Etna volcano (Italy): continuing ash emissions
Monday Feb 18, 2019 10:57 AM | АВТОР: T
Etna erupting ash from NE crater as seen last evening from Lipari (!) during extremely clear weather (image: Emanuela Carone / VolcanoDiscovery Italia)For more than a month, sometimes intense ash emissions have been taking place from the NE crater and, to lesser extent, from Bocca Nuova.
These ashes are currently believed not to be formed by fresh magma rising in the conduits, but instead are composed of older material that is now being vented from the inner conduits. It can be interpreted as the surface expression of internal re-adjustments that followed the brief, but intense eruption at Christmas last year, which drained (some of the) magma from the conduits and reservoirs.
Another factor are likely the seismic events around the volcano in the days and weeks after, which also might have caused internal shifts in magma storage.
Continuing ash emissions from Bocca Nuova and NE crater
Update Tue 29 Jan 2019 13:43
The activity at the volcano continues with pulsating, often strong ash emissions from the NE and Bocca Nuova craters at intervals of few minutes.
Ash emissions from Etna this morning from Bocca Nuova visible in backgroun, with the SE crater in front (image: LAVE webcam)
However, seismic activity remains low and there are currently no indications that these ash emissions (even though they are quite spectacular sometimes) are caused by fresh magma rising and might herald possible new activity in the near future.
More likely, they reflect internal adjustments of the conduits and internal reservoirs still drained by the flank eruption on Christmas 2018 (i.e. the ashes could be largely from fragmented older material).
Ash emissions from NE crater
Update Wed 23 Jan 2019 20:37
The volcano continues to be restless, although it has been calming down overall during the past weeks. Small earthquakes, although less in numbers and size (rarely exceeding magnitude 2) continue to occur in clusters under the western, southern and eastern flanks.
Aerial view of Etna on 22 Jan 2019 showing the ash plume from the NE crater, view from the west
Earthquakes under Etna volcano during the past 7 days
On the surface, the NE crater has been producing dense (but rather cold) ash emissions that form a sometimes impressive plume drifting from the summit area.
Heat emission from Etna during the past weeks (image: Modis / MIROVA)
Etna volcano (Italy): shallow magnitude 4.1 earthquake under NE rift zone
Wednesday Jan 09, 2019 08:51 AM | АВТОР: T
Seismic signal of this night's quake under Etna (image: INGV Catania)
The volcano remains restless in form of earthquakes. A magnitude 4.1 earthquake at 2 km depth beneath the northeastern rift zone occurred early this morning at 00:50 am.
Location of the earthquake
Some residents in the area, e.g. from Linguaglossa town reported to have been woken up by the tremor (detail info for this earthquake).
Whether the earthquake is caused by magma intrusion in this area prone to flank eruptions or of other origin (tectonic adjustment of the east flank) is unclear.
Etna volcano (Sicily, Italy) activity update: small ash emissions from NE crater
Monday Jan 07, 2019 10:53 AM | АВТОР: T
After several days of bad, unusually cold weather (and heavy snowfalls on the upper flanks), Etna has again been visible in its splendor since yesterday morning.
Ash emissions from Etna volcano yesterday (image: Boris Behncke / facebook)
Volcanologist Boris Behncke (INGV Catania) observed small, dilute ash emissions from the NE crater, which occurred at short intervals and caused small peaks in seismic activity.
Other than that, the volcano has continued to calm down overall, but this can of course change rapidly.
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Etna volcano (Italy): earthquakes under SW flank
Friday Jan 04, 2019 09:39 AM | АВТОР: T
Recent earthquakes under Mt Etna volcanoThe volcano continues to show signs of unrest. A swarm of shallow small earthquakes has been occurring under the SW flank during the past days and seems to be increasing.
The strongest shock so far was a magnitude 3.5 event at very shallow depth 7 km north of Ragalna about 5 hours ago (at 06:10 am local time), felt as weak shaking in the villages on Etna's southern and western flanks.
Whether these quakes are related to possible magma intrusions under the western rift zone can be speculated about.
At the surface, the volcano seems rather quiet and bad weather currently prevents detailed visual observation.
