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Volcanoes
Structure of a Volcano
What is a volcano?
• a landform produced by magma emerges via an opening in the crust as lava flow
•Lava cools and solidifies to form a layer of volcanic material with each eruption, layer upon layer built up to form a volcano
•Lava continues to rise through a passageway – pipe. Lava ejected at a top opening – crater
•Crater when blown off calderaCaldera eventually filled with water crater lake
Explosive or Quiet Eruptions?
Basic lava• Low in silica• Non-sticky• Less viscous, more
fluid• Temp usually higher • Gas and steam escape
easily
Acidic lava• High in silica• Sticky, more viscous,
less fluid• Temp usually lower • Thick sticky lava does
not allow gas and steam to escape easily
Explosive eruptions! Quiet eruptions…
Shape of volcano?
Basic Lava Volcano
• Fluid lava flow covers larger areas gently-sloping volcano shield volcano
• E.g. Island of Hawaii, regarded as a single shield volcano with 3 active peaks maua Kea, Mauna Loa, Kilauea
Acidic Lava Volcano
• Less fluid lava, moves very slowly solidifies quickly a steep-coned volcano
• Most common composite volcano (alternate layers of hardened lava, ash & cinder)
• E.g. Mt Mayon, Mt Merapi, Mt Fuji, Mt Etna, Vesuvius
A Volcano formed by acidic Lava
Most common type – composite volcano
A Shield Volcano
Mauna Loa
Mauna Kea
Lava Plateau – formed when huge volumes of magma erupted from several cracks in the earth’s crust rather than from a single pipe
Lava Plateau
Distribution of volcanoes(Map)
Distribution of volcanoes
Along convergent plate boundary where subduction takes placeProduce chain of volcanic islands
e.g. Pacific Ring of Fire
Away from plate boundary, a plate moving over fixed ‘hot spots’Which are localised heat sources in the mantle
to produce groups of volcanoese.g. the Hawaiian Islands
Along divergent plate boundary where new sea floor materials produce submarine volcanoese.g. Mid-Atlantic oceanic ridge
Hot Spots
Impacts of Volcanic eruptions
Volcanic eruption affects the environment thorough:
Lava flows
•Pyroclastic materials of ash and
•cinder bombs
Emission of toxic gas
Disturbances on ocean floor may trigger off tsunamis
•Mudflows of rocks and ash
Impacts of Volcanic eruptions
Destroy property – farmlands, buildings, infrastructure
Cause injury and loss of lives
Disrupt economic activities
Brings about misery and aggravates poverty e.g. in 3rd World countries
Why do people still live near Volcanoes?
Economic ReasonFertile soils for agriculture
Economic ReasonTourism
e.g.geysers & hot Springs
Cultural RootednessSense of belonging
Generations live there
Economic ReasonMining of minerals, sulphur
Employment opportunity
Economic ReasonEnergy Resource
Harnessing of geothermal power for development
Economic ReasonPoverty- no means to relocate