1. Jury:
Dr. Luca Caricchi
Supervisors:
Prof. Costanza Bonadonna
Dr. Laura Pioli
Dr. Paul Cole (Plymouth University)
https://feww.wordpress.com
Tephra plume developed at 13:27 on 11 Feb 2010

2. 2
Fine airborne volcanic particles (< 63 µm) adhere to each other:
 electrostatic forces (Gilbert and Lane 1994)
 moist adhesion (James et al 2002)
 hydrometeor formation (Durant et al. 2009)
… and form ash aggregates.
http://ehp.niehs.nih.gov/121-a197

3. Consequence : reduction atmospheric residence time of fine ash.
 Increase fine ash fallout 10 -100 km from volcano
 Reduction airborne fine ash 1’000 km distance
(Brown et al. 2012)
http://www.arctic-dreams.com/en/living_earth
Eyjafjallajökull 2010

4. 4
 Aggregation is not fullly understood
 Modelling of tephra fall
 Improve hazard assessment :
‒ Health impact (particles < 10 µm)
‒Economic impact (risk to aviation)
Tephra fall , Eyjafjallajökull 2010
http://icelandinpictures.com
https://rainbowwarrior2005.wordpress.com
http://www.strangedangers.com

5. 5
 New info about aggregation by correlating aggregates characteristics with source
 Variation in size and shape of aggregates with distance from source
 Internal structure and internal grain size of aggregates

6. 6
 Introduction
 11 Feb 2010 partial
dome collapse
 Methodology
 Results
 Conclusion
 Perspectives
https://volcanosss.wordpress.com

7. 7
Introduction 11 Feb 2010 Methodology Results Conclusion Perspectives
http://www.earthweek.com

8. 8
Introduction 11 Feb 2010 Methodology Results Conclusion Perspectives
 17 active volcanoes
 Lesser Antilles Volcanic Arc
 Subduction of Atlantic oceanic
lithosphere beneath the
Caribbean plate (Kokelaar 2002)
http://www.earth-of-fire.com

9. 9
Introduction 11 Feb 2010 Methodology Results Conclusion Perspectives
 Pelean volcano, andesitic magmas
(58-64% SiO2) (Sparks & Young 2002)
 Type of activity: dome collapses and
Vulcanian explosions
 Renewal of activity in 1995
2/3 of population left the island
Current population 5’000 people
 60% of the island : exclusion zone
(access forbidden ) (Kokelaar 2002)
http://commons.wikimedia.org/wiki/File:Montserrat

10. Block-and-ash flow at Soufriere Hills, Montserrat
http://www.photovolcanica.com

11. 11
Introduction 11 Feb 2010 Methodology Results Conclusion Perspectives
 Tephra : fragmented material ejected
during explosive volcanic eruption
 Tephra plume: buoyant volcanic plume
 Tephra fall deposit: tephra settled
from the volcanic plume
 Pyroclatic Density Current (PDC)
fast-moving current (several 100 km/h)
of hot gas (up to 1000°C) and tephra
 Co-PDC plume : ash cloud derived from
PDC by elutriation of fine particles and
air entrainment (Bonadonna et al 2002)
Topinka, USGS, 1997, modified from : Gardner et al , 1995
http://ffden-2.phys.uaf.edu

12. 12
Introduction 11 Feb 2010 Methodology Results Conclusion Perspectives
 Piecemeal collapse of the NE flank of
the dome, lasted 107 minutes and
removed 50 x 106 m3 of material
 6 peaks in PDC generation
2 Vulcanian explosions
 PDCs entered the sea adding 1 km2 of
land to the NE coast
 Co-PDC plume rose to 3 km altitude
 Tephra plume rose to 15 km altitude
(Stinton et al. 2014)
https://feww.wordpress.com
http://www.montserratvolcano.org

13. 13
Modified from Cole et al. 2014

14. Field work near Trants, Montserrat
http://blogs.agu.org/magmacumlaude/2011/04/12/soufriere-hills-volcano-15-years-on-conference

