Chapter 4 Volcanism and Extrusive Rocks

Combination of book questions and lecture/slide notes.

Describe the difference between effusive and explosive eruptions in terms of their eruptive products and the hazards they pose to society.

Effusive Eruptions: LESS DANGEROUS

-Lava flows, Basaltic in composition. Mafic Basalt. -Intermediate and felsic lava can erupt effusively.

Explosive Eruptions: PYROCLASTIC

-pyro clasts (fragments of lava, dust and ash)

-most dangerous situation

What are the three main components of Magma?

-molten silicate rocks

-crystals

-gas

What factors control the viscosity of magma?

-the silica (SiO2) content of the magma

-Temperature of the magma

-amount of gas dissolved in magma

On examining a basaltic lava flow in Hawaii, you discover that close to the vent, the lava flow has a pahoehoe texture, but further from the vent, it becomes an A'a flow. What can explain this?

Pahoehoe:

-lava flows (ropey, broadly, hummocky surface)

-formed by the rapid cooling and solidification of the surface of the lava flow.

A'a:

-lava flow with a jagged, ruby surface.

-formed when basalt is cool enough to have partially solidified (pasty mass).

Basaltic lava is typically low viscous due to low silica content.

What do pillow structures indicate about the environment of volcanism?

Pillow structures indicate about underwater volcanism.

What roles do gases and viscosity play in the generation of explosive eruptions?

Higher viscosity and gas content = Higher the eruption.

Describe how a caldera forms.

Caldera:

a large volcanic crater with a diameter of 1 km formed by the explosive volcanic eruption and collapse of surface rock into a partially emptied magma chamber.

Compare lava flows, pyroclastic flows, and lahars as volcanic hazards.

a volcanic hazard is any volcanic activity that harms life.

Pyroclastic flows: intense volcanic eruption

Lahar: water and rock fragments flowing down the slopes of a volcano or river valleys. (can get up to 80km/h)

You are a volcanologist working on a volcano that has been active

in the past but is currently quiet. What methods would you use to

monitor this volcano, and what would those methods tell you about

processes beneath the surface?

tilt meters and satellites are used to measure changes in the ground surface.

Seismographs monitor seismic activity beneath volcanoes that are likely to erupt.

What are the three components of volcanic hazard mitigation?

Provide examples of each

-Hazard mapping: study of deposits from past eruption of a volcano

-Monitoring: seismographs, tilt meters, satellites.

-Alerts: given to the aviation industry to alert air traffic.

Which of the following is an example of a shield volcano?

c. Mauna Loa, Hawaii

Volcanic eruptions can affect the climate because:

b. volcanic dust and gas can reduce the amount of solar radiation.

The gas most commonly released during a volcanic eruption is:

a. water vapor

___________ is a rock composed of frothy volcanic glass

d. Pumice

A lava flow with a ropy or billowy surface is called

a. pahoehoe

Which of these is not a type of pyroclastic material?

d. A'a

Which of these is not a major type of volcano?

e. Spatter cone

spatter cone is defined as a low, steep-sided hill or mound that consists of welded lava fragments.

An example of a composite volcano is:

d. all of the above

Which volcano is not usually made of basalt?

b. composite cone

Which of the following is NOT a component of volcanic hazard

mitigation?

b. Preventing a volcanic eruption

Sedimentary rocks consist of particles derived from the _ of other rocks.

weathering

_ rocks form when molten rock solidifies at the surface (extrusive) or beneath the surface (intrusive).

Igneous

The Vishnu Schist, a _ rock, formed deep below Earth's surface where temperatures and pressures are high.

metamorphic

Magma forms when rock melts deep beneath Earth's _.

surface

When magma or lava cools and solidifies, _ rock forms.

igneous

Weathering breaks down rock that is transported and deposited as _.

sediment

Sediment is compacted and cemented to form _ rock.

sedimentary

Volcanoes are landforms formed by the extrusion of _ from the earth’s interior to the surface.

magma

_ is the term for any molten silicates material, whether below or on top.

Magma

When magma reaches the earth’s surface and solidifies it is called _.

lava

Mount Merapi, Indonesia, is an example of an _ eruption.

explosive

Kilauea volcano, Hawaii, is an example of an _ eruption.

effusive

Primary lavas that are low in silica are said to be _ in composition.

mafic

Volcanoes contribute to the formation of new land forms, such as the Hawaiian _.

Islands

Soil formation from volcanic _ is one importance of volcanoes.

ash

Geothermal energy released by volcanoes can be used to generate _.

electricity

Volcanic activity can reduce _ that penetrates the earth’s atmosphere, impacting global temperature.

solar radiation

Pompeii was destroyed in A.D. 79 by the catastrophic eruption of _.

Mount Vesuvius

A fluid’s resistance to flow, which determines the ease of gas escape, is known as _.

viscosity

The more viscous the lava and the greater volume of gas trapped, the more _ the eruption.

violent

Factors influencing viscosity include magma’s composition, temperature of magma, and amount of _ it contains.

dissolved gases

The silica content of lava determines its _.

viscosity

Felsic rocks, such as _, typically have greater than 65% SiO2.

