Debunked: Feeling the strain

Hekla resting under a snowcap waiting for the next eruption.

Hekla resting under a snowcap waiting for the next eruption.

Why on earth am I using the term ”debunked” about a piece of equipment that is used by scientists across the globe? The answer is quite simple, it is when laymen start interpreting them that they are overused, or used in ways they were never intended. And this causes a plethora of faulty reasoning and wild theories.

But, first we need to explain how they work and what they do measure before we get to a few interesting things that they do measure that has nothing to do with eruptions or earthquakes as such.

Types of strainmeters

Quartz Rod Strainmeter. Image from UNAVCO.

Quartz Rod Strainmeter. Image from UNAVCO.

The first strainmeter was built in 1932 by the great seismologist and inventor Benioff. It consisted of an iron pipe that was attached inside a borehole with a strain-gauge at the top. As such it was intended to measure changes in distance up and down, or in other words if the mountain was expanding up and down. The values given was increased strain if the steel pipe was stretched or decreased strain if the pipe was relaxing.

The only problem was that this did not work that well. Benioff had forgotten that metal tend to expand and contract due to temperature differences, so if the mountain heated up even minutely it showed as a strain decrease, and vice versa if it cooled down. But, the theory behind the instrument was sound.

So, the steel pipe was after a while replaced by pre-stressed quartz crystal rods and finally useful data started to emerge. It was now possible to accurately measure very long frequency waves and record increase in strain over months or even years. The big problem was that it was only measuring what happens in a single direction.

The second type of strainmeter works like the common laser range finder. This version uses a laser beam that is reflected back to measure changes in distance over hundreds of meters. It is either placed in long boreholes or inside old mines. Otherwise it works in the same way as the quartz rod strainmeter and has the same drawback in that it only measures one direction of movement.

The third and most useful member of the strainmeter family is the volumetric strainmeter, or as it is also known, the dilatometer. It is basically a metal tube filled with silicone oil that is topped with a pressure gauge. The tube is inserted into a borehole of equal diameter and as the mountain flexes and bends it will measure how the volume changes over time. At times the pressure becomes too large and a special valve will automatically open resetting the pressure to a baseline value.

This type measures changes in all directions and will give you very exact readings, but there is of course a drawback. You will only know the sum of changes, but you will never know the direction of the changes. Think about it for a while and you will understand why.

What is measured?

Schematic of a Laser Strainmeter. Image from the Carpathian Strainmeter Experiment / CALAS.

Schematic of a Laser Strainmeter. Image from the Carpathian Strainmeter Experiment / CALAS.

A strainmeter will only pick up changes in the rock that is surrounding it. It will not pick up changes that are even relatively nearby. Basically, it is the surrounding rocks motion that is measured and motion on the other side of a small fault may not be picked up at all. Therefore, largescale tectonic motion is not possible to pick up and should be left to GPS-trajectory analysis.

Now quite a few of you will be protesting and saying that you can pick up both earthtides and distant large earthquakes on strainmeters. And the answer is that yes, you can pick those up. But what you are seeing is the effect on the local rock by the distant cause.

Schematic for a Dilatometer / Volumetric Strainmeter. Image from DTM.

Schematic for a Dilatometer / Volumetric Strainmeter. Image from DTM.

In other words, a large earthquake is the cause, the low frequency waveforms are the mode of transportation of energy that ultimately has the effect that it causes deformation of the local rock around the strainmeter. So, unlike a seismometer a strainmeter does not measure the original cause at a distance, it measures the local effect in the surrounding bedrock of the distal event. This definition is important, and the lack of understanding of this leads people astray when interpreting strainmeters.

But let us take a closer look at one of the most important strainmeter networks on the planet and discuss its uses and limitations.

The Hekla Strainmeter Network

The HSN consists of 7 stations, Búrfell, Geldingaá, Hekla, Hella, Saurbaer, Stórólfsvoll and Ytri Skógar. Geldingaá and Saurbaer was taken offline in 2013 and are now kept as backups for the general Hekla Network. It is not known if Icelandic Met Office are still using them internally.

If I am correct Hella and Stórólfsvoll are quartz strainmeters and Búrfell, Hekla and Ytri Skógar are volumetric strainmeters.

So, what do they measure? First of all, they measure strain increase caused by slowly accumulating magma in the Hekla volcano itself. The problem here is that Hekla fissure itself is spreading at the same speed as magma enters the system, so you will not really know if you are measuring magma pressure increase or effects of the spreading rift on the local bedrock.

