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.
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.
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.
The Icelandic Met Office (IMO) has updated the aviation alert for Grímsvötn from green to yellow today (30.09.2020) because the volcano’s activity is above background level, now at a level comparable to that which preceded previous eruptions. They note:
Above average seismicity for September 2020;
Deepening cauldrons in the ice-cap round the caldera from geothermal activity;
Surface deformation exceeding that which preceded the 2011 eruption;
Magmatic gases detected in the summer of 2020.
An eruption is not considered imminent.
Water levels in the sub-glacial lake are high indicating possible jökulhlaups in the coming months. Draining of the lake by a jökulhlaup depressurised the system before the 2011 eruption, so an eruption is considered possible in the event of a jökulhlaup.
Activity may decrease without an eruption in this instance; only time will tell.
Jumping the gun a bit on our next post in the volcanic risk mitigation series, the IMO’s alert is an example of using alert levels to highlight the increased risk of an eruption to those who need to know, without being unduly alarmist – a straightforward statement of the facts supporting the current status. For the exact wording of the alert, please follow the link below.
Grímsvötn is located under the Vatnajökull ice-cap in an active rift zone of the Eastern Volcanic Zone, Iceland. She erupts frequently; her last in 2011 was a large VEI 4, which impacted local farmers and livestock and aviation in Europe.
Googling around a bit more, I note that Iceland’s Department of Civil Protection and Emergency Management, Almannavarnir, have reported in their 25 September 2020 bulletin that an eruption is considered likely this Autumn (use Google Translate or other tool, if you need to, as it is in Icelandic).
A large earthquake swarm started in Iceland in the Tjörnes Fracture Zone (TFZ) on 19 June 2020, still ongoing at the time of writing. The Civil Protection Authority, Iceland, has declared a state of uncertainty; the TFZ is capable of producing large destructive earthquakes.
The Icelandic Meteorological Office (IMO) has reported that over 9,000 earthquakes have been detected by their SIL earthquake monitoring system. The swarm includes three earthquakes over 5.0: on 20/06/2020 a 5.6 and a 5.4, both 20 km north east of Siglufjörður; and, on 21/06/2020, a 5.8 30 km north, north east of Siglufjörður. The day before the swarm started there was a small earthquake with a depth of 92.3 km, which is unusually deep for the area.
IMO is in the process of manually confirming the earthquakes – a mammoth task! We have updated our earthquake data set up to 28 June 2020 based on the earthquakes confirmed so far in order to take a look at the swarm. In the area, 65.25°N, 21.5°W to 67.25°N, 15.0°W, 2,010 earthquakes from 1 June 2020 to 28 June 2020 were available to download.
Statistics so far
Updated earthquake plots
Our plot for month 54 (1 June 2020 to 28 June 2020) shows that the swarm is occurring on the western end of the TFZ, near the junction of the Eyjafjarðaráll Rift and the Húsavík-Flatey Fault.
So what is going on?
Prior to this swarm, most activity in our data set from 1 January 2016 had been on the Grímsey Oblique Rift and Húsavík-Flatey Fault, with a large swarm occurring to the north west of Grímsey in February 2018 (see our earlier post). The current swarm appears to be the western end of the system catching up.
This swarm is, however, relatively deep for oceanic crust. Whether or not there is any associated volcanic or geothermal activity remains to be seen.
The swarm on the Reykjanes Peninsular that started in late 2019 is still ongoing, albeit at a reduced rate. Are the two swarms linked? The obvious answer is yes – they are both on transform fault systems which accommodate the spreading from the Mid Atlantic Ridge as it crosses Iceland. But is there more to it? Possibly, the crust could be fracturing to accommodate other activity in Iceland – e.g. uplift from the mantle plume. If yes, we may see some more activity e.g. in the vicinity of the Vatnajökull Icecap in the next few months. But we’ll have to wait until the real experts opine.
Having visited Katla, let’s go further north to the Eastern Volcanic Zone and take a look at Hekla.
Hekla is an active snow-covered elongated stratovolcano, lying at the southern end of the Eastern Volcanic Zone in Iceland in a rift transform junction. Following the 1104 AD eruption, Hekla was called “The Gateway to Hell” – a name that stuck until the 19th century.
