Volcanic EruptionsNotes

By: Mrs. Hudson

Objectives:

• Distinguish between non-explosive and explosive volcanic eruptions.

• Identify the features of a volcano.• Explain how the composition of magma

affects the type of volcanic eruption that will occur.

• Describe four types of lava and four types of pryoclastic material.

Vocabulary Words:1. Volcano: are areas of Earth’s surface through

which magma and volcanic gases pass.2. Magma: molten rock3. Lava: molten rock that flows onto the Earth’s

surface4. Vent: an opening at the surface of the Earth

through which volcanic material passes.5. Magma chamber: the body of molten rock that

feeds a volcano.6. Ash : dust sized particles

Volcanic Eruptions

• Explosive pressure of a volcanic eruption can turn an entire mountain into a billowing cloud of ash and rock in a matter of seconds.

• Eruptions are also creative forces – they help form fertile farmland

• During an eruption, molten rock, or magma, is forced to the Earth’s surface. Magma that flows onto the Earth’s surface is called lava.

Non-explosive Eruptions

• Most common type of eruption• Produces relatively calm flows of lava• Can release huge amounts of lava• Huge amounts of the sea floor and the

Northwest region of the United States, are covered with lava from these types of explosions.

Explosive Eruptions• Much rarer than non-explosive eruptions• Incredibly destructive• Clouds of hot debris, ash, and gas rapidly

shoot out from a volcano• Causes molten rock to be blown into tiny

particles that harden in the air• Blast millions of tons of lava and rock • Can demolish an entire mountainside

Diagram of a Volcano

What is inside a Volcano?

• Magma chamber is a body of molten rock deep underground that feeds a volcano.

• Vents is where magma rises from the magma chamber through cracks in the Earth’s crust to openings

What Makes up Magma?

• The composition of the magma affects how explosive a volcanic eruption is

• Key to whether an eruption will be explosive lies in the silica, water, and gas content of magma.

Water and Magma are an Explosive Combination

• Water content of magma is high, an explosive eruption is more likely

• Magma underground, it is under intense pressure and water stays dissolved in the magma

• Magma quickly moves to the surface, the pressure suddenly decreases and the water and other compounds, such as carbon dioxide, become gases. Gases expand rapidly and explosion can result.

Silica-Rich Magma Traps Explosive Gases

• Magma that has a high silica content also tends to cause explosive eruptions

• Has a stiff consistency• Flows slowly and tends to harden in a

volcano’s vents (plugs vents)• The more the magma pushes up from below

the more pressure increases and an explosive eruption takes place

• Stiff magma also prevents water vapor and other gases from easily escaping

• Magma that contains less silica has a more fluid, runnier consistency. Because gases escape this type of magma more easily, explosive eruptions are less likely to occur.

What Erupts from a Volcano?• Magama erupts as either lava or pyroclastic

material• Pyroclastic material forms when magma is

blasted into the air and hardents• Non-explosive eruptions produce mostly lava• Explosive eruptions produce mostly

pyroclastic• Volcano’s eruptions may alternate between

lava and pyroclastic eruptions

Types of lava

• The viscosity of lava, or how lava flows, varies qreatly

• Lava that have high viscosity is stiff• Lava that have low viscosity is more fluid• Four types: Aa (ah ah), Pahoehoe (puh Hoy

Hoy) Pilow lava, Blocky lava

• Aa: is so named because of the painful experience of walking barefoot across its jagged surface. This lava pours out quickly and forms a brittle crust. The crust is torn into jagged pieces as molten lava continues to flow underneath.

• Pahoehoe: lava flows slowly, like wax dripping from a candle. Its glassy surface has rounded wrinkles.

• Pillow lava: forms when lava erupts underwater. This lava forms rounded lumps that are shape of pillows.

Blocky lava: is cool, stiff lava that does not travel far from the erupting vent. Usually oozes from a volcano and forms jumbled heaps of sharp-edged chunks

Types of Pyroclastic Material

• Forms when magma explodes from a volcano and solidifies in the air

• Also forms when powerful eruptions shatter existing rock

• The size of the material ranges from boulders that are the size of houses to tiny particles that can remain suspend in the atmosphere for years

Pyroclastic Flows• Dangerous type of volcanic flow• Produced when enormous amounts of hot

ash, dust, and gases are ejected from a volcano

• Can race downhill at speeds of more than 200km/h – faster than most hurricane-forces winds

• Temperature in the center can exceed 700 degrees Celsius

Four types of Pyroclastic Material

Volcanic bombs: are large blobs of magma that harden in the air. The shape of this bomb was caused by the magma spinning through the air as it cooled.

• Volcanic blocks: the largest pieces of pyroclastic material, are pieces of solid rock erupted from a volcano

• Lapilli: which means “little stones” in Italian, are pebble-like bits of magma that hardened before they hit the ground

• Volcanic ash: forms when the gases in stiff magma expand rapidly and the walls of the gas bubbles explode into tiny, glasslike silvers. Makes up most of the pyroclastic material in an eruption