An amateur volcanology enthusiast with an interest in volcanic and seismic activities, viewed from the comfort and safety of my armchair.
Meandered into this from using publicly available earthquake data to improve my Excel modelling skills. Then had to research the results both to understand and verify them. :)
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 have updated our earthquake plots to 19.10.2021 8:41:10. Since our previous update there has been more seismic activity, mainly between depths of 9-15km and 32- 42km. The former is consistent with the initial and subsequent stages of the swarm; the latter is consistent with the deeper earthquakes which started on day 21 (1.10.2021).
We’ve Googled around to see what’s likely to be going on at these depths. The 1585, 1949 and 1971 eruptions may shed some light on this. Researchers have found that the erupted lavas are formed by fractional crystallisation and stored in the upper mantle; during ascent, these lavas stall in the lower crust or near the Moho; there are no long-lived shallow magma reservoirs.
Fractional crystallisation is an indicator of the depths at which magma stalls in reservoirs. Earthquakes tend to occur around magma reservoirs or during the ascent of magma in response to the stresses on rock that changes in magma produce. Hence our interest in them.
The 1585 eruption produced 0.03km3 of lava, which was composed of basanites, tephrites, tephriphonolites and phonolite. The eruption is famous for the extrusion of phonolitic spines, named “Devil’s horns” by eye-witnesses, at the start of the eruption. Examination of the 1585 lavas indicate that the more evolved lavas were the result of fractional crystallisation. Magma differentiated at three levels: in the deeper mantle, c.20km depth, basanite evolved to tephrite 1550 to 1750 years, collecting in more than one reservoir, before the eruption; basanite also stagnated at the base of the crust, c.14km depth, to differentiate to tephrite; and, differentiation also occurred in the edifice. Further evolution of to tephriphonolite / phonolite may have occurred in the lower crust and upper crust. The basanite erupted may have originated from a different batch of magma than the erupted tephrite. 14km is the depth of the Moho under La Palma.
The 1949 eruption started on 24 June 1949 and ended on 30 July 1949. It had been preceded by weak seismic activity from 1936. Seismic activity picked up in February 1949, being felt mostly at the southern tip of the island and accompanied by ground cracking. Stronger seismicity and ground cracking immediately preceded the opening of the first vent. The primary melt was sourced at depths between 80-100km. Fractional crystallisation occurred at 20 to 26km with some possibly at 26-36km. Magma was stored temporarily in the crust before eruption. Magma mixing occurred in the mantle three months prior to eruption, causing a dike to propagate southwards. A 3km long fissure eruption started with the Duraznero crater emitting tephrite for 14 days. This was followed by the Llano Blanco crater opening to erupt tephrite for three days, followed by basanite for three days. The Hoyo Negra crater opened 4 days later to erupt basanite, tephrite and phonotephrite, during which the Llano Blanco crater continued to erupt basanite. The Duraznero crater then erupted basanite. The eruption started on 24 June 1949 and ended on 30 July 1949. The primary melt was sourced at depths between 80-100km. Fractional crystallisation occurred at 15 to 26km with some possibly at 36km. Magma mixing occurred in the mantle three months prior to eruption, causing a dike to propagate southwards. Magma was stored temporarily in the crust between 7-14km before eruption. Later calculations put the depth of fractional crystallisation at 35-45km.
In 1971 Cumbre Vieja erupted again, this time at Teneguía, emitting 135,000 m2 of lava and created a 290,000 m2 lava platform – 40 million m3 of lava in total. This eruption produced basanitic to phonolitic lavas. The eruption was Strombolian and in two phases: initially a 300m fissure opened on 26th October 1971, producing effusive lava flows from vents; and, new vents opened on 8th November 1971, with rhythmic explosions, lapilli, scoria and lava bombs. CO and CO2 were emitted; these gases were thought to be the cause of death for the eruptions two fatalities. Examination of the lavas showed that magma stalled at two depths: clinopyroxene and plagioclase crystallised at depths of 20-45km; and the crystallisation of aluminium augite indicated that magma then ascended to 20-35km. Variations in the samples tested indicates that magma formed in batches over a range of depths in the lithospheric mantle to combine before ascent.
Taburíente, Cumbre Nueva and Bejenado each have zones of clinopyroxene crystallisation between 25-45km. Earlier Cumbre Vieja eruptions had shallower zones of 15-30km, before the deeper zones of the 1949 and 1971 eruptions (35-45km and 25-45km, resp.). In the earlier Cumbre Vieja eruptions magma stalled beneath the Moho and the in the later eruptions magmas depths were more in line with Taburíente, Cumbre Nueva and Bejenado.
How does this Compare to the Current Earthquakes?
To make any conclusions we need to wait until there is a detailed analysis of the erupted lavas. However, we can note that the current earthquakes are at two distinct depth ranges: 7 -16km and 30 to 42km, with not much in between. 7-16km correlates to a possible zone of magma storage beneath the crust and magma migration through the crust. 30 to 42km correlates to part of the lower zone of fractional crystallisation of the 1949 and 1971 magmas.
Time will tell how this eruption will pan out. In the meantime, the eruption is still going strong. Our thoughts continue to be with those affected.
Kursten Galipp, Andreas Klügel, Thor Hansteen, “Changing depths of magma fractionation and stagnation during the evolution of an oceanic island volcano: La Palma (Canary Islands)”, Journal of Volcanology and Geothermal Research Volume 155, Issues 3–4, 15 July 2006, Pages 285-306. Link: Source
T. S. Johansen F. Hauff K. Hoernle , A. Klügel, T.F. Kokfelt, “Basanite to phonolite differentiation within 1550–1750 yr: U-Th-Ra isotopic evidence from the A.D. 1585 eruption on La Palma, Canary Islands”, Geology; November 2005; v. 33; no. 11; p. 897–900. Link: Source
Andreas Klügel , Kaj A. Hoernle, Hans-Ulrich Schminck , James D. L. White, “The chemically zoned 1949 eruption on La Palma (Canary Islands): Petrologic evolution and magma supply dynamics of a rift zone eruption”, Journal of Geophysical Research, Vol 105, No. B3, Pages 5997-6016. Link: Source
Abigail K. Barker, Valentin R. Troll, Juan Carlos Carracedo, Peter A. Nicholls, “The magma plumbing system for the 1971 Teneguía eruption on La Palma, Canary Islands”, Contributions to Mineralogy and Petrology 170, Article number: 54 (2015). Link: Source
The eruption at La Palma is continuing unabated, sadly with more evacuations for areas in the path of the lava.
