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A Hazard Assessment of Mount Etna: Inference from Evolution
& Geochemical DataOliver Charles Wright
Hemis 339860
Project Aims
• Research the eruptive history of Mount Etna
• Analyse the volcanic hazards and from this create a hazard map
• Discuss remediation and mitigation measures
Logistics
• Fieldwork 13th June – 10th July 2006• Catania used as a base• Hire car used for transport• Cable car at Rifugio Sapienza used to
reach summit & Valle del Bove• Detailed literature study of 130+ papers on
return
Location
• Etna lies on the east coast of Sicily near Messina & Catania
• N 37º45 E 14º59• Covers 1,190km², circumference 140km, 3350m
high
Multimap.com (2003)
Tectonic Setting
• ‘Slab-Window theory (Doglioni et al, 2001) creating magma through rollback of lithosphere
• Patane et al (2006) believe rollback occurs along the Malta Escarpment
Above: Doglioni et al (2001); Right: Behncke (2001)
Ancient Activity• Basal Tholeiite Volcanics 500ka-170ka
producing pillow lavas and intrusives
•Trifoglietto 170ka-25ka producing hawaiites & mugearites, caldera collapse & block and ash deposits
Ancient Activity• Ancient Mongibello 25ka-5ka
producing hawaiites, basic mugearites, mugearites & benmoreites. Evidence of caldera collapse from Biancavillaignimbrites
• Mongibello 5ka-1ka producing hawaiites. Caldera collapse to form Valle del Bove, allowing older products to be observed
Historical & Present Day• Hawaiites & Trachybasalts
• 4 Active summit craters constantly degassing. Can produce strombolian eruptions and up to 7km lava flows
• Flank activity produces larger volumes and higher effusion rates, generating more evolved lava flow fields
• Eruptions of between 0-3 VEI
Behncke et al (2006)
Eruptive Characteristics
• Flow length dependent on eruptive volume, slope angle, effusion rate and composition
• Majority of flows are aa lavas, with major lengthening in 48 hours
• Channelling and tube-fed flow fronts allow further extension than in open channels
• Complex flow systems
2001 Eruption• Most explosive event in
living memory• 7 vents formed a 6.9km
flow field, destroying a road and cable car station
• Ash caused closure of Catania airport, and reached 500km from Etna
• Summit-lateral and eccentric eruptions occurred together, only seen before in 1974
Behncke and Neri (2003)
Pyroclastic Flows• Remain uncommon, but continue to occur• 1999 flow from Bocca Nuova Crater reached 700m in length
covering 20m/s
• Similar pyroclastic flow advanced 1km from SE crater in 2000Behncke et al (2003)
Thin section Analysis• 5 lava thin sections: 170ka, 1950, 1983, 1992, 2001• All samples silica undersaturated• Abundant olivine gives way to augite and plagioclase• Recent lavas abundant in phenocrysts, forming
glomerolar textures, which suggests a crystal mush forms beneath the surface
170ka lava scale in 0.2mm increments 1992 lava
TAS Discrimination Diagram
35 45 55 65 750
5
10
15
SiO (wt %)2
NaO
+ K
O (
wt %
)2
2
Rhyolite
Phonolite
Tephri-Phonolite
Phono-Tephrite
Tephrite(Ol<10%)Basanite(Ol>10%)
Picra-Basalt Basalt
BasalticAndesite
Andesite
Dacite
Trachyte(Q<20%)Trachydacite(Q>20%)
Trachy-Andesite
BasalticTrachy-Andesite
TB
ocw500kaocw170ocw1950ocw1983ocw1992ocw1993ocw2001Aocw2001B
Key:
41362360509.10.9223.01.93180701A260701C
• After Le Maitre (1989)
• Over time magma has evolved from basaltic to trachybasaltic
AFM Discrimination diagram
Na O + K O2 2 MgO
FeO*
Tholeiitic
Calc-Alkaline
ocw500kaocw170ocw1950ocw1983ocw1992ocw1993ocw2001Aocw2001B
Key:
41362360509.10.9223.01.93180701A260701C
• After Irvine and Baragar (1971)• Shows activity has moved from a tholeiitic to calc-alkaline trend• Suggests that the ‘Slab Window’ Theory is correct, as it contrasts with thin
section findings, suggesting a subduction relationship
Major Element Variation Diagrams
44
45
46
47
48
49
50
SiO
(w
t %)
2
0
1
2T
iO (
wt %
)2
9
11
13
15
17
19
2122
AlO
(w
t %)
23
8
9
10
11
12
13
14
FeO
* (w
t %)
2 4 6 8 10 120
0.1
0.2
MgO (wt %)
MnO
(wt
%)
8
10
12
14
CaO
(wt %
)
2
3
4
5
6
Na
O (
wt %
)2
0
1
2
3
4
KO
(wt
%)
2
2 4 6 8 10 120
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
MgO (wt %)
PO
(w
t %)
25
• Two activity cycles of eruptions observed
• Cycles from 1950-1992 and 1993-present
•CaO, FeO, & TiO2decrease throughout a cycle
•SiO2, Al2O3, & Na2O increase throughout a cycle
ocw500kaocw170ocw1950ocw1983ocw1992ocw1993ocw2001Aocw2001B
Key:
41362360509.10.9223.01.93180701A260701C
Cyclic Behaviour• Project confirms the findings of Behncke and Neri
(2003), who suggested the same cycles• Three cycle phase:1) Degassing of summit area2) Strombolian summit activity with short lava flows3) Flank eruptions producing lava flows. Increased
explosivity of summit craters
• Cycle ends with voluminous eruption, e.g. 1950-51 & 1991-1993 flows
• Third stage of current cycle began in 2001?
