chapter 4 volcanoes and volcanic hazards Flashcards
Where does partial melting happen?
The uppermost atmosphere
Where does basaltic magma rise and then proceed to pond and differentiate?
lithosphere
Silica rich magma ascends through the crust creating a _____
magma chamber
from the magma chamber a _____ travels up through the crust, through a volcano and out of its vent.
conduit
highly viscous, rhyolitic magmas may produce explosive clouds of hot ash and gases that evolve into buoyant plumes called _______
eruption columns
_____ flows have surfaces of rough jagged blocks with dangerously sharp edges and spiny projections
aa
_____ flows exhibit smooth surfaces that often resemble the twisted braids of ropes
pahoehoe
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
lava tubes
Their upper surface consists largely of vesicle-free, detached blocks
block lava
a lava flow composed of numerous tube-like structures called _______, stacked one atop the other
pillow lavas
When volcanoes erupt energetically they eject pulverized rock, lava, and glass fragments from the vent. The particles produced are referred to as _______
pyroclastic materials
As the gas-rich magma moves up through a fissure, its path is usually localized into a circular ______
conduit, or pipe
In particular, _____ is the name applied to vesicular ejecta that is a product of basaltic magma
scoria
When magmas with intermediate (andesitic) or felsic (rhyolitic) compositions erupt explosively, they emit ash and the vesicular rock ________
pumice
Located at the summit of most volcanoes is a somewhat funnel-shaped depression, called a ______
crater
Continued activity from a flank eruption may produce a small ______
parasitic cone
Many vents emit only gases and are appropriately called _____
fumaroles
_____ are produced by the accu- mulation of fluid basaltic lavas and exhibit the shape of a broad, slightly domed structure
shield volcanoes
Earth’s most picturesque yet potentially dangerous volcanoes are _______
composite cones or stratovolcanoes.
One of the most destructive forces of nature is the ______
pyroclastic flow
_____ are large depressions with diameters that exceed 1 kilometer and have a somewhat circular form.
Calderas
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
Fissures
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 ______
lava dome
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 _____
volcanic neck
Volcanism associated with convergent plate boundaries may also develop where slabs of oceanic lithosphere are subducted under continental lithosphere to produce a ________
continental volcanic arc
as rock rises ______
it experiences a decrease in confining pressure and undergoes melting without the addition of heat
Geologists now recognize that most intraplate volcanism occurs where a mass of hotter than normal mantle material called a _________ ascends toward the surface
mantle plume
The primary factors that determine the nature of volcanic eruptions include the ___________
magma’s composition, its temperature, and the amount of dissolved gases it contains
As lava cools, it begins to congeal and, as viscosity _______, its mobility _________
increases, decreases.
The materials associated with a volcanic eruption include
________
(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)
Successive eruptions of lava from a central vent result in a mountainous accumulation of material known as a _______
volcano
Located at the summit of many volcanoes is a steep-walled depression called a ______
crater
_________ have steep slopes composed of pyroclastic material
Cinder cones
__________ , are large, nearly symmetrical structures built of interbedded lavas and pyroclastic deposits
Composite cones, or stratovolcanoes
Most volcanoes are fed by _________
conduits or pipes
As erosion progresses, the rock occupying the pipe, which is often more resistant, may remain standing above the surrounding terrain as a ________
volcanic neck
The summits of some volcanoes have large, nearly circular depressions called _______ that result from collapse
calderas
Active areas of volcanism are found along mid-ocean ridges where __________
seafloor spreading is occurring (divergent plate boundaries)
Active areas of volcanism are found in the vicinity of ocean trenches where one plate is __________
being subducted beneath another (convergent plate boundaries)
Active areas of volcanism are found in the interiors of the plate themselves (intraplate volcanism), _________ are the source of most intraplate volcanism
rising plumes of hot mantle rock
Volcaniclastic materials
- Pyroclastic flow
- Pyroclastic Surge
- Pyroclastic fall
How magma forms
- Decrease pressure
- Add volatile material (water)
- Increase temperature
Types of pryoclastics
- Tephra
- Ash
- Lapilli
- Bombs
- Pumice
