EAPS EXAM #3
crater
(1) A circular depression at the top of a volcanic mound; (2) a depression formed by the impact of a meteorite.
volcano
(1) a vent from which melt from inside the Earth spews out onto the planet's surface; (2) a mountain formed by the accumulation of extrusive volcanic rock.
Decompression Melting
*occurs at mid-ocean ridges and rifts* Lowering pressure while keeping TIME about the same can cause melting of rock
Shield Volcanoes
-can have small summit craters -fluid magma from fissures and scoria cones -fissures fed by dikes
Stratovolcano
:large and cone-shaped with alternating layers of lava and pyroclastic materials, Also known as composite materials
laccolith
A blister-shaped igneous intrusion that forms when magma injects between layers underground in a manner that pushes overlying layers upward to form a dome
Crater
A bowl shaped depression atop a volcano resulting from piling of material from around the vent and summit collapse as magma drains back up to 500M deep, 200M across
volcanic arc
A curving chain of active volcanoes formed adjacent to a convergent plate boundary.
Caldera
A gigantic volcanic depression. Much larger than a crater. 1-10ʼs of kilometers across. Formed when a volcano collapses into an emptied magma chamber.
pumice
A glassy igneous rock that forms from felsic frothy lava and contains abundant (over 50%) pore space.
Eruption Style- Vulcanian eruption
A moderate-sized explosive eruption and is named for the island of Vulcano, where they occur occasionally
tuff
A pyroclastic igneous rock composed of volcanic ash and fragmented pumice, formed when accumulations of the debris cement together.
large igneous province (LIP)
A region in which huge volumes of lava and/or ash erupted over a relatively short interval of geologic time.
Mafic
A rock (or melt) with relatively LOW silica IT crystallizes (vice-versa) melts at high temperature
fragmental igneous rock
A rock consisting of igneous chunks and/or shards that are packed together, welded together, or cemented together after having solidified
crystalline igneous rock
A rock that consists of minerals that grew when a melt solidified, and eventually interlock like pieces of a jigsaw puzzle
shield volcano
A subaerial volcano with a broad, gentle dome, formed either from low-viscosity basaltic lava or from large pyroclastic sheets.
Dike
A tabular (wall-shaped) intrusion of rock that cuts across the layering of country rock.
Batholith
A vast composite, intrusive, igneous rock body up to several hundred km long and 100 km wide, formed by the intrusion of numerous plutons in the same region.
Supervolcano
A volcano that erupts a vast amount (more than 1,000 cubic km) of volcanic material during a single event; none have erupted during recorded human history.
extinct volcano
A volcano that has not erupted for a long time and has completely shut off and will not erupt again
dormant volcano
A volcano that has not erupted for a long time, but may erupt again one day.
Deadly Lahar: Mount Pinatubo, Philipines, 1991
Andesitic Volcano, 90 km from Manila Previous 400 years: no eruptions Philipine volcanologists and U.S. Geologic Survey began monitoring volcano Geologic mapping showed 600-year-old pyroclastic flows across densely populated areas and Clark Air Force Base
Lahars
Annual rainfall at Mount Pinatubo ranges from 80 inches on the volcano's northeast flank to more than 160 inches on the summit. -creating conditions for the lahars Since the eruption Lahars have been responsible for more deaths and property damage than the original eruption
Pyroclastic flows
Are 200*C to 850*C -Race downslope up to 300 km/hr -Incinerate all in their path -Immediately deadly to life form
Wide size range
Ash: Powdery pumice -Lapilli: Pea and -Blocks and bombs: Pyroclastic (Ash) Flows Aka a "nuee ardente" French for glowing cloud.
Poisonous Gases
At depths of more than a few kilometers, pressures keeps gas dissolved in magma At surface, gases exsolve Increasing volume of escaping gases near volcano can warn of impending eruption Gas in atmosphere forms aerosols -> volcanic smog, vog
Shield Volcano
Broad gentle domes composed primarily of mafic lava flows, made from successive layers of low- viscosity basaltic lava, has very gentle slopes
Poisonous Gases Cont.
