Volcanoes5th Year Geography
Molten magma forces its way through FISSURES and VENTS. At the surface it becomes LAVA
Parts of a volcano
Mount Etna, Italy
2012 Higher Level Paper
Violent!
Type of Volcanoes
Active e.g. Mount Etna Dormant Volcanoes
e.g. Mount St Helen’s had not erupted in hundreds but in 1980…
Extinct Volcanoes e.g. Slieve Gullion, Co. Down
Slieve Gullion, Co. Armagh – an Slieve Gullion, Co. Armagh – an extinct volcanoextinct volcano
Products of Volcanoes Lava Pyroclasts and Pyroclastic Flows Poisonous gases Ash, Pumice and dust (tephra) Water Vapour Lahars (muddy flows)
Lava
Lava – Two Types
Acidic – produced at destructive plate boundaries. This lava is sticky and has a silica content of over 70%. Causes very destructive eruptions
Basic – produced at constructive plate boundaries and hotspots like Hawaii – the lava is runny and has a silica content of under 55%. Less violent eruptions.
Pyroclasts and pyroclastic flows
Poisonous Gases
Ash, Pumice and Dust(Tephra)
MatchupHotspots Volcanic bombsAcidic Rock full of gasHawaii Asleep VolcanoVent Sticky LavaBasic Mid plate volcanoesPumice Dead VolcanoPyroclasts Runny LavaActive A hotspot volcanoDormant Gap in the crustExtinct Erupting Volcano
Water Vapour
Lahars
Snow mixed with ash to form a “cement”
External/Extrusive Volcanic Landforms
Plateaus. E.g. Antrim Plateau and Deccan Plateau
Volcanic Cones. E.g. Mount Etna Craters and Calderas Volcanic Plugs
Volcanic Cones
Dome Volcanoes
Cinder Ash Cones
Composite Volcanoes
Volcanic Plug – core of an ancient volcano
Caldera filled with water
Santorini Caldera
Intrusive Volcanic Landforms Formed underground by “failed” eruptions Exposed by erosion and weathering Useful measure of weathering/erosion in an
area Lead to the creation of Metamorphic rocks
(quartzite in Dublin/Wicklow)
Veins… Similar formation to sills (magma flowing into
existing cracks) BUT – little or no pressure. Just filling existing
cracks, NOT pushing rock layers apart
Sills, Dykes, Lopolith, Laccoliths Unlike Veins, all involve magma forcing apart
rock strata under pressure More likely to lead to metamorphic rock
formation (heat AND pressure) Dykes – NOT the same thing as volcano vent
(compare diag on P41 with PPT) Lopolith – Pushes down on layers Laccolith – Pushes up!
Laccolith & Dike
Laccolith in Montana, USA
Dike
Leinster Batholith (Dublin & Wicklow Mountains)
Positive Effects of Volcanoes New Land Created Geothermal Energy Fertile Soil New Minerals (which can be mined) Tourism
Surtsey – a new volcanic island
Geothermal Energy
Use of Geothermal in Iceland
Fertile Soils – Mt. Vesuvius
Tourism – Giants Causeway
2011 Leaving Cert QuestionQ1. (B) Discuss the positive impacts of volcanic activity. [30m]
Marking SchemePositive impacts identified 2 + 2 marks Discussion 13 x SRPs Credit one named volcano or volcanic area from discussion SRPs All other positive impacts must be discussed for SRPs Credit relevant extra information on relevant labelled diagram(s) relating to positive impacts Give credit for 1 SRP for diagram without annotation
Iceland Ash Cloud, 2011
Negative Effects of Volcanoes Lava Flows & Lahars destroy land, infrastructure, cause
death Pyroclastic flows – searing hot causes widespread
destruction Poisonous gases Ice sheet melting (Jokulhlaups) Tsunamis (Japan) Volcanic Ash disruption (Iceland 2011)
Predicting Volcanic Eruptions Ground Deformation Historical Records Gas Emissions Seismic Patterns
Case Studies – Mount St. Helens and Montserrat
Location of Mount Saint Helens
Mount Saint Helens – before 1980
Mount Saint Helens – after 1980
2013 Higher Level Paper
2009 Ordinary Level