Chapter 5 Volcanoes

What is the primary hazard of concern associated with the composite volcanoes in the Aleutians?

Ash causing aviation hazards

What mafic volcanic rock is formed at seafloor spreading ridges?

Basalt

The viscosity of magma is its resistance to flow and is controlled by the silica content. Which is more viscous: mafic or felsic magma?

Felsic

What will a decrease in pressure do to a rock that is already nearly hot enough to melt?

It will cause the rock to start melting

What causes the earthquakes that precede volcanic eruptions?

The movement of magma and gas (they push on the rocks)

What are 2 ways to describe the volcanoes of the Cascade Range?

They are created through the process of subduction They are composite volcanoes

Melting of the asthenosphere can occur due to a ________________ in pressure, which is how magma is formed at spreading ridges and hot spots.

drop , decrease, lowering OR reduction

Moving magma and gas within the lithosphere create _________________ that are common precursors to volcanic eruptions

earthquakes

Earthquakes, harmonic tremors, and changes in topography and gas emissions are all precursors to volcanic ___________

eruption(s) , explosion(s) , activity OR activities

Mafic magmas flow much more easily, or are less viscous, than _________ magmas

felsic

Magma that has a relatively high silica content is ______ magma.

felsic

Eruptions of lava from cracks in Earth's surface, as opposed to from single vents, are called ________ eruptions.

fissure

Carbon monoxide, carbon dioxide, fluorine, sulfur compounds, and water vapor are all ______________ emitted by volcanoes

gases

The volcanic activity in Iceland is the result of both the island's location on a spreading center and being over a ___ ____

hot spot

The volcanic activity in both Hawaii and Yellowstone is the result of _____ ______.

hot spots

A fast-moving volcanic mudflow created through the combination of ash and water is called a

lahar

Magmas that contain 45% to 50% silica are called ______; they are relatively rich in iron and magnesium.

mafic

Even though the most recent eruption was about 50,000 years ago, geologists became concerned about the potential of an eruption in the Long Valley Caldera in California in 1980 because of a sudden increase in ____________ activity

seismic

The Volcanic Explosivity Index is a way to categorize the size of eruptions based on three categories which include the volume of _______________ produced.

pyroclastics

Mafic magmas

result in less violent eruptions than felsic to intermediate magmas.

Magma composition is controlled by the type of ___________ that is being melted and the extent to which it is melted.

rock OR material

Volcanoes that are labeled _______ have erupted within recent history, whereas ______ volcanoes have not erupted during recent history but have the potential to do so.

active ; dormant

Composite volcanoes develop from eruption of

andesitic (intermediate) lava and pyroclasts.

What particular pyroclastic material can bury cities, is slippery, can cause roofs to collapse, is bad for people's lungs, and is damaging to engines and other mechanical equipment? Volcanic ___

ash

Low viscosity lava is

basaltic or mafic in composition.

A relatively small and steep volcano, a __________ _____ is made of pieces of basaltic magma thrown into the air near the vent due to the escape of dissolved gases.

cinder cone

A volcano that is relatively small, symmetrical volcano made of pieces of basaltic lava is a

cinder cone

The volcanoes of the Aleutian Islands are ___________ volcanoes that are _________ in composition.

composite (volcanoes) ; andesitic

The eruption of Mt. Rebdoubt in 1989-1990 included an ash column, the building and subsequent destruction of a volcanic dome, lahars, pyroclastic flows, and earthquakes; all of this unsurprisingly given that it is one of many ______________ volcanoes created by the ____________ of the Pacific Plate underneath the North American Plate.

composite ; subduction

Most magma originates in the _____________ ______.

upper mantle (because the combination of temperature and pressure is just right to either partially or wholly melt rock)

Evacuations necessitated by impending volcanic eruptions have saved significant numbers of lives, yet they can be seen as inconvenient and disruptive because

volcanoes don't always erupt in the time and fashion they are expected to

What is the primary gas emitted by volcanoes?

water vapor

Lava is typically _____ or hotter.

850 degrees Celcius

What are 3 common things that happen before a volcanic eruption?

