VOLCANIC ERUPTIONS Flashcards
Three types of magma
basaltic, andesitic, and rhyolitic magmas
The type of magma and consequent type of eruption of a volcano depends on the ________.
tectonic setting it is formed
Volcanoes are mostly found along ______ boundaries
convergent
Hot spot volcanoes in an oceanic setting produce _________, and those on continents generate more rhyolitic magma
basaltic magma
silica content of Basalt, andesite, rhyolite
48-52%,52-68%. 68-77%
The viscosity of magma ________ with increasing SiO2 and decreasing temperature.
increases
how magmas evolve
- Over time, a volcano may extrude lavas that vary in composition.
- The Bowen’s reaction series depicts the sequence in which minerals crystallize from a magma
o formed minerals are denser (heavier) than the liquid (melt) and sink toward the magma chamber.
- Crystal Settling
o The formation of one or more secondary magmas from a single parent magma.
- Magmatic Differentiation
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
The composition of magma changes when the molten mass incorporates pieces of surrounding host rock, a process
assimilation
is 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
- Most magma that erupts on the Earth’s surface is basaltic in composition and has a temperature of_______
1000oC to 1250oC.
partial melting of the ultramafic rock peridotite will yield a magma of ______composition
basaltic
Basaltic (mafic) magmas that originate from partial melting of mantle rocks are called __________ magmas because they have not yet evolved
primary or primitive
- Partial melting that produces mantle-derived magmas may be triggered by a reduction in confining pressure during the process of _________
decompression melting.
- These evolved (changed) magmas are termed secondary magmas.
secondary magmas.
Granitic magmas are mostly generated by the __________ of continental crust.
partial melting
- Higher content of dissolved gases within a magma will result to a________ volcanic eruption.
more explosive
formed when lava eventually cools and solidifies into an igneous rock body
lava flow
differentiate two types of lava flow
Pāhoehoe – Lava flows with smooth, billowy, or ropy surfaces.
‘A’ā – Lava flows with rough, jagged, or clinkery surfaces.
are steep-sided mounds that were formed from viscous lava (rhyolitic lava); lava domes 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. The following are the three types of volcanic cones: cinder, composite, and shield.
volcanoes
relatively small and is formed when lava is ejected into the air and cools into pyroclastic material called cinders, which then fall and accumulate around the vent
cinder cones
are come-shaped volcanoes with steep slopes consisting of alternating layers of pyroclastic material and lava flows.
composite cone
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
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
Erupted within historical times (within the last 600 years), accounts of these eruptions were documented by man erupted within the last 10,000 years based on the analyses of material from young volcanic deposits.
active volcanoes
Morphologically young-looking but with no historical or analytical records of eruption.
potentially active volcanoes
No recorded eruptions physical form has been intensively weathered and eroded, bearing deep and long gullies
inactive volcanoes
a zone of molten material where magma accumulates and occurs at a considerable depth.
magma chamber
the ___________ caused by the overlying rocks gives the molten material within the magma chamber a tremendous amount of fluid pressure
confining pressure
- 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 a ___________
volcanic eruption
- Eruptions create pulverized rock that is ejected along with the lava which is collectively known as _________.
pyroclastic material
are solidified lava and pulverized rock.
tephra
finest material, called _________, 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
- It is a relative measure of the explosiveness of volcanic eruptions.
Volcanic Explosivity Index (VEI)
primary hazards near a volcano
violent eruption and lava flow
secondary hazards
, mudflow, lahar, suspension of volcanic ash and toxic gases into the atmosphere, tsunamis, and landslides
- the explosive power typically comes 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
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
example of volcanic ash that triggered regional to global cleaning
(1) Mt. Pinatubo’s eruption (1991) led to a 0.25 degrees Celsius drop in global temperature while the
(2) 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”
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 earthquakes.
volcanic landslide
also called a 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 mudflow
is mainly composed of water vapor (H2O), followed by carbon dioxide (CO2 ), and sulfur dioxide (SO2 ),
volcanic gas
predictive tools in eruptions
geologic history
topographic changes
seismic monitoring
Monitoring of Volcanic Gases
Geophysical and Groundwater Changes
- strain accumulates when rising magma forces its way through crustal rocks, creating what geologists call
magmatic earthquakes
