Anatomy of an unstable volcano from InSAR: multiple processes affecting flank instability

at Mt. Etna, 1994-2008

ACOCELLA V1., SOLARO G2., PEPE S2., RUCH J1. NERI M3. SANSOSTI E2.

1 Dip. Scienze Geologiche Roma Tre, Roma, Italy; 2 IREA CNR, Napoli, Italy;

3

INGV, Catania, Italy.

PROBLEM

Important studies on volcano deformationproduced in the last decade, improving our knowledge

Most studies focused on specific episodes (unrests, eruptions or parts of), so that this knowldege remains

confined to the short-term

(<years)

Large data archives enable studying the mean-term

(decades) deformation, putting the single episode in a wider perspective and

capturing the dynamic behavior of volcanoes

Here we consider the mean-term, ‘piece by piece’

deformation of Etna over 15 years to understand its behaviour

METHODOLOGY

InSAR analysis

Database139 ascending and 120 descending SAR data

acquired by the ERS 1, ERS 2 and Envisat sensors between 1992-2008to compute 372 interferograms from ascending orbits and

347 interferograms from descending orbits

SBAS (small baseline subset) approach developing time seriesresolving horizontal (E-W) and vertical displacements from LOS displacement

using a multi-sensor analysis

TECTONIC SETTING OF ETNA

Ionian oceanic

lithosphere

3 radialRift zones

STRUCTUREOF ETNA

Pernicana + Ragalna:boundaries of

collapsing sector

Volcanic activity (1994-2008):

a)

Progressive increase in summit activity (‘94-’00)

(magma storage)

b) Major eruptions (‘01-’03) (dike emplacement on flanks)

c) Minor eruptions (‘04-’08)(volcano summit)

Study deformation at Etna in the 1994-2008 period, characterized by distinct features, and possibly belonging to a cycle of activity

(Neri et al., 2009)

E flank eastwardW flank westward.

Asymmetries increase after 2003.

Periods with linear behaviour (‘94-’00 and ‘03-’08)

Volcano inflation before 2000.

Continuous distal uplift.

The E Flank

1994-20002003-2008

The distal E Flank

Fault–bounded sectors (some are rigid blocks) with defined

E-W and/or vertical kinematics

E-W

E-W

Vertical

Vertical

The W Flank

1994-20002003-2008

The distal W Flank

Fault-bounded sectorswith quite defined

E-W or vertical kinematics

E-W

Vertical

E-W

Vertical

E flank eastwardW flank westward.Most deformation

within E-W elongated area.

Nward migration of deformation

Period with non-linear behaviour (2000-2003)

Deflation of summit,where most E-W

deformation occurs.Distal uplifted areas.

2001 eruption dike

2002 eruption dike

See poster by Ruch et al

Distal uplifted areas (‘94-’08)

3 examples of cross correlation analysis (index =0.95) of pixels with consistent trend of uplift

Uplift due to fault-propagation fold.Uplift tangential to distal edifice:

due to volcano load(Borgia et al., 2000; Lundgren et al., 2004),

rather than regional compression(Monaco et al., 2002).

A synthesis: linear periods

2003-2008 period:a)

significant asymmetry in the slip of the E flank;

b)

influenced by the emplacement of the 2001 and 2002 dikes.

3 main processes responsible for deformation at Etna between ‘94-’08

Asymmetric deformation (> eastward) due to the differential buttressing at the volcano base.

Inelastic strain due to dike emplacement, even though shorter in

time, is much larger (in amount) than elastic strain due to inflation.

always 1994-2000 2001 and 2002

Asymmetric deformation due to differential buttressing (Froger et al., 2001)

Confirmed by analogue models (Norini and Acocella, 2011): differential unbuttressing is the preparing factor for E flank instability at Etna

CONCLUSIONS

Whatever the activity (dike emplacement, magma storage, inactivity), flank instability is widespread and remains the

dominant type of deformation at Mt.Etna,amplified by the differential unbuttressing conditions.

The distal portions of the flanks of Etna consist of fault-bounded sectors, at times with rigid behaviour.

Deformation results from 3 processes (loading, inflation, diking), acting at different time-scales and

different amount of elastic and inelastic strain.

Solaro et al., 2010, JGR

4th International WORKSHOP on Collapse CALDERASSeptember 23-29, 2012, Vulsini Calderas, Bolsena, Italy

2nd International COURSE on Collapse CALDERASSeptember 19-23, 2012, Bolsena Caldera, Italy

http://www.gvb-csic.es/CCC.htm

1994-2008E-W deformation

time

seriesfor

each

sector

1994-2000 and 2003-2008deformation

time

seriesfor

each

sector

A part of

the post-2003deformation

is

influencedby

the emplacement

ofthe 2001 and 2002 dikes(sectors

keep

on showinga consistent

kinematics)