Tag Archives: mantle plume

A Quick Look at Iceland: Total Earthquakes by Year 2009 to 23 October 2020

Good Morning!

While we are waiting to see if there is any volcanic activity at Grímsvötn or her neighbours, let’s take a look at how the current seismic activity in Iceland compares to previous years. 

Our database, comprised of earthquake data downloaded from IMO (see Sources below), now goes back to 29 December 2008 and extends to 23 October 2020, although we may reupload the last week soon because IMO may have been in the process of updating the record when we downloaded the data. 

Fig 1: Iceland: Total Earthquakes by Year and Magnitude by the author, using data downloaded from IMO (see Sources below).  © Copyright remains with the author; all rights reserved, 2020.

From our graph, we can see that the total number of earthquakes was up in 2010, 2014, 2017 and 2020.  In 2010, Eyjafjallajökull erupted, in 2014, Barðarbunga erupted at the Holuhraun fissure; in 2017, there was no subaerial volcanic activity, although Katla may have had some subglacial activity, and, in 2020, there is rifting both in the Reykjanes Peninsula and Tjörnes Fracture Zone but we have yet to see what, if any, volcanic activity emerges.  Interestingly, the 2011 eruption of Grímsvötn did not push the total earthquakes up in 2011.

Let’s take a look at activity by region. Here we look at the four main volcanic regions: the Tjörnes Fracture Zone, Vatnajökull, Myrdalsjökull and the Reykjanes Peninsula, where there is most seismic activity.

Fig 2: Iceland Total Earthquakes by Region and Year by the author, using data downloaded from IMO (see Sources below). Note: not all regions

Fig 3: Iceland Total Earthquakes > 2.0M by Region and Year by the author, using data downloaded from IMO (see Sources below). Note: not all regions are shown.  © Copyright remains with the author; all rights reserved, 2020.

We see that the eruption of Eyjafjalljokull increased the number of earthquakes in Myrdalsjökull but not to the extent that the eruption of Barðarbunga at the Holuhraun fissure and subsidence in the caldera pushed up the earthquakes for Vatnajökull in 2014 and subsequent years.  In fact, the total number of earthquakes in all regions, except Myrdalsjökull, has remained elevated since Holuhraun.

Our database does not extend back far enough to draw any firm conclusions, however, it would appear that rifting events such as Holuhraun produce far more earthquakes than volcanic activity on its own. 

Tjörnes Fracture Zone and on the Reykjanes Peninsula

This rather begs the question as to what is happening this year with the large earthquake swarms both in the Tjörnes Fracture Zone and on the Reykjanes Peninsula.  Unless our database does not go back far enough, neither the 2011 Grímsvötn nor the 2014 Barðarbunga eruption was preceded by such large earthquake swarms in other regions.

The fact that there is significantly raised activity this year in both regions suggests to us that we may be witnessing the normal plate separation on the Mid Atlantic Ridge (it is not entirely smooth), possible local magma ascent, and / or the plates accommodating an ascending blob of magma from the mantle plume, which is believed to be under the Vatnajökull icecap. There is ground deformation at several spots under the Vatnajökull icecap which points to magma ascent. 

IMO have reported that there could be a magmatic intrusion at depth on the Reykjanes Peninsula; this is supported by ground deformation. 

Gas measurements, ground deformation and recent seismic activity at Grímsvötn (not enough to show in our graphs but above the background levels for the volcanic system) have led to the Icelandic authorities to consider that an eruption is possible there in the not too distant future and to raise the alert level a notch (see earlier article). 

It is too soon to tell whether or not the rifting events, themselves, will result in eruption(s); it is possible that it is just a coincidence that we are seeing two large rifting events at roughly the same time – both areas are seismically active.  Time will tell. 

In the meantime, we will continue to watch.

The Armchair Volcanologist

© Copyright remains with the author; all rights reserved, 2020.


For raw earthquake data and updates:

Icelandic Met Office: https://en.vedur.is/

A Brief Introduction to Iceland

This is a test post as a starter for my blog. I hope you find this and later posts interesting.

Iceland, home to Eyjafjalljökull and Grimsvötn, whose eruptions in 2010 and 2011, resp., disrupted European airspace, is recommended as a great place to study volcanology, with many types of volcanic activity and relatively easily accessible. It is also a great holiday destination, not that I have been privileged enough to visit.

Iceland, located between 67.2°N 23.0°W and 63.0°N 13.0°W, has an area of 103,000 km2 and a population of 364,000.  Lying on both the North American Plate and the Eurasian Plate, it is the only large surface expression of the MAR where its volcanic activity can be easily studied by field volcanologists.  Iceland, itself, was formed from magma and accretion.

The Mid Atlantic Ridge in the northern hemisphere is the boundary the North American Plate and the Eurasian Plates.  As the plates separate, the ridge widens and allows rising magma to come to the surface.  The magma rises under its own buoyancy; hotter magma is less dense than the colder surrounding rock.

In addition to the MAR, the Icelandic Hotspot, a mantle plume, contributes to both plate separation and volcanic activity. The Iceland Plateau, itself, is a large basaltic igneous province. The plume head is thought to be located in the region of the Vatnajökull icecap. 

The MAR crosses Iceland in a series of transform and extensional faults, starting at the Reykjanes Peninsula in the south west to the Tjörnes Fracture Zone in the north.  Plotting the earthquakes reported by the Icelandic Meteorological Office (IMO) from January 2016 to 12 April 2020 shows the path of the MAR. 

Fig 1.  Earthquakes from 2016 to 2020 (12/04/2020).  Circles roughly denote four of the many volcanic zones. © Copyright remains with the author; all rights reserved, 2020.

If we take a look at a three-dimensional plot of the same earthquake looking from the south, we can see that there are deeper earthquakes under the volcanic regions Myrdalsjökull and Vatnajökull. 

Fig 2. Three-dimensional plot of earthquakes from 2016 to 2020 (12/04/2020).  © Copyright remains with the author; all rights reserved, 2020

A geodensity plot of the same earthquakes, weighted by magnitude, shows most activity (yellow areas) at the western end of the Reykjanes Peninsula and on the Tjörnes Fracture Zone to the north.  Other areas of interest are Myrdalsjökull (Katla), Vatnajökull (Barðabunga) and Herðubreið.

Fig 3. Geodensity plot for the same earthquake data set as above.  © Copyright remains with the author; all rights reserved, 2020

Iceland is often touted as having every form of volcanism going but it does not have an obvious active subduction zone; eruptions tend to be associated with fissures.  Not to worry, Iceland has many active volcanoes, including: Askja, Bárðabunga, Eyjafjalljökull, Katla, Grimsvötn, Hekla and Surtsey – plenty to offer us in terms of volcanic and seismic activity.

Our plot is data-heavy (in the region of 104,000 earthquakes) so we cannot see much more without further analysis. We will look at each volcanic region in turn in later posts.

Thank you for reading this and I look forward to sharing the next post with you.

The Armchair Volcanologist

© Copyright remains with the author; all rights reserved, 2020


All plots are the author’s own work.

Raw earthquake data: Icelandic Meteorological Office, IMO:  https://en.vedur.is/

Software used for 3D and geoplots: MatLab