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
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).
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
before.
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.
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.
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