Let’s take a moment to look at her fellow island, El Hierro. La Palma and El Hierro occupy the same N-S line at the western end of the Canary Island archipelago: La Palma to the north and El Hierro to the south. El Hierro experienced a N-S aligned fissure eruption between October 2011 and March 2012.
Fig 1: La Restinga as seen from the harbour wall. Image captured from Google Maps, 2021.
Background
El Hierro is a shield volcanic island which formed around 1.2 million years ago. It is made up of three volcanoes, Tiñor, El Golfo, and, later rift volcanism.
The island has a population of c. 10,000. The capital is Valverde, located near the eastern end of the island. The earliest known inhabitants were the Bimbaches, thought to be descendants of the Guanches who had migrated from Tenerife. Sadly, many of the Bimbaches were sold as slaves by the son of the first Spanish conquistador. The island was then populated by both the Spanish and Normans. Some the slaves were later returned to the island having won their freedom.
The island’s climate is influenced by the Trade Winds. Warm moist air is deposited on the northern side of the island. The climate varies from warm-summer Mediterranean climate in the centre of the island, to mild semi-arid and to a tropical mild, desert climate on the coasts.
The island, home to endemic species such as the endangered El Hierro giant lizard, has been designated as a Biosphere by UNESCO to preserve its natural and cultural diversity.
Fig 2: The island of El Hierro. Image captured from Google Maps, 2021. El Golfo, El Julan, Las Playas and Tiñor added by the author. The embayment of El Golfo can be seen as the cliffs encircling La Frontera.
Tiñor was the first subaerial volcano to emerge, comprising primitive basalts to trachybasalts and tephrites. It is dated between 1.2 – 0.88 million years old, having developed rapidly in the Lower and Middle Pleistocene. It has three units: the lowest unit with steep sides and thin steep-dipping lava flows; a middle unit of thicker lavas; and, an uppermost unit, the Ventejis Group, with craters After the emergence of the Ventejis Group, the north western flank of Tiñor suffered a large gravitational collapse which may have taken out more than half of the Tiñor edifice.
The El Golfo volcano emerged c. 545,000 years ago, located near the current town of Frontera. This volcano has two identifiable layers: a lower unit made up of basalt Strombolian and Surtseyan pyroclasts with dykes implying the presence a triple rift system; and, the upper unit made of lava flows, overlain with trachybasalts and trachyte lava flows and block-ash deposits. The youngest lavas are the trachyte, aged at c. 176,000 years. Gravitational collapse of the southwestern flank of the volcano occurred at El Julan.
The San Andrés fault system on the north east rift developed between 545,000 -176,000 years ago. The presence of cataclasites and pseudotachylytes, rocks typically found in the early stages of volcanic collapse indicate that there was incipient gravitational collapse that did not develop further. Cataclasites are formed through faulting or fracturing in the upper crust. Pseudotachylytes may be formed by frictional melting of the wall rocks during rapid fault movement during an earthquake.
The impressive El Golfo embayment resulted from gravitational collapse of the El Golfo volcano. This may have occurred in a single or multiple events. One possible is scenarios is that an initial subaerial lateral collapse of the volcanic edifice occurred 130,000 years ago and a second one occurred 17,000 – 9,000 years ago affecting the submarine lava platform.
Rift volcanism, defined as when the three arms of the rift were active at the same time without a central vent, occurs along the three arms of the island, with vents occur along the ridges of the rifts. Before the 2011-2012 eruption, rift volcanism had been dated to between 134,000 years ago to 500BC. GVP lists 6 eruptions prior to the 2011-2012 eruption: 3 confirmed in 550BC, 950BC and 4790 BC; and, 3 unconfirmed in 1793, 1692 and 1677. The associated lavas are alkaline picro-basalts, basanites and tephrites.
2011 -2012 Submarine Eruption
Fig 3: Stain from the submarine eruption south of the island. Image cropped from NASA Earth Observatory EOSDIS on 10 February 2012. Source: El Hierro Submarine Eruption (nasa.gov). “El Julan” and the “Eruptive vent” added by the autho
In 2011 a submarine flank eruption commenced, preceded by an intense seismic swarm. The submarine cone has been named Tagoro, from the Guanche language for meeting place or circular enclosure of stones.
Build up to the eruption
Before the eruption, El Hierro had been quiet since a seismic episode in 1793, which may or may not have been connected to an eruption. In the absence of eye-witness accounts then, it has been suggested that there was an eruption of Lomo Negro volcano, a submarine eruption or a magma intrusion.
Fig 4: Crater of Tanganasoga. Image cropped from one by Areuland, 5th January 2017. published under CC BY-SA 4.0. Source: Wikipedia
In July 2011, a seismic swarm started under El Golfo at a depth of 20-25km. Seismicity then ascended to 11±3km and headed southward across the island, after which it ascended to 3km between 8-9 October prior to the eruption on 10 October 2011. A 4.4M earthquake at a depth of 10km 1.5km south of La Restinga preceded the eruption. Magma had risen under Tanganasoga, the main volcano on El Hierro, to migrate south towards La Restinga.
Basanite fractionation and magma replenishment may have occurred during these seismic swarms while magma was being injected into the lower crust.
