geology chapter 6

In the movie "Volcano" basaltic lava flows are shown running down flat streets at speeds faster than humans could run. From your knowledge of magma viscosity, is this realistic?

no the viscosity of basaltic magma is much higher than water, and thus, would flow much slower than water

the famous destruction of the Roman city of Pompeii was produced by ___

a pyroclastic eruption from a composite volcano that buried the city in ash and smothered the people living there

Mount Pelée on the island of Martinique killed thousands of people in

a pyroclastic flow, also called a nuee ardante Nuée Ardante

laccolith

a tabular intrusive body with subparallel intrusive contacts

How does the viscosity of the magma fed to volcanoes affect nearby life and property?

a volcano that expels highly viscous magma is greater threat to life and property because it is more explosive, and thus, is more difficult or impossible to predict

which type of basaltic lava flow has its surface covered with sharp-edged, angular blocks and rubble

aa

how are volcanic eruptions determined as violent or relatively quiescent

amount of dissolved gas in the magma, temperature of the magma, and the composition of the magma

sill

an intrusive, igneous rock body that is tabular and concordant

most lava flows erupted by Mt St Helens are ___

andesite

what type of magma is considered to be intermediate in composition

andesitic

volcanic bombs originate

as erupted magma blobs that partly congeal before falling to the ground

pyroclastic flows move ____

as gravity flows similar to snow avalanches; very rapidly, too fast to outrun on foot; as a dense cloud that contains hot magma particles suspended in hot gases and moves rapidly downhill

most granitic batholiths are generated ____

as intrusions beneath composite volcanoes along convergent plate margins

the dominant rock type erupted by submarine volcanoes at spreading ridges is

basalt

cinder cones

consist largely of pyroclastic, have very steep slopes, and are usually less than 300 meters high

Mt. St. Helens is located along what type of plate tectonic boundary

convergent

in what plat tectonic setting are magmas generate predominantly by fluids from ocean waters in trenches "fluxing" the melting process by decreasing melting temperature

convergent plate margins

the main mechanism for melting at spreading ridges is ____

decompression melting of ultramafic mantle rock

tabular, intrusive bodies

dikes and sills

dikes and sills

dikes are discordant igneous intrusions, and sills are concordant igneous intrusions; both are tabular

which type of plate boundary generates the greatest quantity of magma

divergent

When you open a bottle of soda slowly, it tends not to spill. Whereas if you open it too fast, you may get a wet hand. What parallel is there with effusive vs. explosive eruptions

effusive eruptions = slowly. the air is released, but cannot build up in the magma, thus keeping the eruption non-violent

If you are in the path of a pyroclastic flow or a lahar, how much time would you have to escape

enough time in a car, but not enough on foot

t/f: a basaltic volcano is likely to produce an explosive column that would endanger flying aircraft

false

t/f: during the eruptive period of Mt. St. Helens, the mountain peak was substantially built up by new lava flows and pyroclastic debris

false

t/f: powerful, explosive, volcanic eruptions can result in climatic cooling for millions of years following the eruption

false

Kilauea is an example of a ________.

shield volcano

crater

funnel-shaped depression around the vent

what does a fumarole emit

gases only

over what time span do most typical cinder cones form

generally the product of a single eruption and thus are constructed in less than a year, maybe less than a month

the bedrock in the Sierra Nevada Mountains in the California are best described as

granite and batholiths

________ tend to increase the explosive potential of a magma body beneath a volcano.

high viscosity and high dissolved gas content

the steep, upper slopes of composite volcanoes are generally produced by __

high-viscosity, low-volume silicic magmas that are erupted from the summit

the higher the viscosity of a magma, the ____ the potential for explosive eruptions

higher

the viscosities of magmas _____ with increasing percentages of silica

increase

volcanic activity in Yellowstone National Park is related to ___

intraplate, hot spot volcanism

pluton

intrusive body

a ____ is a near surface, intrusive igneous rock body that results from local inflation of a horizontal sill

laccolith

why is Mt. Rainier considered the most hazardous volcano in the lower 48 US states

large amounts of glacial ice on the mountain could be melted by even a small eruption, potentially generating dangerous lahars that would travel rapidly down river valleys to heavily populated areas

cinder cone volcanoes

short lived volcanoes that last a few days to months and then shut down

the big hawaiian volcanoes are best described how?

situated in the interior of a large, Pacific plate above a hot spot deep in the mantle

stocks

smaller than batholiths

volcanoes have ____ impact on weather and climate

some definite

which of the following was a precursor to the 1980 eruptions of Mt St Helens

steam and ash eruption, bulge beneath the volcano, small earthquakes

the most dangerous of the volcano types is

stratovolcano

rocks melt because of the introduction of water mainly at ___

subduction zones

the eruptions of the Hawaiian volcanoes are ____ explosive than the 1980 Mount St. Helens eruption

less

shield volcanoes form from what type of magma?

low viscosity basalt magmas

what is the source of magma for most intraplate volcanism

mantle plumes

what primary factors determine the nature of volcanic eruptions

temperature, composition, dissolved gases

lahar

mudflow of volcanic debris saturated with water

What role do water and other volatiles play in the formation of magma?

the addition of water and other volatiles allows the rock to melt at lower temperatures than if they had not been added

Note in the above image there are bodies buried by the pyroclastic flows from Mt. Vesuvius in 79 AD. These are not the actual bodies, as those were vaporized by the heat, but Plaster of Paris casts of individuals affected by the reaction, with casts made in the areas where the bodies were. How could this discovery help local residents to plan for the future?

