Tag Archives: Holuhraun

Update on the eruptions at Fagradalsfjall and La Soufrière St Vincent, and status of Mount Pelée

Good Afternoon!

Fig 1: Image from Civil Protection / Webcam 11.05.2021

Fagradalsfjall

At the time of writing the eruption at Fagradalsfjall is not only continuing unabated but getting stronger.  After the opening of five new fissures, eruptive activity has focused on one crater, fissure 5. Lava now covers the Geldingadalur valley floor and threatens to engulf the first cones; lava has been flowing steadily into Meradalir since 24 April 2021.

Eruptive activity changed from continuous fountaining with effusive lava flows to periodic jetting after midnight on 2 May 2021. The change is thought to be due to degassing of the magma in the upper part of the eruption channel where a small chamber may have formed.  Each jet is now accompanied by strong gas emissions.  Lava flow, itself, is mostly being carried in lava channels under the crater rim, rather than ejected in the current jets so periodic jetting has not adversely impacted the output.

The onset of jetting can be seen in the tremor plots from local stations. We have included KRI because, being further away, we can see more of the lower frequency lines.

Fig 2: Tremor plots for KRI and MER showing the onset of jetting on 02 May 2021. Source: IMO
Fig 3: Unrest seen on seismometers near the eruption sites with pulses in volcanic activity from midnight on 2 May 2021.  Source: IMO
Fig 4: This image shows the unrest on days 8-9. May. Source:  IMO

Some stats as at 10 May 2021 (Source: Institute of Earth Sciences (hi.is))

  • Area of the Geldingadalsgos lava field: 1.78 Km2 (1.41Km2, 03 May 2021)
  • Volume of erupted lava: 30.7 million m3 (23.0 million m3, 03 May 2021)
  • Lava discharge rate: 12.9m3/s, (7.5m3/s, 03 May 2021)
  • Mg0: varies from 8.5 to 9.8
  • K20/Ti202 ratio: increasing from 0.1 to 0.3

In the first two weeks of the eruption lava flow decreased steadily from 7-8m3/s to 4-5m3/s.  In the second two weeks, five new fissures opened with lava flow varying between 5 – 8m3/s.  In the two weeks to 3 May 2021, one crater dominated with lava flow increasing.  In the week to 10 May 2021, there has been a large increase in the output of lava to 12.9m3/s; the lava field now covers an area of 1.78km2 with a volume of 30.7 million m3.  It is thought that the increase in output reflects changes in the lava channel from the mantle to the surface; it has widened over time.

Changes in chemical composition may mean that materials are mixing in the upper mantle before ascent or there is less partial mantle melt in the magma.  If the latter, the eruption will end when the mantle source is sufficiently reduced.

Geldingadalsgos is still a toddler compared to Holuhraun; Geldingadalsgos’ eruption rate is 5% – 10% of the average eruption rate at Holuhraun between September 2014 and February 2015. Let’s hope it stays that way as it is a lot closer to residential areas.

La Soufrière St. Vincent

The alert status was lowered to orange after a period of relative quiescence on 6 May 2021; only a few long period events and volcano-tectonic earthquakes are occurring each day.  People are allowed back into the orange zone but the red zone remains an exclusion zone.

The last explosive event was on 22 April 2021.  However, a possible lava spine was spotted on photos on 27 April 2021.  Tephra fills the crater, increasing the risk of pyroclastic flows should eruptive activity pick up again.  In the meantime, lahars are the main hazard.

Mount Pelée

Mount Pelée remains on alert level yellow.  Volcano tectonic events are occurring and seismic activity remains at above baseline level.  An area of brown and dead vegetation was confirmed on 8 February 2021 caused by diffuse CO2 emissions; the vegetation has not recovered.   The volcano is slowly reawakening.

Armchair Volcanologist

© Copyright remains with the author; all rights reserved, 2021.

