Shield VolcanoesBasaltic Lava – low silica content, low
viscosity, low gas contentHot spots – magma moves up from lower
mantle and plates move over it Ex. Hawaii
(note: see video on favorites)
Shield Volcanoes
• Mid Ocean Ridges - volcanoes grow out of mid ocean ridges (constructive margin)– Ex: Iceland – only MOR with an actual volcanoDivergent boundary – forming islands from
accumulation of basaltic lava
Contd.
• Fissures – a crack! The beginning of volcanic activity as magma moves up through the crack towards the surface
Anatomy of a volcano
Shield Volcanoes
• Broad shape, gentle slopes - Why???• Quiet eruptions – Why??– Lava flows - • Basaltic lava – Why??• From vents and craters – why??
• 70% of all gases produces from volcanoes is water vapor
Cinder VolcanoesCinder Cones – • smallest volcanoes • usually products of a single volcanic eruption lasting only a few weeks (rarely more than 1 year) • Forms on continents• tall with steep slopes•Extremely violent eruptions
Eruptions
• Very high silica content• Very little to no lava flow – why?
Eruption characteristics
• Once cinder cone volcanoes erupt the pipe that connects the vent to the chamber solidifies and volcano never erupts again
• Fragments that come from eruption range from ash to bombs but consists mostly of lapilli (cinders) 2-64 mm in size
Pyroclastic materials
• Lapilli – cinders ranging from 2-64 mm in size
• Bombs- semimolten material upon ejection and become streamlined after ejection
• Blocks – particles that are larger than 64mm in size.