La Palma's Cumbre Vieja volcano eruption of 2021
After the surge of magma during the past days, the activity has dropped again significantly, but a new signal of ground uplift announced that a new batch of magma is on the rise and being stored, and will be coming out as a new surge. Volcanic tremor remains comparably high and has strong temporary peaks, indicating magma flux remains significant. There is certainly no sign of the eruption ending soon.
In the morning, ash plumes rose to 1,900 m and drifted into southerly and southwesterly directions over the ocean (leaving the airport free). Lava flows continued to be active near the new vents and along the path towards La Laguna. Some of the older lava tubes also remain active with smaller breakouts mostly in the central area of the flow field, but no or very little lava is currently reaching the ocean entries.
The intense lava fountaining has already created a new cone adjacent and now morphologically likely soon merging with the main cone. Several lava flows descended from the vent area over a steep slope into the area of Tacande and the northern margin of the existing lava flow field. The new lava flow was labelled #12 and is in parts parallel to #8 and downslope joins or overlies it. On its way, it covered new areas and destroyed additional buildings, unfortunately. As of yesterday evening, its active fronts were located about 800 meters from La Laguna.
The new lava flow at the southern margin of the flow field is advancing southwesterly towards Camino La Majada, covering land that had been left untouched between the previous lava flows labeled #3 and #11. The new lava flow, which was initially fast-flowing, has slowed down by now, as it lost fluidity along its path. Lava flows #7, 8 and 10 continue also be fed, but less than during the past days, and no lava is currently arriving at the sea deltas. The lava flows from the new vent system that had been extremely active in the past days were practically inactive today.
The activity at the vents has decreased significantly as well. Lava fountaining has apparently ceased, and is replaced by intermittent and weaker strombolian activity. Ash emissions have become less vigorous and discontinuous, but low plumes were still produced, reaching approximately 2,000 m altitude and drifted westerly over the Atlantic.
However, despite the lower activity, the gas emissions, in particular sulfur dioxide (SO₂), remain high, which suggests that there is still a high amount of magma available at depth.
The affected area by lava flows stands at estimated 1,146 hectares, with a maximum width of 3,350 meters.
Activity overall continues to decline. Ash emissions and explosions at the vent have been rare and intermittent, but produce occasional plumes rising up to approximately 2 km in altitude.
Lava effusion continues at similar levels, but seems to be now again mainly coming from the vents at the main cone, while the new fissure that opened last week at the southern margin of the flow field west of Montaña Cogote is less active and has merged with the southernmost older flow. Its front has merged with flow number #9 in the flat lava delta that had formed in the 1949 eruption, but has so far not entered the ocean.
Volcanic tremor remains similar as yesterday at low levels without many fluctuations.
Seismic activity continues to decrease as well. On December 6, only about 20 quakes were registered during a 24 hour period, likely the lowest number since the beginning of the eruption.
No significant changes have been seen in other monitored parameters, such as deformation and gas emissions.
Around noon local time, a sudden large explosion occurred at the main crater of the cone, producing a steam and ash plume that quickly rose to estimated 5,000-6,000 meters altitude. The event was likely a so-called vulcanian explosion, typically caused when a larger plug in the upper conduit has formed and is suddenly thrown out when gas pressure underneath overcomes a threshold (comparable to a cannon-shot mechanism). Today's explosion likely might be due to the fact that the conduits have gradually been closing up and filling with debris in their upper parts as supply of rising material is less abundant. This fits with the model that the eruption has entered its final waning stage, but also creates highly dangerous conditions, because such explosions could (and likely will) repeat in the days to come.
Apart from this, the eruption—now on its 87th day of activity being the longest in recorded history on La Palma Island—has continued at low levels similar as in the past days. There is now mainly steaming, with only occasional smaller explosions, at the main cone, while lava effusion continues at reduced rate. The arriving lava first goes into the tube system, and feeding flows in similar areas as during the past days overlapping older flows. Seismic activity has been low, with only 24 quakes detected during 24 horus, the maximum being only a 3.2 event. Deformation and tremor remain basically unchanged at low values, although the explosion earlier resulted in a short-lived intense tremor peak.
After yesterday's large explosion at noon, the eruption gained in intensity, both explosive and effusive, during the evening and night. After being quieter most of the day today, it increased again in the evening, shown by the strongly fluctuating volcanic tremor signal. Phases of strong ash emissions and lava fountains have been alternating with quiet periods when only steaming could be seen at the craters.
Ash plumes reached 4,200 m above sea level this morning, and reportedly up to 7,000 m in the afternoon, and drifted southeast. Absence of wind near the ground created very high SO2 concentrations in El Paso today, with values surpassing 2.590 micrograms per cubic meter this morning. Lava continues to flow from the (hidden) vents on the western base of the cone into the tube system and crate breakouts in the central part of the flow field. One of the more active surface flows began to eat away one of the remaining islands of so-far untouched land in the area south of Todoque and east of Las Norias. The number of quakes has again increased in numbers: During the past 24 hours, there have been 4 quakes of magnitudes 3.0-3.4 and 46 quakes between 2.0 and 2.9. Most of these occurred at the shallow layer around 10-15 km depth while only very few ones occurred at the deeper layer of 30 km or below.
The decrease of seismic activity in the deeper layer might indicate that magma supply from that area is less now than during previous weeks when lots of magnitude 4+ quakes occurred there, but this remains speculative. No significant changes in deformation has been recorded.