Sources and Further Reading:

In the text and:

Iceland

Icelandic Met Office: https://en.vedur.is/ (English site)

Icelandic Met Office: https:// vedur.is/ (Icelandic site)

Reykjavik Grapevine: https://grapevine.is/

Department of Civil Protection and Emergency Management | Almannavarnir

La Soufrière St. Vincent

St Vincent and the Grenadines:  https://news784.com/

Barbados: https://www.nationnews.com/

Mt Pelée

Observatoire volcanologique et sismologique de Martinique (OVSM – IPGP): http://www.ipgp.fr/fr/ovsm/observatoire-volcanologique-sismologique-de-martinique-ovsm-ipgp

Askja and Herðubreið, The Start of Our Exploration of the Northern Volcanic Zone, Iceland

Good Morning!

As the new volcano at Geldingadalur continues to grow, opening and closing new fissures, we have returned to our tour of Iceland.  We have now reached the Northern Volcanic Zone, where the plate boundary heads northwards from Kverkfjöll to meet the Tjörnes Fracture Zone.   Active volcanoes in the zone are Kverkfjöll, Askja, Fremrinámur, Heiðarsporðar, Krafla and Þeistareykir; Herðubreið, itself, is Pleistocene palagonite table-mountain.

We are starting with the currently most seismically active volcanoes, Askja and Herðubreið, located where the Eastern Volcanic Zone meets the Northern Volcanic Zone, north of the Vatnajökull ice-cap. The mantle plume, itself, is thought to be located to the north west of the Vatnajökull ice-cap.

Askja

Fig 1: Combined images of Askja, cropped from photos by Michael Ryan, 1984 (U.S. Geological Survey): Askja Shield (top) and Askja Caldera (bottom) from GVP

The Askja volcanic system comprises a 1,516 m high central volcano and 190 km long fissure system, the central volcano being the Dyngjufjöll massif. It has three nested calderas, the latest of which formed in a rhyolitic eruption in 1875.  The central volcano, itself, is made up of Pleistocene glacio-volcanic tuffs, hyaloclastites, pillow basalts and intercalated sub aerial lava and capped by Holocene sub aerial lavas and pumice.  The fissure system, itself, extends from beneath the Vatnajokull ice-cap to the north coast of Iceland and includes small shield volcanoes.

This volcanic system does not erupt frequently; GVP records 14 Holocene eruptions which range from VEI 0 to VEI 5, the VEI 5s occurred in c. 8910 BC and 1875.  Askja’s lava types are tholeiitic basalt / picro-basalt and rhyolite.  Her main eruption types are effusive basalt with occasion explosive basalt or rhyolite.  The 1875 eruption created a 4.5-km-wide caldera which is now filled by Öskjuvatn lake. The most recent eruption in 1961 was a VEI 2 effusive basalt one.

Fig 2:  The Askja volcanic system from Icelandic Volcanoes . The boundary of the fissure system is delineated with a dotted line, the central volcano with a black line and the calderas with bold lines.  The three letter abbreviations are other volcanic systems in the area: BAR is Barðarbunga, KVE is Kverkfjöll, SNF is Snæfell, ASK is Askja, FRE is Fremrinámur, HEI is Heiðarsporðar, KRA is Krafla and TEY is Þeistareykir.  The author has added the names Herðubreið and Herðubreiðartögl.

The Askja Fires, 1874 to 1929

Askja was little known before the Askja Fires.  The area is sparsely inhabited, sited in lava fields and ash deserts.   The Fires occurred during a volcano-tectonic episode between 1874 to 1929.

A steam column rising from the central volcano in February 1874 was the first observed sign that the volcano was active. Northern Iceland was rocked by many large earthquakes in December 1874.  Steam and ash were seen in early January 1875 and light ashfall was noted south of Öxarfjörður.  By 15 February 1875, 10m subsidence had occurred in the main caldera along with the formation of a crater erupting mud.  A basalt lava flow at Holuhraun to the south of Askja occurred around this time. 

On 18 February 1875, a fissure eruption started on the Sveinagjá fissure north of the volcano; this generated 0.2 to 0.3km3 of basaltic lava over the course of several months.