Etna volcano (Italy): satellite data reveal part of the volcano has moved by 50 cm during 24-26 Dec 2018
Wednesday Jan 02, 2019 11:44 AM | АВТОР: T
Italian scientists have analyzed satellite data from the Italian Cosmo-SkyMed and the European Sentinel satellites, which passed over Etna both before and after the short, but intense flank eruption that began on 24 December 2018 and the seismic crisis that accompanied this event and culminated in the 4.8 magnitude early on 26 Dec with an epicenter near the villages Viagrande, Trecastagni and Fleri on the southeastern side of Etna.
Maps showing the displacements during the 24-26 Dec eruption and seismic crisis (image: CNR)
Comparing the data, they were able to calculate how the shape of the volcano changed due to the intrusion of the magma, which in parts rose to the surface through the new eruptive fissures, and in parts became "stuck" as shallow and deeper intrusions. The results are stunning:
- the western slope of Etna has moved 30 centimeters to the west (in red on the map, figure c);
- the eastern slope moved 50 centimeters to the east (in blue on the map, figure c).
The star at the bottom right indicates the epicenter of mentioned strongest quake.
The main fault involved was the so-called Fiandaca fault, where the earth's crust has moved eastwards by 12-14 centimeters and westwards by 15-17 centimeters. Other faults were also involved in the swarm, but more indirectly, as reactions to the main movement on the Fiandaca fault: the of Pernicanca fault (on the north-eastern side) moved 3 centimeters, the Ragalna fault (south-west slope) and that of Borello-Ognina (south slope) of 2 centimeters.
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- Misurati gli spostamenti del suolo avvenuti a seguito dell'eruzione dell'Etna e del terremoto del 26 dicembre (CNR - Consiglio Nazionale delle Ricerche)
Etna volcano (Italy): volcano remains restless as small earthquakes and steam emissions continue
Sunday Dec 30, 2018 19:26 PM | АВТОР: T
Ash emissions from Etna volcano yesterday (image: Emanuela Carone / VolcanoDiscovery Italia)
Location of recent earthquakes under Mt Etna volcano during the past 7 days (red: past 48 hours)
Steam and ash emissions from Etna volcano yesterday (image: Emanuela Carone / VolcanoDiscovery Italia)
The volcano remains highly restless. Although no more lava is being erupted right now, strong gas and dense ash emissions continue from the Bocca Nuova crater as a sign that magma is close to the surface.
Steam and ash emissions from Etna volcano yesterday (image: Emanuela Carone / VolcanoDiscovery Italia)
Seismic activity as well remains elevated. Today, a cluster of small earthquakes occurred at shallow depths (1-8 km) beneath the SW flank, which could indicate another intrusion beneath that area. The largest was a magnitude 3.4 event at 19:30 local time, felt by some residents nearby.
Decreasing activity for now, but this could change soon
Update Thu 27 Dec 2018 17:06
The decreasing trend in surface and earthquake activity on and around Etna continues and there is little to nothing left of the vigorous flank eruption that had started on Christmas Eve (24 Dec 2018). However, the volcano is far from quiet and there are indications that more and potentially more dangerous activity could be in the making.
Tall steam and ash plume rising from Etna's Bocca Nuova (GuidEtna webcam)crater
Current tremor amplitude showing a gradual decrease
Aerial view of the western headwall of Valle del Bove and crater area from the east, showing the now almost inactive eruptive fissure from the 24 Dec eruption (image: INGV)
A tell-tale sign that the flank eruption could only be a prelude is that magma continues to stand high inside the volcano's conduit: glow and intense gas and steam emissions are visible from the Bocca Nuova, producing a tall plume rising vertically into the evening sky. The recent eruption has drained only very little of the available magma. Will more come out soon?
Map of earthquakes around Etna during 24-26 Dec 2018, the M4.8 event from 03:19 on 26 Dec marked in blue (image: INGV)
Eugenio Priviera, director of INGV (the National Institute of Geology and Volcanology) mentioned in an interview quoted in a Sicilian newspaper that new eruptive fissures could open up even at lower altitudes. INGV posted a special report about the current situation and the recent earthquakes on its blog site:
Even though the current surface phenomena are weakening, the general decrease in eruptive activity could be misleading: information obtained from geophysical cannot exclude that magma supply into the same dike that fed the recent eruption is still in progress, and could open its way with new fissures down to altitudes beneath 2,400 m, especially in the area of the southern and western walls of Valle del Bove.
