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  caldera Caldera 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

Mauna Loa Mauna Kea A Shield Volcano

Lava Plateau Lava Plateau – formed when huge volumes of magma erupted from several cracks in the earth’s crust rather than from a single pipe

Distribution of volcanoes (Map)

Distribution of volcanoes Along convergent plate boundary where subduction takes place Produce chain of volcanic islands e.g. Pacific Ring of Fire Along divergent plate boundary where new sea floor materials produce submarine volcanoes e.g. Mid-Atlantic oceanic ridge Away from plate boundary, a plate moving over fixed ‘hot spots’ Which are localised heat sources in the mantle to produce groups of volcanoes e.g. the Hawaiian Islands

Hot Spots

Impacts of Volcanic eruptions Volcanic eruption affects the environment thorough: Emission of toxic gas Lava flows Mudflows of rocks and ash Pyroclastic materials of ash and cinder bombs Disturbances on ocean floor may trigger off tsunamis

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? Cultural Rootedness Sense of belonging Generations live there Economic Reason Fertile soils for agriculture Economic Reason Energy Resource Harnessing of geothermal power for development Economic Reason Tourism e.g.geysers & hot Springs Economic Reason Mining of minerals, sulphur Employment opportunity Economic Reason Poverty- no means to relocate