On 29 March 1975, the Plinian eruption at the central volcano started in earnest.  The initial output was a wet and sticky tephra.  Shortly after 05:30, pumice was erupted, reaching as far as Scandinavia; this phase lasted until the following day. The Víti crater was formed later in a short hydro-magmatic episode.  The caldera, itself, formed over a period of 40 to 50 years, is now filled by Öskjuvatn lake.  As the volume of the new caldera is greater than the calculated erupted volume of lava and ash, it is thought that the excess lava is stored in the fissure system.

In 1929 to 1930, five eruptions occurred on ring faults around the Öskjuvatn caldera, with a 6 km long fissure eruption occurring on the southern side of the volcano that created the Þorvaldsraun lava.

The 1875 eruption is not the first time Askja has erupted rhyolite. Two other instances have been occurred: the c.10ka Skolli eruption and one around 2.1ka; these deposited thick layers of tephra and ash from the latter reached as far afield as Scotland and Sweden.

Holuhraun, which should be familiar to those interested in volcanology, is the area where a fissure eruption occurred in 2014.  This time the central volcano responsible was Barðarbunga.  At the time there was some concern at the time that the activity in Holuhruan would extend to Askja, triggering a rhyolitic eruption.  Fortunately, that did not happen.

Herðubreið

Fig 3: Image of Herðubreið, cropped from a photo by Icemuon, published under CC BY-SA 3.0

 Herðubreið is a 1,682m high Pleistocene palagonite table-mountain (tuya) made up of pillow lavas, hyaloclastite, capped by a 300m thick lava shield. Herðubreiðartögl, a small ridge extending from the south of Herðubreið, may be part of the same system.  Although Herðubreið is close to the Askja and Kverkfjöll volcanic systems, in the absence of any post glacial activity it not known if it belongs to either system.  We are including the volcano here as it is difficult to allocate the seismic activity in the area to each volcano without more local knowledge.

Herðubreið has been studied as an indicator of climate change during the last glacial periods. Werner et al, (1996) proposed that Herðubreið developed in stages from initial sub-aerial, sub-aqueous, subglacial to sub-aerial.  The first sub-aerial activity occurred during an interglacial, creating an olivine tholeiitic shield volcano in the vicinity of Herðubreiðartögl.  A lull in volcanic activity coincided with the onset of the last ice-age. Activity resumed with the deposition of olivine tholeiites, followed by hyaloclastites in a lake environment until the volcano breached the lake surface to produce subaerial lavas. The tuya, itself, was formed during the last glacial maximum when the volcano erupted pillow lavas under hyaloclastite deposits in the ice-cap; these were later topped by subaerial lavas when the volcano broke through the ice-sheet.  At the end of the last ice-age, activity at Herðubreið had ceased, however, Herðubreiðartögl produced some later olivine tholeittic lava flows and ash deposits.

Recent Seismicity

We plotted the area between 64.95°N,17.2°W and 65.3°N,16.0°W, a total of 45,899 earthquakes.  As you can see from Fig 4, the area is very active (although perhaps we should not have used green dots in retrospect– Askja looks very unwell as a result).

Fig 4: Geoscatter plot by the author of earthquakes between 64.95°N,17.2°W and 65.3°N,16.0°W for the period 31.12.2007 to 31.03.2021. Green dots denote earthquake epicentres; red stars denote those of 3.0 or more M. Blue triangles denote volcanoes. © Copyright remains with the author; all rights reserved, 2021.

The latitude v longitude scatter plot shows that activity follows a NE-SW pattern around Herðubreið, with a swarm to the south east; activity around Askja is focussed on the SE section of the caldera with some further east.  The plots are data-heavy so we have broken these down by year.

Fig 5: Lat v Lon scatter plot by the author of earthquakes between 64.95°N,17.2°W and 65.3°N,16.0°W for the period 31.12.2007 to 31.03.2021. Colours denote year of occurrence. Blue triangles denote volcanoes. © Copyright remains with the author; all rights reserved, 2021.
Fig 6: Depth v Lon scatter plot by the author of earthquakes between 64.95°N,17.2°W and 65.3°N,16.0°W for the period 31.12.2007 to 31.03.2021. Colours denote year of occurrence. Blue triangles denote volcanoes. © Copyright remains with the author; all rights reserved, 2021.