In the newspaper article mentioned, Priviera explains that one area particularly at risk for this could be the area of Piano del Vescovo south of Valle del Bove in the SE sector of Etna. Whether this will happen or not cannot be predicted. According to the newspaper, Priviera said that the recent earthquakes have shown that the known Fiandaca fault was activated, which is a potentially dangerous situation. He announced that ground deformation monitoring is being intensified in the area.
Yesterday's destructive M4.8 earthquake that hit the lower SE flank of Etna t 03:19 local time (26 Dec) occurred 1 km S of Lavinaio (CT) village and caused lots of damage to houses and buildings. Its depth was localized to be at only 1 km below sea level (i.e. approx. 1500 m below the surface).
The quake coincided with the 3rd day of the eruption of Etna. INGV writes that "it should be noted that the earthquake was not generated by movements of magma masses present in the epicentral area, but probably was the response of the eastern flank of the volcano to a stress induced by the magmatic system that at that time fed the eruption."
In other words, the pressure induced by rising magma in the central conduit might have been the trigger to activate the fault lines on the eastern flank, but are likely not a sign that magma was intruding in the same area of the quake (at the lower eastern flank).
Eruption update - continuing earthquake swarm
Update Tue 25 Dec 2018 18:09
Bad weather has mostly prevented clear sights of the new flank eruption today, but it seems that while it is still going on, lava emission from the new fissure vent high in the Valle del Bove that opened yesterday has decreased.
Earthquakes under Etna volcano during the past 7 days
Thermal image of Etna this evening seen from the west (image: INGV thermal webcam in Bronte)
The area remains obscured in clouds, but thermal cameras show continuing activity from the Bocca Nuova.
An impression from what it looked like yesterday when Barbara, a friend of ours from Stromboli, was en route from Catania to Milazzo, passing the ash plume (image: Barbara Engele)
Seismic activity remains elevated, showing that the eruption is certainly not over and still evolving: the recent earthquake swarm continues (albeit at decreased intensity) with approx. 20 earthquakes with magnitudes between 2 and 3.4 having been detected during the past 24 hours. Most quakes were at shallow depth in the SE sector of the volcano.
First images / videos from the new eruption
Update Mon 24 Dec 2018 23:11
Our Etna specialist Emanuela climbed Etna earlier today, witnessing the onset of the new flank eruption in the upper Valle del Bove.
Ash emissions from Etna at the onset of the eruption (image: Emanuela Carone / VolcanoDiscovery Italia)
You can find the images in this gallery.
Video from the beginning of the eruption:
Video compilation showing the ash emissions and the lava flow from the new fissure vent:
Etna volcano (Sicily, Italy) activity update
Monday Dec 24, 2018 17:54 PM | АВТОР: T
Eruption of new lava flow from Etna this afternoon (image: LAVE webcam)The following video shows the beginning of Etna volcano's new flank eruption, starting around noon on 24 Dec 2018: a series of quakes accompanies the progressive opening of several fractures, accompanied by strong ash emission, on and below the SE crater.
An eruptive fissure opens around 17:00 local time in the upper western headwall of the Valle del Bove, followed by a river of lava descending from there and quickly reaching the bottom of it:
Magnitude 4.5 earthquake
Update Mon 24 Dec 2018 17:01A magnitude 4.5 quake occurred a few minutes ago near Etna. The eruption is still evolving fast.
Link to earthquake information
Flank eruption confirmed from new fissure in upper Valle del Bove
Update Mon 24 Dec 2018 16:53
Beginning of darkness makes it easier to see what is going on: a flank eruption in from the a new effusive vent in the upper western headwall of the Valle del Bove, SE of the SE crater.
The new lava flow at Etna (image: LAVE webcam)
The lava flow has already reached and is spreading in the Valle del Bove itself. For now, it does not pose any danger.
Eruption visible from satellite
Update Mon 24 Dec 2018 16:37
The strong ash emissions can also be seen on satellite images - impressive!
