Science- Chapter 18-20 Study Guide

Which type lava-basaltic or rhyolitic lava-flows faster?Explain

Basaltic lava flows faster because lava continues less silica.

When magma reaches Earth's surface, it is called

lava.

What three factors affect the formation of magma?

Temperature, Pressure and Water

Rock fragments thrown into air during a volcanic eruption are called

tephra .

Forms when tephra are ejected into air then fall back to Earth and pile around a vent.

Cinder Cone

Magma that fuels this type of volcano contains large volumes of gases but not silica and water.

Cinder Cone

Small volcano with steep sides.

Cinder Cone

Forms from lava that us higher in water and silica content than lava that from shield volcanoes.

Cinder Cone, Composite

Forms when layers of tephra alternate with lava.

Composite

Fueled by magma that contains large amounts of silica, water, and gases

Composite

Mount St. Helens and Mount Rainier are examples

Composite

Potentially the most dangerous to humans and most destructive to the environemt

Composite

Does cooler magma flow more less quickly than hotter magma?

Cooler magma flows less quickly as viscosity increases.

Why isn't Earth's entire mantle liquid?

Even though temperature are high enough to melt rock the great pressure increases the melting temperature of the rocks most of the rock in the mantle do not melt.

Pressure decreases with depth below Earth's Surface

False

Pluton

Intrusive igneous rock body

Stock

Irregular shaped pluton that is similar to a batholith, but smaller in size.

Batholith

Largest pluton

Is the viscosity of magma that is high in silica higher or lower than magma that is low in silica?

Magma that is high silica has a higher viscosity than a magma low in silica.

Laccolith

Mushroom-shaped pluton.

Dike

Pluton that cuts across preexisting rocks.

Sill

Pluton that is parallel to the rocks it intrudes.

Mountain-Building

Process responsible for the formation of many plutons.

Forms from lava that contains relatively small amounts of gases and silica.

Shield Volcano

Forms when layers of basaltic lava accumulate during a nonexplosive eruption

Shield Volcano

Has broad, gently sloping sides and a nearly circular base.

Shield Volcano

Mauna Kea in Hawaii is an example.

Shield Volcano

As pressure increases, the temperature at which a dry substance melts increases.

True

Magma forms when rocks begin to melt.

True

Magma is a mixture of molten rock,suspended minerals, and gases.

True

Wet minerals and rock melt at lower temperatures than do dry minerals and rocks.

True

How does the viscosity of magma change as magma cools?

Viscosity increases with a decrease in temperature.

How is water present in rocks and minerals?

Water can either be held withing pore spaces within a rock or bound directly into a mineral structure. Clay minerals often times hold large amounts of water.

Which of the following forms when the top or side of a volcano collapses into the magma chamber?

caldera

A bowl-shaped depression that forms around the vent of a volcano is a

crater

The smallest tephra are

dust

Fast-moving clouds of gas,ash, and other tephra are

pyroclastic flows

Lava erupts through an opening in Earth's crust called a

vent

Large, angular volcanic fragments are called

volcanic blocks.

Large, rounded or streamlined tephra are called

volcanic bombs.