Two New Strainmeters Installed on Mt. Etna
In November 2014, a DTM team led by Alan Linde travelled to Mt. Etna in Sicily, Italy, to install two strainmeters and double the number of such sites on the volcano. This program is in collaboration with the Istituto Nazionale di Geofisica e Vulcanologia (INGV) of Italy with principal collaborator Alessandro Bonaccorso.
Mt. Etna, which is in an almost constant state of activity, is the tallest active volcano in Europe, currently reaching an elevation of 10,922 ft. On 28 December 2014, the volcano endured its most intense eruption since December 2013, which was well recorded by Linde and DTM staff member emeritus, Selwyn Sacks, thanks to their two newest strainmeters.
These strainmeters are placed in boreholes to measure the deformation of the hole, in particular they record the change in volume of the sensing volume (2.75 inch diameter, 10 feet long) with a sensitivity of 10**-11 (0.01 nano strain) over a very wide frequency range. Data are then logged on site at 24 bit resolution and sample rate 50 sps.
Wintery weather conditions presented a real concern for one of the installation sites, Pizze Deneri, situated close to the summit of the volcano. Luckily a couple of exceptionally good days this past November, together with the expertise of the INGV team, helped the installation reach completion. This high elevation site promises to be an important location.
Located just 1,922 ft from the summit, Linde and Sacks are now able to collect the most detailed characteristic behavior of the mountain’s volcanic activity. Following the December 28 eruption, the Pizze Deneri strainmeter collected a more pronounced upswing before the decrease in amplitude, shown below, whereas the other sites’ upswing recording of the same eruption was less obvious due to it’s far proximity from the magma reservoir, or the activity’s source.
|DPDN raw data from 27 to 29 Dec2014. Raw data in the upper figure, linear filtered data in the bottom figure. Negative change started on 28 Dec around 13:40 to 15:36 showing a positive signal of ca. 11.500 counts preceding the paroxysm, then till 19:06 a negative signal is recorded cumulating 37.500 counts. (2014)|
“It’s because of that sort of characteristic behavior that we needed to get a site in as close as we could to the source of the activity,” says Linde.
The second site, Monte Scavo, was positioned at a much lower elevation and was installed successfully a week following the first insallation.
Etna has been particularly active in recent years. The Dec. 28 eruption produced two main lava flows, one of which reached the entrance of the park road Linde and his team, including DTM’s Michael Acierno, Tyler Bartholomew, Mike Crawford, and Brian Schleigh, used to reach the Monte Scavo location just weeks before.
The installation sites range from just a couple of kilometers to about 10 km from the summit. This allows the team to coherently determine the location and other properties of the magmatic reservoir. They search for strong, competent rock, at approximately 130 m to 200 m in depth, for their installation sites by relying on the best available geological advice.
Their first strainmeter was installed in 1979 at Mt. Hekla in Iceland. Since then, they’ve installed them at a number of active volcanoes, including Stromboli, Mt. Vesuvius and Campi Flegrei in Italy, Soufriere Hills in Montserrat, and Long Valley caldera in California.
Later this year two more will be installed, one in Campi Flegrei and another in Iceland close to the Katla volcano.
Recent papers by the collaborative team are linked below.
"From source to surface: dynamics of Etna’s lava fountains investigated by continuous strain, magnetic, ground and satellite thermal data." A. Bonaccorso, S. Calvari, G. Currenti, C. Del Negro, G. Ganci, A. Linde, S. Sacks, and A. Sicali. Bull. Volcanol., 75, 690. 2013.
"New data from borehole strainmeters to infer lava fountain sources (Etna 2011-2012)." A. Bonaccorso, G. Currenti, A. Linde, and S. Sacks. Geophys. Res. Lett., 40, 3579-3584, doi:10.1002/grl.50692. 2013.
This research project is funded by the Instituto Nazionale di Geofisica e Vulcanologia (INGV) with the Italian Civil Defense.
Written by Robin Dienel, 15 January 2015
Photos from Mt. Etna
(Photos by Alan Linde, DTM)