Lava Types
Basaltic, andesitic and rhyolitic
Basaltic Lava
- 50% silica content
- Low viscosity
- Associated with gentle eruptions (lava flows)
(fissure, shield)
Andesitic
- 60% silica content
- Medium viscosity
- Associated with intermediate eruptions
- Lava flows and ash
Rhyolitic
- 70% silica content
- Doesn’t travel far from vent
- Violent eruptions/directed blast
- Pyroclastic flows
Fissure/Icelandic
- Low profile
- Fissure/fracture
- Basaltic lava
- Divergent plate boundaries
- Many kilometer’s long
- “Curtain” lava
- Gentle eruptions
Shield/Hawaiian
- Low profile/dome shape
- Crustal rock is bent upwards due to magma chambers
- Basaltic lava (Gentle Eruptions)
- Mostly lava flows (“boil over”)
- Lava runs far from vent in thin layers
Difference between Magma and Lava
Magma is below the ground, lava is above
Dome/Acid
- High profile due to andesitic and rhyolitic
- Lava cools mostly in vent due to high viscosity
- Thick lava associated with “acid lava”
- Intermediate eruptions (ash and pyroclastic)
Ash/Cinder
- High profile to a 45 degree max
- Composed of individual ash particles from past eruptions
- Lava escapes through lava tubes at base
- Intermediate eruptions produce ash which escapes through vents
Composite/Strata
- Classic style
- Alternate layers of ash and lava
- Rhyolitic lava creates violent eruptions
- Pyroclastic flows, nuvee ardents, ash and directed blasts
- High viscosity means much magma solidifies in the vent creating more pressure. = bigger explosion
Caldera
- Skeleton of past composite volcano. Violent eruption caused magma chamber to empty and sink.
- Still existing convection currents mean young volcanoes can form within the creator
- If an island previously, sea water can flood the creator
- Rhyolitic lava
Icelandic Eruption
Lava flows gently from fissure
Hawaiian Eruption
Lava is admitted gently from the vent
Strombolian Eruption
Small but frequent eruptions occur
Vulcanian Eruption
More violent but less frequent eruptions
Vesuvian Eruption
Violent explosion after a long period of inactivity
Krakatoan Eruption
Exceptionally violent that may remove much of the original core
Peléan Eruption
Violent eruption accompanied by pyroclastic flows that may include a growing cloud
Plinian Eruption
Large amounts of lava and pyroclastic material are ejected