To glean any data in regards of this you would need a complete record spanning years if not decades. And only the Icelandic Met Office has those records. So, for an amateur sitting at home watching the Hekla strainmeters they will not tell anything about the state of the volcano itself between eruptions.

The strainmeters also measure changes ranging from the Hekla fissure over to the next large fissure. To the east that would be the Vatnafjöll Volcanic Fissure and to the west it would be the closest fissure(s) in the Southern Icelandic Seismic Zone. Every other volcanic signal would be filtered away by the fissures and a pesky law of nature that states that for every time you double the distance the signal strength decreases fourfold.

The Búrfell Dilatometer. In this image you can see both earthtide swings and the Solomon Island M7.8 earthquake. Image courtesy of Icelandic Met Office.

The Búrfell Dilatometer. In this image you can see both earthtide swings and the Solomon Island M7.8 earthquake. Image courtesy of Icelandic Met Office.

It also measures strain changes in the nearest Faultline out from Hekla.

So, we have several different signals affecting the network at the same time and no way of knowing in which direction the signals are emanating from. And remember that there have been large earthquakes on both sides of Hekla, so the seismic effects of the tectonic motion is far larger than any volcanic signal in the years in between eruptions.

Now you may be thinking that they are pretty useless. After all they only record that strain is increasing or decreasing in an area over years or even decades and that we will never get to know where the changes are. Well, that is only partially correct.

The great use of a strainmeters are twofold, one is to give a longterm baseline and the other is for when the shit hits the fan. It is as a large nearby earthquake happens or a large eruption happens that the strainmeter comes into play and gives the most beautiful data of what is going on during the event. Let us take a closer look.

Hekla 2000

Recording of the Strainmeters at the Hekla Strainmeter Network during the 2000 eruption. Note how small the earthtides are compared to the effect of the eruption. Also note that the Búrfell strainmeter is inverted due to the anomaly. Image from Icelandic Met Office.

Recording of the Strainmeters at the Hekla Strainmeter Network during the 2000 eruption. Note how small the earthtides are compared to the effect of the eruption. Also note that the Búrfell strainmeter is inverted due to the anomaly. Image from Icelandic Met Office.

During the eruption of Hekla in the year 2000 the strainmeters gave the best instrumental data. The eruption yielded very little data in the form of GPS-trajectory changes and earthquake data. Instead it was the strainmeters that gave results that are still being analysed and reinterpreted.

One thing that became clear was that something was “off” with the Búrfell strainmeter. Where the others gave a rapid and large strain increase Búrfell gave off an even larger and equally rapid strain release.

In the end, it was apparent that the anomaly was caused by an old semi-solid magma reservoir under the preholocene volcano of Búrfell and that the magma chamber did both relax during onset of Hekla eruption and that it did amplify the inverted signal.

This data was later used to further correct the earthquake depths recorded around Hekla during the eruption making it possible to incrementally refine the location of the magma reservoir under Hekla. It was previously believed that Hekla had a discretely located magma chamber like most Icelandic central volcanoes, instead the reinterpreted data gave at hand that Hekla has a magma reservoir open at depth to the mantle and that is running all along the fissure underlying Hekla and that it is rising to a depth of about 1km below the base of the volcano.

Another result given is that Hekla does not erupt due to pressure increasing above the threshold of what the overburden can constrain, instead Hekla erupts due to tectonic forces pulling the fissure apart.

This last part explains the extremely rapid onset of eruption. During onset of the 2000 eruption Hekla opened up a conduit 4 km deep and 5 km long in a period that lasted 32 minutes, during the same time magma rose the same distance. The entire event took about 60 minutes, but it is during those 32 minutes that the main onset happens.

Cool strainmeter stuff

I have so far said that strainmeters are only measuring changes in the immediately surrounding bedrock or showing distal signals affecting that bedrock. So, what distal effects can be seen?

The first and most common effect are earthtides. These are not the same as oceanic tidal waves, instead these are the very minute movements in the mantle that is caused by tidal stress from the moon.

I always chuckle a bit about this because all the people stating that the moon causes earthquakes use the oceanic tides when they try to prove their erroneous theory. Instead they should be using earthtides since they move the crust minutely. They would still be wrong, but they would at least try to use the correct power. For those who missed the debunking of the moon as a cause for earthquakes I recommend reading GeoLurkings Tour de Force piece about it where he tried to prove the hypothesis that the moon is causing earthquakes by using all of Iceland’s recorded earthquakes without finding any proof.

