Volcanic Eruptions Flashcards
Where does volcanoes mostly found?
Convergent boundaries
Continents generate more what type of magma?
Rhyolitic magma
Hot spots generate more what type of magma?
Basaltic magma
The viscosity of magma depends on ________.
SiO2
The process where the early formed minerals are denser than the liquid.
Crystal setting
SiO2 content of Basaltic lava
41-52%
SiO2 content of Andesite/Dacite
52-68%
SiO2 content of rhyolite
68-77%
Which magma is hotter when ejected?
Basaltic magma
Which type of magma is cooler when ejected?
Rhyolite
True or False. The remaining melt solidifies either in place or in another location, if it migrates into fractures in the surrounding rocks it will form a rock with a mineralogy much different from the parent magma
TRUE
The richer _______, ________, and ________ crystallize and settles at the bottom of the magma chamber.
iron, magnesium, and calcium
The remaining melt will be enriched with _____, ______, and ______. Should a subsequent eruption occur, the rocks generated will be more ________ and closer to the __________ end of the compositional range than the initial magma.
sodium, potassium, and silica
silica-rich
felsic (granitic)
What is Magmatic Differentiation?
The formation of one or more secondary magmas from a single parent magma.
What is Assimilation?
Surrounding country rock may be incorporated to the upwelling magma.
What is magma mixing?
Occurs during the ascent of two chemically distinct magma bodies as the more buoyant mass overtakes the more slowly rising body
True or False. Minerals with the highest melting temperatures are the first to melt
FALSE. lowest
The process that generates a magma that’s nearer the felsic (granitic) end of the compositional spectrum than the parent rock from which it was derived.
Partial melting
Basaltic magma have a temperature of __________
1000 degrees celsius to 1250 degrees celsius
TRUE or FALSE. Under the high-pressure conditions for the upper mantle, partial melting of the ultramafic rock peridotite will yield a magma of granitic composition.
FALSE. basaltic composition
Basaltic (mafic) magmas that originate from partial melting of mantle rocks are also called ___________.
primary or primitive magma
What is decompression melting?
Partial melting that produces mantle derived magmas may be triggered by a reduction in confining pressure
TRUE or FALSE. Basaltic magmas are also generated at subduction zones where water driven from the descending slab of oceanic crust promotes partial melting of the mantle rocks that lie above
TRUE
How andesitic magma formed?
When rising basaltic magmas assimilate crustal rocks that tend to be silica rich.
One way andesitic magma can form is when a rising mantle derived basaltic magma undergoes ______________ as it slowly makes its way through the continental crust
magma differentiation
What are the various types of gas molecules form when rock body begin to melt?
H2O, CO2, SO2, H2, CO, H2S
Gases remain dissolved within the magma until the magma gets near the surface , where the __________ allows the gases to escape.
Decreased pressure
TRUE or FALSE. Lower content of dissolved gases within a magma will result to a more explosive volcanic eruption.
FALSE. Higher content.
A type of landform when lava eventually cools and solidifies into an igneous rock body
Lavaflow
A type of landform is a steep-sided mound formed from viscous lava ( rhyolitic lava). They can also act like a ________ when it begins to solidify and thus allow pressure to build in the magma chamber and result in a more explosive eruption.
Lava dome; plug
A type of landform 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
A type of landform that’s relatively small and is formed when lava is ejected into the air and cools into pyroclastic material.
Cinder cones
What is a composite cone?
-also known as “stratovolcano”
-cone shaped volcanoes
-is generally associated with viscous ad gas charged andesitic magmas that generally erupt in an extremely explosive
What is shield volcano?
- composed primarily of basaltic lava flows
- broad cross sectional shape due to the low viscosity
- Eruptions are quiescent as basaltic magma contains small amounts of dissolved gases.
A circular depression where lava and pyroclastic material is being ejected
Crater
What is a caldera?
- circular depression forms after volumes of magma ejected, leaving it relatively empty.
How many active volcanoes in the Philippines?
24
Give an example of an active volcano.
Taal, Pinatubo, Mayon, Mt. Parker
A zone of molten material where magma accumulates and occurs.
Magma chamber
True or False. If the overlying rocks at some point are no longer capable of containing the fluid pressure, then significant amounts of magma can make their way to the surface, resulting in a volcanic eruption.
