Lesson 3: Volcanic Eruptions Flashcards
Volcanoes are mostly found in what general area?
along convergent boundaries
The type of magma and consequent type of eruption of a volcano depends on what?
the tectonic setting it is formed.
the 3 types of magmas
basaltic:
andesitic;
and rhyolitic
Hot spot volcanoes in an oceanic setting
produce what type of magmas?
basaltic magma
Hot spot volcanoes in an continental setting
produce what type of magmas?
rhyolitic magma
how many percent of silica (SiO2) is in basalt?
48-52%
how many percent of silica (SiO2) is in andesite/dacite?
52-68%
how many percent of silica (SiO2) is in rhyolite?
68-77%
range of eruption temperature?
1,160 to 900 degrees C from basaltic to rhyolitic magma
describe the consistency of lava depending on the type of magma
low resistance to flow (thin, runny lava, less viscous) to high resistance to flow (thick, sticky, viscous), from basaltic to rhyolitic
relationship of lava mobility to temperature
directly proportional, decreasing mobility with decreasing temperature
depicts the sequence in which minerals crystallize from a magma (magma evolution)
Bowen’s reaction series
enumerate the Bowen’s reaction series
discontinuous
Olivine→pyroxene→amphibole→biotite mica
continuous plagioclase feldspar (Ca-rich to Na-rich)
Anorthite→bytownite→labradorite→andesine→oligoclase→albite
meet at
potassium feldspar→muscovite mica→quartz
is the process where the early-formed minerals are denser (heavier) than the liquid (melt) and sink toward the magma chamber
crystal settling
for crystal settling, when the remaining melt solidifies—either in place or in another location, if it migrates into fractures in the surrounding rocks, what happens?
it will form a rock with a mineralogy much different from the parent magma.
The formation of one or more secondary magmas from a single parent magma
magmatic differentiation
T or F: Magmatic differentiation, by itself, cannot account for the entire compositional spectrum of igneous rocks.
True
The composition of magma changes when some of the surrounding rock (country rock) may be incorporated to the upwelling magma
assimilation
occurs during the ascent of two chemically distinct magma bodies as the more buoyant mass overtakes the more slowly rising body
magma mixing
T or F: Minerals with the lowest melting temperatures are the last to melt.
False, Minerals with the lowest melting temperatures are the FIRST to melt
is the process that generates a magma that is nearer the felsic (granitic) end of the compositional spectrum than the parent rock from which it was derived.
partial melting
Most magma that erupts on the Earth’s surface is ______ in composition and has a temperature of ______
basaltic; 1000C to 1250C
Experiments show that under the high-pressure conditions calculated for the upper mantle, partial melting of the ultramafic rock _________ will yield a magma of _________composition.
peridotite; basaltic
Basaltic (mafic) magmas that originate from ________ of ________are called _______or _______ magmas because they have not yet evolved
partial melting; mantle rocks; primary; primitive
Partial melting that produces mantle-derived magmas may be triggered by a _________ during the process of ________
reduction in confining pressure; decompression melting
Basaltic magmas are also generated at ________, where water driven from the descending slab of oceanic crust promotes ________ of the mantle rocks that lie above.
subduction zones; partial melting
forms when a rising mantle-derived basaltic magma undergoes magmatic differentiation as it slowly makes its way through the continental crust.
andesitic magma
These evolved (changed) magmas are termed ?
secondary magmas
form when rising basaltic magmas assimilate crustal rocks that tend to be silica rich.
andesitic magmas
these magmas are mostly generated by the partial melting of continental crust.
granitic magmas
describe the occurrence of gases in magma
- gas molecules that form when minerals within a rock body begin to melt.
- These gases remain dissolved within the magma
- until the magma gets near the surface, where the decreased pressure allows the gases to escape
this is similar to how carbon dioxide (CO2) gas in a soda remains dissolved until the can is opened.
relationship of dissolved gas content to the explosiveness of volcanic eruptions
Higher content of dissolved gases within a magma will result to a more explosive volcanic eruption.
