Volcanoes

Water vapor and other gases trapped in magma creates

• silica
• lava
• pressure
• tephra

More iron (Fe) and magnesium (Mg) makes magma 

• more viscous
• thinner and more fluid-like
• thicker
• lighter in color

Volcanoes can form at

• hot spots and rocky locations
• plate boundaries and islands
• islands and fissures
• hot spots and plate boundaries

The one characteristic that is most important in telling how a volcano will erupt is

• the type of plate boundary
• the type of lava
• silica content
• iron and magnesium content

Unlike pahoehoe lava, A'a lava is

• smoother, rope-like, silica-poor, and faster moving
• blockier, jagged, silica-poor, and generally slower moving
• blockier, jagged, silica-rich, and generally slower moving
• low in silica, high in water, and high viscosity

magma when it reaches the Earth's surface

• molten rock
• epimagma
• lava
• tephra

lava that contains large amounts of silica

• tends to be quicker flowing with more Fe and Mg
• tends to be less viscous and faster flowing 
• tends to appear smoother
• tends to be thicker and more viscous

flood basalts as seen in the Pacific Northwest of the US were formed by

• fissure eruptions with high Fe and Mg contents
• cinder cone eruptions
• lava flows from shield volcanoes
• collapsing calderas

viscosity means

• how much a solid melts
• the amount of silica in magma
• the resistance to flow of a fluid
• the resistance to flow of a solid

When plates collide, the more dense plate _____ below the less dense plate.

• reducts
• subducts
• inducts
• conducts