VOLCANOES 21 2 What is a volcano Volcano

What is a volcano? • Volcano: opening in the Earth’s crust where magma erupts

How Does A Volcano Form? v Under certain conditions, small amounts of mantle rock

3 Factors That Determine the Viscosity of Magma: 1. Temperature – the higher the

TYPES OF LAVA v v Felsic - high silica content - light colored -

LAVA FRAGMENTS v Tephra: solid fragments of lava - ash: less than 2 mm

OTHER LAVA FRAGMENTS v aa – broken, sharp blocks of lava v Pahoehoe –

VOLCANO ZONES Pacific Ring of Fire - zone around the Pacific Ocean - most

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

1. CINDER CONE Steep sides v Smallest, most abundant v Active for a short

2. COMPOSITE Consists of alternating layers of ash, cinders, and lava v Steep sides

3. SHIELD Consists of layers of mafic lava v Gently sloping sides, wide base

FAMOUS ERUPTIONS Vesuvius, Italy – 79 A. D. v Krakatau, Indonesia – 1883 v

VOLCANOES IN OUTER SPACE The Moon – no volcanoes v Mars - Olympus Mons

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VOLCANOES 21. 2

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? v 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 v 2. Water Content – the more water, the lower the viscosity v 3. Silica Content – the higher the silica content, the higher the viscosity. Silica acts like glue. v

TYPES OF LAVA v v Felsic - high silica content - light colored - slow moving - explosive eruptions Mafic - low silica content - dark colored - fast flowing lava - quiet eruptions

LAVA FRAGMENTS v Tephra: solid fragments of lava - ash: less than 2 mm diameter - lapilli: 2 – 64 mm diameter - bombs: 64 mm or higher diameter

Ash Lapilli Bombs

OTHER LAVA FRAGMENTS v aa – broken, sharp blocks of lava v Pahoehoe – smooth, wrinkled lava

VOLCANO ZONES Pacific Ring of Fire - zone around the Pacific Ocean - most active area of volcanoes in World v Mid-Ocean Ridges - zone along divergent plates v Eurasian Belt - zone along south border of Eurasian plate v

Hot Spots A hot spot is a region where hot rock extends deep within the mantle to the surface. v Example: Hawaii v

3 TYPES OF VOLCANOES

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

2. COMPOSITE Consists of alternating layers of ash, cinders, and lava v Steep sides v Thick magma v Lot of gases v

3. SHIELD Consists of layers of mafic lava v Gently sloping sides, wide base v

FAMOUS ERUPTIONS Vesuvius, Italy – 79 A. D. v Krakatau, Indonesia – 1883 v Mount St. Helens, U. S. – 1980 v Mt. Pinatubo, Phillipines – 1992 v Eyjafjallajökull volcano in Iceland – April, 2010 v

Mt. Vesuvius

Mt. Krakatau 1883

Mt. St. Helens 1980 BEFORE AFTER

Mt. Pinatubo 1992

Mt. Kilaeau Present

VOLCANOES IN OUTER SPACE The Moon – no volcanoes v Mars - Olympus Mons - 3 times higher than Mt. Everest v Io - Moon of Jupiter - volcanic activity v