We have updated the earthquake plots for Fagradalsfjall, Iceland, for the swarm which started on 21 December 2021.
The swarm had an intense initial period while magma moved along a lateral dike, followed by a less intense period, accompanied by magma ascent. The Icelandic Met Office, IMO, say that the swarm is following the same pattern as that which preceded the eruption in March 2021.
Magma is ascending under Fagradalsfjall, itself. The outlying earthquakes, e.g., at Svartsengi and Krýsuvík, are what Iceland calls triggered earthquakes. Triggered earthquakes are tectonic in nature, arising as local faults respond to magma movement.
Following a drop in seismicity over the past couple of days, visitors are now advised to avoid the area.
A similar drop in seismicity was observed immediately before the March 2021 eruption.
If the volcano does erupt again, this would be considered a new eruption in the same place; the earlier eruption was declared over three months after the cessation of activity on 19 September 2021.
Update 28/12/2021
The earthquake swarm at Fagradalsfjall, Iceland, is continuing. While the swarm has slowed down a bit, 19,000 earthquakes have been recorded by the automatic SIL system since the swarm started. 14 earthquakes over 4.0 magnitude have occurred. An alert for the risk of rockfall and landslides in the area has been raised; visitors are advised to stay away from the area.
We have plotted the confirmed earthquakes from 20 December 2021 to 28 December 12:50. This shows the dike propagation south west of Geldingadalur, with additional activity near Kýsuvík and Svartsengi.
Only time will tell where and when lava will emerge. In the meantime, if you are lucky enough to be in the area, be aware of the risk of rock fall and landslip.
A large earthquake swarm started at Fagradalsfjall late on 21 December 2021, 2-4 km NE of Geldingadalir, thought to be caused by a lateral dike intrusion. Due to the increased seismic activity, the aviation code was raised to Orange yesterday, 22 December 2021.
Fig 1: Icelandic Met Office, IMO’s map of the swarm. Source: IMO
The eruption at Fagradalsfjall had stalled on 18 September 2021, with no new lava flows to the time of writing. Ground deformation indicated that magma was still flowing into the crust.
Fig 2: Ground deformation at Krýsuvík. The red line denotes the start of the March 2021 eruption. Source: IMO
We have downloaded and plotted the earthquakes from 1 September 2021 to 23 September 2021 (source for raw data: IMO ). This includes the swarm which started near Mount Kelir in late September 2021, which may or may not have heralded the current reactivation of the dike.
The alert level has been lowered to Yellow. To date no eruption has followed the jökulhlaup or increased seismicity. As Grímsvötn may erupt with little warning, the situation remains closely monitored.
The alert level for Grímsvötn has been raised to orange following the draining of the caldera lake over the past few days, the resulting jökulhlaup, and increased seismicity today.
Fig 2: Aviation codes for Icelandic Volcanoes. Grímsvötn is orange. Source: IMO
The ice-cap has subsided by c. 77 metres. The water drained via the Gígjukvísl river; the discharge in Gígjukvísl river yesterday around noon was 2800 m3/s, reducing later in the day.
Fig 3: Measurements of the jökulhlaup as it impacted the Gígjukvísl river. Source: Línurit (vedur.is)
At the time of writing, there have been 25 earthquakes in the last 48 hours in the vicinity of Grímsfjall. A magnitude 2.3 occurred at 06:15, followed shortly afterwards at 06:16 by a magnitude 3.6. There have been a few aftershocks. No volcanic tremor has been detected.
Fig 4: Map of earthquakes at Vatnajökull. Grímsfjall is roughly where the green star is; the green star is the location of the 3.6M earthquake. Source: Vatnajökull (vedur.is)
Volcanic eruptions have occurred after draining of the caldera lake in the past, attributed to the sudden decrease in pressure destabilising the system; IMO cite the 2004, 1934 and 1922 eruptions.
It has been a week since we updated our last earthquake plots for La Palma so time to take another look. The eruption has continued in the meantime, with seismicity and seismic signals increasing. Earthquake activity continues mainly within the two levels 7 -16km and 30 to 42km identified in our previous plots.
Several partial collapses of the main cone have occurred. The latest was yesterday, releasing a large amount of the lava to the west, which went over existing lava flows.
The latest statistics reported on 26th October 2021 are:
908.2 hectares of land have been affected by lava.
2,162 buildings haven been destroyed by lava, with a further 124 suffering damage.
66.2km of roads have been lost, with a further 3.4km damaged.
6,800 hectares of land have been covered by ashfall (reported 22nd October 2021).
Cost of lost banana plantations c.100m Euros, 150 hectares are under lava and others are in the exclusion zones; other crops, vineyards and livestock farming are also impacted.
