Volcanoes

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