GEO 100 Volcanoes
Stratovolcanoes- also known as ______________ -large, cone-shaped volcanoes with steeper slopes -made of alternating layers of lava, tephra, and debris -often symmetrical, but can be odd shapes from landslides, etc.
"composite volcanoes"
____________________________- higher SiO2 content increases viscosity; don't flow far from vent (remain close to vent)
Andesitic (INTERMEDIATE) lava flows
4. ____________________________ -fierce winds from a passing typhoon blew the ash in all directions before it "showed" down on nearby buildings *many roofs collapsed under the sheer weight, killing hundreds in their homes -ash clouds can also block the sun and lead to temporary global cooling
Annihilation from ash clouds
______________- angular rock fragments -angularity indicates the absence of rounding by transport -deposited relatively close to clast source (ex: talus under a cliff face)
Breccia
2. ____________________________ *as pyroclastic flows exploded, they melted the glaciers on the mountain--> 40 mph Lahar -Lahars- thick mixtures (think wet concrete) of mud & water that slide down slopes like an avalanche
Buried by fast-flowing mud
______________- rounded rock fragments -clasts rounded as flowing water wears off corners & edges -deposited farther from the source than breccia (ex: river channel)
Conglomerate
1. ____________________________ -Mount Vesuvius (a stratovolcano) erupted explosively, sending fast moving waves of super heated gas down the sides of the volcano as a pyroclastic flow (gas, ash, & rock) traveling up -effected two ancient roman cities: Pompeii & Herculaneum -This is arguably the most deadly volcanic event -can travel for miles and are impossible to outrun -produced by ____________________________ *suring eruption, the rock layer is smashed into tiny particles, which mix with hot ash and gases to form a giant mushroom cloud *the cloud then collapses and cascades down the side of the volcano as a pyroclastic flow
Cooked by super-hot waves of gas; explosive 'composite volcanoes'
Clastic sedimentary rocks consist of: 1. ______________ (loose clasts)- mineral grains & rock fragments 2. ______________
Detritus; cementing
Sedimentary rocks form at or near ______________
Earth's surface
Hot spot intersecting a MOR- ______________
Iceland
5. ____________________________- threats are mostly from ______________ lava -may completely destroy immovable objects -bigger threat to property than to people (rare to kill people)
Lava flows; basaltic
In 79 CE, the citizens of Pompeii in the Roman Empire were buried by pyroclastic debris derived from an eruption of ______________
Mt. Vesuvius
____________________________ provide the raw material for all sedimentary rocks
Physical & chemical weathering
______________- round blobs of basalt cooled underwater (common on mid-ocean ridge)
Pillow basalt
______________ is a dominant control on volcanism
Plate motion
____________________________- the highest level of SiO2--> makes it the most viscous lava
Rhyolitic (FELSIC) lava flows
______________- clastic rocks made of sand-sized particles -common in beach and dune settings -quartz is, by far, the most common mineral sandstones
Sandstone
3. ____________________________ -when a volcano sits beneath a lake, gases from the magma can filter up through cracks in the crust and become trapped under the water as carbon dioxide -______________ (ex: an earthquake/landslide) can cause the CO2 to rise rapidly to the surface of the lake -this rare but deadly event is called a ______________
Suffocated by poisonous gases; violent movement; limnic eruption
Which of the following is true concerning the 1980 eruptions of Mt. St. Helens?
