What is a volcano?A volcano is an opening, or vent, in

the Earth’s crust through which magma and gases are expelled.

Where do volcanoes form?A large number of volcanoes lie directly on tectonic

plate boundaries where it is possible for magma to form and rise to the surface.

80% of active volcanoes form where plates collide.

15% of active volcanoes form where plates separate.

The remaining volcanoes occur far from any tectonic plate boundary.

The plate boundaries in the Pacific Ocean have so many volcanoes that it is known as The Ring of Fire.

Volcanoes can also form at subduction zones where temperature and pressure

build to create magma.

What are the parts of a volcano?

Volcanic EruptionsThe composition, or make up, of magma can

determine how explosive a volcanic eruption will be.

At this moment eruptions are occurring around the world and on the ocean floor.

Non-explosive EruptionsMost common type of eruptionProduce relatively calm flows of lavaCan release huge amounts of lavaMuch of the sea floor is made up of lava from

non-explosive eruptions

Explosive Eruptions

Occurs much more rarelyCan be incredibly destructiveExpells clouds of hot debris, ash & gas into

the airInstead of lava flows, causes molten rock to

be blown into the air where tiny particles harden and fall

Larger pieces of debris fall closer to the volcano

Can blast millions of tons of lava and rock in a matter of seconds, demolishing entire mountain sides

Effects of EruptionsClimate change

Other example: In 1815,Mount Tambora blanketed Indonesia in darkness from the volcanic ash that remained in the atmosphere after it erupted. 12,00 died in the blast, but 80,00 died from resulting hunger and disease. Volcanic ash can blocked the sunlight and caused a drop in temperature, causing crops to fail.

Volcanic LandformsVolcanic eruptions can cause profound changes

in climate, but they are best known for their volcanic landforms.

Shield VolcanoesFormed from layers of lava released from

repeated non-explosive eruptionsSides are gentle slopes, but can be enormous

in sizeHawaii’s Mauna Kea is the tallest mountain

on Earth! Measured from its base on the sea floor, it is taller than Mount Everest.

Cinder Cone VolcanoesMade from pyroclastic materials that where

usually produced from moderately explosive eruptions

Usually erode quickly because the material is not cemented together.

Small, but has steep slopes Often occur in clusters, commonly on the

sides of other volcanoes

Composite Volcanoes (also known as stratovolcanoes)Most common type of volcano.Formed from explosive eruptions of

pyroclastic materials followed by quieter flows of lava.

Have broad base and sides that get steeper toward the pointed peak.

Lava Dome VolcanoesFormed from thick lava that doesn’t flow far

as it pours over and around its vent, or opening.

CratersA crater is a funnel shaped pit near

the top of the central vent of a volcano.

CalderasA large, semicircular depression that forms

when the magma chamber below a volcano partially empties and causes the ground to sink.

Lava PlateausA wide flat landform that results from repeated

non-explosive eruptions of lava that spread over a large area