Volcanic ActivityVolcanic ActivityEarth Science Ch. 18Earth Science Ch. 18

Factors affecting magma Factors affecting magma formationformation

►Pressure Pressure

►TemperatureTemperature

►Water-causes rock to melt at a lower Water-causes rock to melt at a lower temptemp

►YouTube - Volcano EruptionsYouTube - Volcano Eruptions

Map of volcanoes Fig. 18-2Map of volcanoes Fig. 18-2

ViscosityViscosity-resistance to flow-resistance to flow►Honey has a high Honey has a high

viscosityviscosity

►Water has a low Water has a low viscosityviscosity

► The hotter the The hotter the magma, the lower magma, the lower the viscositythe viscosity

► YouTube - YouTube - OlOl DoinyoDoinyo LengaiLengai Volcano Volcano

►Magma=below surfaceMagma=below surface►Lava=above surfaceLava=above surface

►Vent-what lava erupts throughVent-what lava erupts through►Crater-depression around the ventCrater-depression around the vent►Caldera-collapsed volcanoCaldera-collapsed volcano

Caldera (in AK)Caldera (in AK)

Crater Lake, OR (caldera)Crater Lake, OR (caldera)

Types of VolcanoesTypes of Volcanoes►1. Shield Volcanoes1. Shield Volcanoes

-- broad slopebroad slope -largest type of volcano-largest type of volcano -usually nonexplosive eruptions-usually nonexplosive eruptions Ex. Hawaiian IslandsEx. Hawaiian Islands

►Fig. 18-12Fig. 18-12

HawaiiHawaii

Cinder-cone volcanoesCinder-cone volcanoes►Smallest type of volcanoSmallest type of volcano►Less than 500mLess than 500m

►More viscous magma, lots of gases, so More viscous magma, lots of gases, so it makes it very explosiveit makes it very explosive

Cinder cone antomyCinder cone antomy

Composite volcanoesComposite volcanoes►Layers of ash/volcanic fragments and Layers of ash/volcanic fragments and

lavalava

►Violent eruptionsViolent eruptions

►Ex. Mt St. Helens and Mt. Rainier in Ex. Mt St. Helens and Mt. Rainier in USAUSA

layerslayers

►Cinder cones=smallest; steepest Cinder cones=smallest; steepest slopesslopes

►Shield=largestShield=largest►volcanic eruption - Google Videovolcanic eruption - Google Video►HowStuffWorksHowStuffWorks

Videos "Mt. Saint Helens' Powerful Videos "Mt. Saint Helens' Powerful ErruptionErruption""

Mt. St.Mt. St.HelensHelens

TephraTephra► Fragments thrown Fragments thrown

in air from eruptionin air from eruption

► Pyroclastic flows-Pyroclastic flows-clouds of ash, gas, clouds of ash, gas, and tephra down and tephra down slope up to 150 slope up to 150 mph. Temp can mph. Temp can exceed 700 C.exceed 700 C.

Distribution of volcanoesDistribution of volcanoes is not random is not random

►Found along plate boundaries (Ring of Found along plate boundaries (Ring of Fire), mid-ocean ridgesFire), mid-ocean ridges

►Fig. 18-16Fig. 18-16

►Some found at hot spots, where plumes Some found at hot spots, where plumes of mantle (magma) rise up-ex. Hawaiiof mantle (magma) rise up-ex. Hawaii

►Fig. 18-17Fig. 18-17

The EndThe End