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