Earthtides are best followed on the Búrfell strainmeter where they are visible as regular swings up and down on the plot.

The other thing that you can watch on the HSN are distal large earthquakes. What you will see are the low-frequency waves that has travelled inside the crust around the planet. On the image you can see the energy transferred from the M7.8 Solomon Islands earthquake.

I once again repeat, what you are seeing is not the event itself, instead what you see is energy moving around the globe that is affecting the bedrock close to the strainmeter.

Another thing you can see is a bit more surprising, and that is wind. As storms pass over the top of the strainmeter the rapidly shifting wind will both buffet the bedrock and cause rapid pressure changes that affect the pressure gauge. The effect will cause the plot to show a thickened curve.

Debunking myths

Map showing most of the Hekla strainmeters. Note that the map is a bit old and that two new strainmeters have been brought online. Image courtesy of the Icelandic Met Office.

Map showing most of the Hekla strainmeters. Note that the map is a bit old and that two new strainmeters have been brought online. Image courtesy of the Icelandic Met Office.

Many people think that strainmeters are useful to predict eruptions and earthquakes, this mistake was even common among geologists in the seventies when they emplaced strainmeters to predict earthquakes along the San Andreas fault in California.

So far, the only result is that there has been a recorded strain increase running for years between eruptions of Hekla, otherwise no other useful predictive data has been given by any strainmeter on earth. They have though given lots of useful data about events as they happen.

Currently there is a lot of talk outside of the scientific community about the usefulness of the Hekla Strainmeter Network as a predictive tool for Bárdarbunga earthquakes. The original hypothesis was that a concerted strain raise was a signal that a larger seismic episode was coming at Bárdarbunga. This did not pan out against statistics. Instead an ad hoc extension of the hypothesis was added to save it. The new hypothesis was that a concerted strain increase or a concerted strain release was a sign of an impending seismic episode. After this deus ex machine intervention the theory could on the surface of things predict 90 percent of all seismic episodes at Bárdarbunga. Theory proven? Quite not.

The first hurdle here is that the strainmeters at Hekla does not measure the bedrock around Bárdarbunga. They are not even on the same plate shard, in fact they are several fissures over from Bárdarbunga. In fact, they are not recording any direct event at Bárdarbunga since they are on a completely different stress regimen.

So, can we save the hypothesis that you can predict earthquakes at Bárdarbunga via the HSN if we see it as distal energy transferal? Let us test that. After a large earthquake we would be seeing a marked strain drop that should occur immediately after the event. We have never seen this happening after a Bárdarbunga earthquake, not even after the largest of them. Why would we see a strain drop? Well, an earthquake is the release of pent up strain so by pure laws of physics we should see it if the strain increase measured was relevant to the earthquake.

Also, if we could predict anything it would look pretty much like what happens just prior to and during a Hekla eruption, and that is that we would get an inverse signal from the Búrfell strainmeter due to the magma anomaly. This is actually chucking an enormous spanner in the hypothesis. Now, have we seen an inverse signal before a Bárdarbunga event? No, we have not. Nor will we since the strainmeters can’t record things from Bárdarbunga to begin with.

Now some of you are saying that I just admitted that the amended hypothesis is accurately predicting 90 percent of the seismic episodes. Yes I did, but not in the way you think. The fact is that 90 percent of the time the strainmeters will move up and down together due to the common earthtide, so you would naturally find 90 percent of the seismic events during a concerted movement anyway. And here the hypothesis moves into the realm of myths and as such it is debunked utterly.

Or in other words, the entire idea is unscientific balderdash without any hope of ever being saved.

Conclusion

The Icelandic Met Office and other agencies around the world are giving the volcano amateur community access to loads of wonderful advanced tools to watch and to speculate about. It is quite possible to get at least a helpful understanding as an amateur of what a volcano is up to by looking at seismometers and GPS-signals prior to an eruption. But the strainmeters are a completely different set of beasts altogether since they are good at measuring data during the absolute onset of eruption and during an eruption, but are useless in between. They are as such in the realm of mathematical interpretation by geophysicists, and even we have a hard time getting it right.

They may though give relevant data for Hekla itself as a predictive tool, but only if used in conjunction with other types of instruments like seismometers and GPS-stations.