the bodies indicate how rapidly the pyroclastic flow came, and this could be an indication of what could happen in the future

conduit

the circular path through which magma ascends to the vent

country rock

the crustal rocks into which igneous bodies intrude

Shiprock, New Mexico

the eroded remains of a volcanic pipe and radiating dikes

what is the geothermal gradient, and how does it relate to the melting curve of peridotite

the geothermal gradient is the increase in temperature with depth under the Earth's surface. the melting curve of peridotite is consistently higher than the geothermal gradient

batholiths

the largest type of igneous bodies and occur in a linear fashion with a distance of 100km or more

vent

the surface opening of the conduit

Mount Pelee on the island of Martinique erupted in the early 20th century. why is this eruption famous

the volcano produced a pyroclastic flow that swept down the mountain, killing thousands of people

t/f: cinder cones are composed of generally basaltic pyroclastic material and scoria

true

pyroclastic debris

volcanic ash

how do volcanic bombs differ from blocks of pyroclastic debris

volcanic blocks are made of hardened lava, whereas volcanic bombs are made incandescent lava

________ is a major dissolved volatile constituent in both magmas and volcanic gases.

water

________ are usually the most abundant gases emitted during basaltic volcanism.

water and carbon dioxide

As magma approaches the surface, water contributes to the explosive potential of the eruption because

water dissolved in magma flashes to steam as pressure decreases, and the volume increases leads to an explosive potential

how do Hawaiian-type calderas form

when magma gradually drains away from the magma chamber, causing the summit to collapse

Mt St Helens has formed as a result of subduction of the _____ lithospheric plate beneath the ____ lithospheric plate

Pacific Oceanic, North American oceanic

caldera classifications

several miles across, volcanic rock, crater

what are the two types of lava flows

Aa and Pahoehoe

Mt St Helens is located in the ____ Range, which is classified as a ____

Cascade Range, continental margin volcanic arc

where can we find the most active volcanoes in the world

Hawaii

it has been said that living hear a Hawaiian volcano puts buildings in danger but not humans. why?

Hawaiian volcanoes are not explosive, and the lavas flow at a slow enough speed for humans to get out of the way

in 1980, _____ became the first Cascade Range volcano to erupt since Mt. Lassen in 1915-16

Mt. St. Helens

the location of a currently active shield volcano is

Muana Loa in Hawaii

if you had to live on a volcano, which of the following would you choose if safety was your only concern

Muana Loa in Hawaii, on the Big Island of Hawaii near Kilauea

most of the active volcanoes on land are located in a belt known as the

Ring of Fire

what region of the world has the greatest concentration of composite volcanoes

Ring of Fire

what type of structure is Shiprock, NM and how did it form

Shiprock is a volcanic neck that formed when the volcano itself eroded away, leaving the crystallized igneous rock piercing through the Mancos shale

in addition to composite volcanoes, what other type of volcanic landform can generate pyroclastic flow

a lava dome

a volcanic deposit comprised of red to black lapilil-sized pyroclastic material associated with pahoehoe laval flows was probably deposited on ___

a cinder cone

dissolved gases may comprise up to ____ of a magma

a few percent of

pyroclastic flow

a hot mixture of gas, ash, and pumice that races down the flanks of volcanoes at speeds of up to 125mph

A geologist is working in an area of old volcanic rocks exposed by erosion. He finds a large rock outcrop that contains flat lying gravels in the base of the outcrop. These gravels are overlain by basalt that forms a series of layers representing flows. The uppermost basalt lava flows have a dip of about 10 degrees to the west. What does this outcrop record?

basalt flows formed after gravels were deposited, covered the local terrain, and built a shield volcano with dips of about 10 degrees

___ magma is the most abundant type of magma erupted on Earth

basaltic

pillow lavas

basaltic lava tubes erupted on the seafloor in volcanic piles (think of toothpaste being pushed out of a tube)

how do batholiths get exposed at the surface

batholiths crystallize below the surface but were later exposed by way of erosion of overlying material

laccoliths

bend the sedimentary layers above them, and the ones below remain undeformed

volcanic blocks and bombs

bombs are ejected as magma limps; blocks are ejected as solid fragments

what volcanic events formed Crater Lake, Oregon? when?

caldera collapse followed major ash and pyroclastic-flow eruptions 6000 years ago

paricutin volcano in Mexico is an example of

cinder cone

cinder cones

cinders are most commonly basaltic, they are built mostly or entirely during one eruptive cycle, and they are small volcanoes with fairly steep sides

Mount Pelee on Martinique is an example of a __

composite volcano

what type of volcano would be most likely to generate large landslides

composite volcano

Mt. St. Helens in the U.S. and Mt. Fujiyama in Japan are examples of

composite volcanoes

When contrasting lava from composite volcanoes with lava from shield volcanoes, _________________.

composite volcanoes most often produce silica-rich lavas with high viscosities, whereas shield volcanoes produce basaltic lavas with low viscosities

where do most shield volcanoes form

on the ocean floor

Which type of basaltic lava flow has a fairly smooth, unfragmented, ropy surface?

pahoehoe

what type of volcanic material is indicative of eruption under water

pillow lavas

the location of most volcanoes closely correlates with

plate boundaries

pumice often floats, yet the density of the rock is greater than water. why

pumice is a pyroclastic rock comprised largely of open voids formed by gases released when the magma solidified as froth-like material

_____ people have been killed by pyroclastic flows erupted from cinder cones

relatively few

order of decreasing magma viscosity in order of composition

rhyolite, andesite, basalt

correct order of magmas from the most silica rich to the least

rhyolitic, andesitic, and basaltic

What is scoria, and how does it differ from pumice?

scoria is a vesicular ejecta produced from mafic magma. pumice, however is felsic magma