The Hekla volcanic system comprises a 1490m high central volcano and a 60 km fissure swarm. The Heklugjá fissure, 5.5 km long cutting across the central volcano, is the site of many eruptions and gives Hekla its elongated shape. The Vatnafjöll fissure system, 40 km long and 9 km wide is considered part of the Hekla volcanic system. Hekla may have a small magma reservoir 4 km below the surface. She has permanent snow cover but no large glacier.
Hekla’s lavas differ from the rift zone volcanoes; her lavas are andesite, basaltic andesite, basalt / picro basalt, rhyolite and dacite. She erupts tephra and silicic to intermediate lavas from the central volcano. Eruptions tend to be a short plinian / subplinian phase followed by lava flows. Larger explosive silicic eruptions have produced enough tephra for the deposits to act as time markers in dating other eruptive activity in Iceland. She is a large fluorine producer which is hazardous to livestock. The hazards listed are tephra fallout, fluorine gas, pyroclastic flows and lava flows; the absence of a large glacier means that jökulhlaups are not a major hazard for Hekla.
The fissure system produces basaltic lavas and a small amount of tephra; its hazards are listed as lava flows and volcanic gas pollution.
According to GVP, Hekla has had 65 Holocene eruptions ranging from VEI 1 to 5. Larsen and Thordarson state that there have been 100 eruptions in the past 9000 years, 23 of which occurred in the last millennium with VEIs ranging from 0 to 5. The central volcano produces eruptions of VEI 2 to 6, VEI 3 to 4 being the most frequent; the longer the repose time between eruptions, the larger the ensuing eruption. The fissure system produces less explosive eruptions (VEI 1 to 2). Hekla’s largest known eruption, a VEI 6, occurred between 3000 to 4300 years ago. Traces of ash from Hekla have been found in Scandinavia, Germany, Ireland and the UK.
Hekla’s eruptive style has changed over time: from effusive basalt 9000 to 7000 years ago; to large explosive silicic eruptions between 7000 to 3000 years ago; and, then smaller more frequent mixed silicic and basaltic eruptions from 3000 years ago to the present day.
The most recent eruption was in 2000, with a VEI 2 to 3, 0.01km3 of airborne tephra 0.01km3 and 0.12km3 of lava; it thought that magma rose through a conduit from a depth of more than 10km to 1km below before heading towards a fissure on the Hekla ridge.
Hekla has an unusually low level of seismic activity. Her largest earthquakes are in the order of 2M when dormant and 3M during an eruption. She does not give much warning of an eruption: known precursors are earthquakes 25 to 90 minutes beforehand. Monitoring has increased since the last eruption so there should be more information about any precursors to future eruptions.
Recent Seismic Activity
From the data set of earthquakes downloaded from IMO’s site for period 1 January 2016 to 31 May 2020, we extracted those for the Hekla – Vatnafjöll area: 63.7578°N, 19.4687°W to 64.0952°N, 19.9399°W. We found 1,018 earthquakes, compared to Katla’s 6,505 for the same period. The largest quake was 2.62 and the deepest 25.11km.
In our latitude v longitude scatter plot we can see that most earthquake activity is scattered along the fissure systems, with an E-W “cluster” to the south of GPS station HEK3, north of Hekla. The latitude v depth plot shows the activity near Vatnafjöll is occurring in the lithosphere, whereas there appears to be a conduit under Hekla. A close up of the cluster confirms this impression.
Our geodensity plot of the earthquakes shows a hot spot south of HEK3, north of Hekla.
We looked for swarms in the data set to see if these account for the hot spot but did not find any large ones; the hot spot appears to be an accumulation of activity over the period. Hekla seems to have a slow magma feed.
“Hekla”, Guðrún Larsen (Institute of Earth Sciences – Nordvulk, University of Iceland) and Thor Thordarson (Faculty of Earth Sciences, University of Iceland). In: Oladottir, B., Larsen, G. & Guðmundsson, M.T., Catalogue of Icelandic Volcanoes. IMO, UI and CPD-NCIP. Retrieved from Icelandic Volcanoes: http://icelandicvolcanos.is/?volcano=HEK
Fig 2: Map: After Jóhannesson and Einarsson (1992), Jóhannesson and Saemundsson (1998a), Larsen et al (2013a), Base data, Iceland Geo Survey, IMO, NLSI | Base map: IMO. In: Oladottir, B., Larsen, G. & Guðmundsson, M.T., Catalogue of Icelandic Volcanoes. IMO, UI and CPD-NCIP. Retrieved from Icelandic Volcanoes: http://icelandicvolcanos.is/?volcano=HEK
Continuing our theme of seismicity in Iceland, we have now reached the Mýrdalsjökull Region and are heading towards the Fire Districts in the Eastern Volcanic Zone.