Contour Map in 250m increments
Population Centre
Key
Summit Craters
2km
N
Number-Density Distribution of Vents
10+
8-9
6-7
4-5
2-3
The number-density distribution of vents
per 4km2
2km
N
Final Hazard Map
Strombolian eruptions and Pyroclastic FlowsLava flows from summit cratersLava flows from flank eruptions
Key
Summit Craters
2km
N
Mitigation and Management• Before an Eruption• Tourist area should be protected by lava barriers• Shelters built to protect tourists from summit eruptions• Warning system and education for locals
Barriers installed before the 2001 eruption (Barberi et al, 2003)
Mitigation and Management• During an Eruption• Alerts given if threat to population or
explosive activity such as 2001 & 2002-03 via TV radio and possibly text message
• Barriers can be installed at lower altitudes
• Breaking of lava channels is successful
• Lava cooling is not feasible due to lack of water
Lava diversion through explosives (Romano, 1992)
Mitigation and Management & Future Work
• After an Eruption• All shelters and lava diversions should be checked for
damage and restored• Hazard map should be updated
• Future Work• Hazard map requires use of smaller contour intervals• Continued tests on lavas to better understand Etna’s
hazards• Creation of a GIS model to aid hazard map and produce
vulnerability and risk maps
Conclusions• Present day lavas are predominantly trachybasaltic aa
flows• Cyclic activity producing:• Strombolian products and Pyroclastic Flows close to
summit areas• Extensive lava flow fields from flank vents produced
along fault zones• Possible but rare ash falls to the SE• An alert system and shelters should be installed• Hazard map should be updated after each eruption
References• Barberi, F., Brondi, F., Carapezza, M.L., Cavarra, L., & Murgia, C. (2003) Earthen barriers to
control lava flows in the 2001 eruption of Mt. Etna.• Behncke, B. (2001) http://boris.vulcanoetna.com/ETNA_evolution.html• Behncke, B., & Neri, M. (2003) The July-August 2001 eruption of Mt. Etna (Sicily). Bulletin of
Volcanology, Volume 65, pp 461-476.• Behncke, B., Neri, M., & Carniel, R. (2003b) An exceptional case of endogenous lava dome
growth spawning pyroclastic avalanches: the 1999 Bocca Nuova eruption of Mt. Etna (Italy). Journal of Volcanology and Geothermal Research, Volume 124 pp 115-128.
• Behncke, B., Neri, M., Pecora, E., & Zanon, V. (2006) The exceptional activity and growth of the Southeast Crater, Mount Etna (Italy), between 1996 and 2001. Bulletin of Volcanology, Volume 69, pp 149-173.
• Doglioni, C., Innocenti, F., & Mariotti, G. (2001) Why Mt Etna? Terra Nova, Volume 13, pp 25-31.• Irvine, T.N., & Baragar, W.R.A. (1971) A guide to the chemical classification of the common
volcanic rocks. Canadian Journal of Earth Sciences, Volume 8, pp 523-548.• Le Maitre, R.W. (1989) A Classification of Igneous Rocks and Glossary of Terms. Cambridge:
Cambridge University Press.• Multimap.com (2003) Map of Italy. Retrieved on 24th April, 2007, from
http://www.multimap.com/map/browse.cgi?client=public&X=1800000&Y=4500000&width=700&height=400&gride=&gridn=&srec=0&coordsys=mercator&db=IT&addr1=&addr2=&addr3=&pc=&advanced=&local=&localinfosel=&kw=&inmap=&table=&ovtype=&keepicon=&zm=0&scale=2000000&left.x=4&left.y=146. Last updated in 2003.
• Patanè, G., La Delfa, S. & Tanguy, J-C. (2006) Volcanism and mantle-crust evolution: The Etna case. Earth and Planetary Science Letters, Volume 241, pp 831-843
• Romano, R. (1992) Continued lava production from SE flank fissure; Lava diversion summarised. BGVN 17:07
Any Questions?