The years with most seismic activity in the sequence are: 2007, 2008, 2014 and 2019. 

Fig 7: Earthquakes in the plotted area by year by the author.  The years highlighted in green have above average seismicity. © Copyright remains with the author; all rights reserved, 2021.

In 2007 and 2008, there was a swarm that started in Upptyppingar and progressed to Álftadalsdyngja; this is thought to be due to magma movement. 2014 is the same year as the Barðarbunga eruption at Holuhraun; perhaps some of the seismicity is the result of the crust accommodating magma movement in the region, although the swarm here preceded the swarms at Barðarbunga.   In 2019, there was a swarm to the east of the Askja caldera.

The earthquake density plots and depth v longitude plots for these years are set out in Figs 8 to 11 below.

Fig 8: Earthquake density plot and depth v lon scatter plot by the author of earthquakes between 64.95°N,17.2°W and 65.3°N,16.0°W for 2007. Colours denote year of occurrence. Blue triangles denote volcanoes. © Copyright remains with the author; all rights reserved, 2021.
Fig 9: Earthquake density plot and depth v lon scatter plot by the author of earthquakes between 64.95°N,17.2°W and 65.3°N,16.0°W for 2008. Colours denote year of occurrence. Blue triangles denote volcanoes. © Copyright remains with the author; all rights reserved, 2021.
Fig 10: Earthquake density plot and depth v lon scatter plot by the author of earthquakes between 64.95°N,17.2°W and 65.3°N,16.0°W for 2014. Colours denote year of occurrence. Blue triangles denote volcanoes. © Copyright remains with the author; all rights reserved, 2021.
Fig 11: Earthquake density plot and depth v lon scatter plot by the author of earthquakes between 64.95°N,17.2°W and 65.3°N,16.0°W for 2019. Colours denote year of occurrence. Blue triangles denote volcanoes. © Copyright remains with the author; all rights reserved, 2021.
Fig 12: Video of earthquake density plots by the author for the period 2006 to 2021(3m) for the area 4.95°N,17.2°W and 65.3°N,16.0°W . © Copyright remains with the author; all rights reserved, 2021.

Let’s see what the scientists have said. Greenfield et al (2016) have noted from seismic studies that there is considerable melt storage and transportation (movement) under the lower crust in the region (which may or may not be typical of Icelandic volcanoes – more study would be needed); there is likely to be a magma intrusive complex in the shallow crust round Askja; and, the activity round Herðubreið is caused by fracturing in the region.

The region is well monitored due to the risk of another rhyolitic eruption from Askja; this time around one may cause some disruption to aviation and communication systems, by how much would depend on the size and length of the eruption.   In the light of the reawakening of Fagradalsfjall on the Reykjanes Peninsula, perhaps the Pleistocene volcanoes should be added to the watch list, although the monitoring of Holocene volcanoes is likely to pick up unusual activity. 

La Soufrière St. Vincent

We have not forgotten La Soufrière St. Vincent; our thoughts are still with the islanders.  We will do a fuller update soon. In the meantime, the volcano is still erupting and a new lava dome is forming in the crater.  The island has lost up to 50% of its GDP.  More aid is now reaching the island.  For updates, we use News 784 (link below).

Barbados continues to clear up the volcanic ash; this is putting strain on local water supplies. For updates, we use Nation News Barbados.

The Armchair Volcanologist

© Copyright remains with the author; all rights reserved, 2021.

