Geology Reference
In-Depth Information
Table 3.1. Classi
cation of volcanic eruptions
Physical
nature of
the magma
Character of
explosive activity
Nature of effusive
activity
Nature of domi-
nant ejecta
Structures built
around vent
Eruption type
EFFUSIVE (
ow)
Basaltic
ood
Fluid
Very weak
ejection of very
Voluminous wide-
spreading
Cow-dung
bombs and
spatter; very
little ash
Small spatter
cones and
ramparts of
limited extent;
broad lava
plain
flows of
fluid blebs; little
lava fountaining
very
fluid lava from
ssures
“
or
Icelandic
Plains
”
Fluid
Weak ejection of
very
Moderately wide-
spreading
Cow-dung
bombs and
spatter; very
little ash
Very broad
at
fluid blebs;
little lava
fountaining
flows of
thin sheets, often
through lava tubes
and channels;
aligned vents
lava cones
(shields), which
frequently
coalesce, some
spatter cones
Hawaiian
Fluid
Weak ejection of
very
fluid blebs;
lava fountains
Thin, often extensive
flows of
fluid lava,
frequently involving
lava tubes and/or
channels
Cow-dung
bombs and
spatter; very
little ash
Shields; spatter
cones and
ramparts
EXPLOSIVE
Strombolian
Moderately
Weak to violent
ejection of pasty
Thick, short
flows of
Spherical to
fusiform
bombs;
cinder; small
to large
amounts of
glassy ash
Cinder cones
uid
moderately
uid
fluid blebs
lava;
ows may be
absent
Subplinian
Viscous
Moderate to
violent ejection
of solid or very
viscous hot
fragments of
lava
Flows commonly
absent; thick and
stubby when
present; ash
Essential, glassy
to lithic,
blocks and
ash; pumice
Ash cones, block
cones, block-
and-ash cones
ows
rare
Pelean
Viscous
Like subplinian,
commonly with
glowing
avalanches
Domes and/or short
very thick
Like subplinian Ash and pumice
cones; domes
ows; may
be absent
Plinian
Viscous
Paroxysmal
ejection of large
volumes of ash,
often with
caldera collapse
Ash
flows, small to very
voluminous; may be
absent
Glassy ash and
pumice
Widespread
pumice, lapilli,
and ash beds;
generally no
cones
Ultraplinian
Viscous
Relatively small
amounts of ash
projected
upward into the
atmosphere
Voluminous wide-
spreading ash
Glassy ash and
pumice
Flat plain, or
broad
ows;
at
shield, often
with caldera
single
ows may
have volume of tens
of cubic kilometers
PHREATO-MAGMATIC
Surtseyan
Fluid
Water plus
magma;
moderately
explosive
Little or none
Juvenile,
hydroclastic,
accretionary
lapilli, base
surges
Cones, tult cones