The eruption might have stopped or is pausing today, which is day #89 since it started on Sep 19, 2021. After a temporary strong increase yesterday producing lava fountaining and tall ash plumes, visible activity decreased drastically and more or less ceased today. No significant explosions or lava flows can be seen. Volcanic tremor has dropped to its lowest levels since the eruption began, and is close to absent now. The absence of tremor in the signal in turn allows to detect tiny quakes of magnitudes below 2, which leads to an increase in the number of total detected quakes - IGN reported 129 events, but only 5 of them were at least of magnitude 3 and none above 3.2, which is among the lowest-by-energy combined values counts since the beginning of the eruption. Whether or not the eruption is now already at its end is hard to say, but it is most likely at least close to it.
No new activity has been reported at the eruption site since it ceased yesterday. No signs of moving magma have been registered for 24 hours, all vents have ceased to emit lava and the seismicity has also dropped. Chances increase that the eruption is over, although this is far from certain.
There are several parameters which are key to predict the end of the eruption and they all bode well: There is no deformation, volcanic tremor is absent, intermediate and deep seismicity are nearly non-existent, and the levels of SO₂ are below 5 tons per day, well below the 100 tons per day threshold which, if maintained between 5 and 10 days, would indicate the end of the eruption.
Whether the eruption has ended or not will depend on whether magma still stored in the reservoir beneath the surface is able to ascend, which in turn is likely dependant on two main factors: First, whether the shallow reservoir is being resupplied by magma from the deeper source, which should manifest with the occurrence of deeper earthquakes which, lately, have been mostly absent, suggesting that supply from the deep source has ended. Second, the ascent of magma from the shallow reservoir is driven by gases dissolved in the magma and forming bubbles to increase volume and pressure and eventually make the magma rise to erupt as lava.
If, and this is maybe a likely scenario, most of the gases have already left the system or if the remaining gases can separate efficiently from the liquid (magma), and rise and degas at the vents and through the surface, the magma will slowly start cooling down and eventually crystallize over a very long period of time. It is also very much possible that the current pause of the eruption leads to a blockage of the upper conduits, which disables the degassing process and generates conditions that could lead to sudden explosions and allowing probably smaller batches of remaining magma to erupt in short phases of reactivation.
Nobody knows for now. The situation remains volatile and care should be taken to make any predictions of whether activity will resume or not.
A small lava flow has been detected flowing over older ones and gushing over the cliffs of Las Hoyas. This remaining lava flows from a still active lava tube. However, signs for exhaustion are maintained, but the possibility of peaks in strombolian activity and lava emission should not yet be ruled out.
On the other hand, visible emission of gases is punctual and sporadic, and are concentrated on the area of the eruptive centres and in jameos (volcanic tubes whose roof collapsed). Continuous small landslides occur on the walls of the craters of the main and secondary cone, facilitated by existing faults and fissures. On December 17, the diffuse emission of CO₂ was 8.9 times higher than the normal average amount. In some areas of Cumbre Vieja, these emissions can represent a danger to people if the values are high and there is no good ventilation. It has even been advised to inhabitants of the evaquated areas to be very aware of the gases, to use FFP2 masks and to not remain alone in any moment. SO₂ concentration levels have been good in all stations for the fourth day in a row, with regular levels in Tazacorte and reasonably good in San Antonio. As for microparticles, in the station of Los Llanos, the values are reasonably good, and good in the rest of stations.
On the other hand, tremor is at background noise level, and seismicity remains the same at all depts as on past days.
On December 19 at 10:00 pm, an unexpected elevation of 8 centimetres has been detected in the nearest station to the eruptive centres—LP03, at the Roques de Jedey. Deformations indicate a reactivation of the volcano, and up until now, these deformations have tended to be accompanied by a paroxysm 24 or 48 hours later. However, it is the only worrysome parametre that has been detected. For the moment, there are no other alarming signs; there is still no volcanic tremor and seismic activity remains low. On December 20, the elevation is reverting, and decreasing to an elevation of 6 centimetres. Episodes with residual deformation and seismicity such as this can continue happening for months and even years, as occurred with the eruption of Tagoro of 2011 in El Hierro.
The eruption is today declared dormant on December 13 at 22:22 UTC, when the tremor suddenly decreased, and the lava emission, seismicity and sulfur dioxide levels dropped to very low levels. But the end of the eruption does not entail the end of the emergency, nor that of the danger. Now, a post-eruptive phase is initiated, in which the risks to the population persists, mainly due to the presence of lethal gases. The origin of these gases is still being studied. The situation requires constant surveillance, and the decrease needs to be complete in order for people to return to their homes.
It is likely for remnant seismicity to occur in the coming months. It is also possible for a similar case to that of El Hierro's eruption of Tagoro to develop, with several magmatic reactivations in the following two years which, nonetheless, did not conclude in a new eruption. Such a phenomenon also took place in the eruption of Arafo in Tenerife, between 1704 and 1705, which was followed in 1706 by another eruption on the other side of the island and buried part of the town of Garachico.
On the other hand, the last remaining worrisome parametre—the 8 centimetre ground elevation that was registered near the main cone on December 19—has reverted today. Volcanic tremor and seismic noise are also close to pre-eruptive levels.
The terrain still has very high temperatures. The outermost layer of lava cools down, and isolates the interior keeping it from cooling rapidly. This isolation also accumulates the gases in the lava by not allowing them to escape. Degassing can occur at any moment, and it can pose an important threat. The toxicity of the emanating gases is dangerous, they can cause damage in minutes, from the most visible such as irritation from skin and eyes, to serious internal problems that cannot immediately be detected. There are also incandescent points over 100 °C, and time is needed for them to cool. Some are more than 50 metres below surface and have openings of 10 metres.