CARL REHNBERG

 

64 thoughts on “Debunked: Feeling the strain

  1. An important lesson. These articles about data interpretation, can not be praised enough. 🙂
    Great work, very helpful, thanks Carl!

    • Of all the Equipment used around volcanoes they are the hardest to understand and get a grip around.

  2. do they never lay 3 strainometers orthogonally at one site ?
    I think that would let you resolve direction as well as volumetric stress.

    • To the best of my knowledge that has never been done.
      For regular quartz rod borehole strainmeters there is the problem of drilling sideways in a manner that would allow you to install the strainmeter.
      For a dilatometer there would still be no advantage since all of them would happily just sum up the volumetric change.
      Easiest would be installing a 3-axial laser strainmeter in a suitable mine, but as far as I know this has never been done, closest are the LIGO type arrangements that are 2-axial.

      In the end it is just easier to set up one dilatometer and pair the result with GPS-stations like they do in Iceland. It yields the same result at a fraction of the cost.

  3. This is a great explanation of the use of strain meters.
    I must admit I have never understood the usefulness of strain meters in a fractured rock mass. Measuring the strain in a single direction in a block of rock which may have sliding planes surrounding it seems illogical to me. I have only dealt with strain meters in engineering where they only produce accurate results on a homogenous subject to which they are perfectly bonded.
    In terms of Hekla, taking an engineering view, then the most obvious (but expensive) solution would seem to be a horizontal borehole across the fissure with a tension meter strung across from one side to the other ?

    • They actually work pretty well. Problem with drilling across the fissure is that it can move a lot rapidly, and is prone to suffer from thermal Changes.

  4. Does the energy transfer through the bedrock as well as strain increase/decrease signals affected (similarly to sound through water) and interfered with across thermocline layers? If so, wouldn’t any fissure or semi-solid dyke intrusion through the bedrock next to a strain meter mask, distort, or bend those signals away?

    • Ding!
      Yes they would! 🙂

      And this is not only true for strainmeters, it is obviously also true for seismometers.
      The signal (energy carrier) is attenuated by the media (crustal layer or mantle material) it travels through. As it hits a boundary layer between different materials, viscosities, temperatures (and so on and so forth) it will be filtered, attenuated, difracted, refracted and generally be messed with. The effect would be the same in many cases as if soundwaves in water passes through a haline or a saline.

      But that is something that is far beyond the scope of this particular article, let it suffice with me stating that you have grasped more than I wrote about in the article.

      • Yep, and somehow, seismologists are able to perceive the different pathways that wave forms take while they pass through various strata.

        • As you know it is even possible to use the signal degradation to find out what is down below the ground.

          • Then, how on (in) earth do you measure “strain” when plastic rock is being pushed into slightly-less-plastic rock many km’s below where you are able to place a meter? How can you “see” anything that gravity isn’t immediately cancelling (tides, rock column density, rock column metallic content, etc)?

            I know you talked about that a little above, but I am just not getting it.

  5. Thanks for another great learning opportunity, Carl. Question: what about measuring tilt? expensive? useful? too complicated to answer? I don’t see it being used very often.

    • Oh, old school! 🙂

      I love tiltmeters, they are dirt cheap, they do not break down (well, not often at least) and they are the most exact instrument known to man for measuring inflation or deflation around a volcano.
      All you need to build one is a bit of tube or a hose running for a suitable distance and two transparant millimeter graded tubes at each end and you are good to go.

      No GPS-system has still broken the level of accuracy of the recordings taken by the Kröfluvirkjun tiltmeter during the Krafla Fires.

      Personally I just can’t get my head around why this perfect and simple instrument fell out of usage.

    • Looks like these also pick up rock tides. Unless there’s some other explanation for the green squiggle having a lot of energy in the frequency domain right around (43200s)^-1.

  6. ,,, about that moon thing. It wasn’t iceland quakes that I tried to correlate, it was a 30 year pull of the USGS catalog. I got the time-stamp for each quake and piped it through Alcone Ephemerides and imported the sun-moon-earth positions. That was the monster spreadsheet that I accumulated. When I backed out the dwell period for the moon (it slows at perigee) the apparent correlation goes away. There was still some residual correlation signal, but like Jack@Finnland pointed out, it was trivial compared to a random noise data-set. Far less than 2 sigma signal strength. I think the outcome was that if there is a lunar component to quakes, it maked them appear maybe a couple of seconds before they would have occurred anyway. On a localized basis, the effect of lunar gravity is many magnitudes less than the forced involved in making the quake.