4 volcanic landforms
- lava flow
- lava dome
- continental flood basalt
- volcanoes
formed when lava eventually cools and solidifies into an igneous rock body
lava flow
are steep-sided mounds that were formed from viscous lava (rhyolitic lava); can act like a plug when it begins to solidify and thus allow pressure to build in the magma chamber and result in a more explosive eruption.
lava dome
formed when large volumes of basaltic lava will flow onto the surface along large fracture zones.
Continental flood basalt
an accumulation of extrusive materials around a vent (sometimes a fault or fracture) through which lava, gas, or pyroclastics are ejected.
volcanoes
3 types of volcanoes
cinder, composite, and shield.
A volcanic vent can coincide with a fault or fracture, resulting in a linear extrusion known as ?
fissure eruption
relatively small and is formed when lava is ejected into the air and cools into pyroclastic material, which then fall and accumulate around the vent
cinder cone volcanoes
cooled pyroclastic material
cinders
aka stratovolcanoes
composite cone volcanoes
are cone-shaped volcanoes with steep slopes consisting of alternating layers of pyroclastic material and lava flows.
composite cone volcanoes
are exceptionally large landforms composed primarily of basaltic lava flows. It has a broad cross-sectional shape due to the low viscosity of basalt which can travel considerable distances from the vent and spread out over large areas.
shield volcanoes
describe the eruptions of shield volcanoes, why are they like that?
Eruptions are quiescent as basaltic magma contains small amounts of dissolved gases and has a low viscosity.
a circular depression where lava and pyroclastic material is being ejected.
crater
a circular depression that forms after an eruption when large volumes of magma are ejected from a shallow magma chamber, leaving it relatively empty and thus causing it to subside/collapse
caldera
3 eruption status of volcanoes in the philippines
active, potentially active, inactive
a zone of molten material where magma accumulates and occurs at a considerable depth.
magma chamber
what gives the molten material within the magma chamber a tremendous amount of fluid pressure.
The confining pressure caused by the overlying rocks
describe what happens as magma rises
As magma rises and encounters less confining pressure, it expands and pushes outwards on the surrounding rocks, thereby creating fractures and faults and subsequent earthquakes. The fractures and faults also provide a pathway for the magma to the surface.
If the overlying rocks at some point are no longer capable of containing the fluid pressure, then significant amounts of magma can make its way to the surface, resulting in ?
volcanic eruption
Explosive eruptions are associated with more ________ and ________ magmas in which the dissolved gases _________, ejecting rock and ash into the atmosphere.
viscous;
gas-charged;
rapidly decompress
Nonexplosive eruptions are associated with _______ magma containing _______, in which case the eruption generates _______ and _______.
hot fluid;
less dissolved gas;
lava fountains;
lava flows
Subduction zone volcanoes tend to erupt in an what manner? and why?
- in an explosive manner
- because their andesitic magmas usually contain large volumes of dissolved gas—mostly water vapor.
Hot spot volcanoes located in the interior of continental plates erupt in what manner? why?
they erupt violently, as their rhyolitic
magmas usually contain abundant water
Eruptions create pulverized rock that is ejected along with the lava which is collectively known as ?
pyroclastic material
solidified lava and pulverized rock.
tephra
The finest material that can travel hundreds, even thousands, of miles before falling back to Earth’s surface
volcanic ash
3 ways to classify pyroclastic deposits and rocks
- grain size
- grain size mixture
- components
It is a relative measure of the explosiveness of
volcanic eruptions.
Volcanic Explosivity Index (VEI)
the VEI was devised by whom?
-Chris Newhall of the United States Geological Survey and
-Stephen Self at the University of Hawaii in 1982.
The way in which humans respond to potential volcanic threats depends on several factors, in particular what 2 things?
the frequency at which eruptions occur
and the availability of habitable living space.
2 primary hazards near a volcano
Violent eruption and lava flow
5 secondary hazards
- pyroclastic flow
- volcanic ash
- mass wasting on volcanoes: volcanic landslides/debris avalanche, volcanic mudflow/lahar
- volcanic gases
- tsunami
occurs whenever magma reaches the surface and begins to move across the landscape.
lava flows
how fast and how far a flow will travel is largely determined by what 3 things?
- the slope of the land surface
- volume of lava being emitted at the vent
- and the lava’s viscosity
typically results from highly compressed gases (primarily water) dissolved within andesitic and rhyolitic magmas.
