Earth- An Introduction to Physical Geology #2

In what year did Paricutin form in a Mexican cornfield?

1943

Which of the following choices best explains the difference between a crater and a caldera?

A crater is a small, funnel-shaped depression; a caldera is a large depression that has a diameter of over 1 km.

Which of the following objects has a size similar to that of lapilli?

A marble (15 mm)

What is an accessory mineral?

A mineral that makes up a relatively small portion of the total rock composition

What is the difference between aa lava and pahoehoe lava?

Aa lava has a prickly texture; pahoehoe has a smooth, ropy texture

How do the crystallization and settling of the earliest formed minerals affect the composition of the remaining magma?

After the earliest formed minerals have settled, the resulting magma will be more felsic than the original magma.

Diorite is to

Andesite

What kind(s) of lava are most closely associated with composite cones?

Andesite

What is the rock name of an intermediate rock with two distinct grain sizes?

Andesite porphyry

This dike is exposed on the heavily-forested area surrounding the Spanish Peaks of south-central Colorado. As you can see, the igneous rock that makes up the dike is more resistant to erosion than the country rock surrounding it.

Answer from oldest to youngest:Magma is injected far below earths surface cutting through sedimentary box, magma crystallizes and a Dike is formed, sedimentary country rocks are eroded away, human build a tunnel and road through the resistant igneous rocks.

Which of the following eruptive materials can be associated with cinder cone volcanoes?

Ash, lava flows, and scoria fragments

Gabbro is to

Basalt

Why are the dikes and sills so easily distinguished in Sinbad Country?

Basalt and the hardened, baked zones are more resistant to erosion than the sedimentary rocks.

Which one of the following statements is NOT true about andesite and basalt?

Basaltic lava is thicker than andesitic lava.

How is basaltic magma transformed into felsic magma?

Basaltic magma partially melts the continental crust, which is more felsic in composition.

Why does partial melting result in a magma having a composition different from the rock from which it was derived?

Because different minerals melt at different temperatures, minerals that melt at lower temperatures will melt from the rock first, creating a magma formed from the minerals that melted first.

What is one way that cinder cones differ from composite and shield volcanoes?

Cinder cones are smaller than composite and shield volcanoes.

Using the choices below, select the statement that best explains how dissolved gases drive volcanic eruptions.

Confining pressure decreases on a rising magma, allowing gas bubbles to expand and fracture the magma. This process further decreases pressure on the magma and will result in an explosive event.

Which of the following regions will primarily erupt silica-rich lavas?

Continental Margins

Which two processes commonly generate magma?

Decompression melting and wet melting (the addition of volatiles)

What causes an elevated geothermal gradient in a divergent plate setting?

Decompression melting in the mantle

What is the difference between a dike and a sill?

Dikes crosscut sedimentary layers; sills pry between horizontal layers.

Once a source rock partially melts, what does it produce?

Felsic magma and mafic residue

Which of the following best describes the difference between granite and rhyolite?

Granite is phaneritic and rhyolite is aphanitic.

Which of the following statements best describes the relationship between pressure and melting point in the Earth's Interior?

Higher melting points are determined by higher pressures.

The partial melting of mafic rocks would produce what composition of magma?

Intermediate

Around which volcano is a scientist likely find pillow basalts?

Kilauea

What magma forms from the partial melting of mantle material?

Mafic magma

________ describes the formation of one or more secondary magmas from a single parent magma.

Magmatic Differentiation

Which of the following is the location of a currently active shield volcano?

Mauna Loa in Hawaii

Volcanic ash is best described as which of the following?

Microscopic pieces of rock ejected by a volcano

Use your understanding of Bowen's reaction series and crystal settling to determine which of the following mineral associations should not be found in nature.

Olivine, potassium feldspar, quartz

Contrast pahoehoe and aa lava flows.

Pahoehoe flows exhibit smooth surfaces, are hotter, and are more fluid than aa flows, which exhibit jagged surfaces with sharp edges.

According to Bowen's Reaction Series, __________ is one of the first minerals to melt, but last to crystallize.

Quartz

If an igneous rock is heated, which mineral melts first according to Bowen's reaction series?

Quartz

Granite is to

Rhyolite

What region of the world has the greatest concentration of composite volcanoes?

Ring of Fire

Which of the following statements about rock melting is most accurate?

Rock can remain solid, become partially melted, or melt completely at the same depth within Earth, depending on the temperature.

Why are sills only located fairly close to the Earth's surface?

Sills form as magma intrudes with enough force to overcome the weight of the rocks above.

Why is decompression melting common at mid-ocean ridges but not at subduction zones?

Tectonic plates are moving apart at mid-ocean ridges, resulting in a lowering of pressure beneath the ridge. Tectonic plates are moving together at subduction zones, resulting in an increase of pressure under new mountains.

Why is water a necessary component of the melting process in subduction zones?

The addition of water lowers the melting temperature of rock

The rate at which magma cools influences igneous rock texture, specifically the size, shape, and arrangement of minerals. If magma cools slowly, larger crystals form. Conversely, small crystal size results from magma that has cooled rapidly.

The magma cooled slowly at first, forming large crystals, and then quickly, forming small crystals from the remaining magma.

Approximately how long did it take for the magma that fed each dike in Sinbad Country to be injected?

The magma was injected in a matter of hours to days.

What is peridotite?

The rock making up the mantle

Which of the following is true based off your observation of intrusive igneous rocks on Earth's surface?