We took a slight detour to set up a Glossary to explain some of the terms used here to help out. You can find it on the Menu bar.
Mýrdalsjökull lies at the southern end of the Eastern Volcanic Zone, near its junction with the South Iceland Seismic Zone. The South Iceland Seismic Zone is a transform fault system that links the West and East Volcanic Zones. The Eastern Volcanic Zone accommodates 40 to 100% of the spreading between the North American and the Eurasian Plates; the Western Volcanic Zone takes up the remainder. Active rifting on the Eastern Volcanic Zone terminates at Torfajökull volcano at the rift’s southern end. Katla, Eyjafjallajökull and more southerly volcanoes are on the Eurasian Plate.
We updated our earthquake dataset so we are now looking at the period from 1 January 2016 to 31 May 2020. Apart from the continued swarm on the Reykjanes Peninsula, there has not been any unusual activity (to the untrained eye, at least). We used IMO’s latest earthquake map for Mýrdalsjökull as an indicator for the coordinates to extract the data for the region. This picked up five seismically active volcanic systems (Eyjafjallajökull, Hekla, Katla, Torfajökull and Vatnafjöll) and three inactive areas (Krakatindur, Þórólfsfell and Tindfjallajökull).
Let’s start by taking a closer look at Katla; the other volcanic centres will be covered in later posts.
The Katla Volcanic System
Katla is one of Iceland’s most active volcanoes. The volcanic system is 80 km long, made up of a 30 km wide central volcano and fissure systems. The central volcano has a 10km by 14km wide, 600m to 750m deep caldera with a 5km wide magma reservoir at a depth of 1.5 km. The Katla fissure, Kötlugjá, is located in the caldera. At the north west of the system is the Hólmsá fissure and to the north east, the Eldgjá fissure. There are also inactive fissures to the south. The Mýrdalsjökull ice cap covers most of the central volcano.
Katla’s lavas are basalt/picro basalt, rhyolite and dacite, with a few intermediate hybrids, andesite and basaltic andesite. The basaltic eruptions are the most voluminous , sourced from the mantle via a spreading rift. She has also had many dacite eruptions. Lavas from the Eldgjá fissure are basaltic.
Volcanism at Mýrdalsjökull began over 800,000 years ago and at Katla, 200,000 years ago. Studies of tephra have identified 200 basaltic and 14 silicic eruptions in the last 8,500 years; unfortunately, no more is known about what happened before the end of the last ice age.
Katla’s largest known eruption was a rhyolitic VEI 6 in 10600 BC which produced more than 10 km3 of rhyolite in pyroclastic flows and airborne tephra that reached 1,300 km from the volcano. The Sólheimar ignimbrite formed from the pyroclastic flows; and the tephra is referred to as the Skógar tephra (Iceland) or Vedde Ash (Norway, after the place where it was discovered).
GVP notes 132 Holocene eruptions for Katla, which range from VEI 3 to VEI 5. All Holocene eruptions occurred in the caldera, except for the 934 AD to 940 AD eruption of the Eldgjá fissure to the north east and the Hólmsá Fires in 6600 BC. Her recent eruptive style tends to be explosive basaltic eruptions from the caldera with tephra volumes up to 2km3, accompanied by jökulhlaups (glacial outburst floods). Water from melting ice cap contributes to the explosivity of the eruptions.
The last eruption to break the ice-cap was a VEI 4 in 1918 which produced an ash column up to 14 km in height, 0.7 km3 of airborne tephra, 1 km3 of debris from jökulhlaups and a small volcanic fissure; no lava emission was reported. The 1625 and 1755 eruptions, both VEI 5s, produced more tephra which reached further than 1,000 km from the central volcano.
The average time between eruptions has been cited as between 40 and 80 years on average. On that basis, Katla is expected to be gearing up for another eruption in the near future.
A period of unrest started in 1999 with a jökulhlaup, seismic tremors, geothermal activity and cauldron formation. There have been more recent subglacial eruptions: a jökulhlaup occurred in 2011, accompanied by a harmonic tremor and the formation of several ice-cauldrons, was thought to be indicative of a sub-glacial eruption; and the most recent jökulhlaup was in 2017, it is not clear if this was accompanied by a harmonic tremor.
