Grindavik - Demonstrating Ground Cracking

[@CharlotteRose-cz6np]

For a non-geologist like me, this is terrific explanation of what's happening in Iceland, as it really helps visualize what's going on underground. Thanks so much for taking the time to set up this experiment and share it with us!

[@geomechanic]

Thank you for the encouragement. I am glad you enjoyed it.

[@jimjimgl3]

A simple way to explain the Iceland eruption but also fun to watch

[@geomechanic]

I am happy that in this way it can be fun to watch. Thanks

[@klausolekristiansen2960]

As my high school physics teacher used to say: so simple, and yet so straightforward.

[@geomechanic]

Yes, exactly. That is what we were aiming for - a simple explanation. Thanks!

[@orelonsidney724]

Excellent presentation!

[@geomechanic]

Glad you enjoyed it!

[@janh5199]

Excellent explanation and demonstration. I wish I had this when I taught earth science.

[@geomechanic]

Glad you enjoyed it! Where did you teach?

[@janh5199]

@@geomechanic Southeast Ohio many years ago.

[@sindrisigurarson9070]

Well explained ! Thank you Greetings from Grindavik

[@geomechanic]

Thank you!

[@andrearochow138]

Wow, what a great way to demonstrate this.

[@geomechanic]

Thank you, glad you enjoyed it!

[@user-wk1mw9nj3i76]

Thanks for the physical demo! It looks like a cookie dough volcano, haha. Enjoyed this.

[@geomechanic]

Glad you enjoyed it!

[@crimsonjennifer]

I've learned so much since the Grindavik earthquakes started in November. I had thought of it like stretch marks growing on the earth's skin. This is a good visualization. I'm happy to see the bird strike protection on your buildings windows too. I've seen it work often on my home window.

[@geomechanic]

Thank you.

[@allynhansen7398]

A very good explanation, the best yet on what was or is happening to that town.,.....thank you. Regards, Allyn Hansen New Zealand

[@geomechanic]

Thank you, I am glad the explanation helped. Hopefully it ceases for the time being.

[@kunjanrupakheti7322]

Excellent demonstration!! It is easy to understand when we can visually see what is going on underneath the surface. Loved it!!

[@geomechanic]

Glad you enjoyed it! It was fun to setup.

[@jennifersherman8838]

Cool presentation! I had an "ah ha" moment! lol I never thought abojt the fissures getting hard as they cooled after the magma subsided! I never even thought about why new fissures showed up in new places. Also, the reason for the earthquake swarms just before an eruption! Thank you for broadening my mind! 😀 Jennifer San Francisco Bay area USA

[@geomechanic]

Thanks Jennifer. I am so glad you enjoyed another one of my videos!

[@rickschlosser6793]

I’m a geek about these things, but I’m also a measurement technician. Measuring the height of a column of fluid (like in a huge tank) by measuring the ‘head’ pressure at the bottom of the tank is something I did for a living. So I asked myself what that pressure must be at the magma chamber to support a column of fluid magma to the surface. If the top of the chamber is 3 miles deep that is 15,840 feet. A column of water that tall creates a pressure of 6867 psi. Magma is liquid rock, it is heavier than water, so I searched for the ‘specific gravity’ of magma and got a range of 2.9 - 3.4 and decided to use 3 because it is a nice round figure. So, 6867 X 3 = 20,601 psi. Per square inch. There are a little more than 4,000,000,000 square inches per square mile. Mentally I can see we are around 80 trillion pounds of force pushing up per square mile of magma chamber. Mind numbing big numbers and I am sure there are many variables that would adjust those numbers up or down, but it was just a mental exercise anyway…

[@geomechanic]

Wow, thanks for the rough pressure calculation. Indeed, this is part of the reason we cannot stop it!

[@Mp57navy]

There is one more thing missing. Lava has a lower density than cooled rock, since it has gases dissolved in it. When, or if the pressure drops below a certain level, you get the same effect as opening a large bottle of coke after shaking it.

[@rickschlosser6793]

@@Mp57navy That is why I used the specific gravity of magma, which is by definition liquid rock. Otherwise I might have used the specific gravity of basalt. (Just an assumption that Grindavik magma has the right proportion of silica to be considered basalt when cool)

[@Trylobyte]

Brilliant!

[@geomechanic]

Thank you

[@francesdlopez6736]

Nice explanation

[@geomechanic]

Thank you.

[@PlayNowWorkLater]

That was a great demonstration!

[@geomechanic]

Thanks. Glad you enjoyed it!

[@1258-Eckhart]

Very well explained, thanks!

[@geomechanic]

Thanks so much.

[@jerrielindsey5939]

Very cool demonstration

[@geomechanic]

Thank you very much!