The eruption
The eruption occurred in phases.The lavas in the first phase were evolved basanites. The second phase was more primitive lava with 8-9 wt% MgO.
A harmonic tremor started on 10 October 2011 between 04:15 and 04:20 and is thought to indicate the start of the eruption. Magma had risen from the base of the ocean crust to the vent in c. 30 hours. Areas of discoloured, sulphurous-smelling water and dead fish were seen off the coast of La Restinga. Vigorous bubbling in the sea resembling a jacuzzi was observed above the vent, caused by gas emissions and heat from the vent; bubbling reached several metres high on occasion.
On 15 October 2011, lava bombs were observed. These comprised white to grey pumice encased in black basanite lava. Basanites are typical of the western Canary Islands. A small amount of U-depleted rhyolite was found in the lava bombs, though to have originated from differentiated trachyte incorporating quartz-rich sediment during melting when mobilised by the basanite. The boundary between old oceanic crust, continental crust and volcanic island may act as a magma trap where sediments can be assimilated. A few days later basanite lava balloons were emitted.
The second phase of the eruption started in November 2011 with seismicity at depths of 10-15km and a decrease in tremor intensity. This correlated with the eruption of more primitive lavas.
During November 2011, the eruption was confirmed as Surtseyan. Several plumes of material aligned N-S were visible from the air, confirming a fissure eruption. Tanganasoga experienced rapid inflation and released CO2. On 24th November a sulphur smell was reported in El Golfo. On 4th December 2011, vigorous phreatic bubbling (“the jacuzzi”) was observed. In December 2011, there was a temporary lull: the harmonic tremor and seismicity decreased.
The eruption picked up again in January 2012 with increased seismicity, a larger area of eruption and pumice clasts. In late February 2012, seismic activity, deformation and gas emissions decreased. The eruption was declared over in March 2012.
Tagoro’s cone was found to be 85m below sea level in April 2012. The eruption has been classified as a VEI 2.
Post eruption
Magma movements were detected from seismic swarms. In June 2012,accompanied by rapid inflation, magma moved south-westward towards El Julan-La Dehesa, northwest of the submarine vent. Earthquakes picked up again in September 2012 indicating magma movement under Tanganasoga.
The last reported seismicity was in March 2013 when another swarm occurred near the NW tip of the island, initially at 20km depth, migrating westward at a depth of 12-15km. The swarm was accompanied by inflation and CO2 emissions.
Plotting Seismicity
We have downloaded the earthquake data from IGN’s publicly available database and plotted the earthquake swarms for the period July 2011 to December 2012. The results are shown in the video below.
Only time, and a lot of work by the various scientists studying the eruption on La Palma, will tell how many similarities are shared between the two eruptions.
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.
Our thoughts are with those impacted by the eruption. While no lives have been lost, the economic damage and personal impact could be huge.
The official source for updates is IGN. You can find them on Twitter at IGN-CNIG @IGNSpain.
Update 27.09.2021
Fig 10: The volcano taking a short break this morning, looking deceptively tranquil. The main cone is in the centre of the image. Source: screen shot from TV Canarias: www.youtube.com
The eruption is now in its ninth day. The volcano took a break for a couple of hours today, to resume with a thick ash column and a few explosions. The new seismic swarm today may indicate that the volcano is recharging. It would be unusual for an eruption here to be so short.
The airport was closed for a period over the weekend while ash was cleared.
The cone broke in its southern section releasing a new lava which flowed over the older flow. The new lava reached speeds of 250 – 300 metres per second. Sadly, the church and other buildings in Todoque were razed.
Lava may now reach the sea. It is now between 800m and 1,000m from the sea, reaching the outskirts of Tazacorte. People in San Borondón, Marina Alta, Marina Baja and La Condesa are confined to their homes with their doors and windows closed due to the risk of ash and gases. We can only imagine the stress they are under right now.
There have been up to 4 eruptive centres and two lava flows. New emission points emerged in the NE section of the cone; they have since merged.
On 26 September 2021, the lava covered an area of 2.62 km2, with an average thickness of 12.1 metres a maximum thickness of 50 metres and a volume of 31 million cubic metres. The latest estimate of damage at the time of writing is that over 500 homes and 237.5 hectares of land are now covered by lava. 18.9 km of roads have been destroyed. 1,507 hectares of land are covered by ash.
The Ramón Margalef is to carry out a survey of the sea floor to check for submarine emissions.
The explosive phase, combined with the opening of new vents on the south west of the cone, has led to the evacuation of Tajuya, Tacande de Arriba and Tacande de Abaja.
The total number of evacuated is now 6,200.
Large pyroclastic materials are being ejected, and highly fluid lava with speeds of 60-80m/s is being discharged from the new vents.
There are fears that the main cone may collapse as a result of new vents and more explosions. This would lead to high-speed pyroclastic flows. You cannot outrun a pyroclastic flow.
The eruption column reaches 6km above sea level.
Although airspace is still open, Iberia, CanaryFly and Binter have suspended flights to / from La Palma, and Vueling has cancelled its Saturday flight from Barcelona to La Palma.
The Roque de los Muchachos Observatory has closed its telescopes to protect the mirrors from ash; it is still monitoring the gas and ash clouds from the volcano.
Lava covers 190 hectares; 420 buildings and 15.2 km of roads have been lost.
The area impacted by the volcano to be formally been declared a disaster zone.
It is thought that the older lava flows are slow due to the gradients they are on; they may speed up if they hit a higher gradient.
The eruptive style has changed from effusive to more explosive: of the two lava flows, the northern flow has nearly stopped and the southern is c.2,100 metres from the sea, advancing at 4 metres per hour having fanned out. It is now thought that it is unlikely that lava will reach the sea. IGN have reported several large explosions.
The aviation code for La Palma has been raised from orange to red, due to gas and ash. Airspace remains open except for two restricted areas. Airlines are advised to get flight plans checked before planes depart.
