Chp 5 Volcanic Activity Reading Quiz

How is this chain of volcanic islands forming?

A tectonic plate is moving over a mantle plume, which burns through the plate to create a chain of volcanoes.

What kind(s) of lava are most closely associated with composite cones?

Andesite

Pyroclastic materials are generally associated with which type of magma(s)?

Andesitic and rhyolitic

What type of lava is produced at a divergent plate boundary?

Basaltic

Which of the following lavas make up 90 percent of the total volume of lava on Earth?

Basaltic

How do craters differ from calderas?

Calderas, which have diameters of 1 km or more, are much larger than craters.

All types of volcanic cones share which feature?

Conduit

Using the choices below, select the statement that best explains how dissolved gases drive volcanic eruptions.

Confining pressure decreases on a rising magma, allowing gas bubbles to expand and fracture the magma. This process further decreases pressure on the magma and will result in an explosive event.

The more the silica in magma, the lower the viscosity.

False

Define magma.

Molten rock found at depth that contains dissolved gases and some crystals

The ring of fire is a narrow zone of composite cone volcanoes rimming the ________ Ocean.

Pacific

Contrast pahoehoe and aa lava flows.

Pahoehoe flows exhibit smooth surfaces, are hotter, and are more fluid than aa flows, which exhibit jagged surfaces with sharp edges.

Which statement accurately describes a pyroclastic flow?

Pyroclastic flows, which consist of incandescent ash and lava fragments, can reach many miles away from their sources because they are nearly frictionless and are driven by gravity.

Which of the following choices best explains the difference between a crater and a caldera?

A crater is a small, funnel-shaped depression; a caldera is a large depression that has a diameter of over 1 km.

How is magma generated along convergent plate boundaries?

The subducting slab drives water and carbon dioxide into the mantle, which reduces the temperature at which it melts, allowing mantle rock to melt and rise.

A ________ is a cone-shaped structure created by successive eruptions of volcanic materials such as lava or pyroclastic materials.

Volcanic cone

What is a lahar?

a mudflow of volcanic debris saturated with water

Which of the following would decrease the viscosity of magma?

an increase in temperature

Most magma on Earth is produced at ___ plate boundaries.

divergent

Which volcanic landform listed below is primarily composed of loose fragments of scoria?

the Paricutin cinder cone

________ is a material's resistance to flowing.

viscosity

Which type of volcanic hazard can decrease global temperatures?

volcanic ash