3. Types of eruption
Christoph Breitkreuz,
TU Bergakademie Freiberg
Magmatic fragmentation: by
expansion of vesicles and high
deformation rate
Fig. 2.4 A schematic volcanic eruption column,
showing the variation of velocity with height and
relative importance of buoyancy and momentum.
Buoyancy carries column to height HB; lateral
spreading takes place above HB. Momentum drives
some material upwards to a maximum height HT
(Orton 1996, from Self & Walker, 1994).
Fig. 2.2 Schematic diagram of a
explosive volcanic system showing
different regions and rheological
regimes from non-vesiculated magma
to eruption plume. (From Fisher &
Schminke 1984, after Wilson et al.,
1980).
Magmaticphreatomagmaticphreatic
after Pyle 1989
Bc = distance of“MPS/2“
after Walker 1973
Hawaiian Eruption:
- low-viscosity, SiO2-poor magma
- Lava fontains
- Crater lava lakes
- extended lava fields
Fissure eruption
Strombolian eruption: Etna, Boris Behnke
- Medium-viscosity SiO2-poor magma (phenocrysts + microlith!)
Southern Vent, 2002
Encyclop. Volc 1999
Etna (Photo K. Berg)
Evolution of an intra-plate volcanic field:
Springerville Volcanic Field, AZ (Condit & Connor 1996)
Plinian eruption:
- high-viscosity magma
- volatile-rich
- high magma eruption rate
(many weeks)
Mt. St. Helens, 1980
Pinatubo 1991
e.g. Santiaguito,
Vulcanian Guatemala
eruption: Fossa on Vulcano 1888-90
J. Lyons, MTU
Typical vulcanian eruptions:
- short (< 120 sec.) eruptions (canon shot-like sound)
- differentiated magma, moderate volatile content
- low magma eruption rate
Soufriere Hills, oct. 1997, p-flow
2002
e.g. Soufriere Hills
(Montserrat):
4.8. - 21.10.1997
88 vulcanian eruptions;
ballistic bombs (up to 1 m)
Up to 1,7 km distance,
2/3 p-flows, 1/3 fallout
Transition between vulcanian
eruptions and those related to
lava dome failure
Druitt et al. 2002
Morrissey & Mastin 1999
(Encycl. Volc.)
Phreatomagmatic
eruptions:
Surtsey 1963-64
1966
Ukinrek, Alaska, 1977:
Maar-forming eruptions
(USGS + Lorenz)
Ruhapehu, NZ
Phreatomagmatic eruptions:
- Magma – water interaction
(groundwater, ice, lake, sea)
- high F, low D, relatively cool
- Fragmentation processes:
among others „true“ explosions (according to physical definition) >>>
Leidenfrost film
Physikalisch Vulkanologisches Labor
Universität Würzburg
vapor film collapse induced by shock-wave passage at stable film boiling conditions
Stable film boiling (1 – 4 mm): reduced heat transfer
Polished steel cylinder, 7.5 cm in diameter at 350 °C
Water temperature of 85 °C
Spark-flash camera at 0.1 Mframes/sec
Physikalisch Vulkanologisches Labor
Universität Würzburg
...after about 1.1 ms...
Polished steel cylinder, 7.5 cm in diameter at 350 °C
Water temperature of 85 °C
Spark-flash camera at 0.1 Mframes/sec
Well-known and feared in industrial plants:
FCI = Fuel-Coolant-Interaction
Zimanowski et al. 2004, U Würzburg
Physikalisch Vulkanologisches Labor
Universität Würzburg
Transparent carbonate melt
Air gun bullet
HiCam 2, 10 Kframes/sec
Physikalisch Vulkanologisches Labor
Universität Würzburg
HiCam 2, 10 Kframes/sec
experiments02
Processes in a surtseyan vent
Another phreatomagmatic process:
Englacial volcanism
Grimsvötn, Iceland
2-11-2004
Prior to the large eruption of May, 18th, 1980:
Rising magma caused boiling and phreatic eruption of groundwater:
Phreatic activity:
Magma / Lava /
or pyroclastic flow
deposits provide
heat for phreatic
eruptions
Mt. St. Helens
(USGS)
Water / magma ratio and type of
fragmention
Fig. 2.6 Interrelations of explosive energy, water-magma ratio, style of volcanic activity and volcaniclastic fragments in basaltic
hydrovolcanic eruptions (largely after Wohletz & Sheridan, 1983). The smallest fragments are produced in Taalian eruptions when
most thermal energy is transferred to mechanical energy. The shape of shards produced (1-5) depends on the viscosity of the magma
and its degree of vesiculation: blocky shards (1) of poorly vesicular magma are most common; irregular, globular and spherical shards
(2-4) indicate fluidal melts; platy and cuspate shards are part of vesicle walls and develop if vesiculated, generally more viscous magma
interacts with water. Non-explosive quench fragmentation can occur in any environment. For instance, views of hyaloclastites are from
the Mid-Atlantic ridge (Schmincke et al., 1978) and a Permian example where lava flowed over unconsolidated nearshore marine
sediments (From Orton 1996).