GLG 101-Illustrated Vocabulary-Chapter 4
Volcanoes and Plutons
Copyright 2003-Roger Weller
aa lava flow
-is a lava flow with a very blocky, sharp surface. Aa is a word used by bare-footed
Hawaiians to describe this sharp, skin-ripping type of basaltic lava.
-aa lava flow near Flagstaff, Arizona
-aa lava flow in Craters of the Moon National Park, Idaho
Aleutian Islands
-consist of a prominent curved chain of volcanic islands extending from Alaska
westward. Structurally, these islands are an island arc adjacent to a subduction zone.
assimilation
-is the process by which magma melts surrounding rocks (country rock) and adds these
new elements to its composition.
batholith
-is a very large igneous intrusion.
cactolith
-is an igneous intrusion (pluton) that has many cracks radiating from the main magma
body and filled with magma from the intrusion; so named because of a fanciful
comparison to a cactus.
caldera
-is a large collapse depression on top of a volcano.
-Halemaumau in Hawaii-overview
-Halemaumau in Hawaii-crater wall
carbon dioxide
-is a gas denser than air; each molecule consists of one carbon atom and two oxygen
atoms. It is used to produce the bubbles in soda pop.
carbon monoxide
-is a deadly gas produced by incomplete combustion of fossil fuels. Each molecule of
this compound consists of one carbon atom and one oxygen atom.
Cascades
-consist of a chain of andesitic volcanoes extending from California to British Columbia.
Located within the Cascades are Mt. Rainier, Mt. St. Helens, Lassen Peak, Crater Lake,
and others.
chill zone
-is the outer part of a magma body that cools quicker because it is in contact with the
cooler country rock; consequently grain sizes in the chill zone are smaller than for the
rest of the magma body.
cinders
-are small pyroclastic fragments of vesicular basalt ejected from a volcano; commonly
about one quarter inch to one half inch in diameter.
-cinders near Flagstaff. Arizona-1
-cinders near Flagstaff. Arizona-2
cinder cone
-is a small volcano made of loose cinders at the angle of repose (about a 35 degree angle
slope).
-cinder cone near Flagstaff, Arizona
-cindercone in Craters of the Moon National Park, Idaho
-aerial photograph of cinder cones
Columbia River basalts
-represent huge outpourings of fluid basaltic lava which inundated a large area of the
Pacific Northwest of the United States.
columnar jointing
-Upon cooling, igneous bodies shrink and crack in a hexagonal pattern on a horizontal
plane; these cracks continue to migrate downwards through the cooling igneous body to
create a structure built of six-sided columns.
-Devils Postpile, California-vertical columns
-Devils Tower, Wyoming
composite volcano
-is a volcano made out of alternating layers of ash and lava flows; also known as a stratovolcano.
concordant intrusion
-is an intrusion of magma, such as a sill, that goes between the layers of the rock that it is
intruding.
contact metamorphism
-is a form of metamorphism where rocks are baked by the heat from an igneous intrusion.
crater
-is the large depression on top of a volcano.
-Halemaumau in Hawaii-overview
country rock
is the pre-existing rock that into which a magmatic intrusion invades.
Devils Postpile, California
-Devils Postpile-vertical columns-1
-Devils Postpile-vertical columns-2
Devils Tower. Wyoming
-is an igneous intrusion in northwestern Wyoming that cooled and formed prominent
columnar jointing before being exposed by erosion.
-Devils Tower-1
-Devils Tower-2
dike
-is a discordant igneous intrusion that cuts across the layering of the country rock; the
structure is often just igneous material filling a crack.
-dike in the Santa Catalinas neat Tucson, Arizona
-aplite dike in decomposed granite, Huachuca Mountains, Arizona
discordant intrusion
-is an intrusion, such as a dike, that cuts across the grain or layering of the pre-existing
rock (country rock).
dissolved gases
-Within a can or bottle of soda there a significant amount of gas dissolved within the
fluid; without it the soda would be flat. Similarly, there are many varieties of gasses
dissolved in magma which are released when lava erupts: steam, carbon dioxide, sulfur
dioxide, hydrochloric acid, chlorine, hydrofluoric acid, etc.
Flagstaff volcanics
-are located north of Flagstaff, Arizona; the area has many cinder cones and lava flows.
-cinder cones near Flagstaff, Arizona
-S.P. crater and lava flow-aerial view
flank eruption
-is an eruption from the side of a volcano
flood basalt
-is a form of basaltic eruption in which huge flows of very fluid lava issue from fissures.
-Idaho-Craters of the Moon
fumarole
-is the location where volcanic gasses emerge from the ground.
-fumarole in Halemaumau, Hawaii
-fumarole in Craters of the Moon, Idaho
Galapagos Islands
-are a group of small shield volcanoes that form islands in the eastern Pacific Ocean.
glowing cloud eruption
-is an explosive, violent, red hot eruption of a viscous silicic volcanic ash and
pyroclastics.
gravitational magmatic segregation
-Under the influence of gravity crystals that form as as a magma cools either settle to the
bottom of the magma chamber (dense compounds) or rise to the roof of the magma
chamber (low density compounds).
