Volcanoes
Volcano weak spot in crust where magma and gases come up Magma Lava molten mixture of rockforming 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 -resistance of a liquid to flow -greater viscosity, slower it flows Viscosity of Magma -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
Inside a Volcano 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
Lava Flow -area covered by lava as pours out of vent Types of flow: Aa Pahoohoe Pillow Blocky Pours out fast forms brittle crust Flows slowly rounded wrinkle Under water rounded lumps Oozes cool and stiff stays near volcano,high visocity
Types of Lava Flow
explosive eruption hurls out mixture of hot gases, ash, lapilli, bombs, and blocks 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 Explosive and non-explosive Pyroclastic
Ash Types of Pryoclastic Material smallest; fine, rocky particles Lapilli Bombs Blocks cinders- pebble-sized - large pieces of magma that harden in the air Solid rock erupted Largest pieces
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
Life Cycle of Volcanos 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
Volcanic Eruptions and Climate Change Large scale volcanic eruption Gases and ash go into the Earth s atmosphere Block sunlight Global temperatures drop
Landform Effects of Volcanos Types of Volcanos 1. Shield 2. Cinder Cone 3. Composite Other types of landforms 1. Craters 2. Calderas 3. Lava plateaus
Shield Volcanoes Types of Volcanos -wide, gently sloping mountain made of layers of lava from quiet eruptions -ex. Hawaiian islands
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 Funnel shaped pit Located near central vent Lava plateau Wide flat landforms Caused by repeated eruptions of nonexplosive 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