2 more fissures have opened since our previous update.
Ground uplift is now c. 24cm.
26 million cubic metres of lava have been emitted, razing 220 hectares of land and covering 180.1 hectares. The northern flow is 12m thick at the front and the southern flow, 10m thick.
390 properties and 14km of roads have been destroyed.
Banana harvesting has been suspended in the area to allow people to collect their belongings.
Farmers in restricted areas require permission from PEVOLCA to irrigate their crops.
More than 6,000 people have been evacuated to date.
The Official College of Psychology of Santa Cruz de Tenerife has reminded us that those losing property to the eruption are suffering trauma; they are not helped by seeing images of this repeated multiple times on social media.
Sources: El Mundo (link below) & IGN-CNIG (link above)
We have updated our earthquake plots for the current swarm. We have put them together in a short video.
Air traffic is not affected; the airport remains open. Visitors are encouraged to the island.
166 homes have been confirmed as lost. More than 6,000 have now been evacuated.
Land covered by lava will not be cultivatable; to date, 103 hectares of land are covered. Contaminated soil may take 20 years or more to be usable. Loss of land is expected to cause considerable poverty.
Lava is approaching the Todoque in Los Llanos de Aridane.
Several roads are closed in the vicinity of the eruption: LP-211, LP-212, LP-213, LP-215 and LP-2.
At the time of writing lava has not been reported as reaching the sea. When it does, clouds of toxic and acid vapours, including chlorine, sulphur, carbon and hydrogen sulphides, hydrochloric acid, carbonic acid and CO2, will be released, forcing further evacuations.
SO2 emissions reached between 7,997 – 10,665 tons per day on the second day. SO2 emissions have reached the cost of Africa.
It is too early to say how long the eruption will last. The 1971 Teneguía eruption lasted 24 days and the 1949 Cumbre Vieja eruption lasted 33 days.
20.09.2021
No lives have been lost or injuries reported.
The airport remains open. Air traffic is not currently affected.
2 fissures had opened 200m apart, with 8 vents.
The temperature of the lava is over 1,000°C (last reported: 1,113°C).
The ground is continuing to inflate; more earthquakes are possible.
The south west coast of the island is at risk of landslides and rock falls.
The lava discharge rate is 0.7km per hour. The lava is expected to reach the ocean at c.8:00pm (has not happened yet; the lava slowed and diverted). When the lava reaches the ocean, toxic vapours will be released due to the chemical reactions between the hot lava and sea water; the areas impacted would be Tazacorte, near Playa Nueva, Los Guirres.
Between 6,000 and 9,000 tons per day of SO2 were emitted on the first day.
5,500 people evacuated.
A 3.8M earthquake signalled the opening of a new vent (the 10th) 900m from the main vent. The new stream of lava led to the evacuation of Tacando.
An earthquake swarm which started on 11 September 2021, accompanied by uplift, resulted in PEVOLCA raising the alert level for La Palma to yellow on 13 September 2021.
The eruption, itself, started on 19 September 2021 at 2:15pm (UTC) in Cabeza de Vaca, El Paso; the alert level is now red. c.5,000 people have been evacuated. To date, no lives have been reported as lost, property damage is yet to be assessed. Our thoughts are with those affected.
Fig 1b: Displacement and ground deformation measured pre-eruption. On the left, displacement is for the period 10/09/2021 and on the right, deformation is for the period June 2021 to September 2021 (to date). Source: IGN (link below).
At the time of writing, there are lava fountains and a large lava flow that is threatening people’s homes.
La Palma is a volcanic island with an area of 708 km2, located at the northwest end of the Canary Island archipelago above the Canary Island hotspot. The population of the island is c85,840; 15,720 live in the capital Santa Cruz de la Palma and 20,470 in Los Llanos de Aridane. The climate is tropical semi-arid. Its economy relies on agriculture and tourism; banana cultivation is centred in the valley of Los Llanos de Aridane; and, other crops include oranges, avocados and grapes. Fishermen operate from Tazacorte, Puerto Naos and Santa Cruz de la Palma. The island has abundant flora and fauna.
The island is comprised of many volcanoes, including an extinct Pliocene – Pleistocene northern shield volcano and the active Pleistocene – Holocene Cumbre Vieja. Cumber Vieja is the most active volcano in the Canary Islands, last erupting in 1971.
The northern shield lavas comprise basanites, alkali basalts, tephrites, phonolites and trachytes, reflecting magma evolution during the shield-building stage. The younger Cumbre Vieja volcano has more basaltic lavas.
Fig 3: Caldera de Taburiente, Bejenado and Cumbre Vieja. Source: Google Earth
Building the Island
The island emerged in five stages: the initial submarine-building of a seamount, followed by the creation of four volcanoes during the shield-building stage, as shown below.
Time scale
Volcano
Lavas
Pliocene
Sea-mount
Basalt, trachybasalt, phonolite, trachyte
1.7Ma -1.2Ma
Garafía
Basalt
1.2Ma – 0.4Ma
Taburiente
Basalt, tephrite, phonolite
0.56-0.49ka
Bejenado
Basalt, tephrite, phonolite
125ka-present
Cumbre Vieja
Basalt, basanite, trachyte, phonolite
Garafía is covered by the later Taburiente volcano; its rocks being visible only in a few outcrops. Around 1.2Ma gravitational collapse of its southern flank left debris avalanche deposits in the sea.
Activity at Taburiente volcano commenced without a break following the collapse at Garafía. Its growth included the development of triple rift zones – parallel swarms of dikes at c 120° angles, indicative of magma doming. Activity then migrated southwards.
A landslide, clearly visible on maps, occurred between the building of Taburiente and Bejenado, and was responsible for the creation of the Caldera de Taburiente. Bejendo volcano is a small volcano that emerged to fill the collapse embayment. Subsequent erosion enlarged the caldera.
