volcanoes 21.2 what is a volcano? volcano: opening in the earth’s crust where magma erupts onto...

VOLCANOES21.2

What is a volcano?What is a volcano?

• Volcano: opening in the Earth’s crust where magma erupts onto the surface

• Magma: molten rock underground

• Lava: magma that has reached Earth’s surface

How Does A Volcano Form?

Under certain conditions, small amounts of mantle rock can melt, forming liquid magma. The magma rises upward through the crust, erupting at the surface as a volcano.

Structure of a Volcano

3 Factors That Determine the Viscosity of Magma:

1. Temperature – the higher the temperature, the lower the viscosity

2. Water Content – the more water, the lower the viscosity

3. Silica Content – the higher the silica content, the higher the viscosity. Silica acts like glue.

TYPES OF LAVATYPES OF LAVA Felsic

- high silica content- light colored- slow moving- explosive eruptions

Mafic- low silica content- dark colored- fast flowing lava- quiet eruptions

LAVA FRAGMENTSLAVA FRAGMENTS Tephra: solid fragments of lava

- ash: less than 2mm diameter

- lapilli: 2 – 64mm diameter

- bombs: 64mm or higher diameter

Ash

Lapilli

Bombs

OTHER LAVA FRAGMENTS

aa – broken, sharp blocks of lava

Pahoehoe – smooth, wrinkled lava

VOLCANO ZONESVOLCANO ZONES

Pacific Ring of Fire

- zone around the Pacific Ocean

- most active area of volcanoes in World Mid-Ocean Ridges

- zone along divergent plates Eurasian Belt

- zone along south border of Eurasian plate

Hot Spots A hot spot is a region where hot rock extends

deep within the mantle to the surface. Example: Hawaii

3 TYPES OF VOLCANOES3 TYPES OF VOLCANOES

1. CINDER CONE1. CINDER CONE Steep sides Smallest, most abundant Active for a short time, then become

dormant

2. COMPOSITE2. COMPOSITE

Consists of alternating layers of ash, cinders, and lava

Steep sides Thick magma Lot of gases

3. SHIELD3. SHIELD

Consists of layers of mafic lava Gently sloping sides, wide base

FAMOUS ERUPTIONSFAMOUS ERUPTIONS

Vesuvius, Italy – 79 A.D. Krakatau, Indonesia – 1883 Mount St.Helens, U.S. – 1980 Mt. Pinatubo, Phillipines – 1992 Eyjafjallajökull volcano in Iceland – April,

2010

Mt. VesuviusMt. Vesuvius

Mt. KrakatauMt. Krakatau18831883

Mt. St.HelensMt. St.Helens19801980

BEFORE AFTER

Mt.PinatuboMt.Pinatubo19921992

Mt.KilaeauMt.KilaeauPresentPresent

VOLCANOES IN OUTER VOLCANOES IN OUTER SPACESPACE

The Moon – no volcanoes Mars

- Olympus Mons

- 3 times higher than Mt.Everest Io

- Moon of Jupiter

- volcanic activity