SO2 emissions 40,800 tons per day. CO2 emissions up.
In the last 24 hours ground uplift of 10cm has been recorded at the station on the south of the volcano near the eruption site, which the volcanologists monitoring the eruption think may signal an increase in lava flow or the opening of a new vent.
Fig 2: Ground deformation at the station nearest the eruption site. We have circled the latest data point to make it easier to spot. Green line marks the onset of the eruption (added by IGN). Source: IGN
We have made geoscatter and scatter plots of the swarm from day 21, the onset of the deeper earthquakes. We have also made plots of the earthquakes over 3.0M, as these tend to get lost in the in the middle level swarm (7-16km).
There are now a few earthquakes between the two swarms but little in the way of reported earthquakes heading for the surface; the latter may mean that lava is flowing freely through the existing conduit, or that a new conduit may be in the offing. The hike in ground deformation reported above near the eruption site may indicate that whatever ensues, it is likely to be near the current eruption site – speculation on our part.
The eruption is now in its sixth week, lasting longer than recent previous eruptions, with no sign of waning. Has the initial eruption of magma created the right conditions for new magma to erupt from a greater depth, e.g. by creating a pathway for it and/or removing some of the constraining pressure? Only time, and a lot of research by the experts, will tell.
The eruption at Fagradalsfjall has halted. No lava has been erupted in the period 18 September to 18 October 2021 (or to the time of writing). The seismic swarm at Kelir has lessened. Gas emissions have decreased. The aviation code has therefore been lowered.
The eruption will not be declared over for some time. It is not possible to tell if this is a temporary lull or the eruption has ended; the eruption may resume at the same location in Fagradalsfjall or at a new fissure. As the authorities have pointed out, this can only be determined in retrospect.
The volcanic hazards are currently: gas, high temperatures both in the area and the lava field, earthquakes and rockfalls.
It’s been a few days since we looked at the latest earthquake swarm at Kelir, which is on-going. Here are the updated plots.
We are no longer updating this post; future updates will be included in new posts.
Update 2 12.10.2021: Plots of the Earthquake Swarm SSW of Mount Kelir, 27/09/2021 to Date
Fig 16: Mount Kelir, cropped from an image by Michal Klajban, published under CC BY-SA 4.0. Source: Wikimedia Commons
Mount Kelir is at the northern end of the earthquake swarm which started on 22 February 2021. In that swarm, earthquakes started near Mount Kelir and migrated towards and beyond Fagradalsfjall prior to the eruption at Geldingadalir on 19 March 2021.
The current swarm which started on 27 September 2021 near Mount Kelir is ongoing at the time of writing. Over 10,000 earthquakes have been recorded, of which IMO have confirmed c. 1,245. It is thought that an eruption may ensue near Mount Kelir.
We have plotted the earthquakes and made a video of the geoscatter and scatter plots.
Whether or not a new eruptive site emerges, magma migrates to the existing site at Fagradalsfjall, or, it all quietens down, only time will tell. At the moment the swarm is migrating SSW.
Source for raw earthquake data: Icelandic Met Office: IMO
12.10.2021 1: Update on La Palma Seismicity
Good Morning!
Let’s take look at status of the eruption and seismicity at La Palma.
The eruption is still going strong. The cone has grown substantially, despite partial collapses.
Fig 11: Cone growth. On the left, the new cone on 20 September, 2021, cropped from an image by Eduardo Robaina, published under CC BY-SA 3.0; on the right, screen shot earlier today from RTVC
The following was reported earlier today:
The lava reached the cement works, Callejón de la Gata, today. Local residents were confined to their homes due to the risk of toxic fumes from burning chemicals.
A large volume of lava was emitted after the wall of the lava lake [cone?] was destroyed.
The northern arm of the lava flow is now 300 metres from the sea and expected to make a new lava delta near the beach of Perdido.
591.1 hectares have been affected by lava. This includes 132 hectares of crops , of which 70 hectares were banana crops; 33 hectares vineyards; and, 8 hectares avocado crops.
The maximum width of the lava flow is 1,520 metres.
1,281 buildings have been impacted, of which 1,186 have been destroyed.
The lava delta is now 34 hectares.
Seismicity remains high. To date, over 35,000 earthquakes have been recorded. The most recent earthquakes remain below 10km, with depths reaching more than 20km.
The high level of seismicity is thought to indicate rising magma because there have been spasmodic tremors and a strong volcanic tremor at 18 Hz; the latter may be from depressurisation of magma at a depth of c. 10km. In the absence of increased ground deformation, it is not known when or how magma may reach the surface. If it reaches the surface, it may follow the current conduit or emerge at new fissures.
