homework 6

What event triggered the main eruption of Mount St. Helens in May 1980?

A landslide removed rocks and released pressure on the magma.

Which of the following are characteristics of actively erupting volcanoes?

Glowing orange lava flowing downhill. Fragments of molten rock blasting into the air. Billowing clouds of ash rising into the air.

The largest concentration of composite volcanoes on Earth is located along the

Pacific Ring of Fire.

Which of the following are ways that viscosity affects gases in magma?

Viscous magma prevents gas from escaping easily.

A volcanic eruption occurring beneath an ice sheet is likely to cause

a hazardous flood.

Which of the following is NOT a major controlling factor on volcanic eruption style?

age of volcano

Composite volcanoes are so called because they

are composed of lava flows, pyroclastic material, and mudflows.

Shield volcanoes are composed primarily of

basalt lava flows.

A single volcano may produce

both explosive and nonexplosive eruptions.

The main cause of caldera collapse is

collapse of the roof of a magma chamber as magma erupts.

The most dangerous type of volcano is a

composite volcano.

Which of the following plate boundaries is least likely to produce composite volcanoes?

continent-continent convergent boundary with a high mountain range (Himalayas)

When basaltic lava reach the ocean they

form pillow basalts.

Ash layers from the three most recent caldera-forming eruptions at Yellowstone (2.1, 1.3, and 0.64 million years ago) stretch

from Canada to Mexico.

Which of the following is NOT a typical hazard posed to human-made structures by lava flows?

high winds

How does the addition of water cause melting?

it changes the location of the liquid-solid boundary

Eruption types include

lava flow, lava fountain, lava dome, eruption column

What tectonic setting is interpreted to be the cause of volcanism at Yellowstone?

movement of North America over a mantle plume

Which of the following materials is NOT produced by erupting volcanoes?

sandstone

Some scientists think that Yellowstone could cause a future disaster because

the area is part of a caldera. scientists think that magma is still present at depth. past eruptions from Yellowstone carried ash over a huge area of western North America. land near Yellowstone is uplifting in some places and subsiding in others.

The higher the gas pressure builds in a magma,

the more explosive an eruption it is likely to produce.

What are the rounded hills inside the Valles Caldera?

volcanic domes

Which of the following would be evidence that a volcano has NOT been active for a long period of time?

well-developed soils on volcanic rocks