    I think a group at UC Berkley has had some statistical success in the moon vs the San Andreas fault, but from what I understand, it’s just as ephemeral as my results were.

    If I remember, I even tried to see if the lunar declination had any effect. Again, no joy.

    • Sorry Lurking, my memory is not that good nowadays.
      Thank you for clearing that one up.

      • Btw, my neurologist’s advice was to just keep operating normally and I should get my functions back over time. My read of that is that your brain will relearn how to process stimuli. I’ve gotten partial feeling back in my finger, but it is still aggravating with small delicate items.

        • For me it is the memory and the sight on my right Eye that is reduced. Otherwise I am coming around pretty well.

          • Carl-you might look into a product called
            Magmind (Magnesium Theoanate,)
            It is helpful for people with memory
            issues. Made a huge difference with my wife’s recovery from Lyme…
            There is some good science backing it up- Fellow Named Dr.David Pearlmutter
            has a site that my wife finds helpful…
            There are probably sites in Europe, too..
            Good luck.

            The post about Strain Gauges was surprising. I’m a tiltmeter guy myself..
            We are expecting -20C this weekend..
            Been getting as much wood in from the
            rack as possible. Dogs wife and I curled around roaring fire now..

    • Personally, I think your memory is fine. You haven’t pulled any mind numbingly stupid tricks like driving to the wrong city to do a job have you? I’ve done that a few times. My last stunt had me leaving most of my tools at a job site 95 miles away. I had to eat the travel on that one just to get my stuff back.

      • Not gone to the wrong city no, but I have forgotten a Company I own. I was rather surprised when told since I can’t for the Life of me remember why on Earth I bought it.
        There was also two people in the office I had no clue who they where and what they did.

        What I find interesting is that there seems to be some sort of weird algorithm behind what I have forgotten or not. The memories I have lost is evenly spread across my entire Life, but it seems to be ever so slightly themed. My estimate so far is that I have lost 2 percent of my memory.

        • The human brain is a truly wonderful and yet infuriating thing… When it doesn’t work properly. You take it for granted until it starts misfiring.
          I suffer from narcolepsy, and even more than the sleep attacks I find the memory lapses and brief absences too frustrating for words. But at least my lapses tend to be in short term memory, and the worst thing is that sometimes that can make me appear a little dumb. Loss of long term memory would really make me sad.
          I hope you recover as much as possible.

        • If it’s any consolation, I found a spatial anomaly above the drop ceiling at an office I was working at today. You stick your head up there and you cannot see light from the other panel removed from a spot maybe 12 feet away. Put a fiberglass rod across to the other panel, and you can’t see it from that side. Reverse the process and you still can’t see it on the receiving end. I even got a second opinion from the lead tech on the call and he couldn’t see it either. Somewhere at the foil covered air duct there, space no longer connects to itself. I even placed the bright orange rod on top of the duct. From the other side, it’s not there, period.

  7. Unusual waveform on the M3.8 on the edge of Katla this morning.

    This is from the AUS Lowpass plot

    • The Long Valley quakes to me are fairly insignificant. But the 5.0 is interesting, Erik Klemetti even tweeted about it.

      For reference, this is a 5.0 earthquake that is very close to the Clear Lake volcanic field, and more specifically, right above the Geysers geothermal field, which is the most productive geothermal field in the world. This area features what is thought to be a large silicic magma chamber, but it hasn’t seemed to have erupted, at least not in historical time.

      The interesting thing about this quake is that it’s very much an extensional quake, which is somewhat expected given that the Clear Lake and Geysers field is probably dependent on extension for its magma production.

      Interesting to think about at least. the thing I’m curious to know is how significant this is for an extensional quake. I understand extensional earthquakes typically tend to be a little bit weaker than others, but what is the largest extension-oriented earthquake that has been observed?

      • And just for clarification, I do NOT expect anything to happen here, but it’s interesting to see large extensional quakes occur over extremely odd volcanoes such as Clear Lake.

          • An earthquake that occurs when the ground below moves away from each other.

            Most common earthquakes occur from two pieces of crust moving past each other.

            Some earthquakes occur from compression and thrusting, which results when you slide two blocks into each other. Either this forces one slab to slide beneath the other, or the slabs butt into each other and are forced upward (which creates mountains).