Hawaiian volcanoes
-The Hawaiian islands are the tops of shield volcanoes that were formed when the Pacific
plate moved over an active hot spot.
hot spot
-is a term applied to a small region in which a prolific amount of magma is being
generated over a long interval of geologic time; since crustal plates move over these
buried sources of magma, the result is a trail of volcanoes and/or intrusions on the crustal
plate.
hydrochloric acid
-is an acid with the formula, HCl. It is found in increased but minor quantities in your
stomach when you take an algebra or calculus test. It is also one of the volcanic gases.
hydrofluoric acid
-is an extremely powerful acid with the formula, HF. Hydrofluoric acid is capable of
dissolving glass, quartz, and the corneas of your eyes.
intrusion
-is an igneous pluton, where magma has intruded country rock.
-intrusion beneath the Escabrosa Limestone cliffs
island arc
-is a curved chain of volcanic islands ajacent to an oceanic trench and overlying a
subduction zone.
laccolith
-is a large, mushroom-shaped concordant intrusion. The most famous laccoliths are
found in the Henry Mountains of southern Utah.
lahar
-a mud flow coming off of a volcano.
Lassen Peak, California
-is an andesitic cone, part of the Cascades volcanics.
-Lassen Peak-overview
-Lassen Peak-summit
lava
-is molten rock that has erupted at the earth's surface.
lava dome
-is a hill-like structure made of viscous magma, formed on top of a composite volcano
often following a violent explosive event. The present summit of Mt. St. Helens has one
of these structures starting to fill the gap where the top of the volcano was blown off.
Lassen Peak-summit
lava lake
-is a volcanic caldera fills with yellow-hot fluid lava; the surface of a lava rapidly cools to
a dark, non-luminescent material, but beneath the thin crust the lava is still molten.
-Hawaii-lava lake-1
-Hawaii-lava lake-2
lava tube
-is a cylindrical cavity that forms as basaltic lava drains out beneath a hardened surface
crust. Some lava tubes are caves as large as a subway tunnel.
-exiting a lava tube
-Idaho-Craters of the Moon-collapsed top of small lava tube
lunar maria
-are the large areas on the Moon covered by dark, basaltic lava flows.
maar
-is an explosive basaltic eruption that produces a large crater.
-Cerro Colorado, Sonora, Mexico
-Crater Elegante, Sonora Mexico
-Paramore Crater, San Bernardinoi Valley, Arizona
magma
-is molten rock.
magma mixing
-occurs when magma from two or more different sources come together and mix
underground.
magmatic differentiation
-is the process whereby the composition of a magma changes as it cools and newly
crystallized minerals separate from the magma.
magmatic stoping
-occurs when a magma body moves upwards by cracking the ceiling rocks by pressure
and allowing fragments of the country rock to fall into the magma chamber. Stoping is a
mining term for mining upwards.
mantle plume
-hot, low density molten (or semi-molten) material rises from the mantle and comes up
underneath the crust.
Mauna Loa
-is an active shield volcano on the island of Hawaii.
moat deposits
-are the volcanic materials deposited in the moat lake within a resurgent caldera.
-map view of the Valles caldera, New Mexico
Mt. Capulin
-is a cinder cone located in northern New Mexico.
Mt. Fuji
-is a composite volcano located in Japan
Mt. Rainier
-a composite volcano, part of the Cascades, located in the state of Washington.
Mt. Shasta
-isa composite volcano, located in northern California.
Mt. St. Helens
-is a composite volcano, part of the Cascades, located in the state of Washington.
nuees ardentes volcanic eruptions
-are violent silicic eruptions often known as glowing cloud eruptions.
pahoehoe lava flow
-is a relatively smooth surface lava flow; often described as ropey or bulbous.
-surface of pahoehoe lava flow, Hawaii-1
-surface of pahoehoe lava flow, Hawaii-2
Paramore crater, Cochise County, Arizona
-is a maar type eruption located in the San Bernardino volcanic field, southeastern
Cochise County, Arizona.
-Paramore crater
Paricutin
-is a famous cinder cone that formed in a cornfield in Mexico.
parasitic cone
-is a small volcanic cone formed on top of a larger volcano.
partial melting
-occurs as a subducted slab of crust moves down a subduction zone. Minerals within the
slab with the lowest melting temperatures melt first.
pillow lavas
-are underwater eruptions of basaltic lava that form pillow-like shapes.
pipe
-is a tube-like igneous intrusion, circular or elliptical in cross-section.
Pinacates volcanic field, Mexico
-is a volcanic hot spot in northern Sonora, Mexico, consisting several large maars,
numerous cinder cones, and fresh appearing basaltic lava flows.