Sources and Further Reading:

R. Werner, H. U. Schmincke, G. Sigvaldason ,“A new model for the evolution of table mountains: volcanological and petrological evidence from Herðubreið and Herðubreiðartögl volcanoes (Iceland)”, Geologische Rundschau 85, Article number: 390 (1996). https://link.springer.com/article/10.1007/BF02422244

T. Greenfield, R. S. White, S. Roecker, “The magmatic plumbing system of the Askja central volcano, Iceland, as imaged by seismic tomography”, Journal of Geophysical Reseach: Solid Earth, AGU Publications https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016JB013163

Thor Thordarson (Faculty of Earth Sciences, University of Iceland) and Al Margaret Hartley (University of Manchester (November 2019). Askja. In: Oladottir, B., Larsen, G. & Guðmundsson, M. T. Catalogue of Icelandic Volcanoes. IMO, UI and CPD-NCIP. Retrieved from http://icelandicvolcanoes.is/?volcano=ASK

“Classic Geology in Europe 3: Iceland”, Thor Thordarson & Armann Hoskuldsson, Terra Publishing, Third Edition, 2009.

The Smithsonian Institution’s Global Volcanism Program (GVP): https://volcano.si.edu/

Earthquake raw data: IMO:  https://en.vedur.is/

For updates on La Soufriere St Vincent:

News 784: https://news784.com/

Nation News Barbados: https://www.nationnews.com/

For updates on the new volcano at Geldingadalur:

Icelandic Met Office: https://en.vedur.is/ (English site)

Icelandic Met Office: https:// vedur.is/ (Icelandic site)

Reykjavik Grapevine: https://grapevine.is/

Department of Civil Protection and Emergency Management | Almannavarnir

Quick Update on the Earthquake Swarm on the Reykjanes Peninsula

A large earthquake swarm started on the morning of 19 July at around 1:30 am at Fagradalsfjall on the Reykjanes Peninsula.  The largest earthquake had a magnitude of 5.1M.  At the time of writing, there had been 1,635 earthquakes in the last 48 hours recorded on IMO’s website (note that not all of these have been confirmed). IMO’s map and breakdown of the swarm are shown below:

Fig 1: Map of earthquakes in Iceland over the past 48 hours.  Source: IMO

Close up of the Reykjanes Peninsula:

Fig 2: Map of earthquakes in the Reykjanes Peninsula over the past 48 hours.  Source: IMO
MagnitudeNumber
< 1.0720
1.0-2.0723
2.0 -3.0162
>3.030
Fig 3: Breakdown of earthquakes by magnitude

This swarm is occurring on the east side of the swarms on the Reykjanes Peninsula which started late last year.  IMO have reported that these swarms (still ongoing) are associated with multiple magma intrusions.  The aviation code for the area is still green (IMO). IMO are in the process of evaluating the Fagradalsfjall swarm. 

The swarm at the Tjörnes Fracture Zone is still ongoing.

The eagle-eyed amongst you will note that there is some seismic activity at Katla.  Whether this will result in anything is anyone’s guess at the moment. 

We have not yet updated our earthquake data-set for the current swarm.  We will wait until IMO has had a chance to confirm more earthquakes

Update 24 July 2020

The swarm at Reykjanes is now less intense. In the meantime, Katla produced a shallow 3.0 M. IMO have remarked that earthquakes in the summer at Katla are not uncommon.

From memory, Katla was seismically active before the intense swarms started in August 2014 at Barðarbunga in the run up to the eruption at Holuhraun. This may have been a coincidence.

Fig 4: Map of earthquakes in Iceland over the past 48 hours.  Source: IMO

For further updates, please consult IMO.

The Armchair Volcanologist

21 July 2020

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

Source and Further Reading

“An earthquake swarm in Fagradalsfjall”, 20.07.2020  https://en.vedur.is/about-imo/news/an-earthquake-swarm-in-fagradalsfjall

The Barðarbunga Volcanic System

Good Afternoon!

Fig 1: Barðarbunga: cropped image from photo 3 of 11 by Erik Sturkell, retrieved from Icelandic Volcanoes

In this post we continue our journey round Iceland’s many volcanoes.  We have reached the mighty Barðarbunga at the northwest corner of the Vatnajökull icecap.

Barðarbunga volcanic system lies in the Eastern Volcanic Zone, Iceland, near where the head of the mantle plume is thought to be.  The system comprises a 2,000 m high central stratovolcano with a 65 km2, 700 m deep caldera, the Veiðivötn fissure swarm running NE to SW, and the Tröllagigar and the Dyngjuháls – Holuhraun fissure swarms running NE; the entire system is c. 190 km long and 25 km wide.  

