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Presentation on theme: "Volcanoes."— Presentation transcript:

1 Volcanoes

2 Volcano Magma -weak spot in crust where magma comes up -molten mixture of rock-forming substance, gases, water from the mantle -called lava on surface -lava forms solid rock when cooled

3 Volcanic belt Ring of Fire -forms along plate boundaries -magma can reach surface when plates diverge/converge and fracture crust -major volcanic belt -rims (circles) Pacific Ocean


5 Island Arc -string of volcanic islands -formed from subduction at converging oceanic plates -ex. Japan, Caribbean Islands


7 Hot Spots -where magma melts thru crust -found in middle of plates and along boundaries -volcanoes can form above hot spot -ex. Hawaiian Islands


9 Properties of Magma Viscosity Viscosity of Magma
-resistance of a liquid to flow -greater viscosity, slower it flows -depends on silica content and temperature

10 Silica Content -made of oxygen and silicon -one of the most abundant materials in crust -more silica = higher viscosity (sticky, flows slow) -less silica = low viscosity (flows quickly)

11 Temperature -viscosity increases as temp decreases -hotter magma flows faster -cooler flows slower

12 Volcanic Eruptions Magma reaches the surface
-materials in asthenosphere under great pressure -liquid magma less dense than solid material around it -flows upward until opening in rock allows to magma to reach surface

13 Inside a Volcano Magma Chamber Pipe Vent -pocket that collects magma -tube that connects chamber to surface -opening thru which molten rock and gas leave -central vent at top -sometimes, side vents on sides

14 Lava Flow Crater -area covered by lava as pours out of vent -bowl-shaped area that may form at top around central vent


16 Eruption -gases in magma under lots of pressure -gases expand and form bubbles, as magma rises to surface -when erupts, force of gas pushes magma from chamber thru pipe until it flows or explodes out of vent

17 Quiet Eruptions -low silica; low viscosity; flows easily -oozes out quietly and flows for many km -sets fire to and buries everything in path -produces both pahoehoe & aa -ex. Hawaiian islands


19 Explosive Eruptions -high in silica; high viscosity; thick/sticky -builds up in pipe; plugs it like a cork -trapped gases build up pressure until they explode -breaks lava into fast cooling pieces

20 -volcanic ash: smallest; fine, rocky particles
-cinders: pebble-sized -bombs: large pieces; baseball-sized to size of car -ex. Mount St. Helens

21 Pyroclastic Flow Life Cycle -explosive eruption hurls out mixture of hot gases, ash, cinders, bombs -active: live; erupting or showing signs of erupting in near future -dormant: sleeping; expected to awaken in future and become active -extinct: dead; unlikely to erupt again

22 Shield Volcanoes -wide, gently sloping mountain made of layers of lava from quiet eruptions -ex. Hawaiian islands


24 Cinder Cone Volcano -steep, cone-shaped hill or small mountain made of volcanic ash, cinders, bombs piled up -ex. Paricutin


26 Composite Volcanoes -tall, cone-shaped mountain in which layers of lava alternate with layers of ash/other materials -ex. Mount St. Helens


28 Calderas -huge hole left by a collapsing volcano -enormous eruptions empty the vent and chamber, leaving it hollow with no support -sometimes fill with rain water -ex. Crater Lake in Oregon


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