Today's Aqua satellite image of Etna volcano
Magnitude 4 earthquake hits Etna's east flank
Update Mon 24 Dec 2018 16:18
Seismic activity at Etna is significant. The largest quake today so far has been a magnitude 4 quake at 2 km depth under the SE flank. It occurred at 13:09 local time and was widely felt around in the area.
Location of the magnitude 4 quake earlier today under Etna volcano
It was most certainly associated with the opening of the new eruptive fissure below the SE crater.
Etna volcano (Sicily, Italy) activity update: subterminal flank eruption
Monday Dec 24, 2018 13:30 PM | АВТОР: T
View from Catania showing the ash plume from the ongoing eruption (image: Etna Tech webcam 1)
Thermal image of the new lava flow in the upper Valle del Bove on Etna's eastern flank (image: INGV Catania webcam)
The volcano decided to begin a subterminal flank eruption, i.e. effusion of lava from a flank vent connected to the upper conduits in the summit area.
Current seismic signal from ESVO station (image: INGV Catania)
Currently, a large lava flow is currently running into the upper Valle del Bove from a new fissure vent at the southeastern feet of the New SE crater, near the former Belvedere area.
Whether this develops further into a true flank eruption is still unclear. Seismic activity is elevated; our correspondent on location could feel the earth share violently beneath her feet. Tremor is still high, which could indicate that the fractures are still propagating, although seems to be decreasing already. Right now, the eruption poses no danger.
Etna's way to celebrate Christmas is certainly interesting!
Strong lava flow from fracture at eastern base of SE crater
Update Mon 24 Dec 2018 12:46
From webcam imagery, a strong lava flow seems to be coming from a fracture on the eastern base of the New SE crater, headed into the Valle del Bove (where it poses no threat).
Lava flow from eastern foot of New SE crater into Valle del Bove (INGV thermal webcam on Monte Cagliato, looking from the east towards the upper Valle del Bove))
Strong seismic activity
Update Mon 24 Dec 2018 12:24
Something significant is in progress at Etna:
Seismic signal from Etna's ECNE station (INGV Catania)
Emanuela who's on location reported "crazy seismic activity" and that new fractures have opened on the eastern and southern flank of the SE crater (SEC).
Update Mon 24 Dec 2018 12:17
Ash emissions on 24 Dec 2018 around noon (image: Emanuela Carone / VolcanoDiscovery Italy)
Emanuela who's on her way to the volcano sent the above images from the intense activity of ash emissions.
Ash emissions from Etna's New SE crater on 24 Dec 2018 around noon (image: Emanuela Carone / VolcanoDiscovery Italy)
Ongoing eruption seen from the west side
Update Mon 24 Dec 2018 11:57
View of the ongoing activity from Paterno (western side; image: Radio Touring Webcam)
Etna volcano (Italy): eruption intensifies, possibly heading towards a paroxysm
Monday Dec 24, 2018 11:49 AM | АВТОР: T
Strombolian activity from Etna's New SE crater last night (image: Emanuela Carone / VolcanoDiscovery Italy)
Strong ash emissions from the New SE crater now (image: INGV Catania)
Seismic signal (ECNE station, INGV Catania)
A significant event is in progress at the volcano. Strong seismic activity, felt by people, has been accompanying the opening of several fractures in the summit area, most notably on the eastern and southern flanks of the New SE crater, which is emitting dense ash plumes.
The activity of the volcano is increasing and looks as if going towards a paroxysm.
Strombolian activity from the New SE crater has intensified, and currently strong ash emissions are visible, suggesting pulsating lava fountaining.
Our local correspondents reported a seismic swarm was detected and tremor is also rising. They are on their way towards the mountain and we will probably be able to send a more detailed report later. In the meanwhile, you can look at the evolving eruption webcams online.
Etna volcano (Italy): lava flows and strombolian explosions from SE crater
Thursday Dec 13, 2018 23:51 PM | АВТОР: T
Lava flows and strombolian activity at Etna's New SE crater this evening (image: Tom Pfeiffer / VolcanoDiscovery)Mild effusive/explosive activity continues at the eastern vent of the New SE crater, feeding two small lava flows traveling a few hundred meters down the eastern slope of the crater towards the upper Valle del Bove.
