Eruptive style depends on
volatile (H2O, CO2) content of magma
Effusive eruption
lava flow
lava fountain
Explosive eruption
ash flow
ash fall
steam
LOW
HIGH
Lava eruption: very low volatile content
Lava eruption: low volatile content
magma flowing under solid crust
Lava fountain: low volatile content
Lava flow: low volatile content
ash fall
Pyroclastic
eruption: high
volatile content
ash flow
Pelean eruption
nuee ardente
ash flow
Vesuvius:
August 24, 0079
Plinian eruption
ash fall
Eruptive products
depend on eruptive style
Effusive eruption
lava flow: lava flow
pahoehoe (ropey lava)
a a (blocky lava)
Explosive eruption
ash flow: welded tuff
ash fall: tuff
steam
flow: fills in
preexisting
topography
edge of flow
lava flow: complex surface
textures
pahoehoe (ropey lava)
a a (blocky) lava flow
stack of lava flows
columnar joints
vesicles rise to the top of a flow
ash:
blankets preexisting topography
ash deposits
coarse volcanic ash: falls close to vent
ash:
blankets preexisting topography
ash flow deposits: welded tuff
gentle
large: > 100 km
Effusive eruption:
lava flows
slope
smaller: < 100 km
Explosive eruption:
lava flows
welded tuff
unconsolidated ash
circular intrusive
dike: planar
intrusive that
cuts across
country rock
dike
sill: planar intrusive that is parallel to country rock
country rock
granite
magma intruded into country rock
roof of intrusive
batholith: large intrusive complex