Cumbre Vieja emerged after activity had ceased in the north. From c. 125,000 years ago, volcanic activity built the north-south ridge until 80,000 – 20,000 years ago when activity declined. From 20,000 – 8,000 years ago activity picked up again, focusing on the north-south rift and also north-west and north-east rifts. Activity now focuses on the north-south rift. There is concern that another flank collapse could occur following the emergence of west facing normal faults during the 1949 eruption.
Eruptive History
GVP records 13 Holocene eruptions for La Palma, seven of which were VEI 2s, with mild explosive activity and lava flows that caused property damage (the remaining 6 have not been assigned a VEI number). Eruptions during the last 7,000 years have formed cinder cones and craters along the north – south axis of Cumber Vieja. Lava flows reached the sea in 1585, 1646, 1677-78, 1712, 1949, and 1971; a large lava field emplaced during the 1677-78 eruption covers the southern tip of the island.
GVP lists the lava types as Trachybasalt / Tephrite Basanite, Phono-tephrite / Tephri-phonolite, Phonolite, Basalt / Picro-Basalt, Trachyte / Trachydacite.
Seismic Activity
The current swarm was preceded by others: one in 2017, one in 2018, five in 2020, and three in 2021. The earthquakes in the previous swarms were deeper, between 20 and 30 km, and were less intense than the current swarm.
We have downloaded the earthquake data from IGN for 2021 to 19.09.2021 11:09 to see what has been going on. While these are only the earthquakes that have been located (there are thousands that have not), the plots clearly indicate magma ascent.
We do not have a precise location for the vents of the current eruption so are unable to compare it to the earthquake plots.
If you wish to follow the eruption as it progresses, IGN has up to date information on the eruption at La Palma on: Instituto Geográfico Nacional (ign.es).
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.
Our thoughts are with Haiti. Tragically, on 14 August 2021 at 8:29am (local time), a shallow (10km) earthquake of 7.2M occurred on the South West peninsula of Haiti 13 kilometres southeast of Petit Troup de Nippes. The earthquake was felt across the region, including Haiti, Dominican Republic, Jamaica, Cuba, and Puerto Rico. Over one million people may have been exposed to very strong or severe shaking.
A one-month state of emergency has been declared for Haiti. As of 16 August 2021, 1,419 are believed to have lost their lives, more than 6,000 injured and many thousands displaced. Tropical Depression Grace is likely to pass over the stricken area at the time of writing, bringing with it the risk of heavy rains, flooding, landslides and further loss of life.
Aftershocks are occurring, and may do so for some time. There is a small risk that this event is a foreshock to another event.
Haiti is located on the western side island of Hispaniola in the Greater Antilles Archipelago; the Dominican Republic occupies the eastern side of the island. Two large fault zones cross the island: the Septentrional-Orient fault in the north and the Enriquillo-Plantain Garden Fault Zone in the south.
Fig 2: Cropped image from one digitally altered by Mikenorton of the Gonâve Microplate (plate boundaries, main faults, islands and plates were added). Source: Gonâve microplate.
Hispaniola was formed from the collision of volcanic arcs with the North American Plate; the island is made up of 11 former island arcs. Haiti has an estimated population of 11.4 million (2018). The country is poor, politically unstable and yet to recover from the 2010 earthquake.
While the island has a volcanic past, there has not been any reported volcanic activity in the Holocene. There are two Pleistocene volcanoes in Haiti, the nepheline basalt scoria cones of Morne la Vigie, north of Port au Prince, and Thomazeau, east north east of Port-au-Prince, both of which were active around 1.5 million years ago; and, three in the Dominican Republic, the basaltic cinder cones of San Juan, trachyandesite lava domes and flows of the Dos Hermanos volcanic field and the rhyolitic to basalt Valle Nuevo volcanic field. The presence of picrite in the Duarte Complex in central Hispaniola and enriched basalts in southern Haiti are thought to be indicative of earlier hotspot activity
Tektites have been found in the Beloc Formation, Haiti, which are thought to have originated from the asteroid impact in Yucatán Peninsula, Mexico, which caused the K-Pg mass extinction event 66 million years ago.
2021 7.2 M Earthquake
The earthquake occurred in the Enriquillo-Plantain Garden Fault zone on the transform plate boundary between the Caribbean Plate and the North American Plate. The faulting mechanism for this earthquake indicates oblique thrust faulting along the fault zone. This fault zone accommodates 7mm per year of the 20mm per year of the relative plate motion. It is likely that this earthquake occurred in the same fault system as the devastating January 2010 7.0M earthquake which occurred near Port-au-Prince, the capital.
According to the DEC, the January 2010 earthquake not only caused significant loss of life and damage but also severally impacted Haiti’s government and infrastructure: 25% civil servants died, 60% government buildings, 80% schools in Port-au-Prince and 60% schools in the South and West departments were destroyed. In all, over 220,000 were killed, more than 300,000 injured and around 300,000 homes damaged or destroyed.
USGS note that four other large earthquakes are known to have occurred in the region: October 1751 in the Gulf of Azua at the eastern end of the Enriquillo-Plantain Garden fault zone; November 1751 at Plaine du Cul-de-Sac which destroyed Port-au-Prince; June 1770 which also destroyed Port-au-Prince; and, April 1860 which also caused a tsunami.
It is expected that there will be a request for international aid. If you wish to help / donate to the aid effort, refer to your favourite international aid agency, in the first instance.
Today we are taking a trip to Java, Indonesia, away from the gentle effusive eruption at Fagradalsfjall, Iceland, and what looks like the growth of a shield volcano, to the more explosive activity at the subduction zone between the Indo-Australian Plate and the Sunda Plate, focussing on Gunung Merapi.
