Lava Domes 29 March 2019

Importance of lava domes Lava domes really can be considered as “corks” in a champagne bottle…the analogy is a good one It is RARE to see no explosive activity associated with lava domes Lava domes are important in terms of TRANSITIONS between effusive and explosive activity

STRUCTURE OF THE LECTURE 1. Morphology Repeating signals and the effusive-explosive transition 3. Some general laws

Growth rates of lava domes

Lava dome advection and solidification times tS = solidification time tA = advection time Dimensionless number B : Fink JH, Griffiths RW (1998) J Geophys Res 103:527-545

Lava dome morphology Fink JH, Griffiths RW (1998) J Geophys Res 103:527-545

Side views of the four analogue domes from the previous page Fink JH, Griffiths RW (1998) J Geophys Res 103:527-545

Lava dome advection and solidification times tS = solidification time tA = advection time Dimensionless number B : Fink JH, Griffiths RW (1998) J Geophys Res 103:527-545

Unzen lava dome, late May 1991

Soufrière St. Vincent lava dome, 1979

Early Mt. St. Helens lava dome, 1980

Venusian “pancake” domes

1. Morphology 2. Repeating signals and the effusive-explosive transition 3. Some general laws

Volcano seismicity (“VT event”) [or long period earthquake (“lp event”)] courtesy USGS

Mt. St. Helens (USA)

2004-2008 lava dome vent area glacier vent 1980’s lava dome glacier 18 May 1980 collapse amphitheatre vent area glacier vent Thermal infrared image 1980’s lava dome glacier Iverson et al. (2006) Nature 444:439-443

Lava dome evolution, 2004-2005 (about 0.072 km3 extruded in ~15 months) Iverson et al. (2006) Nature 444:439-443

Seismogram of the dome, 1 Dec 2005 Iverson et al. (2006) Nature 444:439-443

Stick-slip model of dome extrusion Iverson et al. (2006) Nature 444:439-443

Soufrière Hills (Montserrat)

Lava dome behaviour, May 1997 Significant lava dome collapses and pyroclastic flows (block and ash flows) associated with these peaks in activity Voight et al. (1999) Science 283:1138-1142

Block and ash flow deposits (Merapi, Indonesia) lava dome fragment

Lava dome growth, 2002-2003

Largest dome collapse at Montserrat: July 2003 collapse peak at 0335 hours local time Herd et al. (2005) J Volcanol Geotherm Res 148:234-252

Vulcanian explosions associated with the dome collapse Herd et al. (2005) J Volcanol Geotherm Res 148:234-252

SO2 gas release (no solid material) Vulcanian eruptions SO2 gas release (no solid material) SPACING COLUMN HEIGHT

Galeras (Colombia)

Summer 1992

Long period seismic signals associated with dome destruction and vulcanian eruptions at Galeras (“tornillos”) These events are a manifestation of pressurization within the shallow plumbing system of the volcano Narváez M L et al. (1997) J Volcanol Geotherm Res 77:159-171

Tornillos with slowly decaying coda Narváez M L et al. (1997) J Volcanol Geotherm Res 77:159-171

Remarkable tornillo signals Narváez M L et al. (1997) J Volcanol Geotherm Res 77:159-171

Key changes before vulcanian eruptions at Galeras 14 January 1993 eruption 23 March 1993 eruption 7 June 1993 eruption The “h” term in (c ) is a damping coefficient…low values correspond to gradually decaying tornillos, while higher values correspond to a more rapidly decaying tornillo Gómez M DM, Torres C RA (1997) J Volcanol Geotherm Res 77:173-193

1. Morphology 2. Repeating signals and the effusive-explosive transition 3. Some general laws

The fragmentation threshold Spieler et al. (2004) Earth Planet Sci Lett 226:139-148

Viscous behaviour of fluids Courtesy Wikipedia

Shear-thinning behaviour Lava dome rheology Shear-thinning behaviour Note the alignment and breakage of crystals log  = -0.993 + (8974 / T) – (0.543 log ) = apparent viscosity in Pa s T = temperature in C  = strain rate in s-1 Lavallée et al. (2007) Geology 35:843-846