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Volcanoes
• Volcano
• Magma
• Lava
• weak spot in crust where magma and gases come up
• molten mixture of rock-forming substance, gases, water from the mantle
• Magma that flows onto earth surface
• forms solid rock when cooled
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
Properties of Magma
• Viscosity
• Viscosity of Magma
• -resistance of a liquid to flow
• -greater viscosity, slower it flows
• -depends on silica content and temperature
• 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)
• Temperature • -viscosity increases as temp decreases
• -hotter magma flows faster
• -cooler flows slower
• Magma
Chamber
• Pipe
• Vent
• Crater
• -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
• -bowl-shaped area that may form at top around central vent
Inside a Volcano
• Lava Flow
Types of flow:
Aa
Pahoohoe
Pillow
Blocky
• -area covered by lava as pours out of vent
Pours out fastforms brittle crust
Flows slowlyrounded wrinkle
Under waterrounded lumps
Oozescool and stiffstays near volcano,high visocity
Types of Lava Flow
• Eruption
• Pyroclastic
• -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
• Explosive and non-explosive
• explosive eruption hurls out mixture of hot gases, ash, lapilli, bombs, and blocks
• smallest; fine, rocky particles
• cinders- pebble-sized
• - large pieces of magma that harden in the air
• Solid rock erupted
• Largest pieces
Types of Pryoclastic Material
Ash
Lapilli
Bombs
Blocks
• 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
• Example: Mount St. Helen
• Quiet Eruptions
Non-explosive
• -low silica; low viscosity; flows easily
• -oozes out quietly and flows for many km
• -sets fire to and buries everything in path
• -produces both pahoohoe & Aa lava flow
• -ex. Hawaiian islands
• Active
• Dormant
• Extinct
• live; erupting or showing signs of erupting in near future
• -sleeping; expected to awaken in future and become active
• -dead; unlikely to erupt again
Life Cycle of Volcanos
Volcanic Eruptions and Climate Change
• Gases and ash go into the Earth’s atmosphere
• Block sunlight
• Global temperatures drop
Large scale
volcanic eruption
Landform Effects of Volcanos
1. Shield
2. Cinder Cone
3. Composite
1. Craters
2. Calderas
3. Lava plateaus
• Types of Volcanos
• Other types of landforms
• Shield Volcanoes • -wide, gently sloping mountain made of layers of lava from quiet eruptions
• -ex. Hawaiian islands
Types of Volcanos
• Cinder Cone Volcano • -steep, cone-shaped hill or small mountain made of pyroclastic materials (volcanic ash, lapilli, bombs, and blocks piled up)
• -ex. Mexican Paricutin
• Composite Volcanoes • -tall, cone-shaped mountains
• Formed from explosive eruptions followed by non-explosive eruptions
• -ex. Mount St. Helens
Other Landforms Created by Volcanos
• Crater
• Lava plateau
• Funnel shaped pit
• Located near central vent
• Wide flat landforms
• Caused by repeated eruptions of non-explosive volcanoes
• Occurred over million of years
• 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
Crater Lake
• Hot Spots • -where magma melts through crust
• -found in middle of plates or along plate boundaries
• -volcanoes can form above hot spot
• -ex. Hawaiian Islands
• Volcanic belt
• Ring of Fire
• -forms along plate boundaries
• -magma can reach surface when plates diverge or converge and fracture crust
• -major volcanic belt
• -rims (circles) Pacific Ocean
Location of Major Volcanoes
• Island Arc
• -string of volcanic islands
• -formed from subduction at converging oceanic plates
• -ex. Japan, Caribbean Islands