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.