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