We extracted the earthquakes for Katla from the above data set using the coordinates 63.785°N, 19.4987°W to 63.4547°N,18.6608°W. This produced 6,505 earthquakes for the period 1 January 2016 to 31 May 2020.
Our plots show most activity in the caldera, some at the Goðabunga cryptodome and a low level of activity to the south and east of the caldera. Activity in the caldera is fed from a depth of 32km.
So what is causing the hot spots? We looked for earthquake swarms to see whether they are the cause of the hot spots in the geodensity plot. We used the criterion of 30 or more earthquakes in one day or in two consecutive days, which is a higher level of activity than Mýrdalsjökull’s “normal” activity. This showed 16 swarms (ref Appendix), of which five had more than 100 earthquakes; four of the five swarms were clustered (Swarms 4, 6, 7 and 12, shown below) and one was more spread out. Note: our analysis of swarms is not intended to pick up any small magma intrusions that have fewer than 30 earthquakes attached to them.
We see that Swarm 4 and Swarm 12 contributed to the hotter spots in the geodensity plots; the remaining hot spots seem to be caused by an accumulation of activity over four plus years in the data set. Without a clear map of the fissures within the caldera (Googling around did not find one), we cannot tell if the swarms coincide with known fissures. However, swarm 12 coincides with the 2017 jökulhlaup. Most of the swarms in the set appear to be part of the run up to a potential subglacial eruption. It is interesting to note that there do not appear to be any larger swarms after July 2017.
Earthquake swarms are precursors to eruptive activity. Unfortunately, as the last eruption to break through the ice-cap preceded any modern volcano monitoring, there is less certainty over what would precede another subaerial eruption, notably in respect of the intensity of swarms, magnitude of the earthquakes, jökulhlaups, and the time-frames.
It has been a while since Katla produced a large eruption. Let’s hope she sleeps for a bit longer; the world has enough to contend with at the moment.
“Iceland”, Thor Thordarson & Armann Hoskuldsson, Classic Geology in Europe 3, Terra Publishing, Third Impression, 2009
“Katla”, Guðrún Larsen and Magnús T. Guðmundsson (2016 March 7). In: Oladottir, B., Larsen, G. & Guðmundsson, M.T., Catalogue of Icelandic Volcanoes. IMO, UI and CPD-NCIP. Retrieved from Icelandic Volcanoes: http://icelandicvolcanos.is/?volcano=KAT
Fig 3: Map: After Jóhanneson and Saemundsson (1998a), Björnsson et al (2000) and Larsen (2000), Base data, Iceland Geo Survey, IMO, NLSI | Base map: IMO. In: Oladottir, B., Larsen, G. & Guðmundsson, M.T., Catalogue of Icelandic Volcanoes. IMO, UI and CPD-NCIP. Retrieved from Icelandic Volcanoes: http://icelandicvolcanos.is/?volcano=KAT
“Katla and Eyjafjallajökull Volcanoes”, Erik Sturkell, Páll Einarsson, Freysteinn Sigmundsson, Andy Hooper, Benedikt G. Ófeigsson, Halldór Geirsson and Halldór Olafsson, Developments in Quaternary Sciences, Volume 13, ISSN 1571-0866
There has been a large earthquake swarm on the Reykjanes Peninsula over recent months, still ongoing at the time of writing, albeit with reduced intensity.
So let’s take a look at what’s been going on.
The Reykjanes Peninsula lies at the south west tip of Iceland on the Mid Atlantic Ridge, the boundary between the North American and Eurasian Plates. The North American Plate is moving westwards in relation to the Eurasian Plate; transform and extension faulting accommodate the relative Plate motions. The Reykjanes Volcanic Belt lies on the Reykjanes Peninsula, comprising five north east trending volcanic systems: Reykjanes, Svartsengi, Krýsuvík, Brennisteinsfjöll and Hengill. The volcanic systems are fissure swarms.
The line of earthquake epicentres in Fig 1 shows the path of the Mid Atlantic Ridge. These earthquakes were extracted from the data set used to generate the plots in the earlier post introducing Iceland. The raw earthquake data is publicly available data downloaded from the Icelandic Meteorological Office for the period January 2016 to 12 April 2020. The plot above is still data-heavy (too much data to see what is happening) so I have extracted the earthquakes by month to see where and when most activity occurred.
