Table of Contents. Volcanoes and Plate Tectonics Properties of Magma Volcanic Eruptions Volcanic Landforms. - Volcanoes and Plate Tectonics. Volcanoes and Plate Boundaries. Volcanic belts form along the boundaries of Earth’s plates. Discussion Questions. What is a volcano?
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- Volcanoes and Plate TectonicsAsking Questions
Where are volcanoes found?
Most volcanoes are found along plate boundaries.
A hot spot is an area where material from deep within the mantle rises and then melts, forming magma.
What are hot spots?
What type of magma would have a higher viscosity? Explain.
- Properties of MagmaMagma Composition
There are three categories of lava, classified on the basis of its silica (SiO2) content, which affects how readily it flows.
1. BASALTIC LAVA
a. Relatively low SiO2 content (less than 52%) b. Relatively low viscosity (flows readily when hot)
2. ANDESITIC LAVA
a. Intermediate SiO2 content (between 52 and 63%) b. Intermediate viscosity (does not flow readily)
3. RHYOLITIC LAVA
a. Relatively high SiO2 content (above 68%) b. Relatively high viscosity (flows like wet concrete)
Pahoehoelava is characterized by a smooth, billowy, or ropy surface. Pahoehoe is hot, moves fast, and has lower viscosity.
Aa is characterized by a rough or jagged surface. Aa lava flows tend to be relatively thick compared to pahoehoe flows meaning they have lower temperature and higher viscosity.
Magma’s viscosity depends on its physical and chemical properties.
Magma is made of elements and of compounds, among them silica.
Viscosity is a property of magma.
Viscosity depends on silica content and temperature.
What You Know
Lava flows out of a volcano.
Eruptions are not all the same.
Some volcanoes are dormant.
What You Learned
Magma rises toward Earth’s surface through a pipe that leads to a vent.
Differences in gas and silica content cause some eruptions to be explosive and others to be quiet.
Dormant volcanoes can become active at any time.
Ash, cinders, and bombs
Lava and ash