Carbon Dioxide in high concentrations is colorless, odorless, denser than air (hugs ground) and deadly 1986 in Cameroon; magmatic carbon dioxide bubbled out of Lake Nyos, swept downhill through several villages as river 50 m thick, 16 km long Carbon dioxide from Long Valley Caldera in eastern California has killed huge areas of trees Other volcanic gases include sulfur dioxide, hydrogen sulfide, chlorine compounds, fluorine
Lava Fountain (Mafic)
Cinders- lapilli-sized, Volcanic bombs- melon-sized (block-sized)
High Viscosity
Cooler, more Sio2 (felsic), More trapped Volatiles
Caldera Examples
Crater Lake, Oregon, Yellowstone National Park, Mammoth Lakes, California.
Dike
Cuts across rock layers and
Felsic
Describes magma or igneous rock that is rich in feldspars and silica and that is generally light in color.
Andesitic magma only erupts in lava flow TRUE or FALSE
FALSE
Large explosive volcanic eruptions can increase the temperature of the earth for a period of a few years after an eruption due to the release of aerosols into the upper atmosphere TRUE or FALSE
FALSE
Large Igneous Provinces
Flood basalts: low-viscosity lava fissure eruptions Basalt plateaus: successive eruptions build thick plateaus (Columbia River Plateau)
Convergent Boundary Volcanoes
Flux melting in subduction zone creates magma Magma forms subaerial volcanoes Volcanic arcs Island arcs
Deadly Lahar: Mount Pinatubo, Philipines, 1991 cont.
Frequency of earthquakes and harmonic tremor increased, moved higher in volcano Sulfur dioxide emissions increased Small pyroclastic flows, and lava dome began growing Major eruption seemed imminent within two weeks Evacuation recommended for area within 30 km of summit - 58,000 people Plinian eruption began June 12 with huge 35-40 km plume of steam and ash Ash layers 30 cm thick blanketed region Typhoon Yunya's intense rain mixed with ash to collapse roofs andform lahars 350 people killed, mostly from ash-collapsed buildings Later 932 people killed by disease Timely warning and broad evacuations saved tens of thousands of lives
Volcanic Gas and Aersols
H2o, Co2, So2
Low viscosity
Hotter, Less SiO2 (Mafic), Less Trapped volatiles
Extrusive igneous bodies
Huge columnar joints in Devils Tower, Wyoming, Extrusive rocks include lava flows and pyroclastic layers
glassy igneous rock
Igneous rock consisting entirely of glass, or of tiny crystals surrounded by a glass matrix.
Multiple rift zones on
Kīlauea
When volcanoes erupt ... Have flows of
Lava, mud, pyroclastics and ash
Eruptive Characteristics
Low Viscosity Melt-->calm eruptions (basalt) can flow for long distances High Viscosity Melt-->Explosive ash eruptions
A hawaiian type eruption has
Low silica
magma properties and volcanic behavior
Low viscosity BASALT magma: about 50% silica Intermediate ANDESITE magma: around 60% silica High viscosity rhyolite magma: around 70% silica
Volcano Structure
Magma Chamber - Location in the upper crust where magma accumulates. an open cavity or area of highly fractured rock. A vent is a location from which lava exits. Can occur anywhere on the volcano. • Summit vent - top of the volcano. • Flank vent - side of a volcano.
Intrusive Bodies
Magma rises because it is buoyant and because of pressure from overlying rocks, Movement rates are directly controlled by a magma's viscosity, The rate of cooling depends on the size and composition of an intrusion
Hot-Spot Igneous Activity
Mantle plume hypothesis Decompression melting creates basaltic magma Basaltic magma causes heat-transfer melting under continental lithosphere, creating rhyolitic lava as well
Hotspot Igneous Activity
Mantle plume hypothesis Decompression melting creates basaltic magma Basaltic magma causes heat-transfer melting under continental lithosphere, creating rhyolitic lava as well Eruption produces pillow basalts.
