Volcanism at different plate boundaries

Question 1

volcanism at convergent plate boundaries

Answer 1

• andesitic magma, highly viscous, forms steep-sided strata volcanoes (lava produced at convergent margins, as subducted oceanic crust mixes with water and sea floor sediment)
• viscous magma traps gases, increasing pressure inside volcanoes causing explosive eruptions
• e.g. Vesuvius, Mt St Helens, Soufriere Hills

Question 2

volcanism at divergent plate boundaries

Answer 2

• most eruptions occur unseen on ocean floor (due to being found along spreading (mid ocean) ridges). exception is Iceland
• volcanic rock is basalt
• because basalt is fluid, it allows gases to escape producing quiet, effusive eruptions
• fluid basalt can flow tens of kilometres before cooling and solidifying, creating huge, low-angled shield volcanoes
• e.g. Icelands Skjadbreidur

Question 3

Hot Spots

Answer 3

• similar to divergent plate boundaries
• main eruptive material is basalt, effusive explosions and shield volcanoes e.g. Mauna Loca (Hawaii)
• exceptions include Teneriefe volcano El Teide (strata volcano) evidence of pyroclastic flows and thick tephra deposits from ashfalls