 cubic km lava during the next 6 months
PS: I don’t live in Iceland
Do you plan fire-works for a living, talk about grand finale 🙂
No, increasing the intensity step-by-step is a common concept and is applicable in every situation everywhere. 🙂
Be you in bed with someone, enjoying dinner, racing etc
What would happen with these eruptions? Being somewhat involved with the air-traffic here in Finland it would be interesting to know your view of resuts of these eruptions.
As far as I know Katla would be like Eyjafjallajökull -only bigger. Are you expecting similar results with the rest of these volcanoes?
How about other consequences? Toxic fumes? Temperature drop? Something else?
Carl could make the “worst case scenario”… 😉
I will actually give the most likely scenario here.
Let me start with saying the Eyjafjallajökull probably was a worst case scenario for the airtraffic due to prevailing winds. The ash couldn’t have taken a worse path probably.
Here goes.
Katla would probably make an eruption that is weaker to only marginally stronger if it is a central vent eruption, and only those would make that kind of explosive eruption. If it is a large fissure eruption gases and lava-flows would be a hazard on iceland and could perhaps influence weather for a year or 2. Could be as disturbing as Eyjafjallajökull with the worst case scenario winds.
Hekla, well that will probably produce a very high ash-column. It did during one of its VEI-3 eruptions produce a 30 kilometre ash-column. Could be as disturbing as Eyjafjallajökull with the worst case scenario winds.
Grimsvötn, probably no effect on air-traffic unless it has one of it’s 500 years large fissure eruptions, but that would just affect weather and produce large lavastreams. And of course large amounts of poisenous gas. But this volcano normally just have weak eruptions that do not really do nothing more than produce jökulhlaups.
Bardarbunga and Askja, lots of gasses, lava, some disturbance on weather. Bardarbunga could have one of these really large eruptions, think Laki.
Askja has a nasty worst case scenario… Large lava eruption through fissures which in the end creates a caldera-formation through subsidence. That would be bad, real bad. Years of weather effect and no air-traffic for months.
Esjufjöll, who would know? But let’s postulate that it really had an eruption 1927 and judging from that it would be no disturbance. I would say that Esjufjöll most likely wouldn’t make more noise than Eyjafjallajökull as a worst case.
Statistically speaking 1 out of 10 eruptions will be as disturbing as Eyjafjallajökull since you need an ashy VEI-4, correct prevailing winds, and it happening under a glacier and the eruption being able to punch through quickly. Ie, to thick ice and no disturbance.
1 out of 100 would be more disturbing.
And about 1 out of 1000 would be real nasty, and that takes a large caldera formation through subsidance like Askja 1-caldera. Neither Grimsvötn, Bardarbunga or Katla would be that bad if they had a caldera event since much would be caught by the ice ontop.
My not so worst case scenario. I think Eyjafjallajökull was the worst for air-traffic for a long time. But others could be much worse for Iceland of course.
Seems like Sigrún Hreinsdóttir and the others are as intressed in Krisúvik as we are. They have installed 3 new CGPS-stations smack-bang in Krísúvik in late 2010. Sadly I cannot seem to find the info they are giving. 🙁
http://notendur.hi.is/runa/cgps.html
And there has been a nice juicy 2.9M quake there now combined with a vigourous little quake-swarm.
Since we are guessing on volcanos.
I would like to put up one on the “hot-list” and that is of course Krísúvik with its propensity for continous quake-swarms, that has been going on about every 4 days for 3 months running now. It had its last known eruptive period from 900 – 1340 with five eruptions.
It has also shown other signs as gas-content in small volcanic lakes, borehole blow-outs, and a mysterious drop in water level at Kleifarvatn lake after a large earth-quake in 2000.
If this volcano goes off it will probably just be a VEI-0 to a VEI-2 and will have marginal effect on Europe, but will probably have large inpact on Iceland due to close location to Reykjavik.
http://www.volcano.si.edu/world/volcano.cfm?vnum=1701-03=
http://en.vedur.is/earthquakes-and-volcanism/earthquakes/reykjanespeninsula/
@Carl: \Might explain the fearsome reputation of vikings… especially if you count in their eating of fly agaric mushrooms.\
Weren’t the mushrooms specifically only associated with the Berzerker cult? Not all Vikings were berzerkers, were they?
They where never a “cult”. Berzerker only means that you during a battle go crazy and rip off your shirt. Hence in only the “särk”, and a särk is the equivalent of t-shirt. So no strange culting here.
The eating of fly agaric was in some places common, and in others not. The best and safest way to ingest it was through having a goat eat it and then drinking the urin.
Was bored and studied a master in archaelogy once, misspent youth.