The eruption began with a lateral blast of debris that was ejected extremely fast
6. ______________ -______________ eruptions can create giant waves (ex: Krakatau)
Tsunamis; island-arc
Crater- ____________________________ -form as erupted lava piles up around the vent -summit eruptions- located within the summit crater; flank eruptions- located on sides of volcano
a bowl-shaped depression atop a volcano
Caldera- ____________________________ -much LARGER than a crater -a magma chamber empties and the volcano collapses inward (ex: Crater Lake, OR)
a gigantic volcanic depression
Death Valley, CA shows a road that curves around a(n) ______________
alluvial fan
Mt. St. Helens eruption: -____________________________ -an initial vertical blast led to a ____________________________ *tore off the entire north side of the mountain
an earthquake-triggered landslide released pressure; much stronger lateral blast
A volcano is ____________________________
an erupting vent through which molten rock surfaces/a mountain built from magmatic eruptions (volcanoes are a clear result of tectonic activity and pose a number of hazards to humans)
Clast shape: - ______________- the degree of edge or corner smoothness -______________- the degree to which a clast nears a spherical shape *Well-rounded indicates long transport distances *Angular indicates negligible transport
angularity; sphericity
Pyroclastic flow- ____________________________ -can move hundreds of miles per hour; are immediately deadly to anything in their path (classic ex: Mt. Vesuvius- wiped out Roman city of Pompeii, 79 CE)
avalanches of hot ash that race downslopes
Protection from eruptions: -Reoccurrence interval- ____________________________ *Active- ____________________________ *Dormant- ____________________________ *Extinct- ____________________________ (tectonics can shut off magma; then erosion takes over)
average time between eruptions; erupting, recently erupted, or likely to erupt; hasn't erupted in hundreds to thousands of years; hot capable of erupting
Beach sediments travel ______________ the ocean during a transgression and ______________ the ocean during a regression
away from; toward
Pahoehoe-______________
basalt with a glassy, ropy texture (w/ flow, the skin is rolled into ropy ridges 7 furrows)
Style of gas escape controls eruption violence: Low viscosity (______________)- ____________________________ High viscosity (______________)- ____________________________
basalt; easy escape, mellow eruption rhyolite; difficult escape, violent release
Which environment would most likely produce sedimentary deposits characterized by very well-sorted, well-rounded grains that are nearly pure quartz?
beach
Geologists call individual layers of sedimentary rocks ______________, whereas several of them together are called ______________
beds; strata
Shield volcanoes- ____________________________ -constructed by lateral flow of low-viscosity basaltic lava -have a low slope and cover large geographic area (ex: Mauna Loa, HI)
broad, slightly dome-shaped
Scientists monitor volcanoes to help predict when eruptions will occur. Which of the following is NOT a potential sign to look for when predicting volcanic eruption?
changes in Earth's magnetic field
Precipitation of gypsum due to evaporation of seawater produces which kind of sedimentary rock?
chemical
Of the primary forms of subaerial volcanoes, ______________consist of a simple pile of tephra often formed in a single eruption
cinder cones
Most important diagnostic for clastic rocks: ______________- the diameter of fragments or grains
clastic size
What type of sediment is typically food in lake bottoms?
clay/mud
Which of the following is NOT true? Sediments deposited in a beach environment are typically ______________
composed of angular grains
Geologists also distinguish sedimentary rocks by ______________ -Siliceous-______________ -Argillaceous- clay-rich -______________- contain calcite or dolomite
composition; quartz-rich; carbonate
Lava tubes- ______________
conduits for basaltic lava
Cinder cone- ____________________________ -the smallest type of volcano -built of ejected lapilli-sized fragments piled up at a vent -often symmetrical with a deep summit crater
conical piles of tephra
Pele's hair ______________
consists of thin strands of basaltic glass
Basaltic lavas ______________
contain more iron and magnesium than rhyolitic lavas
Rhyolitic lavas ______________