Fig 12: Amplitude of seismic signal, source: IGN. Green line denotes onset of the eruption.
04.10.2021: Update Fagradalsfjall Seismic Swarm near Kelir
The swarm near Mount Kelir is ongoing. IMO report that 6.200 earthquakes have occurred in the swarm, although c.624 have been confirmed at the time of writing (Sources: IMO_Earthquakes and Skjálfta-Lísa (vedur.is)).
We have analysed and plotted the swarm. It would appear that the swarm is ascending but still in the crust. The largest earthquake with a magnitude of 4.16 had a depth of 5.669 km.
Good Morning! Today we provide an update on Fagradalsfjall, Cumbre Vieja (with video of earthquake swarms) and Askja.
Fagradalsfjall, Iceland
Fig 1: Mount Kelir, cropped from an image by Michal Klajban, published under CC BY-SA 4.0. Source: Wikimedia Commons
Fagradalsfjall celebrated the six-month anniversary of the start of the eruption, which occurred on 19 March 2021, by taking a break. Low level activity has been observed since 18 September 2021.
An earthquake swarm stared on 27 September 2021 south of Mount Kelir. This is located near the northern end of the earthquake swarms earlier this year which preceded the eruption at Geldingadalir.
We have plotted the swarm to see what is going on.
While it is not clear what the cause of the swarm is (new magma or the crust adjusting to changes in tension), people are advised to avoid the area for the time being. If an eruption does occur near Kelir, it is expected to be similar to that at Fagradalsfjall. The aviation code is still orange.
Cumbre Vieja, Canary Islands
Fig 3: Cumbre Vieja eruption on 20/09/2021, cropped from an image by Eduardo Robaina, published under CC BY-SA 3.0. Source:Wikimedia Commons
The eruption is still going strong. The vents have produced ash columns, jetting lava and effusive lava flows.
Lava reached the sea, following the opening of a new vent earlier this week, which emitted more effusive lava. The lava travelled at 300 m/hr, crossing the coastal road and cascading over 100m high cliffs at Los Guirres. The lava is forming a delta, which has reached an impressive size 21 hectares.
There are now four eruptive vents: a new effusive vent opened 400m north of the main vent on Thursday; and, two more opened on Friday 15 metres apart and 600m north west of the main cone. Lava from Thursday’s new vent also made it to the sea via a flow parallel to the original one. A fumarolic field has developed on the north side of the main vent.
Over 80 million cubic metres of lava have been erupted. Sadly, this has damaged 1,005 buildings, of which 870 have been destroyed. 30.2km of road has been impacted, of which 27.7km have been destroyed. Ash now covers 3,172.9 hectares of land.
SO2 levels are higher but not considered a risk for the population at the moment.
Earthquakes are occurring near the area start of the swarm which preceded the eruption. They are deeper than the earlier swarm leading to concern that lava may be fed from a deeper reservoir. We have plotted the current swarm and previous swarms from 2017 to date.
Time to check out the current status of the volcanoes we have been following, especially as the situation has changed for some.
Askja
Fig 1: Image of Askja caldera by M Ryan, USGS, public domain.
Inflation, thought to be caused by a magma intrusion at a depth of 2km-3 km, started in early August. GPS data and satellite images detected uplift of 5cm per month; the uplift centred on the western edge of the Öskjuvatn caldera.
The aviation code was raised to yellow on 9 September 2021, following near vertical uplift of 7cm.
The epicentres of current earthquake swarm are mostly to the east of the Öskjuvatn caldera following a near linear route, starting at, or near, the area of maximum earthquake density for the period 1995 to 09.09.2021, and heading for the Viti explosion crater; seismic activity is on the opposite side from the area of maximum uplift.
Seismicity for 2021 looks pretty similar; the current swarm follows the pattern of earlier seismicity.
Fig 4a: Crater at Fagradalsfjall erupting on 14 September 2021.
The crater at fissure 5 has grown considerably since we last posted about it; it now dominates the surround hills. The eruption paused on 2nd September 2021, taking a well-earned break; steam and gas emissions continued. The eruption resumed a couple of days ago. The aviation code remains orange.
Fig 5: Merapi 2011 with Prambanan in the foreground, cropped from an image of Prambanan by Arabsalam, published under CC BY-SA 4.0. Source: Prambanan Java243. Prambanan is an 8th Century Hindu temple compound located approximately 17 kilometres (11 mi) northeast of the city of Yogyakarta and designated a UNECSO World Heritage Site.
Both lava domes situated below the south west caldera rim continue to grow, producing numerous pyroclastic flows and avalanches.
The alert level remains at thee and there is a 3km – 5km exclusion zone.