Poisonman: yours is a wish list, mine was a bet list. I don’t think your wish-list of such as sucession of VEI4-6 eruptions in Iceland is likely to occur, that would be very destructive!
Carle, I would not be very worried with Hekla. Assuming it’s behaving like Grimsvotn with very often and small eruptions, I don’t think Hekla would cause much trouble.
Katla I would be more worried. This is a big volcano, and usually Katla eruptions are VEI4 with some VEI 5 and 6, very powerful but over a relatively short period of time. And we are long overdue for an eruption. However, I think this would have no big effect in climate, apparently only Eldgja had a (possible) effect in climate. 1918 VEI6 eruption was a strong one with minor effects. I think Katla problem would the airtraffic disruption, but this would probably be no bigger or longer than Eyja.
Askja,has been erupting in last 100 years with very minor fissure eruptions. Only the central eruption of 1875 was catastrophic. This is a little bit like Krafla, usually activity is explosive but not impacting world climate.
And Esjufjoll, we dont know this one. Apparently the caldera is very large, and the fact that has been long dormant (except something in 1927) it means that an eruption could be large. And that region is very close to the Icelandic plume, so this makes me think that Esjufjoll could be as damaging or worse than Katla. Probably Esjufjoll behaves a bit like Oraefjokull, with rare but very large eruptions.
Irpsit:
Remember that the average of Hekla is actually a strong VEI-3 and it goes all the way up to strong 5s. Yes, Katla has had a couple of sixes, but normally is lower than a 3 when it erupts, and Katla has not had a long build-up sequence yet so it would probably be a 2 or a 3.
Askja normally have larger eruptions on a 250 year or more cycle, but this time around the signs seems to imply a larger eruption in the fissure style. Time will tell. But it could also be a small 2. Krafla mostly have fissure eruptions with lava-fountaining, not explosive style. Think Krafla-fires.
As I wrote, we do not know anything about Esjufjöll, with one possible eruption it might be very weak or very large. If it goes off we will see.
Nota bene, my list above was a bit of me running wild. I do not think we are in for anything major. VEI-3s for Hekla and Katla, VEI-2s for Grimsvötn, Bardarbunga and Krísúvik, VEI-silch for Esjufjöll (at least not gonna happen soon), and a VEI-2 to 5 for Askja depending if it is a central vent or a fissure eruption stretching to Herdubreid-system.
I have to disagree with you here, Katla is VEI-4 on average (http://www.volcano.si.edu/world/volcano.cfm?vnum=1702-03=&volpage=erupt). Plus it had a relatively long build-up sequence, since the last eruption in 1918. The average eruption interval is 60-70 years for Katla, which has been exceeded since a few decades.
I do agree with Hekla, probably ‘another typical Hekla’ eruption of which we had so many the past 40 years, relatively large, but quite harmless.
Askja I don’t have a clue, since the Upptyppingar swarms are related to Kverkfjoll-volcanic system, we haven’t seen much swarm activity except for the recent Herdubreid swarm.
I think Grimsvotn will erupt within a year, but also small-scale 2004-like eruption.
Bardarbunga might be bigger, based on the seismicity and past eruptions, however thats probably gonna take a while.
For Esjufjoll we can indeed just guess, no clue at all, too little information, however the large caldera suggests that this volcano is, or has been able to produce massive eruptions.
I don’t believe Krisuvik will erupt in the near future, Reykjanes activity goes in cycles, and we are currently in a dry period and I think more has to happen before another cycle starts.
You forget the 2 last eruptions in 55 and 99. They where week ones but still eruptions. But I never said it couldn’t do a large one if it chooses to.
Herdubried and Herdubreidartögl has had continous intermittent swarms since the Askja inflation period started at 2007. And according to research since 2007 there is evidence of magmatic influx under the Herdubreid system. References above, look for the paper of Hazel Rymer.
Since Upptyppingar started at the same time one may make a case of it actually not belonging to Kverkfjöll, be that as it may. Herdubreid has had since July more then 10 quake-swarms, and counting.
I also think we are a bit of ways before Krisuvik erupts. I think what we are seeing now is a reconstruction of the magma-reservoir, same as at Herdubreid. And how long the fracture&fill to evolve the magma reservoir takes is as good a guess as any. I would say it will take at least ten years. I just wish we could get access to the 3 new CGPS-stations that has just been installed there. Seems like the icelandic researchers are taking these swarms not so lightly. I hope that they also will install a borehole tensor strain-meter in the near future.