do not flow as far from the vent as basaltic lavas do
Warning signs indicate that an eruption is imminent: -______________ -heat flow -______________ -emission increases
earthquake activity; changes in shape
Nonviolent eruptions characterized by extensive flows of basaltic lava are termed ______________
effusive
Eruptive style- two dominant styles: -______________ eruptions produce ____________________________ *lava flows stream away from vents *lava lakes can from near, or inside the vent. Lava fountains can reach up to 500 m high *common with mafic magma (basalt) -______________ eruptions ______________ *high gas pressure is from more viscous SiO2-rich magma *create pyroclastic debris and cover land with tephra *mostly andesitic and rhyolitic compositions
effusive; lava flows, a vast outpouring of lava; explosive; release pressure catastrophically
Magma composition controls gas content: ______________ magmas have more gas; ______________ magmas have less
felsic; mafic
The cloud that rises from the vent of an actively erupting volcano is composed ______________
fine volcaniclastic debris (ash) suspended in the air
Diverting flows- ____________________________
flowing lava can be diverted
Volcanic soils are ______________ fertile; excellent for crops
highly
Basaltic (MAFIC) lava- very ______________, ______________, and ______________; are often thin and fluid- effusive eruptions and flow rapidly for long distances
hot; low silica; low viscosity
A fast-moving flow consisting of a mixture of water and volcaniclastic debris is termed a ______________
lahar
Volcanoes often erupt ______________ of fragments
large quantities
Rhyolitic lava rarely flows- rather, lava plugs the vent as a ______________
lava dome
______________- lava can be thin and runny, or thick and sticky
lava flows
Pyroclastic debris from basaltic eruptions- ____________________________ (bombs, blocks, Pele's hair, Pele's tears)
lava fragments that freeze mid-air
-Sedimentary rocks form ______________, which record a history of ____________________________ and only occur in the upper part of the crust -Sedimentary rocks cover underlying basement rock
layers; ancient environments
Composition and cementation of grains occurs during the stage of clastic sedimentary rock formation called ______________
lithification
Four classes of sedimentary rock: 1. Clastic- ____________________________ 2. ______________- cemented shells of organisms 3. Organic- ____________________________ 4. ______________- minerals that crystallize directly from water
loose rock fragments (clasts) cemented together; biochemical; carbon-rich remains of Ince living organisms; chemical
What properties of the source magma lead to the formation of a shield volcano?
low viscosity and mafic composition
Compared to felsic lavas mafic lavas have a ______________
lower viscosity
Volcanic architecture- volcanoes come in many shapes and sizes -the shape and size are governed by ______________
magma type
Swamps, channels, floodplains, and submarine slopes all play a role in the development of ______________
marine debris
The products of volcanic eruptions come in three forms: 1. Lava flows- ____________________________ 2. ____________________________- fragments blown out of a volcano 3. Volcanic gases- ____________________________
molten rock that moves over the ground; pyroclastic debris; expelled vapor and aerosols
Volcanic activity is evident on the ______________ and ______________
moon; planets
The textural term for a basaltic lava flow that has a smooth, ropy appearance is ______________
pahoehoe
The primary difference between breccia and conglomerate is that conglomerate ______________
possess more rounded grains than breccia
Explosive eruptions that generate debris: ______________- "frothy" volcanic glass (lots of open space) ______________- fragments of volcanic glass that are less than 2 mm in diameter ______________- angular pumice fragments
pumice; ash; pumice lapilli
A mixture of air, hot ash, and pumice lapilli that rushes down the side of a volcano in a scalding avalanche is termed a(n) ______________
pyroclastic flow
Which of the following poses the greatest hazard to human life associated with volcanoes
pyroclastic flows
Well-sorted sediments with grain sizes falling in between 1/16 mm and 2mm, later cemented together and lithified becomes the clastic sedimentary rock named ______________
sandstone
Limestone is most likely formed in which of the following environments?