Role of Source Area
Melting continental crust forms felsic or intermediate magma Continental crust- felsic Mantle (mafic) Melting mantle forms MAFIC magma
magma
Molten rock beneath the Earth's surface
Plinian eruption examples
Mt. St. Helens, Mt. Vesuvius, Mt. Pinatubo
Mid-Ocean Ridge Igneous Activity
Occurs at divergent boundary/seafloor spreading zone n, Decompression melting produces pillow basalts
KEY ROCK FORMING MINERALS (8 TOTAL)
Olivine Pyroxene Amphibole Plagioclase Feldspar Biotite Quartz Muscovite Potassium Feldspar (K-Spar)
Eruption Style- Plinian eruption
Plinian eruption is an enormous explosion of volcanic material that ejects huge quantities of material into the atmosphere. These eruptions often destroy a part of the stratovolcano that created them. Named for Pliny the Younger, who witnessed the eruption of Mt. Vesuvius in 79 C.E. from a distant boat and lived to write about it.
Continental Rift Igneous Activity
Rifting/thinning of continental lithosphere Decompression melting creates mafic magma Fissure eruptions Stratovolcanoes
intrusive igneous rock
Rock formed by the freezing of magma underground
extrusive igneous rock
Rock that forms by the freezing of lava above ground, after it flows or explodes out (extrudes) onto the surface and comes into contact with the atmosphere or ocean.
igneous rock
Rock that forms when hot molten rock (magma or lava) cools and freezes solid.
Silica Facts
Silicate Tetrahedron- building blocks for major rock forming materials Tetrahedra bond together to and other elements shared oxygen A silica tetrahedron is not electrically neutral [SiO4]^-4 Needs to bond something (metals, itself, etc.) Silicon (Si) and Oxygen (O) combine to form the basic silica tetrahedron, which is the fundamental building block HOW SILICATE MINERALS CRYSTALLIZES FROM A (MANTLE SOURCE) MELT
Rock forming material is dominated by
Sio4
Magmatism with Continental Hot Spots
Some basalt derived from decompression melting of the mantle reaches the surface. Partial melting of the continental crust by that basalt magma gives the rhyolite magma that erupts to form a caldera
Pumice
Styrofoam-like type rock formed from gas-rich lava (felsic)
Volcanoes in the Cascade Range are a result of
Subduction of the Juan de Fuca beneath North America
Pillow lavas are associated with submarine basaltic eruptions TRUE or FALSE
TRUE
Pyroclastic flows is a mixture of hot volcanic ash and steam that travels at high speeds TRUE or FALSE
TRUE
Lahars or Mud Flow
Tephra+ Water= Volcanic debris flow or lahars Deadly Move downslope up to 50 km/hr; can travel up 10s of km. Consistency of wet cement A distinct hazard in volcanic valleys
Lahars or Mud Flows
Tephra+water= volcanic debris flow or lahars DEADLY Move downslope up to 50 km/her; can travel 10s of km. Consistency of wet cement A distinct hazard in volcanic valleys
eruptive style
The character of a particular volcanic eruption; geologists name styles based on typical examples (e.g., Hawaiian, Strombolian).
Accommodating Igneous Intrusions
The crust stretches sideways during the intrusion of igneous dikes. The earth's surface rises to make room for sills.
Bowen's Reaction Series (8 forming minerals)
The higher the silica the more viscous (less able to flow) the magma or lava will be.
partial melting
The melting in a rock of the minerals with the lowest melting temperatures, while other minerals remain solid.
fractional crystallization
The process by which a magma becomes progressively more silicic as it cools, because early-formed crystals settle out.
assimilation
The process of magma contamination in which blocks of wall rock fall into a magma chamber and dissolve
Bowen's Reaction Series
The sequence in which different silicate minerals crystallize during the progressive cooling of a melt.
Melting by heat transfer
Transfer of heat from hot mantle rock (or magma) to continental crust causes melting.
