CLASSIFICATION OF VOLCANIC ERUPTIONS

HAWAIIAN

Magma: fluid
Explosive activity: very weak ejection of fluid blobs
Effusive activity: then, often extensive flows
Ejecta: cow-dung bombs and spatter, very little ash
Structure(s): spatter cones and ramparts; very broad, flat lava cones

BASALTIC FLOOD

Magma: fluid
Explosive activity: very weak ejection of fluid blebs
Effusive activity: voluminous, wide-spread flows
Ejecta: cow-dung bombs and spatter, very little ash
Structure(s): spatter cones and ramparts; very broad, flat lava cones, lava plains

STROMBOLIAN

Magma: moderately fluid
Explosive activity: weak to violent ejection of pasty fluid blebs
Effusive activity: thicker, less extensive flows; flows may be absent
Ejecta: spherical to fusiform bombs; cinder; small to large amounts of glassy ash
Structure(s) cinder cones

VULCANIAN

Magma: viscous
Explosive activity: moderate to violent ejection of solid hot fragments of new lava
Effusive activity: flows commonly absent, thick and stubby if present, ash flows rare
Ejecta: essential, glassy to lithic, blocks and ash, pumice
Structure(s): ash cones, block cones, block-and-ash cones

PELEEAN

Magma: viscous
Explosive activity: like Vulcanian, commonly with glowing avalanches
Effusive activity: domes and/or short, very thick flows; flows may be absent
Ejecta: like Vulcanian
Structure(s): Ash and pumice cones; domes

PLINIAN

Magma: viscous
Explosive activity: ejection of large volumes of ash, with accompanying caldera collapse
Effusive activity: ash flows, small to very luminous; may be absent
Ejecta: glassy ash and pumice
Structure(s): widespread pumice lapilli and ash beds; generally no cone-building

RHYOLITIC FLOOD

Magma: viscous
Explosive activity: relatively small amounts of ash projected upward into the atmosphere
Effusive activity: voluminous wide-spread ash flows; may have volume of ten cubic miles
Ejecta: glassy ash and pumice
Structure(s): flat plain, or broad, flat shield, often with caldera

ULTRAVULCANIAN

Magma: no magma
Explosive activity: weak to violent ejection of solid fragments of old rock
Effusive activity: none
Ejecta: accessory and accidental block and ash
Structure(s): block cones; block-and-ash cones

GAS ERUPTIONS

Magma: no magma
Explosive activity: continuous or rhythmic gas release at vent
Effusive activity: none
Ejecta: none or very minor amounts of ash
Structure(s): none

FUMAROLIC

Magma: no magma
Explosive activity: nonexplosive weak to moderately strong long-continued gas discharge
Effusive activity: none
Ejecta: none or rarely very minor amounts of ash
Structure(s): generally none, rarely very small ash cones

Compiled from Macdonald (1972), Francis (1993), and Williams and McBirney (1979).


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