I forgot to mention that the last Herdubreid quake-swarm has a really nice feature since it is not following the Herdubreid Herdubreidartögl and Upptyppingar rift, instead it is following the old fissure-dike between Herdubreid and Askja.
http://en.vedur.is/earthquakes-and-volcanism/earthquakes/vatnajokull/
I think people are underestimating Katla. It’s never been dormant for this long in the past 1000 years, and there must be an explanation for that. With the 1918 eruption being VEI 5, I can see the next eruption certainly being a VEI 4, possibly VEI 5, when looking at GPS records since the last eruption and the repose period. And not forgetting that there have been VEI 6 eruptions at Katla like the 934 AD fissure eruption.
Askja I think has the potential to be quite powerful next time, as does Bardarbunga. But Hekla and Grimsvotn don’t worry me at all.
Katla still erupted 1999 and 1955. The eruptions are not doubted in any way. It is the starting dates that are questioned since it all started under the ice.
So Katla is just ten years after eruption.
You can clearly see the eruption on these GPS-stations, look at late 1999 early 2000 and it will be clearer.
Havent there been major eruptions every 60-80 years or so?
Is the trend about to stop?
I quote:
“During the summer of 1999 some activity was noted within the Mýrdalsjökull caldera. On the night of the 18th July came a sudden flood in the river Jökulsá á Sólheimasandi. The source of the flood was meltwater from a depression formed simultaneously in the glacier surface, within the ice drainage basin of Sólheimajökull. After the flood existing depressions enlarged and crevasses were formed. The depressions became deeper during the summer and increased in number. The reason was increased geothermal activity. It is possible that there was a small eruption at the head of Sólheimajökull that formed a depression and caused the flood.”
And
” More recently in 1955 and 1979 there have been floods though no eruption that you could see. ”
(http://iceland.vefur.is/iceland_nature/volcanoes_in_iceland/katla.htm)
The only thing that’s for sure is that there has been a subglacial flood, just like the one at Grimsvotn earlier this month.
it isnt really that sure, that there where eruptions in 55 and 99. the glacial outburst might also me explained by higher geothermal activity, due to the rise of magma inside katla.
Katla has several highly active geothermal areas beneath its glacier, which produce ice cauldrons. during the 1955 and 1999 events, a new icecauldron formed, but there was no sign, that an eruption was taking place. all that is, is a “might have taken place”. and i think that any eruption at katla makes it through the iceshield, so the glacial outburst might very well be caused by higher geothermal/hydrothermal activity.
but those are just my thoughts, because nothing is really proven about the 55 and 99 event. we just don’t know, we speculate what might have been.
Haha that’s exactly what I stated in my entire post my friend. ^^
Askja also had several fissure eruptions, last time 1961 and 1920s, but these were small, so I expect a future eruption there to be another small fissure type, probably close to Herbubreid. I say this because last big eruption was relatively recent in 1875, and historically this volcano seldom erupts that powerfully.
Grimsvotn usually it’s small, but remember Laki was a Grimsvotn fissure. I only expect it to be small because it has been erupting so often. On the other hand, Bardarbunga worries me more, because it has been long since its last big eruption.
Krisuvík; well, we cannot be sure about the cycle, volcanic cycles are not precise, the area might erupt this century, even next year, we don’t know, however this would be probably small fissue-type eruptions, that only create trouble because its in proximity of Reykjavik. It might destroy some nearby villages and the blue lagoon complex, but the volcano is far away enough from the capital.
Katla, most eruptions were VEI4, with some VEI3 and some VEI5. Its difficult to predict how big it will be. I would say a VEI5 due to its long dormancy time.
To show you how unpredictable Katla can be, in 1625, just 13 years after a VEI4 eruption, Katla erupted VEI5! The first one in 1612 was just after Eyjafjallajokull.
In 1823 Katla erupted VEI3 or 4, 1-2 years after Eyjafjallajokull. So, I think we can at least expect a VEI4.
Probably Katla erupts much more often that this, with small subglacial fissure eruptions like in 1999 and 1955. We would probably not find these in historical records. So, assuming a 100 years lag between eruptions now, I could tentatively say this time it will be probably a VEI5, due to the long waiting time.
Another interesting thing is that we have a cycle (and again very roughly) of 130 years between periods of major volcanic activity in Iceland that last some decades. The last time was around last big Askja eruption in 1875 and probably 1910 Bardarbunga and 1918 Katla; before that we had a very volcanic decade in 1720s, and the cycle goes back nearly every 130 years, and includes Veidivotn, both Oraefjokull eruptions, etc. In these periods, we also witness more activity in Reykjanes and in Tjornes.
What researchers have found is that this cycle is associated with increased activity at Vatnajokull. However the cycle does not fit with some major eruptions like Laki.
Extrapolating the cycle to the present, the next highly active period would be starting just about now and lasting about two decades. We shall see if the pattern holds.
Burfell is showing some activity now: http://hraun.vedur.is/ja/strain/str_corr/strain_rate.png