Melting Order
Ultramafic, magic, intermediate, felsic
Assessment of volcano hazard
Understanding when a volcano is active Recurrence interval, understanding past volcano behavior Written historical records paleovolcanology Eruption warnings- precursors Harmonic earthquakes or tremors - rolling earthquake waves thattend to rise to the surface before an eruption Small steam and ash explosions Changes in summit elevation and slope (tiltmeters) Gas emissions Changes in surface temperatures
flood basalt
Vast sheets of basalt that spread from a volcanic vent over an extensive surface of land; they may form where a rift develops above a continental hot spot, and where lava is particularly hot and has low viscosity.
Volcanic gases
Water (H20) Carbon Dioxide (C02) Sulfure Dioxide (S02)
Pressure in a higher viscosity magma volcano builds up and leads to explosive eruptions because
Water and gas cannot easily migrate through the magma
A more viscous magma/lava
Would produce more explosive eruptions
tachylite
a basaltic volcanic glass.
lava fountains
a column of molten lava spraying upward under pressure from a volcanic vent.
fissure
a conduit in a magma chamber in the shape of a larger crack through which magma rises and erupts at the surface
lava dome
a dome-like mass of rhyolitic lava that accumulates above the eruption vent
pyroclastic flow
a fast-moving avalanche that occurs when hot volcanic ash and debris mix with air and flow down the side of a volcano
scoria
a glassy, mafic, igneous rock containing abundant air-filled holes
Caldera
a large circular depression with steep walls and a fairly flat floor, formed after an eruption as the center of the volcano collapses into the drained magma chamber below.
Caldera
a large crater caused by the violent explosion of a volcano that collapses into a depression
stratovolcano
a large, cone-shaped subaerial volcano consisting of alternating layers of lava and tephra
a'a'
a lava flow with a rubbly surface
pahoehoe
a lava flow with a surface texture of smooth, glassy, rope-like ridges
Viscosity
a liquid's resistance to flow
volcanic debris flow
a mixture of water and pyroclastic debris that moves downslope like wet concrete
sill
a nearly horizontal tabletop-shaped tabular intrusion that occurs between the layers of country rock
xenolith
a relict of wall rock surrounded by intrusive rock when the intrusive rock freezes
magma chamber
a space below ground filled with magma
cinder cone
a subaerial volcano consisting of a cone-shaped pile of tephra whose slope approaches the angle of repose for tephra
lahar
a thick slurry formed when volcanic ash and debris mix with water, either in rivers or from rain or melting snow and ice on the flank of a volcano.
columnar jointing
a type of fracturing that yields roughly hexagonal columns of basalt; columnar joints form when a dike, sill, or lava flow cools.
active volcano
a volcano that has erupted within the past few centuries and will likely erupt again
Signs or precursors of an eruption include
all of the above
effusive eruption
an eruption that yields mostly lava, not ash.
obsidian
an igneous rock consisting of a solid mass of volcanic glass
pluton
an irregular or blob-shaped intrusion; can range in size from tens of m across to tens of km across
lapilli
any pyroclastic particle that is 2 to 64 mm in diameter (i.e., marble-sized); the particles can consist of frozen lava clots, pumice fragments, or ash clumps.
bomb
arger blobs of lava that squirt out of a vent and then solidify become streamlined bombs, whose surfaces are typically streaked and polished
most dangerous place for a pyroclastic flow
bottom of valley
intrusive igneous rock
cool slowly underground
High Viscosity is
cooler, more Si02 (felsic), more trapped volatiles
Pillow Basalts
develops when lava erupts underwater. Later uplift may expose pillows above sea level
tabular intrusions
dikes and sills
Viscosity Differences
due to composition (mafic-lower viscosity; felsic=higher), due to temperature (lower T= more resistance to flow)
eruption
episodes when volcanoes extrude lava and pyroclastic debris
Pyroclastic Debris
fragmental material ejected from a volcano
pyroclastic debris
fragmented material that sprayed out of a volcano and landed on the ground or sea floor in solid form
Mantle plume hot spots
generate igneous activity independent of tectonic plate boundaries
One of the major hazards for large cities in the Pacific Northwest associated with the Cascade volcano chain is:
giant mud flows or lahars
Higher silica
higher resistance to flow
Pahoehoe
hot, fast lava flow with a have soft, pasty solid jagged rubbly surface surfaces that develop ropelike ridges
Low viscosity is
hotter, less Sio2 (mafic), less trapped volatiles
Black smokers
hydrothermal vents
Considering the relationship between viscosity, gas, and silica content which type of magma should have more explosive eruptions?
