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 13 th June – 10 th 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 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 Behncke et al (2003) • Similar pyroclastic flow advanced 1km from SE crater in 2000

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 Key: 15 ocw500ka Phonolite ocw170 ocw1950 ocw1983 Tephri- Trachyte Phonolite ocw1992 (Q<20%) Na O + K O (wt %) Trachydacite ocw1993 (Q>20%) 10 Phono- ocw2001A Tephrite Rhyolite Trachy- ocw2001B 2 Andesite Tephrite Basaltic (Ol<10%) 413 2 Trachy- Basanite Andesite 623 (Ol>10%) TB 605 5 09.10.92 23.01.93 180701A Dacite 260701C Basaltic Andesite Picra- Basalt Andesite Basalt 0 35 45 55 65 75 SiO (wt %) 2 • After Le Maitre (1989) • Over time magma has evolved from basaltic to trachybasaltic

AFM Discrimination diagram FeO* Key: ocw500ka ocw170 ocw1950 ocw1983 ocw1992 Tholeiitic ocw1993 ocw2001A ocw2001B 413 623 605 Calc-Alkaline 09.10.92 23.01.93 180701A 260701C Na O + K O MgO 2 2 • 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

2 14 Major Element Key: TiO (wt %) CaO (wt %) ocw500ka 12 2 1 ocw170 Variation 10 ocw1950 ocw1983 0 8 Diagrams ocw1992 50 6 ocw1993 49 Na O (wt %) 5 wt %) ocw2001A 48 SiO ( 2 2 • Two activity cycles of 47 4 ocw2001B 46 3 eruptions observed 45 413 44 2 623 22 4 21 • Cycles from 1950-1992 605 Al O (wt %) 19 3 K O (wt %) 09.10.92 17 3 and 1993-present 2 2 2 15 23.01.93 13 1 180701A 11 •CaO, FeO, & TiO 2 260701C 9 0 14 1 decrease throughout a 0.9 13 0.8 FeO* (wt %) P O (wt %) 0.7 12 cycle 0.6 5 2 11 0.5 0.4 10 0.3 0.2 •SiO 2 , Al 2 O 3 , & Na 2 O 9 0.1 8 0 2 4 6 8 10 12 MgO (wt %) increase throughout a 0.2 MnO (wt %) cycle 0.1 0 2 4 6 8 10 12 MgO (wt %)

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?

Population Centre Summit Craters Contour Map in 250m increments Key N 2km

Number-Density Distribution of Vents N 2km The number-density distribution of vents 2 per 4km 10+ 8-9 6-7 4-5 2-3

Final Hazard Map N Key 2km Strombolian eruptions and Pyroclastic Flows Lava flows from summit craters Lava flows from flank eruptions Summit Craters

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

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