15. 15
4 locations
 Harris (2.5 km)
 Farm (4 km)
Spanish Point (5 km)
 Trants (6 km)
HARRIS
FARM
TRANTS
SPANISH POINT

16. 16
Introduction 11 Feb 2010 Methodology Results Conclusion Perspectives
0
10
20
30
109876543210-1-2-3
wt %
φ
Sp-02A
Whole AL
deposit
Aggregates = Accretionary lapilli (AL)
 Manual separation , wt%, dimensions
impregnation with araldite resin
Grainsize distribution of deposit:
 Sieving (particles > 0.5 mm)
 Laser diffraction (part. < 0.5 mm)
Internal structure and GS of aggregates:
 SEM (Scanning Electron Microscope)
Image analysis (J Micro Vision)

17. Lava dome of Soufriere Hills volcano, 18 January 2010
http://www.photovolcanica.com

18. 18
Introduction 11 Feb 2010 Methodology Results Conclusion Perspectives
 PDC deposits sampled low abundances in AL
(0.3 wt % BAF, 2 wt % surge , 3 wt % pumice flow)
 Co-PDC fallout deposit: 13 wt % abundance in AL
 The study focuses on AL from the co-PDC fallout deposit

19. 19

20. 20
Introduction 11 Feb 2010 Methodology Results Conclusion Perspectives
Nearly identical distributions:
 Aggregation is a stable and size
selective process
 Selects particles comprised
(< 1mm and 1μm), majority
fine particles (< 63 μm ) 0
5
10
15
20
25
30
35
-1 0 1 2 3 4 5 6 7 8 9 10
wt %
φ
Ha-02
Ha-03
Fa-01A
Fa-02
Tr-02
Sp-01A
Sp-01C
Sp-02B
Sp-05

21. 21
 Single layer aggregates: coarse grained core coated by a thin layer of finer ash
Introduction 11 Feb 2010 Methodology Results Conclusion Perspectives
 Multiple layer aggregates: 2 – 3 extra layers accreted over the core

22. Introduction 11 Feb 2010 Methodology Results Conclusion Perspectives
Core: main part of aggr.
main stage in
history of formation
Similar Mdɸ , thickness:
 Core and L2
 L1 and L3
22

23. 23
Introduction 11 Feb 2010 Methodology Results Conclusion Perspectives

24. Soufriere Hills, PDC © Dr Paul Cole

25. 25
Introduction 11 Feb 2010 Methodology Results Conclusion Perspectives
 Aggregation selects same range of particles independent
of type of event
 High abundance (13 wt%) aggregates in co-PDC fallout
favorable dynamics within the co-PDC plume
 Estimated volume co-PDC fallout deposit: 2 x 106 m3
Volume 260 000 m3 aggregated = 0.5 % of tot collapsed volume

26. 26
 Abundant vapour : larger particles are aggregated by moist adhesion: core, L2
 Scarce vapour : finer particle are accreted by electrostatic forces: L1, L3
 Size and number of layers of aggregates: indicates conditions in thermally
stratified plume.
Introduction 11 Feb 2010 Methodology Results Conclusion Perspectives
http://www.dunhilltraveldeals.com

27. Plymouth, Montserrat
http://abandoned.photos/post/69080596492

28. 28
Introduction 11 Feb 2010 Methodology Results Conclusion Perspectives
 Chemical analysis aggregates (NaCl) sea water main source humidity?
 Parameters which control, enhance aggregation to improve models
which estimate tephra fall dispersal
 More precise analysis of the hazards
 Aggregation mobilizes the fine ash: reduces the health impact
http://www.photovolcanica.com http://www.montserratvolcano.org

29. Tambora caldera, Indonesia
http://commons.wikimedia.org/wiki/File:Caldera_Mt_Tambora_Sumbawa_Indonesia.jpg