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?