These rocks have been exposed by uplift and erosion.

What do pumice and scoria have in common?

They both exhibit a vesicular texture.

Why don't the baked zones along the edges of the dikes and sills show evidence of metamorphism?

They weren't under enough pressure and didn't remain hot for a long enough period of time.

Why is Tuttle and Bowen's experiment useful to geologists?

This experiment allows geologists to interpret where granitic rock solidifies beneath Earth's surface.

What is the name of the small holes created by gas bubbles on the surface of scoria?

Vesicles

________ is a material's resistance to flowing.

Viscosity

Where does the water involved in melting at subduction zones come from?

Water contained within minerals in the subducting plate is released during metamorphism. Submit

How does water content of granitic magmas change as the magmas move towards Earth's surface?

Water content decreases

How does water content of melt change with increasing pressure?

Water content increases with increasing pressure.

What role does water play in generating magma?

Water lowers the melting temperature of the rock, allowing it to melt.

How does decompression melting occur?

When hot, solid mantle rock ascends, it moves to areas of lower pressure. This reduction in pressure allows the hot material to melt into a less compressed liquid phase.

Which of the following would decrease the viscosity of magma?

an increase in temperature

Andesite

aphanitic, igneous, extrusive, intermediate

A dike is mostly likely to be composed of which of the following igneous rocks?

basalt

What kind(s) of lava generate a cinder cone?

basalt

Which of the following lavas make up 90 percent of the total volume of lava on Earth?

basaltic

Comparing cinder cones to shield volcanoes,

cinder cones have steeper flanks than shield volcanoes, and cinder cones occupy a smaller area of land than shield volcanoes.

What is piled up along the cone of SP Crater that causes it to be so steep?

cinders

When contrasting lava from composite volcanoes to lava from shield volcanoes,

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

Which of the following is the volcanic feature in which magma rises through before it is released at the surface?

conduit

Which two processes commonly generate magma?

decompression melting and wet melting (the addition of volatiles)

Pumice

felsic, extrusive igneous rock

Rhyolite

felsic, extrusive igneous rock

How are basaltic magmas thought to be formed?

from the partial melting of the ultramafic rock peridotite

block lava

has a rough surface composed of smooth-sided fragments. It is formed by viscous lava cooling quickly.

aa flow

has a rough, broken surface. It is caused by rapidly moving basalt that cools quickly.

pahoehoe

has a smooth, billowy surface. It is caused by slowly moving basalt that is still hot.

pyroclastic flow

hot, fast-moving body of expanding gas and ash that hugs the flanks of the volcano.

Which of the following could cause rock to melt?

increase in temperature decrease in pressure change in composition

Peridotite that undergoes partial melting will create a melt enriched in ________.

iron, magnesium, feldspars, and silica

pillow

is composed of solid, bubble-like masses. It is caused by extremely quick lava quenching.

A ________ is a mushroom-shaped pluton that forms by injecting magma between sedimentary strata, forcing the upper layers to arch upward.

laccolith

Which of the following volcanic materials flows out of a volcanic vent?

lava

Gabbro

mafic, intrusive rock

Ultramafic rocks contain __________ and are commonly found in __________.

olivine; mantle

Use your understanding of Bowen's reaction series to determine which of the rocks below will crystallize the fastest. The chemical composition of the rocks is:

peridodite

Diorite

phaneritic, intermediate, intrusive

The photos below show both intrusions and the layered sandstones that they intrude. Igneous rocks are outlined in red, while the orientation of sandstone layers is traced with smaller yellow lines.

photo a: Sill, injected parallel to sedimentary layers, nearly horizontal orientation.Photo B: Cut across sedimentary layers, dike, nearly vertical orientation

We observe some interesting rocks at the Pie Town dike in New Mexico. These photos capture both the igneous rock making up the dike and the surrounding sedimentary country rocks. The dark fine-grained unit represents the dike, while the light-colored layers are dominantly layered sandstones, or country rock. The purple zone between these represents the "baked" margin of the country rock. This sliver of rock was essentially roasted during magma injection.

pic 2, out the lighter sandstones with correct bedding orientation, as well as the darker igneous rock making up the dike. The purple "baked" sandstone margin is not observed at this particular location along the dike.

lava tube

results from a relatively fluid lava cooling and forming an outer shell. The lava continues to flow inside the outer shell.

A ________ is a submarine volcano.

seamount

Lavas erupting from composite cones are generally ________-rich, making them very viscous.

silica

A ________ is a tabular, concordant pluton that is nearly horizontal and forms when magma exploits a weakness between sedimentary layers.

sill

Plutonic bodies that have a surface exposure less than 100 km2 are called ________.

stocks

What experiments did Tuttle and Bowen perform?

tests of the temperature and pressure conditions required to melt granite and form magma

All rocks are classified according to ________ and ________.

texture and composition

At a subduction zone, melting is triggered by _____.

the introduction of water Submit

In a subduction zone, water driven from subducted oceanic crust causes __________.

the melting temperature of mantle rocks to decrease

What causes vesicles to form in lava?

trapped gas bubbles

A ________ is a cone-shaped structure created by successive eruptions of volcanic materials such as lava or pyroclastic materials.

volcanic cone

What material was added to powdered rock during Tuttle and Bowen's experiments?

water

When would a granitic magma remain a magma beneath Earth's surface?

when the magma retains enough water to keep it from solidifying, regardless of depthwhen the magma remains below the depth at which magmas become solid