Merapi has been erupting since the start of the year, with the growth of two lava domes, block and ash falls and pyroclastic flows generated from partial collapses of the lave domes. The current alert level is 3 (Siaga) and the aviation code is orange. (Siaga translates as, using Google Translate, “Stand By” (There was a significant increase in volcanic activity. Eruption is most likely to occur and the area of potential eruption hazard is in the area of Disaster-Prone Areas (KRB) II. The community is prohibited from carrying out activities in the KRB II area). The exclusion zone extends 5km from the summit).
Fig 1: 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.
Background
Merapi is a 2,968 m high stratovolcano located 25 km north of the city of Yogyakarta on the island of Java, Indonesia. Volcanic activity at Merapi is believed to have started around 170,000 years ago. Since then, activity alternated between effusive and explosive, the latter with lava domes and pyroclastic flows. While her eruptions are comparatively modest (VEI 1 to 4), her proximity to a large metropolis means she has the potential to do a lot of damage, hence her status as a Decade Volcano. Over 4 million people live within 30 km of the volcano and over 24 million people live within 100 km of the volcano.
Yogyakarta, itself, is a densely populated city in the Special Region of Yogyakarta. 373,589 people live in the city (Census 2020) and over 4 million in the metropolitan area. It is a sophisticated centre for Javanese fine arts, culture and education. Yogyakarta has been home to the seat of power for the Medang Kingdom between the 8th and 10th century and Mataram Sultanate between 1587 and 1755. Explosive eruptions from Merapi, which destroyed many Buddhist and Hindu temples built between 732 AD and 900 AD (and presumably caused other significant damage), may have been a factor in the migration of the Mataram Kingdom to East Java in 928 AD or 929 AD.
Tectonic Setting
Volcanic activity on Java is driven by the northward subduction of the Australian Plate under the Sunda Plate at the Sunda Trench. The western, southern and eastern boundaries of the Sunda Plate are tectonically very active.
We downloaded earthquake data from EMSC for the period October 2004 to July 2021 between 14.04°S 86.16°E to 12.66°N 127.48°E to take a look. This area is larger than the area under discussion to make sure that subduction zone was captured. The following images are from extracts of that data.
Merapi is located at the intersection of two volcanic lineaments: the north – south trending Ungaran-Telomoyo-Merbabu-Merapi; and the east – west trending Lawu – Merapi – Sumbing – Sindoro – Slamet. Ungaran-Telomoyo-Merbabu-Merapi is a double chain volcanic arc, with Ungaran as the back arc and Telomoyo-Merbabu-Merapi as the trench side volcanoes. Merapi is also bounded by two faults: the north – south Merapi – Merbabu fault and the Baribis – Semarang – Kendeng fault.
Merapi formed in the late Pleistocene and Holocene in three stages: Proto-Merapi, Old Merapi and New Merapi.
Proto-Merapi emerged after 170 ka and includes Gunung Bibi, dated to 190 ± 60 ka, Gunung Turgo, 138 ± 3 ka, and Gunung Plawangan ,135 ± 3 ka.
Gunung Plawangan was home to a volcano observatory until the 1990s but was abandoned due to nuée ardentes from the current cone.
The summit of Gunung Turgo is home to sacred graves including that of Sheikh Jumadil Qubro, a direct descendant of the Islamic prophet, Muhammad.
Old Merapi started to grow around 30 ka, reaching a height slightly more than the current cone; growth ended with flank failures 4.8 ± 1.5 ka. Collapse of the caldera with debris avalanche flows to the south and west left a Somma rim on the eastern slope.
Gunung Batulawang and Gunung Kendil are part of Somma – Merapi. Gunung Batulawang is the highest peak of Old Merapi. Lake Borobudur formed c 3,400 14C years BP.
The latest Somma collapse was around 1,900 14C years BP.
New Merapi, the current cone, grew soon after the growth of Old Merapi ended. Partial edifice collapse of New Merapi may have occurred 1,130 ± 50 14C years BP.
Gunung Selokopo Ngisor, Gunung Pusunglondon, Gunung Patukalapalap, Gunung Dengkeng, Gungung Selokopo Duwur and Gunung Gadjah Mungkur are hills which are thought to belong to New Merapi.
Volcanic Activity
Merapi’s lavas are typical for a subduction zone, being andesite / basaltic andesite, trachyandesite, basaltic trachyandesite with some basalt / picro basalt and trachybasalt / tephrite basanite. Her lavas have evolved over time. Her early lavas were effusive basaltic. The K2O content of the lava has increased over time; Old Merapi had lower K2O lavas than New Merapi and nearby Gunung Telomoyo and Gunung Merbabu.
According to GVP, there have been 111 Holocene eruptions, ranging from VEI 1 to 4. The most recent eruption, currently a VEI 1, started on 31 December 2020, with new lava domes extruded in January and February 2021, and, at the time of writing is ongoing. The most recent VEI 4 was the devastating October 2010 to July 2012 eruption in which partial dome collapse caused pyroclastic flows that destroyed villages, led to the evacuation of more than 300,000 people and caused 386 fatalities; the ash plume reached 18km between 4-6 November; and, the largest pyroclastic flows occurred on 26 October 2010 and 5 November 2010 – the latter produced the widest pyroclastic flow seen in Indonesia for 100 years. By mid-November, eruptive activity subsided, to be followed by lahars as the main hazard.
The 26 October eruption started 19 hours after tsunamis caused by earthquakes on the Sunda Trench swept away villages on the Mentawai Islands, killing 428 people and displacing thousands. The earthquakes were a 7.7 M, preceded by a 5.8 M and followed by aftershocks that included a 6.1 M and 6.2 M. Whether or not the earthquakes triggered the eruption, itself, is open to debate; the volcano was ready to erupt. Since 2007 swarms of volcanic earthquakes had been occurring; deformation and gas emissions increased in September 2010; and, seismicity increased between 15 – 26 October, ramping up during 20 – 26 October. The alert levels were raised to level 2 on 20 September 2010, level 3 on 21 October 2020 and level 4 on 25 October 2020.