1.) Seismic activity 2.) Changes in gas emissions 3.) Changes in the volcano's shape

How is volcanic activity associated with landslides? (3 reasons)

1.) Steep and/or coastal volcanoes may have materials that are weakened and fail suddenly 2.) Landslides may allow volcanic gases to escape 3.) Earthquakes associated with moving magma may cause landslides

What are 2 ways to describe mafic magma?

1.) has a relatively high amount of iron and magnesium 2.) contains 45% - 50% silica

The Long Valley-Mammoth Lakes area in California: (3 things)

1.) is within a volcanic caldera 2.) experienced a major eruption approximately 700,000 years ago 3.) is of concern because of relatively recent seismic activity

What are 2 ways to describe a pyroclastic flow?

1.) it is a very dangerous volcanic hazard (because it moves very quickly and is very hot) 2.) it results from the collapse of a dense could of ash and gas

What are 3 hazards associated with volcanic ash.

1.) it is dangerous to breathe since it is composed of microscopic glass 2.) it can bury entire cities (example : Pompeii ) 3.) it causes mechanical failures (example: when it is covered on the roads, it can cause vehicles to skid and stop working)

Which type of volcanic activity would you least expect to find associated with a hot spot?

Creation of a composite volcano

What type of information do interferograms provide that help to monitor volcanic activity?

Deformation over a certain time period (the distance between the volcano and a satellite is measured at two different time periods, and the change in the distance shows the deformation of the volcano.

What does "active" refer to when talking about the activity level of a volcano

Erupted within recent history

How does volcanic ash and dust cause cooling of the climate?

It blocks sunlight from reaching Earth

How will a large amount of volcanic ash and dust from a single large eruption affect global climate?

It will cause regional or global cooling for months up to a few years.

What is the composition of the magma and rocks formed at seafloor spreading ridges?

Mafic (mafic magma here creates a lot of basalt)

Which of these is a shield volcano?

Mauna Loa in Hawaii

Many of the world's active volcanoes are located along the rim of the ________ Ocean

Pacific ( this is known as the Ring of Fire and is marked by subduction zones)

What does "dormant" refer to when talking about the activity level of a volcano

Potential to erupt again

What are the two primary controls on magma composition?

The extent of melting The parent material

Where does the majority of volcanic activity occur?

Seafloor spreading ridges

What does "extinct" refer to when talking about the activity level of a volcano

Unlikely to erupt again

What is the acronym for the scale used to rank the size of volcanic eruptions based on the volume and height of pyroclastics released, as well as the length of the eruption?

VEI

Fissure eruptions occur ______ and can result in massive outpourings of basalt.

on continents or on the sea floor

Water that is heated because it is near magma may cause a volcanic eruption called a ___________ eruption or explosion.

phreatic

When a volcano erupts due to the creation of large amount of steam, it is called a

phreatic explosion (because the water can be either seawater or ground water)

Most of the world's active volcanoes are located along ______ _____________.

plate boundaries

A very hot, very fast-moving flow of hot gases and ash from a volcano is known as a ____________ flow.

pyroclastic

A hot, glowing cloud of gas and ash that moves swiftly down a steep volcano flank is a

pyroclastic flow

Most damage when a volcano like Mount St. Helens erupts results from

pyroclastic flows and large amounts of ash.

Mauna Loa is the largest volcano on Earth. It is a ______ volcano, created from hundreds to thousands of runny basalt flows.

shield (volcano)

What type of volcano is produced from fluid basalt flows that create a large, broad, gently sloping structure?

shield (volcano)

A volcano built of many thin flows of fluid lava is a

shield volcano

The type of volcano most likely to form over an oceanic hot spot is a

shield volcano.

A felsic magma is rich in the minerals feldspar and quartz, and so has a high __________ content

silica

What type of volcano is composed of both pyroclastic and lava flow layers?

stratovolcano

Most magma originates in the upper mantle because the ______ is high enough and the ______ low enough to at least partially melt the rock there.

temperature ; pressure

Landslides may lead to volcanic eruptions when:

the removal of material allows gases to escape (example: Mount St. Helens erupted in 1980)

Seafloor spreading ridges are the most volcanically active areas on Earth's surface because

there is an extensive network of ridges (there is about 30,000 miles of seafloor spreading ridges)