<p>The Iceland Met Office website has a status page at <a href="https://en.vedur.is/about-imo/news/a-seismic-swarm-started-north-of-grindavik-last-night" rel="noreferrer">https://en.vedur.is/about-imo/news/a-seismic-swarm-started-north-of-grindavik-last-night</a></p>
<p>It has mentioned using models to determine the location and size of the magma body which is threatening to erupt in the vicinity of Grindavík and the Blue Lagoon. They have also published estimates for the inflow rate of new magma into the linear chamber.</p>
<p>How do they determine these things? What data are the estimates based upon? How confident are geologists in the model outputs?</p>

CC BY-SA 4.0
2023-11-16T06:25:08.527Z
there is a gps station in the middle of grindavik and a seismometer at the naval radiostation 1 km outside grindavik.
trond hansen
CC BY-SA 4.0
2023-11-16T09:25:38.117Z
They also make extensive use of satellite radar interferometry, which is sensitive to very small displacements of the crust - and in Reykjanes at the moment the displacements are large! Essentially the earth tremors give an indication of where the magma is, the GPS and interferometry give an estimate of how much magma there might be. The characterization of location and volume at depth is probably fairly accurate - but the large unknown is if, where, when and how much might break through to the surface.
Andy M
CC BY-SA 4.0
2023-11-18T02:04:10.587Z
Thanks for the comments. I'm not a geologist, so my questions might be naive. I can see how GPS stations and radar interferometry can measure slow ground motions, and I can clearly see that the earthquake data outlines the trace of a dike. I don't understand how the thickness or vertical extent of the dike can be estimated from that data. And I'm confused by data showing subsistence in Grindavik. Is that a sign of a graben forming? Or something else?
John McCarthy
<volcanology><models><volcanic-eruption>
How have Icelandic geologists determined the position and length of the magma under Grindavík?
John McCarthy
# How have Icelandic geologists determined the position and length of the magma under Grindavík?

(Asked by: username_0 on 2023-11-16)

The Iceland Met Office website has a status page at <https://en.vedur.is/about-imo/news/a-seismic-swarm-started-north-of-grindavik-last-night>

It has mentioned using models to determine the location and size of the magma body which is threatening to erupt in the vicinity of Grindavík and the Blue Lagoon. They have also published estimates for the inflow rate of new magma into the linear chamber.

How do they determine these things? What data are the estimates based upon? How confident are geologists in the model outputs?

**Tags:** volcanology, models, volcanic-eruption

> **Comments:**
> **username_1**: there is a gps station in the middle of grindavik and a seismometer at the naval radiostation 1 km outside grindavik.  
> **username_2**: They also make extensive use of satellite radar interferometry, which is sensitive to very small displacements of the crust - and in Reykjanes at the moment the displacements are large! Essentially the earth tremors give an indication of where the magma is, the GPS and interferometry give an estimate of how much magma there might be. The characterization of location and volume at depth is probably fairly accurate - but the large unknown is if, where, when and how much might break through to the surface.  
> **username_0**: Thanks for the comments. I'm not a geologist, so my questions might be naive. I can see how GPS stations and radar interferometry can measure slow ground motions, and I can clearly see that the earthquake data outlines the trace of a dike. I don't understand how the thickness or vertical extent of the dike can be estimated from that data. And I'm confused by data showing subsistence in Grindavik. Is that a sign of a graben forming? Or something else?  

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## 0 answers