[@UrbanGrrl69]

Thanks this is a very good demonstration, easy to understand.

[@geomechanic]

Glad it was helpful!

[@GrouchyHaggis]

Great demonstration and well explained! Subbed!

[@geomechanic]

Glad you enjoyed, thanks for the sub! Welcome to the channel!

[@GrouchyHaggis]

@@geomechanic Thanks! Checking out your other videos too!

[@Losttoanyreason]

Really nice simple demo.

[@geomechanic]

Thank you!

[@undersixty]

Love this illustration!!!❤❤❤❤❤

[@geomechanic]

Thanks so much.

[@justjane2070]

Interesting. Thank-you.

[@geomechanic]

You're welcome

[@phreatomagmatic8016]

I was under the impression that this wasn't the only event causing the chasms and crevasses in Grindavik. I believe there is also an ongoing rifting event where the crustal plates are separating, further exacerbating the problem.

[@MalcolmSnelgrove]

It think it could be that the rifting is what causes the magma/fissures/volcanoes in the first place (thin crust) over time. But rifting is very slow & a culmination of all the events trending in a direction, taken together... Individual crevasses have local causes.

[@Vulcano7965]

Yes the fracturing of the ground beneath grindavik is due to reactivating of previous fractures and the formation of small Graben due to the intrusion of a magma dyke beneath.

[@geomechanic]

Yes, there are many elements at play. The illustration tried to show one small aspect that contributes to the overall rifting that is happening at the larger scale.

[@BottleOfCoke]

Trees in Iceland? Hvaða bull er það? Nice video! ❤

[@geomechanic]

Haha, yes. I wanted something help show the movement before cracking! For other geohazards, such as landslides, tree movement can help identify the zone that is moving. So it came to mind to use it in the explanation.

[@judyholdsworth7096]

Great work.

[@geomechanic]

Many many thanks

[@davidmiller6010]

That was pretty neat! Can you do one that shows how the ground is dropping down under Grindavik?

[@geomechanic]

I'll have to think about how I can demonstrate how parts of the ground move up and other down, also at different points in time. Maybe in a few weeks I can bring something together!

[@rhulandjc2008]

I understand you are showing ground deformation over a wide area. Can you figure a way to demonstrate the local ground sinking above a dike as we see within Grindavik? How the earth is pushed aside as magma intrudes the dike and the ground sinks above it.

[@geomechanic]

Yes, the sinking is happening now in Grindavik. I will see what I can come up with to try and demonstrate more specifically the local ground behaviour.

[@marguerithakoldhermann70]

So good. Thanks now i understand.

[@geomechanic]

I am glad that it helped you better understand the situation.

[@flaviamochel1820]

Awesome! 👏👏👏👏👏

[@geomechanic]

Thanks!!

[@alexfrance500]

The tectonic action has been a huge factor in the cracking in Grindavik - the town is not directly over the area of ground deformation caused by the main magma intrusion. It can be seen on the chart you show at 2:04 - the points on the far left is before the magma intrusion started, so is your zero point for ground height. The fact that it drops way below that zero point on November 10th (where you indicate pressure release) shows that the zero point must have in fact moved. The level of the sand in your demonstration has not & cannot sizeably drop below the height at which it started before you started inflating the innertube - therefore we can see that that change on the chart at that point must have been largely resulting from tectonic movement of the ground rather than pressure release caused by magma movement.

[@geomechanic]

Yes, the reality is much more complicated and the lab demonstration cannot capture everything exactly.

[@alexfrance500]

@@geomechanic For sure! Even different experts have different opinions on what exactly is going on down there & it would be impossible to model the unknown ;þ

[@GerardOBrien-l1v]

I've wondered for a while, given the tectonic movement, is there evidence then, of actual expansion of Iceland on the East/West axis?

[@geomechanic]

Potentially it would be possible.

[@drmichaelshea]

The visual image helps to put things in perspective. And we learn from Numbers 16:31-32 to stay away from those cracks. Even our ancient ancestors knew not to fool with God, Moses, or Mother Nature.

[@geomechanic]

Thank you. I am glad it help bring things into perspective.

[@markmd9]

So to stop the eruption people should drill into the gas pocket and release the pressure.

[@geomechanic]

Well, it is impossible to stop the forces of nature. Perhaps re-direct it, but not stop.

[@siggi51991]

Cool tanks. :)

[@geomechanic]

Thank you for watching. Glad you enjoyed it!

[@Vulcano7965]

A model which can be pulled apart would likely be a better analogy for what's happening in Grindavík, since the fracturing is not due to the uplift. Otherwise we would have seen fracturing directly near the Svartsengi powerplant and the Blue Lagoon.

