A Hazard Assessment of Mount Etna: Inference from Evolution & - - PowerPoint PPT Presentation

A Hazard Assessment of Mount Etna: Inference from Evolution & Geochemical Data

Oliver 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 Biancavilla ignimbrites

• 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

• ccurred 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 2000

Behncke 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 75 5 10 15 SiO (wt %)

Na O + K O (wt %)

Rhyolite Phonolite Tephri- Phonolite Phono- Tephrite Tephrite (Ol<10%) Basanite (Ol>10%) Picra- Basalt Basalt Basaltic Andesite Andesite Dacite Trachyte (Q<20%) Trachydacite (Q>20%) Trachy- Andesite Basaltic Trachy- Andesite TB

• cw500ka
• cw170
• cw1950
• cw1983
• cw1992
• cw1993
• cw2001A
• cw2001B

Key:

413 623 605 09.10.92 23.01.93 180701A 260701C

• After Le Maitre (1989)
• Over time magma has evolved from basaltic to trachybasaltic

AFM Discrimination diagram

Na O + K O

MgO FeO* Tholeiitic Calc-Alkaline

• cw500ka
• cw170
• cw1950
• cw1983
• cw1992
• cw1993
• cw2001A
• cw2001B

Key:

413 623 605 09.10.92 23.01.93 180701A 260701C

• 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

• Two activity cycles of

eruptions observed

• Cycles from 1950-1992

and 1993-present

• CaO, FeO, & TiO2

decrease throughout a cycle

• SiO2, Al2O3, & Na2O

increase throughout a cycle

• cw500ka
• cw170
• cw1950
• cw1983
• cw1992
• cw1993
• cw2001A
• cw2001B

Key:

413 623 605 09.10.92 23.01.93 180701A 260701C

Cyclic Behaviour

• Project confirms the findings of Behncke and Neri

(2003), who suggested the same cycles

• Three cycle phase:

1) Degassing of summit area 2) Strombolian summit activity with short lava flows 3) 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

N

Number-Density Distribution of Vents

10+ 8-9 6-7 4-5 2-3

The number-density distribution of vents per 4km

N

Final Hazard Map

Strombolian eruptions and Pyroclastic Flows Lava flows from summit craters Lava flows from flank eruptions

Key

Summit Craters

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&hei ght=400&gride=&gridn=&srec=0&coordsys=mercator&db=IT&addr1=&addr2=&addr3=&pc=&adva nced=&local=&localinfosel=&kw=&inmap=&table=&ovtype=&keepicon=&zm=0&scale=2000000&l eft.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?