9.2 Magma and Erupted 9.2 Magma and Erupted MaterialsMaterials

PurposePurpose: After completing this : After completing this lesson we learn what materials lesson we learn what materials

erupt from volcanoes. erupt from volcanoes.

Types of MagmaTypes of Magma

Magma is molten rock. The main “ingredient” in Magma is molten rock. The main “ingredient” in rocks is a mineral named silica (SiOrocks is a mineral named silica (SiO22); besides ); besides silica, there are many other minerals. silica, there are many other minerals.

Magma also contains significant amounts of Magma also contains significant amounts of fluids dissolved in the molten rock: water vapors fluids dissolved in the molten rock: water vapors and carbon dioxide are most commonand carbon dioxide are most common

Silica, however, is the one that determines the Silica, however, is the one that determines the type of magma in every igneous activity. type of magma in every igneous activity.

Silica determines the viscosity (resistance to Silica determines the viscosity (resistance to flow) of magma as well.flow) of magma as well.

Types of MagmaTypes of Magma

There are three types of magma, There are three types of magma, depending on the content of silica:depending on the content of silica:

1. Basaltic 1. Basaltic

2. Andesitic2. Andesitic

3. Rhyolitic3. Rhyolitic

Basaltic MagmaBasaltic Magma

Some characteristics of basaltic magma are:Some characteristics of basaltic magma are: it has about 50% silicait has about 50% silica has a small amount of gases dissolvedhas a small amount of gases dissolved flows easily (least viscous)flows easily (least viscous) the eruption is rarely explosivethe eruption is rarely explosive it has the highest melting point (>1300 C it has the highest melting point (>1300 C

degrees)degrees)

Basaltic EruptionBasaltic Eruption

Lava flows easily, due to reduced viscosityLava flows easily, due to reduced viscosity

Andesitic MagmaAndesitic Magma

contains about 60% silicacontains about 60% silica Has a moderate amount of gassesHas a moderate amount of gasses Sometimes it generates explosive Sometimes it generates explosive

eruptionseruptions The melting temperature is around 1000 C The melting temperature is around 1000 C

degreesdegrees

Andesitic EruptionAndesitic Eruption

This is an explosive eruptionThis is an explosive eruption

Rhyolithic MagmaRhyolithic Magma

Contains most silica ( over 70%)Contains most silica ( over 70%) Contains a significant amount of dissolved Contains a significant amount of dissolved

gassesgasses It has a high viscosity (flows very slowly)It has a high viscosity (flows very slowly) The eruptions are usually explosive and The eruptions are usually explosive and

create tremendous damage.create tremendous damage. The melting point is below 900C degrees. The melting point is below 900C degrees.

Rhyolithic EruptionRhyolithic Eruption

This type is highly explosiveThis type is highly explosive

Location of Each Type of MagmaLocation of Each Type of Magma

Each type pf magma form in certain areas:Each type pf magma form in certain areas: BasalticBasaltic magma is found at magma is found at rifts and hotrifts and hot

spotsspots Andesitic Andesitic magma is found at magma is found at subduction subduction

boundariesboundaries Rhyolitic Rhyolitic magma is found at magma is found at continental continental

hot spots.hot spots.

Magma versus LavaMagma versus Lava

MagmaMagma is the molten material that rises from the deep. It is the molten material that rises from the deep. It contains a significant amount of volatile compounds; contains a significant amount of volatile compounds; water vapors and CO2 are most common. As the water vapors and CO2 are most common. As the magma reaches the surface of the earth, it loses very magma reaches the surface of the earth, it loses very quickly the volatiles, because of the difference in quickly the volatiles, because of the difference in pressure. (Shake a can of soda and open it quickly; the pressure. (Shake a can of soda and open it quickly; the fizz is nothing else but the CO2 which is released from fizz is nothing else but the CO2 which is released from the liquid)the liquid)

Lava Lava is magma which has lost most of its volatile is magma which has lost most of its volatile components. Lava has temperatures between 700 and components. Lava has temperatures between 700 and 1200 C degrees. 1200 C degrees.

Other Volcanic ProductsOther Volcanic Products LavaLava is the main product that is released from a volcano. is the main product that is released from a volcano. Pyroclastic materials Pyroclastic materials (“pyro” means hot and “clast” (“pyro” means hot and “clast”

means fragment in Greek). These are hot, solid means fragment in Greek). These are hot, solid materials of different sizes. Sometimes the lava cools materials of different sizes. Sometimes the lava cools down on the pipe, creating a plug; the magma is climbing down on the pipe, creating a plug; the magma is climbing up the pipe at great pressures, and breaks apart this up the pipe at great pressures, and breaks apart this plug, creating fragments of different sizes. plug, creating fragments of different sizes.

The most common pyroclastic materials are: The most common pyroclastic materials are: --volcanic ashesvolcanic ashes (the particles have less than 2 mm in (the particles have less than 2 mm in

diameter)diameter) --lapilli- lapilli- pebbles with diameters between 2-64 mmpebbles with diameters between 2-64 mm - bombs or blocks- bombs or blocks, are fragments larger than 64 mm, are fragments larger than 64 mm

Types of Lava FlowTypes of Lava Flow

Pahoehoe Pahoehoe is lava with smooth, ropelike is lava with smooth, ropelike surfaces. surfaces.

Pillow LavaPillow Lava

Lava that cools under water has a Lava that cools under water has a rounded, pillow like form.rounded, pillow like form.

AaAa

Aa is lava that cools quickly with a rough, Aa is lava that cools quickly with a rough, jagged surface.jagged surface.