-Crater Elegante from the air
-cinder cone and lava flow
pluton
-is an igneous intrusion.
resurgent caldera
-is a silicic form of volcanism in which a collapse crater is formed after the explosive
eruption of a magma chamber that has uplifted the surface of the Earth. Magma
production after the main eruption does not cease; at a later time new magma domes the
floor of the crater; in other words the suface surges upwards again to provide the "re" in
resurgent.
-map view of the Valles caldera, New Mexico
rim deposits
-consist of the volcanic ash deposited on the rim of a crater from which it was erupted.
Ring of Fire
-is the collection of volcanoes that are found encircling the Pacific Ocean.
San Bernardino Volcanic Field, Cochise County, Arizona
-is located in the extreme southeast corner of Arizona and consists of basaltic lava flows,
small cinder cones, and a maar, Paramore crater.
-San Bernardino-cinder cone
-San Bernardino-Paramore crater
seafloor spreading
-occurs along the crest of oceanic ridges where the oceanic crust is being pulled apart and
lava is filling the fissures, thereby creating new seafloor.
shield volcano
-is a large basaltic volcano that is very wide but has a low profile. This type of volcano is
so named because it resembles a Roman shield laid flat on the ground. The most famous
volcanoes of this type located on Earth are the Hawaiian and Galapagos islands.
Shiprock, New Mexico
-is an outstanding weathered volcanic neck on the northeastern portion of New Mexico.
All that remains is a shark peak with three radiating dikes.
stock
-is a medium-sized, usually discordant pluton that is between a pipe and a batholith in
size; less than forty square miles.
stratovolcano
-is a composite volcano made of alternating layers of ash and lava; intermediate in
composition. Many of the most famous and prominent volcanoes in the world are of this
type: Mt. Fuji, Mt. Rainier, Mt. St. Helens, Mt. Shasta, Mt. Kilimanjaro, Lassen Peak,
etc.
-California-Lassen Peak
subduction zone volcanics
-In a subduction zone, a slab of oceanic crust with sediments is subducted down into the
hot mantle where low temperature minerals in the slab start to melt. The newly formed
magma rises to the surface adjacent to the trench to produce volcanoes.
sulfur dioxide
-is a poisonous gas given off by volcanoes. Upon exposure to oxygen in the air plus
sunlight, sulfur dioxide turns into sulfur trioxide that then combines with moisture to
form sulfuric acid and then goes on to become acid rain.
sulfuric acid
-is a powerful acid whose formula is hydrogen sulfate.
Sunset crater, northern Arizona
-is a cinder cone north of Flagstaff, Arizona. This small volcano is reported to be the
most recent volcanic eruption in Arizona.
tuff
-is an igneous rock consisting of compacted volcanic fragments smaller than one eighth
of an inch.
Turkey Creek caldera, Cochise County, Arizona
-is a large, eroded resurgent caldera in the Chiricahua Mountains of southeastern
Arizona; radiometrically dated at 26 million years old
- map view of the Chiricahuas
Valles caldera, northern New Mexico
-is a new, hardly weathered resurgent caldera, complete with resurgent dome and moat
volcanics northeast of Albuquerque, New Mexico.
-map-New Mexico-Valles Caldera-1
-map-New Mexico-Valles Caldera-2
Vesuvius
-is an active volcano in Italy that is responsible for destroying Pompeii and Herculaneum.
viscosity
-is the measure of how resistant a fluid material is to flowing. For example, corn syrup is
more viscous than water.
volcanic ash
-consists of very fine volcanic materials, ranging from dust to particles less than one
eighth of an inch.
volcanic bomb
-is a blob of lava ejected out of an active volcano. As the material sails through the air,
the outer surface of the projectile cools and solidifies before it hits the ground.
Commonly, these molten blobs are spinning as they are ejected from the volcano and
may develop aerodynamic or twisted shapes.
-Idaho-Craters of the Moon-volcanic bomb-1
-Idaho-Craters of the Moon-volcanic bomb-2
volcanic dome
-is a steep-sided, hill-like mass of viscous lava extruded by a volcano; after the explosive
eruption of Mt. St. Helens, one of these features slowly formed in the newly created gap
at the top of the volcano; also called a lava dome.
-California-Lassen Peak summit
volcanic gases
-are the most common gases emitted by volcanoes: steam, carbon dioxide, sulfur dioxide,
hydrochloric acid, chlorine, hydrofluoric acid, fluorine, carbon monoxide, and methane.
volcanic neck
-After a volcano has undergone intense weathering, all that often remains is the lava that
cooled and hardened in the conduit that supplied lava to the volcano.
volcanic vent
-is where volcanic materials emerge from the ground.
volcano
-is a landform produced by the eruption of lava and ash from a single vent.
-Idaho-Craters of the Moon-cinder cone
-San Bernardino-cinder cone
-California-Lassen Peak
-Hawaii-Halemaumau
welded tuff
-is hot, silicic ash from a violent volcanic eruption melts back together on the ground due
to its high temperature and the weight of the volcanic ash (tuff) above it.
-welded tuff in the Chiricahuas