Inside Earth Chapter 3.2Pages 93-102

Volcanic Activity

Characteristics of Magma• Force of an eruption depends partly on the

amount of gases evaporated in the magma• The temperature and the contents of the

magma are important factors.

Characteristics of Magma• Silica: a material found in magma composed

of the elements silicon and oxygen–More silica = thicker magma– Low Silica = runny magma

• High Silica makes light colored rock–Rhyolite an extrusive igneous rock

Volcanic Rocks

• High Silica makes light colored rock–Pumice spaces left in the rock by gases

bubbling out.

Volcanic Rocks

• Low Silica makes dark colored rock–Obsidian- cools very quickly giving a glassy

texture.

Volcanic Rocks

• Low Silica makes dark colored rocks–Basalt dark colored extrusive igneous rock

Volcanic Rocks

Types of Volcanic Eruptions

• A volcano’s magma influences how the volcano erupts

• The silica content helps determine whether the volcanic eruption is…

Quiet Explosive!or...

Quiet Eruptions• Lava: oozes out; is runny

and flows smoothly

• Gases: bubble out gently

• Examples: Iceland and Hawaii.

Aa

• Cooler, slow moving lava• Forms jagged chunks of lava.

Pahoehoe

• Fast moving, hot lava• Surface of lava looks like a solid mass of

wrinkles, billows and ropelike coils.

Exit PassHow does the amount of silica in

magma affect the type of eruption?

Explosive Eruptions• Lava: thick and sticky; builds up

in the pipe, plugging it like a cork in a bottle

• Gases: Pressure builds up until gas forces its way past magma, causing the volcano to erupt violently.

• Example: Mount Saint Helens.

Volcanic ProjectilesVolcanic Ash• Rocky, sand-sized particles

Cinders• Pebble-sized particles

Bombs• Large pieces of rock (baseball to the size of a car).

Explosive Eruptions• Pyroclastic Flow• Occurs when an explosive eruption hurls out ash,

cinders and bombs as well as gases (400mph, 1,800˚F).

Volcano Hazards• Time between eruptions can span hundreds of

years (Dormant Volcano)– People may be unaware of the danger– Mt. Saint Helens 123 years.

Volcano Hazards

• Lahar:– A mud flow

caused by melted snow or river

– Carries ash, trees and rocks.

Volcano Hazards• Volcanic Ash:– Bury towns, damage crops, and clog car engines– Wet ash is heavy and can cause roofs to collapse– Plane engines can fail if pulled into the engine.

Volcano Hazards• Pompeii, A.D. 79• Buried for 1700 years

under 12 feet of ash

Exit PassWhat is one type of volcanic projectile? What is a Lahar?

Other Volcanic Activity

• Hot Spring: pool of groundwater is heated by a nearby body of magma

• Geyser - fountain of water and steam that erupts from the ground– Hot water and steam

that become trapped underground

– Builds up pressure until it gushes out of the ground.

Other Volcanic Activity

• Geothermal Energy - clean, reliable energy source provided by magma-heated water – Hot water can be piped

into homes– Steam is piped into a

turbine that spins and generates electricity.

Other Volcanic Activity

Monitoring Volcanoes• Changes around a volcano shows signs of an

eruption and allow short time for a warning– Tiltmeters and Laser ranging devices to see ground

changes due to shifting magma– Monitor escaping gases and water level in a

volcano's crater lake.

• Check the temperature of the ground water to see if the magma is heating it

• Monitor the many small earthquakes triggered by magma moving from the chamber to the pipe

• Still, unable to predict the strength or exact time of the eruption.

Monitoring Volcanoes

Exit PassWhat is the difference between

a Hot Spring and a Geyser?