A phreatic eruption on 11 May 2018, heralded a new phase of lava dome growth. In November 2020, evacuations were ordered due to decreasing stability of the lava dome. Eruptions commenced on 4 January 2021, leading to further evacuations in the Yogyakarta region.
Here’s hoping the current eruption remains a VEI 1.
The Smithsonian Institution’s Global Volcanism Program (GVP): Merapi
Ralf Gertisser, Silvain J. Charbonnier, Jörg Keller, Xavier Quidelleur, “The geological evolution of Merapi volcano, Central Java, Indonesia”, Bulletin of Volcanology (2012) 74: 1213=1233. DOI: 10.1007/s00445-012-0591-3
Newhall, C. G., Bronto, S., Alloway, B., Banks, N. G., Bahar, I., del Marmol, M. A., Hadisantono, R. D., Holcomb, R. T., McGeehin, J., Miksic, J. N., Rubin, M., Sayudi, S. D., Sukhyar, R., Andreastuti, S., Tilling, R. I., Torley, R., Trimble, D., Wirakusumah, A. D., “10,000 Years of explosive eruptions of Merapi Volcano, Central Java: archaeological and modern implications”, Journal of Volcanology and Geothermal Research 100 (2000) 9 – 50. DOI:10.1016/S0377-0273(00)00132-3
The recent eruption Mount Nyiragongo has taken us away from Iceland and the ongoing eruption at Geldingadalur, Fagradalsfjall, Iceland, to look at the East African Rift System. Unlike the current benign eruption in Iceland, there are 32 known fatalities from Mount Nyiragongo’s eruption, 3,629 homes and buildings destroyed, more than 20,000 displaced, many unaccounted for and several hundred thousand evacuated from parts of Goma to Sake. The current alert status for the volcano is orange. Our thoughts are with all those affected by the eruption.
As we refer to different lavas in more detail than originally anticipated, we will explain them in future posts; please bear with us for the moment.
Fig 1: Photo of Mount Nyiragongo by B. Martinelli, 1994 (courtesy of Jack Lockwood, U.S. Geological Survey) (left) and screenshot of the Nyiragongo crater with lava lake pre 2021 eruption from Google Maps (right).
It has been reported that the volcano had not been fully monitored for several months due to lack of funding for the Goma Volcano Observatory. Monitoring improved in May 2021 when an American partner helped to get the internet connection to seismometers restored. This, and the ensuing eruption, must have been worrying times for the Observatory.
2021 Eruption
Run Up to the 2021 Eruption
Reports on GVP for Mount Nyiragongo note that strong thermal anomalies and gas emissions were observed in the period June 2018 to May 2020, along with incandescence, seismicity and gas / steam plumes.
In the period from June 2020 to November 2020, daily thermal activity was observed, indicating the presence of a large lava lake; levels of SO2 emissions fluctuated during the period.
Eruption May 2021
Mount Nyiragongo erupted on 22 May 2021 at around 18:15 local time, sending torrents of low viscosity lava down the side of the volcano, reaching as far as the outskirts of Goma. The following account of the eruption is summarised from bulletins on GVP.
The crater lava lake drained followed by the opening of at least two fissures on the south flank of the volcano. The first fissure’s lava originated near the Shaheru crater flowing eastwards over a main road; lava flows from the second fissure reached villages north of Goma destroying around 3,629 homes and buildings, displacing 20,000 to 25,000 people, and cutting off electricity and water supplies to parts of the city. Ash plumes, caused by collapse in the summit crater, rose initially to 45,000 feet then 20,000 to 30,000 feet.
Eye witnesses report that no felt earthquake preceded this eruption, which is consistent with instrument monitoring. Between 22 and 24 May 2021 earthquakes occurred between the summit and Lake Kivu. Tremors were felt in Goma every 30 minutes from midday 23 May 2021. Cracks appeared in different parts of the city, stretching several hundred metres southwards to the lake, some emitting gases and flames. A 5.1 M earthquake occurred beneath Lake Kivu at 10:37 on 24 May 2021. Seismicity remained intense on 25 May with more than 130 earthquakes between 2M and 5M recorded in a 24-hour period. News reports indicated hundreds of damaged buildings in neighbouring Rwanda. Rwanda suffered 13 earthquakes in excess of 4.0 between 23 May to 27 May 2021. Seismicity has since decreased, although there is some evidence suggesting magma movement beneath the city of Goma.
The volcano is monitored by the Observatoire Volcanologique de Goma (OVG). OVG have given four possible scenarios as to how the eruption could progress:
A new fissure eruption on the southern flanks of the volcano;
A new eruption with fissures in or extending to the cities.
A new eruption with fissures extending to Lake Kivu.
Activity subsides.
Lake Kivu contains dissolved gases, including CO2. Heat or other disturbance from fissure activity beneath the lake may release dissolved CO2 in a cloud that could kill at lower elevations in its path. Although the 2002 eruption did not cause a large gas release from the lake, you can never say never.
Background
Tectonic Setting
Nyiragongo is 3,470 m high stratovolcano with a 1.2 km wide summit crater which contained a small active cone and lava lake, located in the Virunga Mountains in the Kivu Rift on the western arm of the East African Rift. The volcano’s edifice is built of lava flows and pyroclastics. Goma, with a population of 670,000 is located on the shores of Lake Kivu 12 km south of the volcano.
Volcanic and tectonic activity in the area is complex, influenced by to the opening of the East African Rift System in the midst of pre-existing areas of crustal weakness. The East African Rift System is a 3,000 km long continental rift extending from the Afar Triple Junction to western Mozambique. The Nubian Plate is moving away from the Arabian and Somalia Plates. Mantle plumes are thought to be the cause of doming and rifting. Rifting occurs at rates of 1 to 4mm a year, increasing north to south on the western arm of the rift and increasing south to north on the eastern arm. The slower rate of rifting in the continental lithosphere results in different volcanism than oceanic crust settings.
