Etna Decade Volcano, Sicily, Italy
Lava flowing from an ephemeral vent on the western slope of Valle del Bove, 30 April 1999
Updates April 1999
The most recent updates
Etna news archive
1 May 1999
Lava continues to flow from several ephemeral vents on the steep western slope
of Valle del Bove while there is little to see elsewhere. During a visit on
30 April, Boris Behncke (IGGUC) and others succeeded in descending into the
Valle del Bove to reach the effusive vents. The following was stated:
- There is one main effusive vent, at about 2700 m elevation (about 100 m below the rim of Valle del Bove), feeding several lava flows which in part disappear into lava tubes and resurface tens of meters downslope.
- The mean effusion rate appears to be around 1 cubic meter per second or slightly less.
- The maximum flow length is about 300 m.
- The farthest flow fronts are stagnant above the floor of the Valle del Bove.
- There is no explosive activity visible anywhere around the effusive vents.
- Only one feeder tube appears to be still active, located in the central part of the lava flow-field on the western slope of Valle del Bove.
The effusive vents are very difficult to reach. One needs to go across recent lava (most of it from the ongoing effusive activity initiated on 4 February 1999) on a steep slope (about 40 degrees). The material is exclusively blocky lava, which is crumbly and unstable. It is not recommended in any case to people not familiar with the area to try to reach the effusive vents and the lava flows. The best place to view the flows is the "Belvedere", on the rim of the Valle del Bove, some 300 m south of the southern margin of the 1999 lava flow-field. This is approximately located at the gray triangele to the southeast of "TDF" in the map above and can be reached via the dirt road going from Rifugio Sapienza to Valle del Bove (not the road leading up to Torre del Filosofo). Excursions are organized by the mountain guides of the C.A.I. (Italian Alpinists Club) who can be contacted at the lower and upper stations of the cable car (near Rifugio Sapienza).
|30 April 1999 photos|
Panoramic view of the tumulus formed at the end of the currently active
lava tube. Lava is issuing from one major ephemeral vent (at left) and flows
southeastwards (to the right).
Right: Close-up view of the ephemeral vent visible in the photo at left. A part of Valle del Bove is visible in the background.
View of the top of the tumulus with main ephemeral vent. Note uplifted block
of older lava to the right of the vent, and smooth lava in the foreground
which has been squeezed up through a crack in the tumulus..
Right: View from above of the ephemeral vent. Flows fed by ephemeral vents at lower elevations on the Valle del Bove slope are visible in the upper part of the image.
Bifurcating lava river below the main ephemeral vent, on the eastern (downslope)
side of the tumulus.
Right: Peculiarly shaped lava formations on the western (upslope) side of the tumulus.
29 April 1999
There is still lava flowing down the western slope of Valle del Bove, forming an incandescent ribbon several hundred meters long which is well visible at night from Catania and other locations southeast and east of the volcano. The lava issues from ephemeral vents on that slope, about 150 m below the rim of Valle del Bove; above those vents, there is practically no longer any surface lava flow. To the great disappointment of the crowds of tourists who are visiting the volcano each day, all flowing lava is far from accessible areas, and the main attraction is now the cluster of hornitos at the upper end of the 4 February fissure. These hornitos, however, are not active since early March. The upper part of the active lava flows has entirely roofed over, and there was only a small skylight near the Valle del Bove rim in the past few days (information from Jean-Pierre Kloster of the French Association Volcanologique Européenne, LAVE) which showed that active lava was at a depth of about 10 m. Kloster also reported his observations during visits to the summit craters. In the Voragine, the large southwestern vent had deep-seated activity (dull explosion noises were audible), but the floor of the vent was not visible. This is essentially how geologists of the Istituto di Geologia e Geofisica of Catania University saw the crater on 21 January 1999 (see January updates). The central pit of NE Crater was filled with gas so that no view of its interior could be obtained. At Bocca Nuova, the northwestern vent produced emissions of ash while the southeastern vent produced alternating emissions of ash and bluish fumes. Kloster also climbed to the summit of the SE Cone and confirmed the existence of a "terrace" several tens of meters below the crater rim; the lower part of the pit could not be seen due to a dense gas plume. These observations confirm the overall low level of activity in the summit craters.
22 April 1999
Lava continues to flow from the 4 February eruptive fissure at the base of the SE Cone, eleven weeks after the beginning of this eruptive episode. While surface activity above the rim of Valle del Bove has diminished notably (there are no longer any lava flows near the Valle rim), two main lava rivers are still spilling a few hundred meters down the western wall of the Valle, but flow fronts do not extend much below 2500 m. While the effusion rate appears to be constantly diminishing, lava may continue to be emitted for another few weeks. In any case, the most spectacular phase of this activity is over, and many of us who frequently visit Etna's summit area are waiting for a return of the activity to the summit craters, hoping to be greeted again by the spectacle of explosive eruptions such as those seen in the summer of 1998...
