Volcanoes form as molten rock erupts A volcano is an opening in earth’s crust through which molten rock, rock fragments, and hot gases erupt. A volcano.

Volcanoes form as molten Volcanoes form as molten rock eruptsrock erupts

A volcano is an opening A volcano is an opening in earth’s crust through in earth’s crust through which molten rock, rock which molten rock, rock

fragments, and hot gases fragments, and hot gases erupt. erupt.

A volcano can erupt A volcano can erupt violently or gentlyviolently or gently

Volcanoes form as molten rock Volcanoes form as molten rock eruptserupts

A volcano can have tremendous A volcano can have tremendous destruction even with limited molten destruction even with limited molten rock reaching the surfacerock reaching the surface

A volcano can A volcano can

cause damage cause damage

through rock through rock

fragments fragments

starting firesstarting fires

Volcanoes form as molten rock Volcanoes form as molten rock eruptserupts

How violent a volcano is depends on How violent a volcano is depends on the type of magmathe type of magma

The major portion of most magma is The major portion of most magma is silicasilica

Magma also Magma also

contains gasescontains gases

which expand which expand

as the magma risesas the magma rises

Volcanoes form as molten rock Volcanoes form as molten rock eruptserupts

Magma that has less silica will flow Magma that has less silica will flow better and bubble up and escape better and bubble up and escape very gentlyvery gently

Magma will remain in the chamber Magma will remain in the chamber until it cools or eruptsuntil it cools or erupts

Volcanoes form as molten rock Volcanoes form as molten rock eruptserupts

A great deal of material that erupts A great deal of material that erupts from volcanoes are rock fragmentsfrom volcanoes are rock fragments

The fragments form as The fragments form as

1.1. Escaping gas Escaping gas

bubbles pop,bubbles pop,

tearing magma aparttearing magma apart

Volcanoes form as molten rock Volcanoes form as molten rock eruptserupts

2.2. Larger pieces of lava are thrown Larger pieces of lava are thrown into the air cooling and hardening into the air cooling and hardening during their flightduring their flight

3.3. Rocks of all sizes rip loose through Rocks of all sizes rip loose through volcanoes walls during eruptionsvolcanoes walls during eruptions

The rock fragments form volcanic The rock fragments form volcanic ash, volcanic cinders, and volcanic ash, volcanic cinders, and volcanic block/bombsblock/bombs

The smoke risingThe smoke rising

on a volcano is on a volcano is

actually a mixtureactually a mixture

of ash and gasesof ash and gases

Volcanoes form as molten rock Volcanoes form as molten rock eruptserupts

The main gases in magma are The main gases in magma are water vapor and carbon dioxidewater vapor and carbon dioxide

During a eruption volcanic gases During a eruption volcanic gases mix with rock fragments which mix with rock fragments which form a pyroclastic flow, which is a form a pyroclastic flow, which is a dense cloud of superhot gases that dense cloud of superhot gases that race downhill. race downhill.

Volcanoes form as molten rock Volcanoes form as molten rock eruptserupts

Pyroclastic flows are the most Pyroclastic flows are the most dangerous type of volcanic eruption dangerous type of volcanic eruption and can be as hot as 800 Celsius and and can be as hot as 800 Celsius and travel faster than 100 miles per hour. travel faster than 100 miles per hour.

Volcanoes are common along Volcanoes are common along tectonic plate boundaries where tectonic plate boundaries where oceanic plates sink beneath other oceanic plates sink beneath other plates. plates.

Volcanoes form as molten rock Volcanoes form as molten rock eruptserupts

As a plate sinks it heats and begins As a plate sinks it heats and begins to melt forming magma, if the to melt forming magma, if the magma reaches the surface it can magma reaches the surface it can build tall volcanic mountains. build tall volcanic mountains.

More than 400 volcanoes about 80% More than 400 volcanoes about 80% of all active volcanoes are along the of all active volcanoes are along the subduction zones in the pacific subduction zones in the pacific ocean. ocean.

Volcanoes form as molten rock Volcanoes form as molten rock eruptserupts

The volcanoes around the pacific The volcanoes around the pacific ocean form a belt called the ring of fireocean form a belt called the ring of fire

There are 3 types of major volcanoesThere are 3 types of major volcanoes

1.1. A shield volcano is shaped like a broad A shield volcano is shaped like a broad flat dome. Its build up by many flat dome. Its build up by many eruptions of lava that is low in silica eruptions of lava that is low in silica and therefore flows easily and is and therefore flows easily and is spread out in thin layers.spread out in thin layers.

Volcanoes form as molten rock Volcanoes form as molten rock eruptserupts

The largest volcano on earth is the The largest volcano on earth is the Mauna Loa which is a shield Mauna Loa which is a shield volcano. volcano.

2. A cinder cone is a cone shaped hill 2. A cinder cone is a cone shaped hill formed by the eruption of cinders formed by the eruption of cinders and other rock fragments that pile and other rock fragments that pile up along a single craterup along a single crater

Volcanoes form as molten rock Volcanoes form as molten rock eruptserupts

3. A composite volcano is a cone 3. A composite volcano is a cone shaped volcano built of layers of lava shaped volcano built of layers of lava and layers of rock fragments. Its and layers of rock fragments. Its magma is high in silicon and magma is high in silicon and therefore pasty. therefore pasty.

A composite volcano has violent A composite volcano has violent eruptions for two reasons. eruptions for two reasons.

Volcanoes form as molten rock Volcanoes form as molten rock eruptserupts

1.1. Expanding gases trapped in rising Expanding gases trapped in rising magma tend to cause explosionsmagma tend to cause explosions

2.2. Hardened lava often plugs these Hardened lava often plugs these volcanoes, then making it harder for volcanoes, then making it harder for the volcano to erupt and when it the volcano to erupt and when it does, big eruption!does, big eruption!