NOTE: The
restrictions to excursions to Etna's summit area have been
significantly modified.
Free access is now allowed to up to 2500 m elevation (south
flank) and 2600 m (north flank), four-wheel-drive tours
go up to 2900 m on the southern flank (to the place where
there was once the Torre del Filosofo mountain hut, and
close to the newly formed craters) and to about 2500 m on
the northern flank (Piano Provenzana area and entire fissure
of the 2002-2003 eruption). Guided excursions for groups
of up to 10 persons may visit any spot on the mountain.
Read more on the Etna Excursions
page
|
The
latest update is below this line
31
July 2003 update.
There
has been further seismicity in the eastern sector of Mount Etna
in the past ten days, which culminated in a burst of four small
earthquakes (magnitudes up to 2.6) on 30 July 2003 that affected
an area between the villages of Milo and Zafferana on the eastern
flank of the volcano. Earthquakes of similar magnitudes (basically
ranging in magnitude from 2 to about 2.5) had occurred at a rate
of about one every one or two days previously, but they were scattered
over a broad area in the eastern sector of Etna. At the summit craters,
vigorous degassing continues at the Northeast Crater, and some less
intense degassing is occurring at the Bocca Nuova. There are no
indications of true eruptive activity, but the volcano remains restless.
20
July 2003 update.
Mount
Etna does not seem all that much of an active volcano in these days,
except for the (sometimes impressing) gas plume that is being emanated
from the summit craters, among these mostly from the Northeast Crater.
Yet the volcano continues to provide more or less gentle reminders
that the current quiet period is only temporary, that magma is again
accumulating below the mountain, and that new eruptive activity
is probably only a few weeks to months away.
There are four craters at the summit of Etna, two of which have
one single vent (the Northeast and Southeast Craters), while the
Bocca Nuova and the Voragine have two vents, respectively. Of this
total of six vents, three are currently obstructed, while the other
three are showing more or less intense degassing. The presence of
obstructed vents within the summit craters is not really a happy
thing, because one day, the one or the other of them will reopen,
and this process might be explosive to some degree. There are indications
that the southeastern pit of the Bocca Nuova, obstructed since many
months, is gradually reopening. Minor emissions of brownish ash
from this pit were most recently noted on 18 July. No other eruptive
activity has been observed at the volcano ever since the latest
flank eruption ended on 28 January 2003.
But the volcano is restless indeed, and it is very likely that it
is already preparing its next eruption. Seismic activity has never
really ceased since late January 2003, and seems to have picked
up somewhat in the past three to four weeks, culminating in an earthquake
on the Pernicana Fault System on 17 July, which was perceived by
many people on the northeastern flank of Etna. The magnitude of
that earthquake was probably around 3 and its focal depth quite
shallow, as is common at the Pernicana Fault System. A rapid field
investigation carried out a few hours after the event revealed that
there was no evident ground fracturing in the areas affected by
significant ground fracturing and deformation during previous earthquakes
in the same area. However, repeated surveys of the Pernicana Fault
System in many locations between about 1800 m elevation (Northeast
Rift) and the Ionian coast (to the north of Giarre) through mid-July
show that displacement along this fault system has never ceased
since the dramatic slip of Etna's eastern flank at the beginning
of the 2002-2003 eruption (a publication dealing with this subject,
written by Neri, Acocella and Behncke, will likely appear in the
Bulletin of Volcanology later this year). The Pernicana Fault System
is nothing else but the northern boundary of a large portion of
Etna's flank that is slowly sliding towards the Ionian Sea, a process
that seems to be common at basaltic volcanoes and is also observed,
even on a larger scale, at Kilauea volcano (Hawaii). Slippage of
the unstable eastern flank of Etna is often associated with flank
eruptions, which was dramatically manifested in October-November
2002. The fact that movement of the unstable flank is continuing
is not reassuring.
So this is why we return to the good old question "when will
there be the next eruption of Etna?" And the answer is, as
always, that no one really knows. There is a lot of betting among
geologists working on Etna in these times, and most bets are in
favor of a new eruption before the end of 2003. Besides that, it
is quite logical to assume that the volcano is recharging at more
or less the same rate as it has done after the 2001 eruption, because
there is simply no reason to believe that much has changed in the
magma supply rate with the latest eruption. True enough, the 2002-2003
eruption produced about twice as much of magma as the 2001 eruption,
but this does not necessarily hold any clue regarding the length
of the ensuing repose period. It is more likely that the volume
of a flank eruption depends on a very subtle interplay between the
quantity of available magma and the degree of instability of the
volcanic edifice. And currently, the edifice is more unstable than
at any time during the past decade.
A quite sensible question concerns the character of the next eruption.
Will it be as explosive as the previous one, will it once more produce
enormous quantities of ash and thus render life, traffic and business
in the densely populated Etna region difficult? This will be in
part determined by the "new" magma source below the southern
flank of the volcano, which yielded most of the eruptive products
in both the 2001 and 2002-2003 eruptions. If this source continues
to produce magma, the next eruption will probably be quite explosive,
although explosivity is also strongly related to phreatomagmatism,
i.e. interaction of magma with subsurface or surface water. In fact,
much of the ash-producing activity in 2001 and 2002-2003 was phreatomagmatic.
Phreatomagmatism can be expected if the vents of a future eruption
once more open in the area once called "Piano del Lago",
the Plain of the Lake, located between 2500 and 2900 m on the southern
flank. The name is no longer justified, for the area is now dotted
with three large pyroclastic cones that grew during the 2001 and
2002-2003 eruptions, and if another explosive eruption occurs there
it will become a true mountain range.
To see how Etna looks like in these days, visit the new and growing
photo gallery "Return to Etna, 2003".
Many photographs taken during 14 years of visits to, and life near,
Mount Etna are available in the Etna
photo gallery.
A
summary of the 2002-2003 eruption
Piano
Provenzana - a requiem