            Extensional earthquakes on the other hand occur when two pieces of crust pull apart, leaving a bit of a gap. This gap can start to form a rift or a graben, which essentially signifies sunken and thinned crust due to the crust pulling apart.

            Extensional tectonics are quite relevant to volcanism, since the process of extension and rifting lowers the pressure in the underlying crust. Lowered pressure means that rock and mantle material can melt at significantly lower temperatures than it would normally melt at, which can lead to volcanism. In some instances, this can lead to extremely intense volcanism. Similarly, volcanism and heat welling up from below can also cause local extension and spreading (kind of a chicken vs. egg scenario).

          • cbus: Was extensional faulting the cause of the Columbia Flood Basalts? (Tangent – I love stopping at the rest area off I-90 in Ellensburg, WA or the road cut along the Columbia River at Beverly, WA to look at the rocks there; the basalt outcrops have a wonderful red-brown color with a grainy-porous texture.) Or was it due to the subduction of the Farralon Plate?

          • Thanks TG. I never knew that there was such a controversy over the origins of the CRFB. I have always been enamored how ~100 km can make such a noticeable and distinct difference in the composition of the local rock strata. Especially in the US NW. I shot a few pics of some of my collection at my office and uploaded them to my flickr page, if you care to take a peek.

            https://flic.kr/s/aHskN2wKt5

            Greg

      • I do not know what is the record, but the largest I know of is 7.2 North of Theistareykjarbunga in the 19th Century.

  8. Isotopic and
    geochemical precursors
    of earthquakes
    and volcanic eruptions

    I have been looking on the internet and have seen discussions that earthquake activity at the geysers might have been a precursor to the San Francisco eruption in 1906.

    Therefore is this 5.0 something to keep an eye on.

    Apologies if I have misunderstood this.

    http://www-pub.iaea.org/MTCD/publications/PDF/te_726_web.pdf

    • I live in Martinez which is across the river (Carquinez straights) We see the Myacama’s and the White Sulfur spring Hills from our windows. Clear Lake is a bit distant. The Farthest we see is Saint Helena which heads the Napa valley. I have never been able to learn any of the names in the White Sulfur spring hill peaks. Or if we see Mt Vacca.

      Could see the smoke Haze from the lake county fires in the summer. Two friends lost houses there recently. One this year and one the year before.

      Any quakes in this region are going to be calling wolf. Locals (old timers.) worry more when there are NOT quakes around the Geysers. The real risks here are the slip strike faults. The recent research from the recent “Napa” quake a few years back, connected the Rodgers Creek fault with the Hayward Fault. This part of the fault (Berkeley, San Pablo bay.) is active and moves a lot. (one can feel a 4.0 when it is a mile or 2 directly underneath.) I think the fault is locked further south where it has not done anything till the 1880s. As this forms the north east ridge of the Silicon Valley, there is a lot of population where it is likely to strike.

      I still think someone here should write an article on Diablo. The “volcano” that despite it’s name, is pure uplift. As it looks like Vesuvius, hard to convince people that it is not volcanic. It is Limestone. (And other things like serpentine.) What Basalts there are on it are twisted 90 degrees from which they flowed. Like Bread pudding.

      Anyway the popular (Tell me three times and it is true.) Belief is that the drilling into the “Hot springs” is what causes the quakes at the Geysers. That drilling boreholes is more likely to cause an earthquake than not. ARRGGH!

      Also note there is an interesting BBC video on Iceland drilling into a “Volcano.”

  9. Strain meters should be more informative than tilt meters. The latter only measure the difference in vertical displacements between two points. Both points move in three directions, so you only measuring one combination out of a possible 15. It works if and only if the line is pointing at a single source of inflation/deflation, and is not actually on top of the source. The tilt also does not involve any stress, i.e. no compression or shear. You need a lot of tilt measurements to see what is happening. I would assume that satellites have made tilt measurement largely obsolete.

    Strain meters also only measure one number out of the same number of combinations, but it does actually involves stress, so it says something about whether rock is moving towards failure. But what you really want is something that also measures shear, not just the compression, as the shear is what really make rocks fail. Easily done on the surface (couple of GPS’s?), but how do you measure shear a kilometer underground?

    As I write this I am only a few miles from the San Andreas fault. I’d like to know about today’s shear..

    • I just opined that tiltmeters are quite useful in many instances if they are well placed around volcanoes. And they are very cheap compared to all other Equipment.
      But, strainmeters, seismometers and GPSes are often better.