shallow-marine carbonate
Of the three primary forms of subaerial volcanoes, ______________ are typically the largest in area
shield volcanoes
Of the three primary forms of subaerial volcanoes, ______________ have the most gently sloping sides, due to the low viscosity of the basaltic lavas that form them
shield volcanoes
Fine clastics-- composed of silt and clay -silt-sized sediments are lithified to form ______________ -clay-sized particles form ______________ or ______________ -fine clastics are deposited in ______________ (ex: floodplains, lagoons, mudflats, deltas, deep-water basins; often accompanied by organic matter)
siltstone; mudstone; shale; quiet water settings
Biochemical limestones are dominated by carbonate mud and fragments of ______________
skeletons of marine invertebrates made of calcite and aragonite
Columnar jointing-______________
solidified flows may contract, creating vertical fractures that are hexagonal in cross-section (ex: Devil's Postpile)
A'a'-______________
solidifies with a jagged. sharp, angular texture (w/flow, lava crumbles into shards & fragments)
Mt. Fuji in Japan is an example of a ______________
stratovolcano
Volcanic types are linked to ______________ -____________________________ oceanic crust covers 70% of Earth *recognizable basalt "pillows" (basalt erupted from fissures quenches as pillows) -most volcanoes form at ______________ *volatiles from subducting plate initiate melting on the overriding plate -continental rifts- man volcano types -oceanic hot spot- ____________________________ (ex: Hawaii) -continental hot spot- ____________________________ (ex: Yellowstone)--> also called "supervolcano"
tectonic plates; MOR generated; convergent boundaries; a plume under an oceanic plate; up through a continental plate
Pyroclastic deposits: ______________- deposits of pyroclastic debris of any size Tuff- ____________________________- can be deposited hundreds to thousands of miles away from the volcanic source
tephra; lithified ash
Clastic rocks are classified basis of ______________ and ______________
texture; composition
Clast composition- ____________________________ *yields clues about the original source rock; variety hints at transport processes
the mineral makeup of sediments
Sorting- ____________________________ -______________- all clasts have nearly the same grain size -______________- clasts show a wide variety of grain sizes - Degree of sorting ______________ with transport distance (nature of cement- minerals that fill sediment pores; quartz [SiO2] and calcite [CaCO3] are the most common cements) *All of the above provide clues about ______________ and ______________
the uniformity of grain size; well-sorted; poorly sorted; the source area; depositional
Sea level rises locally, and marine sediments are deposited on top of terrestrial sediments during events termed ______________
transgression
Grains become rounded primarily during ______________
transportation
"Pillows" formed ______________
underwater at a mid-ocean ridge
Clastic rocks: -Range from ____________________________ -As transport distance increases, sediment grain size ______________ *Gravel- coarse-grained sediment (boulder, cobbles, pebbles) *Sand *Mud- fine-grained (silt & clay)
very coarse to very fine; decreases
Gas bubbles in rock are called ______________
vesicles
Style of flow depends on ______________, which depends upon: -______________(especially SiO2, Fe, and Mg content) -______________ -______________ -______________
viscosity; composition; temperature; gas content (volatiles); crystal content
More ______________ magmas and more ______________ (rhyolitic lava flows-also makes these volcanoes more prone to explode)
viscous; volcanic gases
If a geologist found preserved mud cracks, he/she could conclude that the environment in which they formed ______________
was once covered in wet mud
Symmetric ripples form when ______________
water deposits sediment in layers, but the direction of flow periodically changes
Gases that are abundantly emitted by volcanoes include ______________
water vapor, carbon dioxide, and sulfur dioxide
The breakdown of exposed rock into small fragments and dissolved ions is termed ______________ and the removal of detritus from weathered rock at an outcrop is termed ______________
weathering; erosion
Clastic sedimentary rocks are create d by: 1. ______________- generation of detritus via rock disintegration *2. ______________- removal of sediment grains from parent rock *3. ______________- dispersal by gravity, wind, water, and ice 4. ______________- settling out of the transporting fluid 5. ______________- transformation into solid rock *compaction- burial adds pressure to sediment (squeezes out air & water ; compresses sediment grains) *cementation- minerals grow in pore spaces (precipitate from groundwater between pore spaces & "glue" sediments together
weathering; erosion; transportation; deposition; lithification
It is unusual for ______________ to carry grains larger than sand
wind