16 April 1999
Decreased lava effusion from the 4 February eruptive fissure at the base of
the SE Cone was observed during a visit by Boris Behncke and a German television
team to the site of the activity on 14 April. Near the western rim of Valle
del Bove, lava came to the surface only in a few places and produced very small
flows and lobes. The second area of extrusion, half way up the distance between
the Valle del Bove rim and the hornitos at the upper end of the 4 February fissure,
had two main effusive vents that fed chanellized flows. Activity here was definitely
more vigorous than in the lower area, but had decreased markedly since one week
A notable feature of the current effusive activity is the formation of pressure ridges, tumuli, and small-volume extrusions from cracks that open in older lavas. Most of this is caused by very slow intrusion of lava from tubes towards the surface once the flux through the tube is blocked or slowed, forcing the lava upwards. Lava oozes upwards through the cracks and may then form a new flow, but in many cases no reak flows form, but the lava rather forms bulbuous protuberances, or lobes, which often resemble the lobes of pillow lavas forming underwater.
The overall impression is that the effusive eruption initiated on 4 February is gradually tapering off, although it may still last a few weeks before ending definitely. However, it cannot be excluded that there will be a re-intensification of the activity, similar to that observed in late March. Once the lava outflow ends, magma will gradually rise again in the conduits of the summit craters and possibly produce more explosive activity.
|14 April 1999 photos|
Lava issuing from an ephemeral vent in the upper area of effusive activity.
Note lava dripping from roof of the mouth from a small surface flow. Width
of the flow channel visible in the foreground is about 1 m, flow velocity
is less than 1 m per second.
Right: HOT STUFF! German television crew filming an ephemeral vent close to the one shown in the left image. Working so close to an active lava flow, one is subjected to an enormous heat radiated from the lava. The expression of the person at left tells all.
View from above of an ephemeral vent and lava flowing through a craggy,
surrealistic landscape, in the upper area of effusive activity.
Right: In the lower area of effusive activity, near the rim of Valle del Bove, lava is slowly oozing up through a crack, without forming a real surface flow. Much of the effusive activity in this area consists of this slow pushing of lava from below, rasing the surface of the lava field without erupting much new material onto it.
13 April 1999
Lava emission from the 4 February fissure is continuing, though at slightly
reduced rate. The farthest lava fronts do not extend below about 2200 m, well
above the most advanced flow fronts in February and early March. Observation
from Monte Pomiciaro, on the southern rim of Valle del Bove, on the evening
of 12 April, permitted brief views of the flowing lava on the steep western
slope of the Valle while weather clouds were tossed and ripped by strong winds,
and a sea of dense clouds crept eastwards over the summit of the volcano.
Claude Grandpey, Roberto Carniel and Marco Fulle supplied information about recent visits to the summit area; Grandpey even managed to visit Bocca Nuova and the Voragine. There was no activity in the Voragine, and in the Bocca Nuova only the southeastern vent area emitted clouds of brown ash, probably caused by collapse deep in the conduits. This indicates that no magma is presently at the surface in these craters, all magma being erupted by the currently active eruptive fissure. Carniel and Fulle report a decrease in the eruption rate between 7 and 9 April at the effusive vents above the Valle del Bove rim.
Another bit of news today is that of an American tourist who ventured to the area of flowing lava yesterday evening or the evening before during bad weather conditions and got lost. He went with a friend, and at a certain point the two lost sight of each other in the dense fog. While the friend returned to the Rifugio Sapienza to ask for help, the American reached the area of flowing lava and awaited help near the active flows which provided a natural heating while air temperatures nearby were below zero. Rescuers eventually reached the unfortunate tourist and brought him to shelter. It was found that he had the soles of his shoes melted on the hot lava and got injured on his arms by falling on the surface of recent flows while walking around without orientation. This incident shows once more how easily one can get lost on the mountain during bad visibility, and that people who do not know the area should in any case avoid climbing to the summit area without trained guides. Weather conditions in these days are highly unfavorable, a condition that is typical of late-March and April at Etna, while in Catania the weather is already much like summer. Do in any case check as many web sites (or television programs) as possible that offer weather forecasts for the area, and only if all say that there will be perfectly fine weather for at least the next three days, there will be a reasonable chance to see Etna cloud-free (although this is by no means granted!).
