chapter 4 volcanoes and volcanic hazards

Question 1

Where does partial melting happen?

Answer 1

The uppermost atmosphere

Question 2

Where does basaltic magma rise and then proceed to pond and differentiate?

Answer 2

lithosphere

Question 3

Silica rich magma ascends through the crust creating a _____

Answer 3

magma chamber

Question 4

from the magma chamber a _____ travels up through the crust, through a volcano and out of its vent.

Answer 4

conduit

Question 5

highly viscous, rhyolitic magmas may produce explosive clouds of hot ash and gases that evolve into buoyant plumes called _______

Answer 5

eruption columns

Question 6

_____ flows have surfaces of rough jagged blocks with dangerously sharp edges and spiny projections

Answer 6

aa

Question 7

_____ flows exhibit smooth surfaces that often resemble the twisted braids of ropes

Answer 7

pahoehoe

Question 8

Hardened basaltic flows commonly contain cave-like tunnels called ____ that were once conduits carrying lava from the volcanic vent to the flow’s leading edge

Answer 8

lava tubes

Question 9

Their upper surface consists largely of vesicle-free, detached blocks

Answer 9

block lava

Question 10

a lava flow composed of numerous tube-like structures called _______, stacked one atop the other

Answer 10

pillow lavas

Question 11

When volcanoes erupt energetically they eject pulverized rock, lava, and glass fragments from the vent. The particles produced are referred to as _______

Answer 11

pyroclastic materials

Question 12

As the gas-rich magma moves up through a fissure, its path is usually localized into a circular ______

Answer 12

conduit, or pipe

Question 13

In particular, _____ is the name applied to vesicular ejecta that is a product of basaltic magma

Answer 13

scoria

Question 14

When magmas with intermediate (andesitic) or felsic (rhyolitic) compositions erupt explosively, they emit ash and the vesicular rock ________

Answer 14

pumice

Question 15

Located at the summit of most volcanoes is a somewhat funnel-shaped depression, called a ______

Answer 15

crater

Question 16

Continued activity from a flank eruption may produce a small ______

Answer 16

parasitic cone

Question 17

Many vents emit only gases and are appropriately called _____

Answer 17

fumaroles

Question 18

_____ are produced by the accu- mulation of fluid basaltic lavas and exhibit the shape of a broad, slightly domed structure

Answer 18

shield volcanoes

Question 19

Earth’s most picturesque yet potentially dangerous volcanoes are _______

Answer 19

composite cones or stratovolcanoes.

Question 20

One of the most destructive forces of nature is the ______

Answer 20

pyroclastic flow

Question 21

_____ are large depressions with diameters that exceed 1 kilometer and have a somewhat circular form.

Answer 21

Calderas

Question 22

The greatest volume of volcanic material is extruded from fractures in the crust called ______, these long, narrow cracks tend to emit low-viscosity basaltic lavas that blanket a wide area

Answer 22

Fissures

Question 23

In contrast to mafic lavas, silica-rich felsic lavas are so viscous they hardly flow at all. As the thick lava is “squeezed” out of the vent, it often produces a dome-shaped mass
called a ______

Answer 23

lava dome

Question 24

all volcanoes will eventually suc- cumb to erosion. As erosion progresses, the rock occupying a volcanic pipe is often more resistant and may remain standing above the surrounding terrain long after most of the
cone has vanished, this is called a _____

Answer 24

volcanic neck

Question 25

Volcanism associated with convergent plate boundaries may also develop where slabs of oceanic lithosphere are subducted under continental lithosphere to produce a ________

Answer 25

continental volcanic arc

Question 26

as rock rises ______

Answer 26

it experiences a decrease in confining pressure and undergoes melting without the addition of heat

Question 27

Geologists now recognize that most intraplate volcanism occurs where a mass of hotter than normal mantle material called a _________ ascends toward the surface

Answer 27

mantle plume

Question 28

The primary factors that determine the nature of volcanic eruptions include the ___________

Answer 28

magma’s composition, its temperature, and the amount of dissolved gases it contains

Question 29

As lava cools, it begins to congeal and, as viscosity _______, its mobility _________

Answer 29

increases, decreases.

Question 30

The materials associated with a volcanic eruption include ________

Answer 30

(1) lava flows (pahoehoe flows, which resemble twisted braids; and aa flows, consisting of rough, jagged blocks; both form from basaltic lavas); (2) gases (primarily water vapor); and (3) pyroclastic material (pulverized rock and lava fragments blown from the volcano’s vent, which include ash, pumice, lapilli, cinders, blocks, and bombs)

Question 31

Successive eruptions of lava from a central vent result in a mountainous accumulation of material known as a _______

Answer 31

volcano

Question 32

Located at the summit of many volcanoes is a steep-walled depression called a ______

Answer 32

crater

Question 33

_________ have steep slopes composed of pyroclastic material

Answer 33

Cinder cones

Question 34

__________ , are large, nearly symmetrical structures built of interbedded lavas and pyroclastic deposits

Answer 34

Composite cones, or stratovolcanoes

Question 35

Most volcanoes are fed by _________

Answer 35

conduits or pipes

Question 36

As erosion progresses, the rock occupying the pipe, which is often more resistant, may remain standing above the surrounding terrain as a ________

Answer 36

volcanic neck

Question 37

The summits of some volcanoes have large, nearly circular depressions called _______ that result from collapse

Answer 37

calderas

Question 38

Active areas of volcanism are found along mid-ocean ridges where __________

Answer 38

seafloor spreading is occurring (divergent plate boundaries)

Question 39

Active areas of volcanism are found in the vicinity of ocean trenches where one plate is __________

Answer 39

being subducted beneath another (convergent plate boundaries)

Question 40

Active areas of volcanism are found in the interiors of the plate themselves (intraplate volcanism), _________ are the source of most intraplate volcanism

Answer 40

rising plumes of hot mantle rock

Question 41

Volcaniclastic materials

Answer 41

- Pyroclastic flow - Pyroclastic Surge - Pyroclastic fall

Question 42

How magma forms

Answer 42

- Decrease pressure - Add volatile material (water) - Increase temperature

Question 43

Types of pryoclastics

Answer 43

- Tephra - Ash - Lapilli - Bombs - Pumice