Reading Assessment for Chapter 5

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

suffocating cloud of carbon dioxide gas.

Shield volcanoes are the most dangerous volcanoes because they are so big.

False

The area around Mt. St. Helens is now safe because the volcano is finished erupting and will stay dormant for the next 200 years.

False

The eruption of Mt. St. Helens was an isolated event and didn't have much impact outside the local area.

False

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

False

There have never been any caldera eruptions in the U.S. and probably won't be in the future.

False

Unfortunately, volcanoes do not give any signs or indications of when they might erupt.

False

Volcanic ash is very lightweight and therefore is not much of a threat to buildings.

False

Volcanic soils are usually too hot and dry to be of use for agriculture.

False

Volcanoes associated with high viscosity magma are usually less dangerous than those with more freely flowing magma.

False

What is the best reason why most lava flows aren't a threat to human life?

Lava flows usually don't flow very quickly, people can outrun them.

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

Local zoning laws require some people to live near volcanoes.

Composite volcanoes can have a long dormant period in which people can 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

Mauna Loa in Hawaii is an example of a shield volcano built over a hotspot.

True

Most volcanoes are found near tectonic plate boundaries because that's where the magma is located.

True

People have successfully diverted lava flows from populated areas.

True

Scientists can use information about earthquakes to determine when a volcano is likely to erupt.

True

Tephra can come in many different sizes from dust size to large pieces called bombs.

True

The history of an area's rocks can give a timeline of past volcanic eruptions.

True

Volcanoes can cause tsunamis.

True

How can volcanoes 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.

Which is NOT a location where volcanoes are found?

central usa

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 lists magma types in order of increasing viscosity (LEAST viscous first)?

Basaltic, andesitic, rhyolitic

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?

Craters are formed from explosions while calderas are formed from inward collapse of volcano tops.

Which of the following is NOT used to determine whether a volcanic eruption is expected?

Decrease in atmospheric pressure.

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

Evacuate

Because of the alert systems and people's willingness to heed warnings, no one was killed in the 1980 Mt. St. Helens eruption.

False

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 the magma

In which two environments are shield volcanoes found?

Hotspots in the ocean and divergent plate boundaries

Which of the following environments has the most explosive volcanoes?

Hotspots on land

Where does tephra come from?

It is the volcanic rock and lava blasted into the air or carried by gases.

Which of following effects might an area see even if a volcano does NOT actually erupt?

Landslides and poisonous gases

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

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.

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

Many subduction zones occur there.

Do humans affect the frequency or size of volcanic eruptions?

No. People do not increase or decrease the volcanic hazard.

Where is the best place to be during a pyroclastic flow?

Nowhere is safe during a pyroclastic flow.

At which plate boundary is more viscous lava found?

Oceanic Subduction zones

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

Pyroclastic flows

Which type of magma typically results in the greatest explosive events?

Rhyolitic

How might you escape from a lahar?

Run up an embankment away from the flow

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

Sets on fire everything it touches

What type of volcano is found in Iceland?

Shield

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 which type of volcano?

Stratovolcano

Which volcano type involves 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.

Several communities around Mt. Rainier are built on enormous old lahar deposits. What might people in these areas expect in an eruption?

Their homes will probably be destroyed by a new lahar.

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 and they are the rarest.

True

Why do scientists study earthquakes to predict a volcanic eruption?

When magma moves, it causes earthquakes.