The larger and more active flow emerges from the rim of the new cinder cone, while the the smaller one to the south of it is coming from a vent located few meters beneath the crater rim.
While the lava effusion seems to have been more or less stable, strombolian (explosive) activity has been decreasing over the past days. On 9 Dec, it was continuous, as pulsating low fountains, with abundant noise audible in several kilometers distance.
When observed this evening, strombolian explosions were smaller and much more intermittent, and only rarely ejected incandescent material to the outer slopes of the eastern flank of the SE crater complex.
Etna volcano (Italy): activity update - strombolian activity from several summit vents
Tuesday Oct 02, 2018 22:30 PM | АВТОР: T
Ash emission from Etna's NE crater on 30 Sep 2018 (image: Emanuela Carone / VolcanoDiscovery Italia)
Map of Etna's summit craters at present (image: INGV)
Strombolian eruption in Bocca Nuova on 30 Sep 2018 (image: Emanuela Carone / VolcanoDiscovery Italia)
A new vent with strong degassing opened in Bocca Nuova a few days ago, discovered on 30 Sep via our guide's infrared camera (image: Emanuela Carone / VolcanoDiscovery Italia)
Over the past few weeks, Etna has been showing mild, sporadic strombolian activity from 5 of the summit vents: 3 vents inside Bocca Nuova (two in the northwestern and one in its southeastern pits), the NE crater and less frequently from the New SE crater.
Recent earthquakes under Etna's eastern flank
The ejection of incandescent bombs rarely reach above and beyond the rims of both Bocca Nuova and NE crater. More or less intense ash emissions, in particular from the NE crater, accompany the activity.
The vent in the upper eastern wall of Voragine (which had formed on 7 Aug 2016) showed a marked increase in degassing activity during the past week.
As a result of the strombolian activity inside Bocca Nuova, a new intra-crater cinder cone has been growing at the bottom of the western pit. During one of our guided tours to the summit last Sunday (30 Sep), mountain guide Francesco Ciancitto could confirm the opening of a new vent inside Bocca Nuova's western pit just next to the actively erupting one. It showed strong degassing; thus, there are currently 4 active vents in Bocca Nuova alone.
Tremor and degassing levels have been low to average according to the latest weekly bulletin of the volcano observatory (INGV Catania). However, it should be noted that a number of volcano-tectonic earthquakes have affected the middle eastern flank recently. The largest events were two quakes of magnitudes 2.9 and 3.5 at depths around 5 km near the Pernicana fault (which often has acted as an "opener" for the NE rift zone in the past). However, there are no signs currently of an impending larger (rift) eruption.
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- Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna 02/10/2018 (INGV Catania)
Eruption seems to decrease
Update Sat 25 Aug 2018 12:38
The strombolian activity from the SE crater which started Thursday evening is progressively decreasing. From time to time weak ash emissions are still observed. The effusive activity has almost stopped. The seismic tremor is still at an elevated level, but it is also showing a decreasing trend.
Strombolian Activity from the SE crater (photo: Emanuela / VolcanoDiscovery Italy)
New eruptive activity at SE crater
Update Fri 24 Aug 2018 08:46
Last night, new activity started at the SE crater. Tremor began to rise sharply at around 20:30 local time, accompanied by mild strombolian activity from the new cone in the saddle between the "old" and "new" SE crater.
Strombolian activity from Etna's SE crater last night (LAVE webcam)
Ash plume from an explosion at the SE crater this morning
A small lava flow also emerged. The activity continues this morning, sometimes generating ash plumes of several hundred meters height.
Earthquake swarms under eastern and western flanks
Update Mon 28 May 2018 16:47
Recent earthquakes under Etna volcano
Depth vs time of recent quakes
The volcano is becoming increasingly restless. Two earthquake swarms have occurred during the past days:
Bocca Nuova on 25 May 2018
The first was at medium depths (mostly 10-30 km) beneath the eastern flank during 24-26 May, the second one started yesterday and is still continuing under the western flank at depths around 5-10 km. Both could indicate an intrusion of magma, and tremor levels are slightly elevated. Whether this heralds a new eruption in the near future (days, weeks?) is matter of speculation. So far, the quakes have been relatively weak.
