VOLCANIC ERUPTIONS

Question 1

Three types of magma

Answer 1

basaltic, andesitic, and rhyolitic magmas

Question 2

The type of magma and consequent type of eruption of a volcano depends on the ________.

Answer 2

tectonic setting it is formed

Question 3

Volcanoes are mostly found along ______ boundaries

Answer 3

convergent

Question 4

Hot spot volcanoes in an oceanic setting produce _________, and those on continents generate more rhyolitic magma

Answer 4

basaltic magma

Question 5

silica content of Basalt, andesite, rhyolite

Answer 5

48-52%,52-68%. 68-77%

Question 6

The viscosity of magma ________ with increasing SiO2 and decreasing temperature.

Answer 6

increases

Question 7

how magmas evolve

Answer 7

• 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

Question 8

o formed minerals are denser (heavier) than the liquid (melt) and sink toward the magma chamber.

Answer 8

• Crystal Settling

Question 9

o The formation of one or more secondary magmas from a single parent magma.

Answer 9

• Magmatic Differentiation

Question 10

some of the surrounding rock (country rock) may be incorporated to the upwelling magma.

Answer 10

assimilation

Question 11

occurs during the ascent of two chemically distinct magma bodies as the more buoyant mass overtakes the more slowly rising body.

Answer 11

magma mixing

Question 12

The composition of magma changes when the molten mass incorporates pieces of surrounding host rock, a process

Answer 12

assimilation

Question 13

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.

Answer 13

• Partial melting

Question 14

• Most magma that erupts on the Earth’s surface is basaltic in composition and has a temperature of_______

Answer 14

1000oC to 1250oC.

Question 15

partial melting of the ultramafic rock peridotite will yield a magma of ______composition

Answer 15

basaltic

Question 16

Basaltic (mafic) magmas that originate from partial melting of mantle rocks are called __________ magmas because they have not yet evolved

Answer 16

primary or primitive

Question 17

• Partial melting that produces mantle-derived magmas may be triggered by a reduction in confining pressure during the process of _________

Answer 17

decompression melting.

Question 18

• These evolved (changed) magmas are termed secondary magmas.

Answer 18

secondary magmas.

Question 19

Granitic magmas are mostly generated by the __________ of continental crust.

Answer 19

partial melting

Question 20

• Higher content of dissolved gases within a magma will result to a________ volcanic eruption.

Answer 20

more explosive

Question 21

formed when lava eventually cools and solidifies into an igneous rock body

Answer 21

lava flow

Question 22

differentiate two types of lava flow

Answer 22

Pāhoehoe – Lava flows with smooth, billowy, or ropy surfaces.
‘A’ā – Lava flows with rough, jagged, or clinkery surfaces.

Question 23

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.

Answer 23

lava dome

Question 24

formed when large volumes of basaltic lava will flow onto the surface along large fracture zones.

Answer 24

• Continental flood basalt

Question 25

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.

Answer 25

volcanoes

Question 26

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

Answer 26

cinder cones

Question 27

are come-shaped volcanoes with steep slopes consisting of alternating layers of pyroclastic material and lava flows.

Answer 27

composite cone

Question 28

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.

Answer 28

shield volcanoes

Question 29

a circular depression where lava and pyroclastic material is being ejected

Answer 29

crater

Question 30

– 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.

Answer 30

caldera

Question 31

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.

Answer 31

active volcanoes

Question 32

Morphologically young-looking but with no historical or analytical records of eruption.

Answer 32

potentially active volcanoes

Question 33

No recorded eruptions physical form has been intensively weathered and eroded, bearing deep and long gullies

Answer 33

inactive volcanoes

Question 34

a zone of molten material where magma accumulates and occurs at a considerable depth.

Answer 34

magma chamber

Question 35

the ___________ caused by the overlying rocks gives the molten material within the magma chamber a tremendous amount of fluid pressure

Answer 35

confining pressure

Question 36

• 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 ___________

Answer 36

volcanic eruption

Question 37

• Eruptions create pulverized rock that is ejected along with the lava which is collectively known as _________.

Answer 37

pyroclastic material

Question 38

are solidified lava and pulverized rock.

Answer 38

tephra

Question 39

finest material, called _________, can travel hundreds, even thousands, of miles before falling back to Earth’s surface.

Answer 39

volcanic ash

Question 40

Ways to Classify Pyroclastic Deposits and Rocks

Answer 40

1. Grain Size
2. Grain Size Mixture
3. Components

Question 41

• It is a relative measure of the explosiveness of volcanic eruptions.

Answer 41

Volcanic Explosivity Index (VEI)

Question 42

primary hazards near a volcano

Answer 42

violent eruption and lava flow

Question 43

secondary hazards

Answer 43

, mudflow, lahar, suspension of volcanic ash and toxic gases into the atmosphere, tsunamis, and landslides

Question 44

• the explosive power typically comes from highly compressed gases (primarily water) dissolved within andesitic and rhyolitic magmas.

Answer 44

Explosive Eruption

Question 45

a dry avalanche consisting of hot rock fragments, ash, and superheated gas, all rushing down the side of a volcano at great speed

Answer 45

Pyroclastic Flow

Question 46

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.

Answer 46

volcanic ash

Question 47

example of volcanic ash that triggered regional to global cleaning

Answer 47

(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”

Question 48

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.

Answer 48

volcanic landslide

Question 49

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.

Answer 49

volcanic mudflow

Question 50

is mainly composed of water vapor (H2O), followed by carbon dioxide (CO2 ), and sulfur dioxide (SO2 ),

Answer 50

volcanic gas

Question 51

predictive tools in eruptions

Answer 51

geologic history
topographic changes
seismic monitoring
Monitoring of Volcanic Gases
Geophysical and Groundwater Changes

Question 52

• strain accumulates when rising magma forces its way through crustal rocks, creating what geologists call

Answer 52

magmatic earthquakes