Explosive Eruption
a dry avalanche consisting of hot rock fragments, ash, and superheated gas, all rushing down the side of a volcano at great speed
Pyroclastic Flow
the typical 2 parts of a pyroclastic flow
- a tumbling mass of large rocks overlain by
- a turbulent cloud of finer material
what type(characteristic) of magmas are pyroclastic flows mostly associated with
almost always associated with more viscous, SiO2 rich magmas.
the most famous example of a pyroclastic flow is the one that struck Pompeii, Italy by what volcano? when?
Mount Vesuvius. In 79 AD
jagged rock and glass fragments less than 2 millimeters in diameter which are propelled into the atmosphere following a volcanic eruption and are transported by wind at considerable distances prior to deposition
volcanic ash
7 harmful effects of volcanic ash
- inhaling the fine particles is particularly dangerous to children or adults
with cardiac or respiratory conditions - additional weight of the ash can destroy crops and cause buildings to
collapse - can also ruin crops when it is impractical to wash off before processing,
or when it disrupts pollination and changes the acidity of soils - can contaminate surface water
- when washed off from the landscape, sediment
load of streams/rivers will increase thereby, increasing the
frequency and severity of flooding - causes considerable damage to mechanical and
electrical equipment due to its abrasive property - may trigger regional to global cooling;
2 types of mass wasting on volcanoes
- volcanic landslide
- volcanic mudflows
aka volcanic landslide
debris avalanche
occurs whenever steep flanks of a volcano become unstable and results rapid downslope movement of rocks, debris, and/or snow/ice. It is often triggered by heavy rains or earthquakes.
volcanic landslide
happens when corrosive gases and groundwater within a volcano breakdown feldspar-rich rocks into much weaker clay minerals
volcanic landslide
aka volcanic mudflows
lahar or debris flow
is a mixture of ash, rock, and considerable amounts of liquid water. Ash and rock may comprise 60 to 90% by weight may resemble a river of wet concrete.
volcanic mudflows
Because of its fluid nature, volcanic mudflows tend to rush down stream valleys that lead away from a volcano, reaching speeds of ?
20 to 40 miles per hour (30–65
km/hr)
T of F: Volcanic mudflows are less destructive compared to ordinary river floods because of its fairly dense and viscous flow; can easily rip up trees and transport large boulders far downstream
False, it is MORE destructive
what are the major volcanic gases?
water vapor (H2O);
carbon dioxide (CO2);
sulfur dioxide (SO2)
3 reasons why volcanic gas cloud dangerous to humans?
- simply because it contains no free oxygen (O2). Therefore, should a volcanic cloud descend into a populated area it poses an asphyxiation (i.e., suffocation) risk to people.
- Because volcanic gases are typically quite hot, severely burned skin and lung tissue is another life-threatening hazard.
- release of toxic volcanic gases may happen even with the absence of any volcanic activity
form when volcanoes explode violently in an oceanic setting and may subsequently strike coastal communities far from the volcano itself.
tsunami
what are the 5 predictive tools for volcano eruptions
- geologic history
- topographic changes
- seismic monitoring
- monitoring of volcanic gases
- geophysical and groundwater changes
makes use of of the size, shape, composition, and layering characteristics of the particles of a volcanic deposit to infer the history of a particular volcano and subsequently device mitigating measures should there be a nearby exposed population to volcanic hazards.
geologic history
accurately surveying changes in the shape of a volcano over time can give an idea to the position of magma within a volcano as well as the volume moving into the magma chamber.
topographic changes
an excellent tool for predicting eruption as earthquake activity invariably increases as magma moves toward the surface.
seismic monitoring
strain accumulates when rising magma forces its way through crustal rocks, creating what ?
magmatic earthquakes (sometimes called harmonic tremors)
do volcanic gases always originate from fresh magma moving up from depth?
nope, Other sources include heated groundwater and older magma leftover from a previous eruption.
provide an early warning so that officials can implement emergency response plans and allow people to safely evacuate.
forecasts
allows baseline data to be collected and analyzed to aid scientist in increasing the reliability of eruption forecasts and development of early warning systems.
Regular monitoring and the use of adequate sensitive ground-based instruments
