Etna "cools down," 180 tremors recorded in three days last week, Mareneve road
repaired to allow tourists to enjoy Pasquetta holiday(SEE ATTACHED PHOTOS)
(LA Sicilia / Ingv Volcanology Institute local reports and photos) Catania -
Fear in the province of Catania last week for a very prolonged seismic swarm
which had its peak on Friday, April 2 at 22:04 with a jolt of magnitude 4.2 on
the Richter scale. The events, located in North-Eastern of the Etna upstream
of Linguaglossa- village Mareneve, were defined by the researchers of the
Institute of Volcanology Catania "very superficial and then well experienced
in many municipalities of Catania". The last four tremors (magnitude 2.0 and
2.5) were recorded last night in the Linguaglossa area.
Numerous telephone calls were made to emergency numbers, but no damage was
reported.
The cracks on Mareneve road caused by the tremors were promptly repaired and
opened over the weekend to allow tourists to enjoy the Pasquetta holiday.
A 2.0 earthquake was also recorded on the Nebrodi mountains (Messina
province) on Sunday night.
Since March 16, volcanologists have indeed been monitoring what they called an
"apparent quietness" of Etna to keep under control a possible ascent of magma
to the surface from the new "mouth" which opened on Nov.
6, 2009 on the Southeast Crater. Already last Tuesday, another shock of
magnitude 2.4 was recorded by instruments of the Ingv Volcanology Institute of
the Linguaglossa area.
On the late evening of 2 April 2010 (22.04 h -local time = GMT+2), the
Pernicana fault ruptured for the first time since nearly 6 years, with a
series of earthquakes the strongest of which had a magnitude of 4.2. The
hypocenter - that is the exact location where the earthquake is generated -
lies only about 1 km below the surface, which is typical for Pernicana
earthquakes. That means, the quake is not very widely felt but close to its
source it is felt very strongly. Most of the Pernicana earthquakes -
especially those with magnitudes above 4 - produce impressive ground
fracturing, and this time is no exception.
The Pernicana fault is the most active of the more than a dozen faults that
cut through the flanks of Mount Etna and often produce shallow earthquakes,
which at times are accompanied by spectacular ground fracturing. Although the
fault was discovered only in 1981, it has produced numerous earthquakes,
sometimes with magnitudes exceeding 4.
Ground rupturing occurred five or six times in the 1980s, then nothing
happened for 14 years, before the Pernicana ruptured spectacularly in the fall
of 2002 and several times again in 2003-2004.
The patterns of fracturation on the "Mareneve" road near the "Ragabo"
mountain hut (at about 1350 m elevation) is strikingly similar to those
observed during earlier events when the Pernicana ruptured. This happened
frequently in the 1980s (1981, 1984, 1985, 1986, 1988) and again in 2002,
2003, and 2004. In this location, photographs taken during some of the earlier
events show nearly exactly the same fracture patterns. In numerous places
along the "Mareneve" road, old cracks remained from previous episodes of
ground fracturing near the Pernicana.
Most of these reactivated during the fault slip last week, and in places
fine-grained material was ejected from the cracks.
The "Mareneve" road, which leads from the town of Linguaglossa on Etna's
northeast flank up to the tourist station Piano Provenzana (or what remains of
it; it was completely devastated by lava flows in 2002, and recently the few
souvenir shops opened at the site were consumed by a mysterious fire), showed
the scars of the fault movement. The Pernicana, which in total is 18 km long,
runs along the "Mareneve" road in three places, and each time the fault
ruptures, the road shows intense ground fracturing. This was first observed in
the 1980s when the Pernicana ruptured nearly every year, and again in 2002,
2003, and 2004. There have been earthquakes at the fault more recently, the
latest occurred (and in a way announced) the 2008-2009 flank eruption of Etna.
This is the first time since 2004 that ground fracturing has occurred.
Deep cracks up to 15 cm wide ripped through the "Mareneve" road in the dense
pine forest "Ragabo" on the northeast slope of Etna. The largest cracks were
temporarily patched with bitumen, though this is a gesture more symbolic than
practical, These wounds will take time to be healed, especially if this new
seismic sequence is the start of a whole series of events, like in the period
2002-2004, local experts said.
Spectacular ground fracturing was also observed in a stretch of terrain (SEE
ATTACHED PHOTO) about 1 km long (possibly a bit more), mostly along
constructions such as buildings, walls, and roads. But here and there the
terrain shows evidence for the violence of the fault displacement, like here,
where a sort of a graben opened, with a drop of 1.2-1.5 m.
The mountain hut "Ragabo" is one of the most charming places to do a miniature
vacation for people living around Etna, and certainly a fine place to stay for
people coming from elsewhere. Each time the Pernicana shakes and rips open
(SEE ATTACHED PHOTO) the nearby "Mareneve" road, the "Ragabo" suffers some
damage - cracks in walls, plaster coming off, and that sort of things.
The attached map of the northeast flank of Mount Etna (SEE ATTACHED PHOTO),
shows the full known extent of the Pernicana Fault (or fault
system) as a red line. The fault produced about 180 earthquakes between
2 and 3 April 2010, the strongest with magnitude 4.2, and spectacular ground
fracturing in the area here marked by a little "2".
Most volcanoes on Earth have one single summit crater, often that's the only
crater they have. Etna has FOUR summit craters (plus more than 300 craters on
its flanks, but each one of these erupts only once, while the summit craters
erupt over and over again). In a May 2008 photo (SEE ATTACHED PHOTO), it is
possible to see the "ensemble" from a helicopter of the Italian Civil Defense
Department. The dense white gas plume at left comes from the Northeast Crater,
which at 3329 m is the highest point on the volcano. In the foreground it's
possible to see an arrangement of large pits that resembles a cloverleaf; the
two nearer pits are what once was a single huge crater named Bocca Nuova (new
mouth). Behind them lies the Voragine (big mouth). A bit to the right stands a
cone with a small, sulfur-rimmed crater, this is the youngest of Etna's summit
craters, born in 1971: the Southeast Crater. This is also the most active of
the four, since 1995 it has been the source of at least 200 short, violent
episodes with amazingly tall (1000+ m) lava fountains, the most recent on 10
May 2008.