TRUE.
The ___________ caused by the overlying rocks gives the molten material within the magma chamber a tremendous amount of ___________.
Confining pressure; fluid pressure
As magma rises and encounters less confining pressure, it expands and pushes outwards on the surrounding rocks, thereby creating ______ , _______, and ________. It can also provide a pathway for the magma to the surface.
fractures, faults, earthquake
What is a pyroclastic material?
Pulverized rock that is ejected along with the lava.
What is tephra?
Solidified lava and pulverized rock
The finest pyroclastic material, that can travel hundreds, even thousands, of miles before falling back to Earth’s surface
Volcanic Ash
Ways to Classify Pyroclastic Deposits and Rocks
Grain Size
Grain Size Mixture
Components
Size of fine ash
<1/16 mm
Size of coarse ash
1/16 mm - 2 mm
Size of Lapillus
2 mm - 64 mm
Size of agglomerate/bomb block
> 64 mm
Who devised the volcanic explosivity index?
Chris Newhall in 1982
What is Volcanic Explosivity Index (VEI)?
Measure of the explosiveness of volcanic eruptions.
Example of primary hazard of a volcano.
Eruption and Lava flow
Example of secondary hazard of a volcano.
mudflow, lahar, suspension of volcanic ash and toxic gases into the atmosphere, tsunamis, and landslides.
Occurs whenever magma reaches the surface and begins to move across the landscape.
Lava flow
How fast and how far a flow will travel is largely determined by the _____ of the land surface, _____ of lava being emitted at the vent, and the lava’s _______.
slope, volume, and viscosity
Explosive eruption comes from __________.
highly compressed gases dissolved within the andesitic and rhyolitic magma.
What is pyroclastic flow
a dry avalanche consisting of hot rock fragments, ash, and superheated gas, all rushing down the side of a volcano at great speed
Most famous example of a pyroclastic flow
Mount Vesuvius, Pompeii, Italy, 79 AD
Another incident of pyroclastic flow happened in 1902
City of Pierre on the Island of Martinique had been decimated by the eruption of Mt Pelée (a stratovolcano which is 7 kilometers away from the city) The eruption which triggered a pyroclastic flow claimed the entire
population of 30 000
A jagged rock and glass fragments less than 2 millimeters in diameter which are propelled into the atmosphere.
Volcanic ash
What happens in 1991?
Mt . Pinatubo ’s eruption (1991) led to a 0.25 degrees Celsius drop in global temperature while the
What happens in 1815?
Eruption of Mount Tambora in Indonesia resulted a maximum of 3 degrees Celsius drop in temperature and was subsequently dubbed as “the year without summer”
What is volcanic landslide?
- also called as debris avalanche
- also called as 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 - it is often triggered by heavy rains or earthquakes
TRUE or FALSE. Corrosive gases and groundwater within a volcano can breakdown feldspar rich rocks into much stronger clay minerals, thereby making slopes more prone to landslide
FALSE. Weaker
What is Volcanic Mudflows?
- also called a lahar or debris flow
- 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.
Mainly composed of water vapor (H 2 O), followed by carbon dioxide (CO 2 ), and sulfur dioxide (SO 2 ), which together account for over 95% of all volcanic gases
Volcanic gases
Why volcanic gases are hazardous to humans?
it contains no free oxygen (O2)
What happened in 1986
Oku volcanic field in Cameroon, Africa, wherein clouds of CO 2 gas silently moved down the slopes and quickly suffocated 2,000 people and thousands of livestock in a 20 km radius around the two water filled craters.
Form when volcanoes explode violently in an oceanic setting and may subsequently strike coastal communities far from the volcano itself. Ex. Eruption of Krakatau
Tsunami
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
Why we need to monitor topographic changes?
Monitoring changes in the topography or shape of a volcano the presence of pressurized magma commonly causes the volcano to swell or inflate
An excellent tool for predicting eruption as earthquake activity invariably increases as magma moves toward the surface.
Seismic monitoring
Why we need to monitor volcanic gases?
regular monitoring of gases (ex. H2O, CO2, SO2) to look for
changes in gas chemistry that may indicate a possible eruption.
Why we need to monitor Geophysical and Groundwater Changes?
-change the physical properties of rocks
-temperature
-chemical composition of groundwater