When we visited Bocca Nuova last Saturday, we noticed relatively strong, pulsating gas emissions from not-very-deep seated explosions inside the main western vent. According to the mountain guides, this activity had increased, as well as degassing from some areas at the southern rim of the central crater as well as the NE crater.
Weak ash emissions from SE crater and seismic activity
Update Thu 21 Sep 2017 21:57
Since last Monday the SE crater is showing small signs of activity again. During last nights weak sporadic glowes were seen from the depression on the eastern slope of the crater and starting this morning small ash emissions are occurring intermittently from the top of the crater.
Small ash emission from the SE crater
Several seismic swarms have been recorded below the southwest slope of Mount Etna since last month. The last swarm occurred on September 18th, close to Mt. Intraleo on the western slope of the volcano. 45 eartquakes were recorded from 04:06 (UTC) to 08:31 (UTC) with magnitudes ranging between M1.0 and M3.3. The strongest earthquake, magnitude M 3.3, took place at 07:21 (UTC) at a depth of 5.5 km. Researchers think this suggests a new phase of deep magmatic recharge is taking place.
Furthermore on August 24 a new eruptive phase began at Salinelle dei Cappuccini with a mud flow that partly invaded the road around the Paternò stadium. The Salinelle dei Cappuccini is one of three mud volcano fields located between the villages of Paternò and Belpasso characterized by persistent emission of mud and gases. It is possible that the recent seismic activity may have modified their level of activity.
Small ash emissions, steam rings, summit access for tours reopened
Update Fri 14 Jul 2017 08:59
The volcano remains restless although no one knows what will come next. After a few weeks of "total silence", tiny ash emissions started again to occur from the SE crater since 9 July, volcanologist Dr Boris Behncke reported on facebook. This activity, which could represent small but deep-seated explosive activity inside the SE crater's conduits, has been continuing over the past days, with a slight increase yesterday (see video below).
Steam ring blown from Etna's Voragine crater this morning (image:Radiostudio7 webcam)
Bocca Nuova with its collapsing crater floor on 13 July 2017 (image: Gio Giusa / facebook)
Access to the summit craters for tours guided by authorized mountain guides has been allowed again.
Small ash puff from the SE crater on 9 July (image: Boris Behncke / facebook)
Other than that, there is intense degassing from the Voragine summit crater, which sometimes also produces beautiful smoke rings (steam ring vortexes), while the Bocca Nouva's crater floor continues to undergo slow concentric collapse (see images on facebook)
Intermittent ash emissions from SE crater
Update Mon 26 Jun 2017 08:24
Ash puff from Etna's SE crater this morning (image: RadioStudio7)
After a period of calm during the past weeks, the SE crater started again to show signs of unrest. Since yesterday morning, small to moderate ash emissions have been occurring intermittently from the summit vent of the SE crater complex. Thermal imagery indicates that the ashes are relatively cold, suggesting that the magma column at the moment resides still low in the conduit. Whether the observed ash puffs are caused by deep-seated explosive activity (=degassing of magma) or by internal collapses is difficult to say. Other than from the SE crater, there is strong degassing from the Voragine as well as weak incandescence in the Voragine and the crater open on the eastern side of the SE crater.
Stronger ash emission yesterday morning (image: RadioStudio7)
Regular "mini-eruptions" at SE crater - an interpretation
Update Fri 19 May 2017 08:48
Since 11 May, Etna has been in an unusual state of activity. At remarkably regular intervals of approx. 8 hours, the "saddle vent", located between Etna's old and new Southeast Crater, has been producing more than 20 brief episodes of mild strombolian activity, each accompanied by a short-lived increase in volcanic tremor amplitude. The episodes are further characterized by the absence of strong degassing.
Strombolian activity at the SE crater's saddle vent and the peaks of tremor accompanying each short-lived episode (image: Boris Behncke / INGV Catania)
What causes this unusual and certainly transient behavior is not exactly known. Researcher Dr Marco Neri tries to give an explanation in an article on La Gazzetta Siracusana(loosely translated):
"In fact, Etna volcano produces "mini-eruptions" that last a few tens of minutes, located at the top of the New South-East Crater, at about 3300 meters. There would be nothing strange about this, except that these events occur with an impressive regularity, about 3 a day, and at fairly constant intervals of about eight hours. A phenomenon that closely resembles that of geysers, although in this case it is magma to erupt at the surface and not water. ...