[@geomechanic]

The pulling apart is happening at a much larger scale across Iceland, but the model is a small representation of one aspect related to this. The gas pressure certainly can causes new fracture growth, but there are many other factors at work in such a complex system.

[@Vulcano7965]

@@geomechanic From what the IMO published, there are two relative small scale Graben being formed at Grindavik. I think that can be well represented in an analogue model. But I generally agree, the oblique rift zone at the peninsula creates much more complex tectonics.

[@MalcolmSnelgrove]

I think you would see fracturing on the surface near the powerplant & Blue Lagoon if the magma wasn't so deep there, but much would depend on the rock types.

[@Vulcano7965]

@@MalcolmSnelgrove greatest vertical difference is ~50cm there over a large area, Rocks are more stable undergoing compressional stress, but break sooner undergoing tensile stress. The ground at grindavik moved horizontally 1.4m Jan.14th and more than 2m at Nov.10th.

[@sarkybugger5009]

It's not _like_ the mid-Atlantic ridge under Grindavik, it_is_ the mid-Atlantic ridge. The town straddles the American and Eurasian plates, apparently.

[@geomechanic]

Yes, it is the mid-Atlantic ridge continuing through. The exact location shifts as it passes through Iceland and these shifts are also seen along the whole ridge.

[@darreno9874]

It's not like the mid Atlantic ridge, Iceland is on the mid Atlantic ridge and the deformation along the ridge is mainly due to thermal currents forcing the crust apart. This is a good demonstration of up lift but its not the whole story.

[@geomechanic]

Yes, of course. The whole story is much more complicated than I could develop in the sandbox. Perhaps I can add further elements to capture different aspects in the future.

[@nolongerlistless]

Parting plates at depth are also needed, of course, lol...

[@geomechanic]

Yes, over course. This is just a near surface explanation.

[@superconscious.]

cute

[@geomechanic]

Thanks

[@poetmaggie1]

I would think that building on the rift is not a great idea. There are problems building close to the rift and building on an island that has a rift running through it but building on the rift, even if it doesn't happen for 900 years, is not a great idea. Nice presentation.

[@geomechanic]

Thank you for the encouragement. Wikipedia says that Vikings settled in the area in 934. So they didn't know about rifting when the town was built up. But it has been an important fishing town since at least the 13th century.

[@MalcolmSnelgrove]

Iceland was created because of the rift, and the whole island can be potentially affected. I think about it like this; while sudden catastrophic events do happen, most geologic events are very, very slow. Most places on Earth have potential for disaster (floods, fires, hurricanes, landslides etc) on much smaller timescales.

[@dojoswitzer]

Are you a geologist? This seems visually similar at the surface but not an accurate representation of the actual ground dynamics. I expected your sand table to be much deeper, maybe with a bed of flat rocks below, and for you to pump in a viscous material that would seek a path to the surface and causing deformation during the process.

[@geomechanic]

I wanted to have a simple explanation rather than a complex system to reach a general audience. Of course the real dynamics are much more complicated and reach much deeper than possible to scale accordingly in a simple lab setting.

[@isilder]

But, the rocks are like layers of lasagna.. repeat with lasagna... please. This is evidenced.. its there for you to se... there are two lines of subsidence, with the surface expression of the fault in the middle... this matches to some of the layers creating cavities to the east of the fault, and some of the layers creating cavities to the west of the fault....

[@geomechanic]

Interesting idea! Thanks.

[@deadastronaut2440]

While the illustration is intriguing, I am wondering a bit about the etiology of factors here. As I understand it's not solely the influence of magma and magma pressure (or the air in your experiment) that drives crack propagation. The stretching of plates, the forces of ridge push, and other plate tectonic forces contribute to this phenomenon. As far I can read the distinction between these elements remains somewhat elusive, emphasizing that it's not just the magma but a complex interplay of diverse tectonic forces that causes these cracks.

[@geomechanic]

Yes, it is much more complicated than illustrated in reality. Different tectonic boundaries have different influencing factors. Where you have mountain building, you have convergent boundaries and different stresses that contribute to crack growth, earthquakes, and fault slip. I would say that faulting in a convergent boundary is the more dominate mechanism of ground movement. Grindavik is a divergent boundary, so the stresses are different and the magma intrusion plays a more dominate role in ground movement, with faulting happening as a secondary affect to accommodate the magma intrusion at different points along the boundary.

[@deadastronaut2440]

My professor, and others, assert the exact opposite; that is, plate tectonic forces, other than magma, are the primary factors. According to this perspective, these forces propagate cracks, clearing space and facilitating the ascent of magma to the surface. While there are dissenting opinions, there is a consensus that Iceland is a geological anomaly in terms of the significant amount of magma extruded onto the surface. Thus, the precise tectonics responsible for the formation of the Icelandic plateau remain relatively unknown. @geomechanic