The Kivu Rift was created c. 5 Ma; it extends between Lake Tanganyika to Lake Albert in the central part of the western branch of the East African Rift System in an area of uplift called the Kivu Dome. There are two areas of volcanism associated with the rift, the South Kivu Volcanic Province and the Virunga Volcanic Province. Lake Kivu, itself, is a complex series of basins, the result of a rift depression whose waters drained northward until blocked by volcanic activity in the Virunga Volcanic Province c. 11,000 years ago, after which they flowed southwards. We will focus on the Virunga volcanism.
The Virunga Mountains comprise eight volcanoes on the border between the Democratic Republic of the Congo, Rwanda and Uganda. The volcanoes are: Mount Karisimbi, a 4,507m a complex basanitic-to-trachytic volcano , last known eruption 8050 BC; Mount Mikeno, a dormant 4,437m volcano; Mount Muhabura, 4,127m basanitic-to-trachyandesitic stratovolcano; Mount Bisoke, a 3,711m trachyandesitic stratovolcano, last eruption1957 ; Mount Sabyinyo, an extinct 3,674m volcano and the oldest in the range; Mount Gahinga, an extinct 3,474m volcano; Mount Nyiragongo, a 3,470m foidite stratovolcano, last eruption 2021 ; and Mount Nyamuragira, a 3,058m high-potassium basaltic shield volcano, last eruption 2021.
In the Virunga Volcanic Province, volcanic activity occurred in two stages: 1) pre-rift doming which produced alkali basalts in west Virunga c. 13 Ma to 9 Ma, after which volcanic activity ceased; and, 2) the opening of a trans extensional fault zone with ENE-WSW displacement c. 2.6 Ma.
Mount Nyiragongo’s Lavas
The Virunga Volcanic Province lavas are leucite basanite (e.g., Nyamuragira) from primitive mantle at depths of between 80km to 150km, or a more enriched leucite-melilite nephelinite (e.g., Nyiragongo) from mantle source at the same depth which has been enriched by contact with a carbonatite source. The source for the carbonatite is thought to be either from contact between rising magma and carbonate containing fluids or melt addition before or during magma generation 500 ma to 800 ma.
Nyiragongo’s melilite leucite nephelinite lavas are classed as foidite with minor basalt / picro basalt. It is the low silica foidites that make her lava’s so fluid, despite the volcano being a stratovolcano. These lavas can reach a speed of 60 – 100 km per hour and, unlike most lavas, cannot be outrun. The edifice, itself, is built of lava flows interspersed with pyroclastics.
Mount Nyiragongo’s Historic Eruptions
Recording of Nyiragongo’s eruptions started in 1884. GVP records 20 Holocene eruptions, all of which are VEI 1, except for the VEI 2 January 2002 eruption. The most recent eruptions were in 1977, 1994, 2002 and now 2021.
In 1991, Mount Nyiragongo was designated a Decade Volcano, worthy of study.
1977 Eruption
On January 10, 1977, a system of N-S fissures opened near the Baruta and Shaheru craters and the lava lake drained. Initial lava flows reached speeds of 100 km per hour due to the altitude of the fissures between 1,500m and 2,000m, combined with the low viscosity of the lava. The lava flow reached 20 km from the fissures. 600 people were killed. A herd of elephants unfortunate enough to be caught up in the flow were preserved as lava formed moulds.
2002 Eruptions
Run Up to the 2002 Eruption
The 2002 eruption was preceded by seismic and fumarolic activity enabling warning to be given and the 400,000 residents in the hazard zone to be evacuated. Initial long period events and volcanic tremors were recorded between December 2000 and January 2002. Mount Nyamuragira erupted in February 2001 for two weeks but the seismicity remained high. In October 2001, seismic activity increased and a tectonic earthquake between 3.5M and 4M was felt, followed by a high amplitude volcanic tremor. White plumes were observed in the Shaheru and central craters and a dark plume was visible from the spatter cone accompanied by new fumarolic activity. In January 2002, seismic activity increased again, along with a >4M earthquake and the resumption of fumarolic activity; an eight-hour lull in seismic activity preceded the onset of the eruption.
Eruption January 2002
On 17 January 2002, a 13 km fissure system opened on the south side of the volcano which reached Lake Kivu; lava reached Goma, itself, covering part of the local airport’s runway and reaching the lake. Again, the initial speed of the lava was high at altitude but much lower in the vents nearer to Goma (0.1 to 1km per hour). Lava erupted from the higher parts of the fissure is thought to have temperatures of c.1370°C with little or no crystal content, whereas that closer to Goma was thought to have cooled to 1,320°C causing some crystallisation and increasing its viscosity. Lava covered 4.7 km2, leaving 120,000 people homeless. 245 fatalities were caused by CO2 and buildings collapsing from lava and seismic activity. A three-month seismic swarm which followed caused more building damaged.
Six months after the first eruption the volcano erupted again in 2002.
A. Pouclet, H. Bellon, K. Bram, “The Cenozoic volcanism in the Kivu rift: Assessment of the tectonic setting, geochemistry, and geochronology of the volcanic activity in the South-Kivu and Virunga regions”, Journal of African Earth Sciences, 121, (2016), 219-246: https://www.sciencedirect.com/
R. Gill, “Igneous Rocks and Processes A Practical Guide”, Wiley-Blackwell, 2010
P. Francis, C. Oppenheimer, “Volcanoes”, Second Edition, Oxford University Press, 2004
R. V. Fisher, G. Heiken, J. B. Hulen, “Volcanoes Crucibles of Change”, Princeton University Press, 1997
An Armchair Volcanologist 
#/media/File:Keilir_distance.jpg){kind=link}