In the plots there is an impression of seismic activity trending along the Peninsula from the east to the west. This impression is born out most strongly in the activity from month 48 onwards. Although it should be noted that the level of activity for these months is unusually high.
There are several possible reasons for the east to west trending of the earthquake swarms:
the plates do not move smoothly past each other, so friction generates faults and earthquakes;
rifting is occurring to accommodate the upward motion of land further to the east, generated by the mantle plume in the vicinity of Vatnajökull; and /or,
magma intrusion in local volcanoes.
Let’s take a look at depth plots of earthquakes under the Reykjanes / Svartsengi area. This shows that the earthquakes over 3 M are largely in the lithosphere.
Plotting depth against longitude, effectively looking northwards through the swarms, also shows that most larger quakes are in the lithosphere but some over 2 M track towards the surface. On its own, this is not enough to draw any conclusions over the likelihood of an eruption; field observations, including gas emissions and ground deformation are required to determine how close to the surface magma may be.
These swarms were accompanied by local uplift, as shown by local GPS stations.
IMO(3) has reported that the most likely explanation for the recent swarms and uplift is a magma intrusion near Mt Thorbjörn at depth; Mt Thorbjorn is located near the Blue Lagoon, Svartsengi. As to whether or not magma will reach the surface for an eruption and where it emerges, we will have to wait and see. In the meantime, let’s look at the recent activity in historical times.
Historic Volcanic Activity
As noted earlier, the volcanic systems are fissure swarms. Activity is driven by rifting which enables magma to reach the surface. The most recent onshore volcanic activity took place between 940 AD and 1340 AD; later activity has been offshore. Onshore lavas from these eruptions tend to be tholeiitic basalts (1). The systems are still active as demonstrated by current geothermal activity.
The Hengill volcanic system is a series of fissure vents, crater rows and small shield volcanoes, with a highest point of 803m. It lies at the triple junction of the Reykjanes Peninsula volcanic zone, the Western volcanic zone and the South Iceland seismic zone. The lava types are basalt / picro-basalt, andesite / basaltic andesite and rhyolite. Hengill’s lavas are more complex that those to the west, reflecting its position at the triple junction. GVP(2) lists 13 Holocene eruptions ranging between VEI 0 and VEI 2; the last known eruption was a VEI 2 in 150 AD.
The Brennisteinsfjöll volcanic system is a series of crater rows and small shield volcanoes, with a highest point of 610m. Its lava types are basalt / picro-basalt. GVP(2) lists 9 Holocene eruptions ranging between VEI 0 and VEI 2. One eruption, previously attributed to Hengill, occurred during a meeting of the Icelandic parliament at Thingvellier in 1000 AD. The most recent eruption was a VEI 2 in 1341.
The Krýsuvík volcanic system is a series of crater rows and small shield volcanoes, with a highest point of 360m. Like Brennisteinsfjöll, its lava types are basalt / picro-basalt. GVP(2) lists 11 Holocene eruptions ranging from VEI 0 to VEI 2; the most recent of which was in 1340. The Krýsuvík Fires spanned a period between 1151 and 1188, producing 36 km2 of lava.
Reykjanes & Svartsengi
The Reykjanes volcanic system is a series of crater rows and small shield volcanoes, which extends offshore and includes several small islands. Reykjanes highest point is 140m. The Reykjaneshryggur volcanic system is a submarine system which is considered part of Reykjanes. GVP includes Svartsengi as a crater row of Reykjanes. Reykjanes lava types are basalt / picro-basalt. GVP(2) lists 22 Holocene eruptions ranging between VEI 0 and VEI 4, of which the most recent was a VEI 0 in 1970; the VEI 4 was in 1226. The 1226 eruption was part of the Reykjanes Fires which started in 1210 and lasted until 1240.
The area is one that has had a period of intense volcanic activity, so the recent earthquake swarms have generated a lot of interest.
Regular updates on seismic and volcanic activity in Iceland are published by the Icelandic Meteorological Office(3).
The Armchair Volcanologist
14 May 2020
References & Further Reading:
David W Peate, Joel A. Baker, Sveinn P. Jakobsson, Tod E. Waight, Adam J. R. Kent, Nathalie V. Grassineau, Anna Cecile Skovgaard , 2009. “Historic Magmatism on the Reykjanes Peninsula”, Contrib Mineral Petrol (2009) 157:359-382
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.
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.
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.
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.