These small eruptive events are always accompanied by an increase in the amplitude of volcanic tremor, which corresponds to a vibration produced by movements of volcanic fluids circulating within the eruptive duct. When the magma approaches the surface and erupts, tremor increases sharply. ... Therefore, the tremor graph shows a series of almost regular peaks for amplitude and intervals. It's like volcano's hiccups!
"Why do these mini-eruptions happen? What makes them so regular and frequent? Without claiming to always understand everything about a volcano, especially Etna which is full of surprises, we can try to give an answer:
Etna's feeding system, and in particular the eruptive ducts that feeds these eruptions, can be imagined like a narrow and long pressure pot. The heat of the magma is similar to the fire lit under the pot, while the gases separating from the magma and accumulating in the top of the duct correspond to the water vapor that forms inside the pot when the water is heated and bubbles.
Finally, the eruptive vent from which the mini-eruptions occur can be compared to the valve of our pressure cooker. Every time the gas pressure inside the duct exceeds a certain critical value, the "valve" opens and some magma erupts on the surface. And to complete the similitude, the characteristic "whistle" of the pot valve that opens can be compared to the hissing sounds that people nearby perceive during these mini-eruptions.
"The extraordinary nature of the phenomenon that we observe at the moment lies, however, in the fact of the remarkable regularity of the mini-eruptions, showing that the system has reached an excellent balance between the magma that is being fed from below into the upper ducts and the magma that is lost (expelled) from the system during these mini-eruptions.
What will happen?
How can the hiccups of Etna cease? The phenomenon may last for a long time, at least until this balance between the rising magma and the eruptions stays in place. Things will eventually change when the available magma volume will decrease, or, if the volume of fresh magma rising from below increases significantly, leading probably to eruptive episodes such as observed during the past months.
Also the geometry of the upper portion of the the vent, or, to stay in the image, our "volcano" vent valve, plays an important role: should this vent change, e.g. collapse, or become obstructed, it would certainly also change the course followed by magma to reach the surface, as well as the energy needed to produce an eruption.
In this case, it would change the eruptive style of the volcano and perhaps also the position of the eruptive vent." (Marco Neri / INGV Catania)
New effusive episode from SE crater during 26-28 April 2017
The two lava flows from the SE crater during the night 26-27 April 2017
The first lava flow on the southern side of the SE crater and lava fountaining at the vent in the early hours of 27 April
Another mainly effusive eruptive episode occurred from the SE crater during 26-28 April.
Steam from a melt-water avalanche on the northern lava flow in the morning of 27 April
Starting from the evening of 26 April at around 18:00 local time, a lava flow started to emerge slowly from the summit vent of the Southeast Cone and descended to the south and then bended eastwards at the foot of the SE crater complex.
There was with no significant explosive activity in the beginning: this was likely because the first lava to be erupted was the remaining, degassed lava still in the conduit from the previous episode being pushed out first by a new batch of rising magma.
SE cone collapses, new lava flow to the north
During the night, after the new magma arrived at the surface and mild strombolian activity (or low pulsating lava fountains) started to occur as well, as effective degassing of the fresher magma. At around 01 am in the night, the SE cone collapsed partially, probably because its edifice, already fractured, could no longer withstand the pressure of magma in its conduit. A second lava flow emerged and traveled north from the vent.
The eruption with two lava flows continued all night and during the morning of 27 April.
Starting from noon of 27 April, the lava flow to the southern flank of the SE crater started to decrease and ceased by around 13:30. The northern lava flow continued during the evening, but also ceased during the night 27-28 April.
During the morning of 27 April, the advance of the new lava flow on the northern side over fresh (not covered by recent flows) snow-covered ground triggered a series of small phreatomagmatic explosions.
The most significant such explosion took place between 08:46 and 08:48 local time. It begins with the emission of steam from the center of the lava flow, shortly followed by the ejection of fragments from the flow itself. This event also triggered a rapid melt-water hot avalanche that traveled about 700 m in less than 2 minutes.
A smaller melt-water flow was also observed earlier at around 06:52 local time.