    • There is no obvious volcanic culprit. Hekla was too small an eruption to do this, and in any case would not have impacted the mediterranean that much. I think cbus05 has kept a list of ice core eruptions. That far back the timing is not precise. I think there is one spike around this time but it is not particularly strong. Traditionally the collapse has been attributed to the ‘sea people’, a kind of sardinian vikings. It was also the start of the iron age, and the first ones to adopt iron weapons would have an advantage.

      • ftp://ftp.ncdc.noaa.gov/pub/data/paleo/climate_forcing/volcanic_aerosols/gisp2_volcanic_markers.txt

        We have this list to go off, which provides So2 based on Ice Core data in Greenland. With that said, I don’t see anything enormous around this time period, although there is a spike around 1400 B.C. and another around 1000 B.C, which are roughly the size of the Tambora spike. With that said, Tambora didn’t effect this region as much since it was a southern hemisphere eruption, so who knows.

        • A propos of nothing, many may find this useful, I check it daily.
          Strangely roughly centered on uk….
          I have stopped it autoloading (I hope) as its animated and would sap bandwidth.

          (delete me)https://earth.nullschool.net/#current/wind/isobaric/1000hPa/overlay=total_cloud_water/orthographic=-6.29,48.44,588

          • Except for UK, parts of coastal Scandinavia and perhaps north part of Portugal, most of Europe looks pretty dry and cold, for the rest of December.

            A high pressure will continue to dominate over most of central and eastern Europe, and moist Atlantic storm fronts affecting the UK.

            Having considered that there hasn´t been much snow over Europe (except the far east), Christmas will probably not be white in most of Europe. Significant cold is more likely.

      • Eruption of Hekla around 1200 BC (called Hekla 3) was the largest ever eruption of Hekla.

        It was pretty powerful and covered much of Iceland with a thick layer of ash and pumice. It wasn´t small. One of the largest eruptions in Iceland during the Holocene.

        Estimates have put it in the VEI5-VEI6 threshold, so nevertheless not big enough to cause climate change.

        But there is another factor: SO2

        Laki and Edlgjá were also same size and cause significant climate change. If Hekla 3 eruption was a powerful SO2 producer, combined with a plinian eruption, then a large amount of SO2 could have made it to the Stratosphere causing severe climate disruption.

        But we dont need a big eruption to explain the late Bronze age cooling. See this https://en.wikipedia.org/wiki/Bond_event

        Every 1500 years, almost regularly ever since the ice ages, there is rapid cooling of the North Atlantic. Last one was the Little Ice Age.

    • Heh… I’ve heard of this connection before. I think the tecnical term is “Earth”.

  10. At http://www.bbc.com/news/science-environment-38296251 “World’s hottest borehole nearly complete”. Drilling into active volcanoes for utilizing supercritical water is not without any risk. In 2009 the IDDP team hit a shallow magma reservoir in the Krafla area causing black smoke billowing from the well.

    https://www.youtube.com/watch?v=FB2NJdr0u9E “Geothermal magma well: Iceland Deep Drilling Project”

    https://www.youtube.com/watch?v=3d8hC71xGpc “Magma well at Krafla: Temperature World Record”

  11. Katla had today some quakes towards Edlgjá fissure. This swarm has been quite unusual in that regard.

    • These Katla quakes get stranger and stranger the longer they occur here, especially as it gets colder, you can’t really blame it on glacial melting or unloading.

      One interesting aspect I’ve picked up on is that many of the shallow swarms that have occurred seem to follow lineaments, at least to a certain degree, albeit, not the same ones in each micro-swarm.

    • “Bad Boyz, ,Bad Boyz,, whatcha gonna when they erupt for you.”
      enjoy any thing about Kamchatka..

  12. If anyone ever goes to study volcanoes in Lithuania (there are none) you should definitely go and have dinner at Meat Lovers Pub. Brilliant food and it is ridiculously cheap. Five out of five stars.
    Now, time to burp my way into sleep mode.

    • I relayed that to CrazyEddie. In his travels he might actually wind up there. He asked my advice about Northern Italy a few months ago. Since airlines are his main mode of transport, he was inquiring about the potential for VAAC issues in the area.

      One of the banes of being the volcano freak in your circle of fiends is that people seek you out for that sort of forecast.

      As for Eddie, I have never seen anyone shut down an online game’s economy quite as adeptly as he does.

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