Reading Assessment #5: Volcanoes

Shield volcanoes are the most dangerous volcanoes because of their immense size.

False

There has never been a globally catastrophic volcanic eruption from Iceland's volcanoes, which only involve gentle lava flows.

False

Which of the following was NOT a hazard associated with the explosion of Mt. St. Helens?

Lava flows that built up the north side of the volcano

Which of the following is NOT a reason why people live near volcanoes?

Local zoning laws require some people to live near volcanoes.

Why are so many volcanoes found on the Ring of Fire around the margin of the Pacific Ocean?

Many subduction zones occur there.

Composite volcanoes can have a long dormant period in which people may forget that they were ever once active volcanoes.

True

Heat from volcanic areas can be used to generate electrical power.

True

If a basaltic lava flow were coming toward you, you could probably outrun it.

True

Magma with a higher silica content will also have a higher viscosity.

True

People have successfully diverted lava flows from populated areas.

True

Studying the geologic history of an area -- assessing rock types and stratigraphy -- can give a timeline of past volcanic eruptions.

True

Tephra can come in many different sizes, from dust-sized to large pieces called bombs.

True

Where does tephra come from?

Volcanic rock and lava blasted into the air or carried by gases.

How might a volcanic eruption contribute to climate change?

Volcanoes can send large amounts of fine-grained ash and sulfuric acid aerosols into the atmosphere, potentially causing global cooling.

In the past 50 years, have there been any deaths attributed to a volcanic eruption?

Yes. Thousands of people have died as a result of an eruption.

What is a pyroclastic flow?

A fast-moving avalanche of hot rock, ash and glass fragments

Where are the majority of the active volcanoes in the United States?

Alaska

Where is the majority of lava extruded?

At divergent plate boundaries

Which of the following magma types will usually flow the fastest?

Basaltic

Which of the following is FALSE about caldera eruptions?

Caldera eruptions result in towering volcanic mountains.

What is the difference between a crater and a caldera?

Calderas are formed from explosions while craters are formed from inward collapse of volcano tops.

What type of volcano structure is composed mostly of pyroclastic debris?

Cinder cone

Which of the following sources of data would NOT be useful in determining whether a volcanic eruption is imminent?

Decrease in atmospheric pressure

Which is NOT a location where volcanoes are found?

Delaware

If a volcanic eruption is predicted for your area, what is the best course of action?

Evacuate

Craters differ from calderas in that craters are created from an explosion and then collapse of the volcano top, whereas calderas are simply the location where lava flows originate.

False

Mudflows or lahars associated with volcanoes do not usually cause much damage in a volcanic eruption because they are constrained to river valleys.

False

What are volatiles?

Gases trapped in magma

In which two environments are shield volcanoes found?

Hotspots in the ocean and divergent plate boundaries

In which of the following environments would you find the most explosive volcanoes?

Hotspots on land

Which of following effects might be seen in a volcanically active area even if a volcano does NOT actually erupt?

Landslides and poisonous gases

What is the difference between magma and lava?

Magma is found below the Earth's surface, lava is found on the Earth's surface.

Which of the following is NOT a benefit of volcanoes to the Earth and its inhabitants?

Many of the world's major oil fields are in volcanic rock.

Which of the following volcanic hazards is responsible for the most deaths?

Pyroclastic flows

How might you escape from a lahar?

Run up an embankment to get out of the path of the flow.

Which of the following is NOT a reason why an ash fall can be hazardous?

Sets on fire everything it touches

Mauna Loa in Hawaii is an example of which type of volcano?

Shield volcano

A very large volcano with gentle slopes is a ________ , which is comprised of ________.

Shield volcano...lava flows

Mt. St. Helens in Washington is an example of what type of volcano?

Stratovolcano

What type of volcano structure evolves from layers of pyroclastic debris and lava flows?

Stratovolcano

Which of the following is FALSE about magma?

Tectonic plates move around on an underground ocean of magma.

Why do scientists study earthquakes to predict a volcanic eruption?

The movement of magma underground causes minor earthquakes.

Why do cinder cone volcanoes have steep slopes?

They are made from pyroclastic materials that pile up near where they were erupted.

Which of the following is NOT a reason why stratovolcanoes are dangerous?

They erupt fast-moving lava flows that kill many people.

Which of the following natural hazards is NOT caused by volcanoes?

Tornadoes

In which of the following tectonic plate settings are volcanoes typically NOT found?

Transform fault

Caldera eruptions can involve the largest volcanic eruptions on earth; luckily, they are also the rarest type of eruption.

True

The disaster at Lake Nyos in Cameroon (Africa) is thought to have been caused by a

a suffocating cloud of invisible volcanic gas.