Volcano Notes Outline

Volcano Notes Outline Name ______Date______Period____

Volcanism : Any activity that includes the movement of magma towards or onto Earth’s surface

Volcano: A vent or fissure in Earth’s surface through which magma and gases are expelled

Formed by: 1. Subduction 2. Rifting 3. Hotspots

Magma: Liquid rock produced under the Earth’s surface. Made up of molten rock, minerals and dissolved gases

Lava: Magma that flows onto the Earth’s surface. Loses some of the gases and has more minerals than magma.

What is magma? Made up of molten rock, minerals and dissolved gases from the upper layers of the mantle

What factors affect the formation of magma?

Temperature -- temps need to be between 800˚C and 1200˚C

Pressure – as pressure decreases, the temperature at which a substance melts also decreases

Water content of the rocks – rocks melt at lower temperature in the presence of water

Composition of the rocks – different types of rock melt at different temperatures

What is Viscosity?

A substance’s resistance to flow is called its viscosity.

Ex: cold syrup is more viscous than hot syrup (cold syrup does not flow easily)

Gases in Magma

Most important: Water vapor, carbon dioxide, and sulfur

Also has: hydrogen (which can combine with oxygen to form steam)

Amount of gas determines type of eruption

Large amt of gases = more explosive eruptions Volcano Notes Outline Name ______Date______Period____

Three types of magma Compositio Source Viscosity Gas Silica Explosive Location n Material Conten Conten of t t Magma Basaltic Upper Low 1 – 2 % About Least Both mantle 50% oceanic and continenta l crust Andesitic Oceanic Intermediat 3 – 4 % About Intermediat Continent crust and e 60% e al margins oceanic – sediments subductio n zones

Rhyolitic Continent High 4 – 6 % About greatest Continent al crust 70% al crust

Lava Fragments:

Tephra: solid fragments of lava produced by explosive eruptions

Smallest pieces: ash

Larger pieces: lapilli

Largest pieces: blocks (solid), bombs (liquid then harden)

Volcanic Hazards

Pyroclastic Flows – clouds of ash, dust, and gases (AKA – Nuee Ardente – “Glowing Cloud”)

Move at speeds of up to 200 km/h

Denser than surrounding air – so it stays close to ground Volcano Notes Outline Name ______Date______Period____ Poisonous

Superheated (5X the temperature of boiling water-~7000C)

Lahar – heated snow covered mountaintop – snow melts  super fast mudslide – more dangerous than nuee ardente (more common)

Lava Flows – obviously dangerous due to heat – but can be diverted or chilled Ash – threat of suffocation

Poisonous gases – kill due to toxicity – but the most common and dangerous is CO2 (drives away oxygen)

Types of Volcanoes

Type of Volcano depends on:

Type of material that forms it and type of eruptions that occur

*We will focus on (3) most common

Shield Volcano (Mauna Loa)

Mountain with broad, gently sloping sides

Generally non-explosive

Cinder-Cone Volcano (Izalco – El Salvador)

Material that is ejected high into the air – piles back up around the vent

Steep sides, but generally small in size

Water and silica laden magmas, and full of gas – somewhat explosive

Composite Volcano (Mount St. Helens)

Large amounts of water, silica, and gases

VERY LARGE – Due to their large size – pose the greatest threat

These can blow their tops completely off forming a CALDERA – Crater Lake Oregon Volcano Notes Outline Name ______Date______Period____

Living vs. Dead Volcanoes

Active Volcano: A volcano that is erupting. Also, a volcano that is not presently erupting, but that has erupted within historical time and is considered likely to do so in the future.

Dormant Volcano: Literally, "sleeping." The term is used to describe a volcano which is presently inactive but which may erupt again. Most of the major Cascade volcanoes are believed to be dormant rather than extinct.

Extinct Volcano: A volcano that is not presently erupting and is not likely to do so for a very long time in the future

Volcano Predictions

Tectonic Activity

The volcanic mountain will “rumble” prior to an eruption

Magma is working its way up the vent or volcanic pipe, and pushes stuff around during its ascent

Topographic “Bulges”

The magma can push up/out on the land as it rises

Gas emissions – volcanic “burps” of sulfur, water vapor, and carbon dioxide

Temperature Spike – the temperature around and inside the volcano will rise

~Questionable~: Animals will bug out of the area –