Volcanic Eruptions

Ms. Pilcher

Vocabulary • Mafic lava- dark in color and is rich in

magnesium and iron.

• Felsic lava- lighter in color when cools, high in silica.

• Pahoehoe- (puh-HOY-hoy) wrinkles that are formed when lava cools rapidly.

• Aa- (AH-ah) refers to the sharp, blocky texture of volcanic rock.

Vocabulary• Pillow lava- round blobs of lava that

separate and cool underwater.

• Pyroclastic material- particles of lava that fly into the air when eruption occurs.

• Volcanic ash- Particles less than 2mm

• Volcanic dust- Particles less than .25mm

• Lapilli- Particles less than 64 mm

Vocabulary• Pillow lava- round blobs of lava that

separate and cool underwater.

• Pyroclastic material- particles of lava that fly into the air when eruption occurs.

• Volcanic ash- Particles less than 2mm

• Volcanic dust- Particles less than .25mm

• Lapilli- Particles less than 64 mm

Vocabulary• Volcanic bombs- clot of lava that spins through

the air and cools.

• Volcanic block- largest pyroclastic particle that blast from the fissure or vent.

• Shield Volcano- covers a wide area and generally result from lava eruptions.

• Cinder Cone- formed from explosive eruption.

• Composite Volcano- results from altering layers of pyroclastic material and lava.

Vocabulary

• Stratovalconoes- also known as composite volcanoes, highest volcanic mountains.

• Crater- funnel shape around the vent of the volcano.

• Caldera- basin in the crater that is created when slippage occurs.

Vocabulary

• Stratovalconoes- also known as composite volcanoes, highest volcanic mountains.

• Crater- funnel shape around the vent of the volcano.

• Caldera- basin in the crater that is created when slippage occurs.

Volcanic Eruptions

• The lava that erupts from volcanoes allows us to determine firsthand the material that emerges from the mantle.

• Scientist has discovered that there are two general types of lava.– Mefic lava – Felsic lava

Mafic Lava• Dark in color when hardens.

• Rich in Magnesium and Iron.

• Forms much of the ocean crust.

• When crust cools rapidly, surface will form a crust.

Felsic Lava

• Lighter in color when hardens

• Common in continental crust

• Contains much silica, with lesser amounts of iron and Magnesium

Rock Formations

• When mafic lava cools and forms wrinkles there called pahoehoe (puh-HOY-hoy)

• Can break into jagged chunks to form aa (Ah-ah)

• When lava flows into the ocean and cools rapidly, it often separates and forms pillow lava.

Kinds of Eruptions

• The kind of lava that reaches the surface determines the force the volcano will erupt.

• Lava that contains large amounts of trapped gases produces a more explosive eruption of lava.

Oceanic Volcanoes

• Usually produced by mafic lava.

• Mafic lava is very hot and thin, and flows like almost as easy as water.

• Gases escape easier from mafic lava, so erupts are usually quiet.

• Will flow from the opening like a red hot river.

Continental Volcanoes

• Most commonly comprised of felsic lava.

• Tends to be cooler and thicker.

• Contains large amounts of trapped gases, mostly water vapor and carbon dioxide.

• When fissure or vent opens, gases escape explosively sending molten particles shooting into the air.

Volcanic Rock Fragments• Felsic lava explode throwing pyroclastic

material into the air.

• Formed when lava cools too fast or is sprayed into the air and solidifies. – Volcanic ash– Volcanic dust– Lapilli (luh-PIL-ie)– Volcanic bombs– Volcanic blocks

Volcanic Rock Fragments

• Volcanic ash– Particles less than 2mm

• Volcanic dust– Particles less than .25 mm

Volcanic Rock Fragments

• Lapilli– Particles less than 64mm

• Volcanic bomb– Round or spindle shape

Volcanic Rock Fragments

• Volcanic Blocks– Largest pyroclastic material, can be as big as

a house!

Volcanic Features • Volcanic activity produces a variety of

characteristic features on the earth.

• The lava and pyroclatic material ejected during eruption can build up around the vent.

• These piles are known as volcanic cones; they are classified into three different types.– Shield Volcano– Cinder Cones– Composite Volcano

Volcanic Features • Volcanic activity produces a variety of

characteristic features on the earth.

• The lava and pyroclatic material ejected during eruption can build up around the vent.

• These piles are known as volcanic cones; they are classified into three different types.– Shield Volcano– Cinder Cones– Composite Volcano

Shield Volcano• Covers a wide area

• Generally results from lava eruption

• Layers of hot mafic lava flow out around the vent, harden, and slowly build up to form a cone.

• The Hawaiian Island

are a chain of

shield volcanoes.

Cinder Cone• Made up of solid fragments ejected from

the volcano.

• Most cinder cones have very steep slopes, often close to 40 degrees.

• Rarely more than a few hundred meters high.

Composite Volcano• Many volcanoes have both quiet and

explosive eruptions.

• Composite volcanoes are formed as a result of alternating layers of lava and pyroclastic material.

• Also known as stratovalcanoes

Craters/ Calderas• A creater is a funnel-shaped pit at the top

of the volcanic vent .

• Formed when material is blown out of the volcano by explotion.

• Calderas are formed when slippage or sinking occurs in the crater.

Predicting Volcanic Eruptions

• Volcanic eruptions can be one of earth’s most destructive natural phenomena.

• Scientist are still making progress toward increase there abilities in predicting volcanic activity.

• Use instruments much like the one they use with earthquake prediction.

Predicting Volcanic Eruptions

• Things they look for:– Temperature changes within the rock

– Fracturing of rocks from pressure build-up

– Increase in # earthquake around volcano

– Increase is strength of earthquakes

– Bulging surface

– Change in gases given off by the volcano in the area