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