Grímsvötn
A jökulhlaup started on 1 September 2021 from the western Skaftlá caldera; the peak flow rate reached 520 m3/s on 2 September 2021. Warnings were issued of the hazard from H2S from water draining from the caldera lake. The ice-shelf had subsided 1m by 5 September 2021.
On 6 September 2021, the peak flow rate increased to 610 m3/s, thought to be due to a second release of water from the caldera lake – this time on the eastern side.
The aviation code remains at yellow.
Fig 6: Top image shows the water levels reached at Eldvatn and the lower one, flow rate. Source: IMO
La Soufrière St. Vincent
The last ash emissions were on 22 April 2021. Seismicity has since remained low. Gas and steam plumes have been observed rising from the crater.
The alert level remains at orange.
Mount Pelée
Volcano-tectonic earthquakes are still occurring in the edifice at depths between 0.2km to 1.2km. The area of discoloured, downgraded, burned and dead vegetation remains on the south west flanks.
At the end of July 2021 underwater gas emissions started between St Pierre and the Prêcheur. This will be investigated to ascertain how it links with the volcano.
The aviation code remains at yellow.
Mount Nyiragongo
The volcano is still active. A [gravitational] collapse in the crater caused and ash plume; ash reached Goma. Incandescence was seen on 26th July 2021 and a gas and ash plume emerged on 4th August 2021.
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
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.
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).
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.
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.
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.
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
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.
Updated earthquake density video added (uses satellite image as background). 12.04.2021
Good Morning!
Geldingadalur – Where Are We at Now?
Since we last wrote, the new volcano at Geldingadalur has continued to erupt with a lava output rate between 5 m3 per second and 10 m3 per second, filling the Geldingadalur valley with more lava. The University of Iceland has confirmed that the early lava erupted has a magnesium content of 8.5%, a low titanium dioxide content and is more depleted in rare earth elements (low HREE to LREE ratio) than earlier historic lavas, indicating that it is a more primitive lava sourced from the lithospheric mantle at a depth of between 17 km and 20 km.
On 5 April 2021 at around midday, a new fissure opened up about 700 m north east of the original eruption site. The fissure, spotted by a sightseeing helicopter, was quickly confirmed by the RUV.is webcam monitoring Geldingadalur. Fortunately, no-one was in the vicinity at the time due to bad weather and sheer good luck; the site had been open to visitors at the time. The fissure is around 200 m long. Lava from the fissure is flowing into the Meradalir valley.
Fig 1: New fissure on 05.04.2021 in the foreground with lava flowing to Meradalir on the left of the image. The original Geldingadalur eruption is on the right of the image. Photo IMO.
Fig 2: Lava from the first new fissure entering Meradalir at 15:00 06.04.2021. The fissure itself is on the ridge in the background (Photograph: Public Protection/Björn Oddsson).
At around midnight on 6 April 2021, a second fissure opened up between the earlier fissure and the original eruption site. This had been preceded by a landslip earlier in the day. Lava from this fissure is now flowing into both the Geldingadalur and Meradalir valleys, linking the eruption sites. It is believed that the three eruption sites belong to the same fissure.
Fig 3: Photograph from Public Protection/Björn Oddsson showing the three eruption sites and lava flows.
Fig 4: Map showing the location of the three eruption sites from IMO. The fissures are shown as red lines and dots; and, lava flows are based on photography.
Unfortunately, one of the webcams set up by mbl.is to monitor the Geldingadalur cones was lost; its last image is shown below. We thank mbl.is for providing the webcam; we viewed its images with a lot of interest.
Fig 5: Screenshot from the mbl.is webcam.is set up to monitor the cones at Geldingadalur. This may be this webcam’s last image. The lava flow to the lower left of the image is from the newest fissure.
Like the original eruption site, neither fissure opening was heralded by an increase in seismicity in the immediate vicinity.
Seismicity Post the Initial Eruption
We have updated our earthquake plots for the period 19.03.2021 to 06.04.2021. We can confirm that there is very little earthquake activity in the vicinity of Geldingadalur. The fissures are not giving any seismic warning; seismic activity near Keilir dominates. It is perhaps surprising that magma has not made its way to the surface north east of Fagradalsfjall; does magma finds it easier to make its way through older fault-ridden Pleistocene rock that has not been covered in tougher historic lavas?
We have also tried our hand at making a video of the earthquake density plots by month from 2008 to 6 April 2021. Months are numbered from January 2008 (Month 1) to April 2021 (Month 160, which only has 6 days). If you make it all the way through, you will see that Fagradalsfjall has had several swarms, albeit much smaller than the current one. Enjoy!
An Armchair Volcanologist 
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