There is second central volcano in the system, Hamarinn, 20 km south west of the Barðarbunga central volcano. Hamarinn may be younger, indicated by the absence of both an intrusive complex and a caldera. 

There are geothermal areas near the caldera rim of Barðarbunga and the east of Hamarinn, the latter is the source of jökulhlaups. 

Fig 2: Map of the Barðarbunga volcanic system: central volcanoes, fissure systems and lava flows. Green barred squares indicate the locations of various volcanoes; BAR is Barðarbunga.  Retrieved from Icelandic Volcanoes.  See Sources for full accreditation.

The area is tectonically very active: the Eastern Volcanic Belt accommodates much of the separation between the North American and Eurasian Plates. The area is close to the junction with the Northern Volcanic Zone, where Barðarbunga’s neighbours, Askja and Herðubreið, can be found.

Eruptive History

According to GVP, there are 55 identifiable Holocene eruptive periods for the Barðarbunga system.  Some of the eruptive history has been hidden by the ice-cap.  However, lavas and tephra deposits on the ice-free sections of the fissures are more accessible.

Barðarbunga Central Volcano

The central volcano has had around 22 eruptions in the last 1000 years, most occurring between 1200 -1500 and in the 18th century.  The last known subaerial eruption was in 1910.

Barðarbunga’s lavas are mainly basalt/ picro basalt.  Her eruption types are explosive, phreato-magmatic with jökulhlaups, reflecting the impact of the ice-cap.  The central volcano produces eruptions in the order of VEI 3 to 4, producing tephra – both airborne and waterborne.  There is a silicic tephra layer in the ice-cap dating to the early 18th century but it is not clear that this came from Barðarbunga.  If it did, any rhyolite would have come from partial melting of the basaltic crust.

Magma is sourced from a depth of 10 km or more below the caldera; above this source is an intrusive complex and a lower density region, probably of caldera in-fill.  Magma may also be sourced direct from the mantle in the fissure swarms.  

Fissure Swarms

Fissure swarm eruptions are basaltic in the order of VEI 1 to 2, with a maximum of VEI 6 on the Veiðivötn fissure. 

The last three eruptions on the south west fissure swarm were the VEI 4 at Vatnaöldur in 877, the VEI 6 at Veiðivötn in 1477 and the VEI 2 at Tröllagigar in 1862-1864.  The first two of these were explosive tephra eruptions, producing 5 km3 to 10 km3 of tephra and small lava flows.  Both the Vatnaöldur and Veiðivötn fissures cut into the Torfajökull volcano, causing it to erupt with silicic tephra and lava.  The largest known effusive eruption on the SW fissure swarm is the Great Þjórsá lava which covers 900 km2 and reached the south coast via the Tungnaá and Þjórsá river valleys.

The Gjálp eruption in 1996 occurred on a subglacial fissure that links the Barðarbunga and Grímsvötn volcanic systems.  While it is thought that the magma was sourced from beneath Barðarbunga, based on seismic and geodetic data, the magma erupted subaerially was characteristic of Grímsvötn’s lavas.

The frequency of eruptions on the northern fissure swarm is not known; the last eruption was at Holuhraun which started on 29 August 2014 and lasted until February 2015.  Precursors to this eruption were a build up of seismic activity at Barðarbunga over seven years, which stopped immediately after the Grímsvötn 2011 eruption but resumed soon afterwards. The largest known effusive fissure eruption north of Vatnajökull is the mid Holocene 15 km3 Trölladyngja lava shield.

Holuhraun Eruption 2014 – 2015

Fig 3: Holuhraun eruption.  Cropped image from Barðarbunga: photo 8 of 11 by Alessandro La Spina, 4 September 2014. Retrieved from Icelandic Volcanoes. Note the fire fountains, spatter cones and volcanic gases.

The subaerial eruption started on 29 August 2014 at the Holuhruan vent 45 km NE of the Barðarbunga caldera; the eruption ended on 28 February 2015, having left an 85 km2 lava field and a 65 m deep depression in the Barðarbunga caldera’s ice cover.  The eruption was a large SO2 and other volcanic gas producer, however there was little ash or tephra.