idk
stock
is less than 100 km^2, usually steeply oriented like a pipe or cylinder, on surface, have steep boundaries and typically resist erosion more than surrounding rocks
Caldera eruptions associated with continental crust tend to have
large and explosive eruptions
block
large, angular pyroclastic fragments consisting of volcanic rock, broken up during the eruption
A'a'
lava flow with a jagged rubbly surface
blocky lava
lava that is so viscous that it breaks into boulder-like blocks as it moves; typically, such lavas are andesitic or rhyolitic.
continental hotspots can produce
low and high viscosity magma and large caldera eruptions
Which composition has more metal ions
mafic
Basic structure
magma chamber connected to the surface by a conduit
lava
molten rock that has flowed out onto the Earth's surface
Batholith
one or more contiguous plutons covering more than 100 km2, Multiple magmas emplaced over long period of time, Cover huge regions
vesicle
open holes in igneous rock formed by the preservation of bubbles in magma as the magma cools into solid rock
Krakatau
pinatubo/st.helens/hawaii
Volcanic Calderas
reflect large explosive eruptions
Eruption Style- Strombolian eruption
regular "burps" of magma at regular intervals, has been erupting every 10 to 20 minutes throughout recorded history, shoots out lapilli and blocks, and these trace arcs in the sky at night.
Viscosity
resistance to flow
spire
rhyolitic lava freezes while still in the vent and then pushes upward as a column-like spire up to 100 m above the vent.
pyroclastic rock
rock made from fragments that were blown out of a volcano during an explosion and were then packed or welded together
Cooling rates of melts
shape and size, For a given shape, a smaller volume cools faster, For a given volume, a pancake shape cools faster, less then 2 KM
lava flow
sheets or mounds of lava that flow onto the ground surface or sea floor in molten form and then solidify.
Viscosity of lava is determined by
silica content and temperature
Cinder Cone Volcano
symmetrical cone-shaped piles of lapilli with pit-like craters at their summit
Viscosity depends on
temperature, volatile content, and silica content
lava tube
the empty space left when a lava tunnel drains; this happens when the surface of a lava flow solidifies while the inner part of the flow continues to stream downslope.
viscosity
the resistance of material to flow
pillow lava
the rind of a pillow momentarily stops the flow's advance, but within minutes the pressure of the lava squeezing into the pillow breaks the rind, and a new blob of lava squirts out, freezes, and produces another pillow. A flow made of these blobs is called pillow lava.
Eruption Style- Surtseytan eruption
the vent erupts in shallow seawater. This creates many steam explosions, which transport rock and ash out of the sea.
ash
tiny glass shards formed when a fine spray of exploded lava freezes instantly upon contact with the atmosphere.
volcanic ash
tiny glass shards formed when a fine spray of exploded lava freezes instantly upon contact with the atmosphere.
aerosol
tiny solid particles or liquid droplets that remain suspended in the atmosphere for a long time
Hot spot volcanoes CAN
track plate movement
Explosive eruptions
typical of high-viscosity lava
Effusive (gentle) eruptions
typical of low-viscosity lava, Still 1,600 F to 2,120
tephra
unconsolidated accumulations of pyroclastic grains
flood basalt
vast sheets of basalt that spread from a volcanic vent over an extensive surface of land; they may form where a rift develops above a continental hot spot, and where lava is particularly hot and has low viscosity.
A felsic eruption will tend to be
violent
explosive eruption
violent volcanic eruptions that produce clouds and avalanches of pyroclastic debris