Rhyolite

Rhyolite is compositionally equivalent to _, an intrusive igneous rock.

granite

Mt. Pinatubo is an example of a large, explosive, and catastrophic _ eruption.

rhyolite

Mafic volcanic rocks typical of ocean basins, such as _, have 50% or less silica.

basalt

Basaltic eruptions are commonly _.

non-explosive

Intermediate rocks, like _, are typical of continental margins above subduction zones.

Andesite

Mt. St. Helens is _ in composition.

andesitic

Basaltic (Mafic) magma has the _ silica content and highest eruptive temperature.

least

Rhyolitic (Felsic) magma has the _ silica content and greatest viscosity.

most

The most abundant gas in volcanic emissions is _.

water vapor

At _ temperatures, magma is less viscous (more fluid).

higher

Materials blown out of a volcano are called pyroclastic debris or _.

tephra

Ash and dust are produced during _ eruptions.

explosive

Walnut-sized pyroclastic material is called _.

lapilli

Pea-sized pyroclastic material (2-64 mm) is called _.

cinders

Incandescent lava fragments larger than 64 mm are called volcanic _.

bombs

A mosaic of interlocking minerals smaller than 1 millimeter describes _ texture.

fine-grained

The volcanic rock texture characterized by holes due to trapped gas is described as _.

vesicular

Frothy glass is called _.

Pumice

Consolidated fine pyroclastic material is called _.

Tuff

The opening through which an eruption takes place is the _.

vent

The basin-like depression over a vent at the summit of the cone is the volcano's _.

crater

A volcanic depression much larger than the original crater (at least 1 km), such as Crater Lake, Oregon, is called a _.

caldera

In a _ eruption, lava pours from a vent on the side of a volcano.

flank

The three main types of volcanoes are Shield, Cinder, and _.

Composite

_ volcanoes are broad, gently sloping cones constructed of solidified lava, typically basalt, with slopes between 2 and 10 degrees.

Shield

The Island of Hawaii is comprised of a series of _ volcanoes.

shield

_ lava flow is characterized by a ropy or billowy surface due to quick cooling.

Pahoehoe

_ lava flow has a spiny and rubbly surface characteristic of basalt flow.

Aa

_ lava forms large rounded blobs when lava erupts under water.

Pillow

Cinder cones are built from loose _ material that forms steep slopes as it falls around the crater.

pyroclastic

Paricutin in Mexico is an example of a _ volcano.

cinder cone

_ volcanoes, also known as stratovolcanoes, are made up of alternating layers of pyroclastic material and solidified lava flows.

Composite

Mount Mayon in the Philippines and Mount Fuji in Japan are examples of _ volcanoes.

composite

Most composite cones are found in the Circum–Pacific belt, often called the _.

Ring of Fire

Mount Vesuvius, Mount Thera, and Mount Etna are examples of composite cones in the _ belt.

Mediterranean

Composite cones produce the _ violent volcanic activity.

most

_ are eruptions that eject hot gases infused with incandescent ashes.

Nuee Ardente

A _ is a mudflow generated by large composite cones, occurring when ash and debris become saturated with water.

Lahar

Shield volcanoes have gentle slopes, typically between _ and 10 degrees.

2

Composite volcanoes typically have slopes less than _ degrees.

33

Cinder cones are the _ of the three types of volcanoes.

smallest

Cinder cones have steep slopes, typically around _ degrees.

33

_ are steep-sided, dome masses of volcanic rock formed from viscous lava, typically rhyolite.

Lava Domes

Columbia Plateau in the NW U.S. is an example of a _ formed from non-viscous lava extruding over wide areas.

lava plateau

Flood basalts are lava from _ eruptions which travel very far from their source.

fissure

When basaltic lava solidifies and contracts, it can form unique six-sided fractures known as _.

columnar jointing

A _ is a natural underground tunnel formed by flowing lava.

lava tube

Volcanic activity at divergent boundaries typically involves _ melting and effusive eruptions of basaltic magmas.

decompression

Most large, well-known volcanoes and explosive composite volcanoes are associated with _ plate boundaries.

convergent

Within-plate volcanic activity, such as Hawaii and Yellowstone, is caused by _, also known as hot spots.

mantle plumes

Extraterrestrial volcanic activity includes shield volcanoes on Venus and _.

Mars

What is the difference between effusive and explosive eruptions in terms of their eruptive products and the hazards they pose to society?

Effusive - Lava flows, secondary fires, land cover changes, and gas emissions.

Explosive - Pyroclastic flows, ash fall, volcanic gases, throw ballistic bombs and other debris in to the air, and can cause earthquakes, landslides, debris flows and tsunamis. 

What are the three main components of magma? 

• Liquid/Melt (molten metals/rocks or mobile ions)

• Solid (silicate minerals)

• Gases/Volatiles (water vapor, carbon dioxide, and sulfur dioxide) 

What factors control the viscosity of magma?

Composition, temperature, and volatile (gas) content.

On examining a basaltic lava flow in Hawaii, you discover that close to the vent, the lava flow has a pahoehoe texture, but further from the vent, it becomes an a′a flow. What can explain this?

Pahoehoe flows often change into a'a flows farther from the vent as the lava cools and becomes more viscous.

What do pillow lavas indicate about the environment of volcanism?

Oceanic Volcano