The central volcano, Barðarbunga had inflated prior to the eruption then deflated during the eruption as evidenced by subsidence in the ice covering.  The volume of the subsidence was consistent with the dyke intrusion and the lava erupted at Holuraun, although there is seismic and geochemical evidence that some of the lava erupted at Holuhraun was fed direct from the mantle. It is estimated that 1.6 km3 lava was erupted. 

Since September 2015, seismic and GPS data show that the volcano has started to refill at a depth of 10 to 15 km.

Recent Seismic Activity

We looked at earthquakes in the Barðarbunga, Askja, Herðubreið and Holuhraun area (64.56°N, 17.65°W to 65.3°N, 16.1°W) for the period 1 January 2009 to 28 June 2020.  Not much activity had been noted in the area to the west and south west of Barðarbunga in our earlier plots; however, we had noted that heightened activity at Askja and Herðubreið had preceded the 2014 eruption at Holuhraun which lies between the three volcanoes, hence we included them in our plots.  The link between the centres is rifting in the crust to accommodate the separation of the North American and Eurasian Plates.

Fig 4: Earthquake plots for the period 1 January 2009 to 28 June2020: lat. v lon. geodensity and scatter plots and a depth plot; all by the author.  Green dots denote earthquakes ≤ 2 M; yellow circles, earthquakes between 2.0 M and 3.0 M; and, red stars, over 3 M.  Note in addition to the intense activity around Barðarbunga and Holuhraun, activity near Askja and Herðubreið. © Copyright remains with the author; all rights reserved, 2020.

There were 70,128 earthquakes in the period, of which 16,573 occurred before the 2014 -2015 eruption, 19,061 during the eruption and 34,494 post eruption; the average per calendar month was 247 pre eruption, 2,723 during the eruption and 539 post eruption; the maximum magnitude earthquake pre eruption was 3.9 M, during the eruption 5.5 M and 4.9 M post eruption; and, the deepest quakes had respective depths of 33.9 km, 31.0 km and 33.9 km.  These numbers include activity at Barðarbunga, itself, the Holuhraun fissure, Askja and Herðubreið.  The larger magnitude earthquakes occurred near the north and south caldera rim during the eruption.  Since the eruption all four centres have had elevated seismic activity.

Seismicity during the 2014 to 2015 Holuhraun eruption

Fig 5: Earthquake swarms: Herðubreið three months prior to the Holuhraun eruption, the swarms at Barðarbunga and Holuhraun in the first month of the eruption and then a sample three months later. The Barðarbunga and Holuhraun swarms started in August 2014 and continued with decreasing intensity to June 2015. © Copyright remains with the author; all rights reserved, 2020.

Three months prior to the eruption, there was an earthquake swarm at Herðubreið, noted here because the rifting event that preceded the Holuhraun eruption occurred on the same plate boundary.  Seismic activity at Herðubreið or Askja may be precursors to activity at Vatnajökull, if they, themselves, are not the main event or brewing something.  Something to watch out for bearing in mind the recent large swarms in the Tjörnes Fracture Zone and on the Reykjanes Peninsula.

The earthquake plots for August 2014 and November 2014 show the intense swarms from caldera collapse and also the rifting event.

We will look at Askja and Herðubreið in future posts.

The Armchair Volcanolgist

17 July 2020.

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

Sources and Further Reading

“Barðarbunga”, Guðrún Larsen and Magnús T. Guðmundsson (Institute of Earth Sciences – Nordvulk, 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=BAR

Fig 2: Map. After Björnsson (1988), Gudmundsson and Högnadöttir (2007), Jóhanneson and Saemundsson (1998a & b), Sigurgeirsson et al (2015). 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=BAR

Smithsonian Institution Natural History Museum Global Volcanism Program (GVP): https://volcano.si.edu

Raw earthquake data: Icelandic Meteorology Office: IMO https://en.vedur.is/earthquakes-and-volcanism/earthquakes

Plots are the author’s own work.