8 April 1999
More than two months after its beginning, the mainly effusive eruption from
a fissure on the base of the SE Cone is continuing, though at slightly diminishing
rate. Lava flows continue to spill down the steep western face of Valle del
Bove, but their fronts extend much less far than those of earlier flows and
stop before reaching the base of the steep slope. A visit to the active area
was made yesterday (7 April) by Boris Behncke and geologists of Catania and
Switzerland together with Marco Fulle (Trieste Astronomical Observatory) and
Roberto Carniel (Stromboli On-line).At this time, numerous small surface flows
were active in two areas above the rim of Valle del Bove, one about half way
between the rim and the hornitos at the upper end of the 4 February fissure,
and the other just above the Valle del Bove rim. In the lower area, three or
four small flows advanced very slowly to a short distance from their feeding
vents which lay around a spectacular tumulus, or pressure ridges, formed as
magma pushed from below, raising blocks and slabs of older lava up to five meters
above their former elevation. Furthermore, the constant effusion of lava since
4 February has formed an impressive, delta-like ridge on the Valle del Bove
rim, built of countless lava tongues that have overflowed in this area.
The upper area of effusive activity, located at about 2850 m elevation, had five or six active effusive vents around a smaller tumulus, some which were rapidly changing in configuration and location while others remained stable. Two closely spaced vents produced fairly voluminous flows that advanced tens of meters downslope and had spectacular cascades in their upper parts. A small vent produced a flow that moved in a beautiful channel some 20 cm wide, whose form (as viewed from above) resembled the letter S; this vent froze over in less than two hours, and a new ephemeral vent became active some 20 m downslope.
No eruptive activity occurred above this area, but strong gas emission occurred from two places in the upper part of the 4 February eruptive fissure. The cluster of hornitos at the upper end of the fissure was quiet while profuse steaming occurred from the upper part of the fracture that split the southeastern side of the SE Cone on 4 February.
On the western wall of the Valle del Bove, lava issued from a number of ephemeral vents located about half way down the slope, feeding flows that advanced a few hundred meters downslope before stopping above the floor of the Valle.
The overall impression during the visit was that while lava effusion continued unabated, the rate of lava production was somewhat lower than during the first six weeks of the eruption, possibly in the range of 1-3 cubic meters per second. The volume of lava produced thus far exceeds 20 million cubic meters, which is fairly large for a summit eruption. The activity is expected to continue, but there are no means to estimate how long, and by what kind of events it will be followed. It is most likely that if the effusive activity ceases, there will be renewed activity from the summit craters, and the SE Cone is the most probable candidate for that activity.
|7 April 1999 photos|
This photo, though slightly hazy, shows clearly the prominent ridge built
by the accumulation of lavas on the rim of Valle del Bove since 4 February
1999 (it is visible in the upper central-right part of the photo), as seen
from the "Belvedere".
Right: As this lava flow slowly moves, its still-incandescent but rigid crust is broken up into slabs which are tilted and pushed over each other, forming a characteristic surface very hard to walk on (one the flow cools).
Two closely-spaced effusive vents in the upper area of effusive activity,
producing vigorous flows.
Right: Small effusive vent in the same general area as that in left image produces a snaking flow in a well-defined channel about 0.5 m wide near the bend at left. White dots on right side of flow in the background are pieces of garbage left by previous observers. This flow crusted over within less than one hour after this photo was taken, and lava began to issue from a point near the upper margin of this photo.
Vigorous effusive vent lying close to those shown in the previous two photos.
Width of the flow at the vent is about 1 m. A crust is slowly extending
downflow from the right to the left, one of the typical processes of incipient
lava tube formation.
Right: Peculiarly shaped lava flow issuing from a small ephemeral vent, located close to those shown in the previous photos, and extending downslope in two small branches (flow direction is from bottom to top).
Looking right into the mouth of a newly formed effusive vent, near the snaking
lava channel shown in the photo above at right. Note lava stalagtites (the
longest in the center is about 10 cm long) hanging from the roof of the
lava tube, and crust rapidly forming on flow surface as lava leaves the
Right: The closely spaced twin vents at sunset, with Montagnola in the background, a last impression of the splendor of the eruption when it was still vigorous.
1 April 1999
Eight weeks after its beginning, the eruption from the fissure at the southeastern
base of the SE Cone is continuing, and lava continues to spill into the Valle
del Bove. Bad weather has frequently hampered visual observations in these days,
but occasional views of the volcano at night revealed that there are surface
flows above the rim of Valle del Bove and numerous flows issuing from ephemeral
vents on the western slope of the Valle.
Note that this page will not be updated unless there are significant changes to the activity, or personal observations by myself or my colleagues.
Page set up on 17 May 1999