(MODULE 7.2) GEOLOGICAL HAZARDS - VOLCANIC ERUPTIONS Flashcards
a mountain that forms when molten rock (magma) reaches the surface of the earth
volcano
volcanoes are formed when ___.
magma forces its way through a crack in the earth’s crust.
a volcano is classified as ___ if it erupts lava, rock, gas, or ash, or if it shows seismic activity.
active
a volcano is ___ if it hasn’t erupted for a long time (less than 1 million years) but could erupt again one day.
dormant
an ___ volcano will never erupt again.
extinct
indicate the parts of a volcano
- crater
- vent
- cone
- conduit
- magma chamber
the opening from which lava flows. dust, ash, and rock particles can also be thrown out of it.
vent
the pile of lava, dust, ashes, and rock around the vent; can be found in different shapes
cone
the top of the volcano; it is a funnel shaped pit formed when the material explodes out of the vent.
crater
some volcanoes have very large circular depressions called ___, that have diameters greater than 1 kilometer.
calderas
a passageway followed by magma in a volcano.
conduit
the subterranean cavity containing the gas-rich liquid magma which feeds a volcano
magma chamber
volcanoes are classified by ___.
how they are formed
this type of volcano is wide and somewhat flat, between 2 to 10 degrees.
shield volcano
what are the characteristics of a shield volcano?
1.
2.
3.
4.
- it is wide and flat
- it is constructed of solidified lava flows
- it forms from a quiet eruption
- lava flows out quietly and for great distances because the shield volcano doesn’t have a long conduit
this type of volcano has a tall, very sleep slope
cinder cone volcano
what are the characteristics of a cinder cone volcano?
1.
2.
3.
4.
- it has a tall, very steep slope
- it is constructed of ejected pyroclastic fragments
- it has explosive eruptions due to its long conduit
- eruptions from cinder cone volcanoes produce a lot of cinder and ash
this volcano is of intermediate steepness and constructed of alternating layers of pyroclastic fragments and solidified lava flows
composite volcano
what are the characteristics of a composite volcano?
1.
2.
3.
- it is constructed of alternating layers of pyroclastic fragments and solidified lava flows
- it is built over long spans of time because eruption is intermittent
- it has intermediate steepness; slope is less than 33 degrees
why does a volcano erupt?
a volcano erupts when magma and gases find a way to escape and burst to the surface through a vent.
since magma is buoyant, it rises up through the curst to erupt on the surface.
there are two factors that determine eruption patterns:
1.
2.
- the amount of gas in the lava or magma
- the ease or difficulty with which the gas can escape into the atmosphere (viscosity)
___ is how thick and gloopy a material is. an example of such material is honey in room temperature.
viscosity
the ___ viscous the lava and the ___ the volume of gas trying to escape, the ___ the eruption.
- more
- greater
- more violent
the three factors that influence viscosity of lava or magma are:
1.
2.
3.
- the silica content
- the temperature
- gas dissolved in magma
the silica content of lava ranges from ___ to ___ by weight.
45% to 75%
___ rocks are silica-rich (>65% silica)
felsic
___ rocks are silica-deficient (~50%)
mafic
mafic lavas which are silica-deficient tend to ___.
flow easily
felsic lavas which are silica-rich are ___ and tend to ___.
much more viscous; flow sluggishly
temperatures at which lavas solidify range from about ___ for felsic rocks to ___ for mafic rocks.
- 700 C
- 1,200 C
if the lava being extruded is considerably hotter than its solidification temperature, the lava is ___ than when its temperature is near its solidification point.
less viscous (more fluid)
water vapor dissolved in magma tends to increase fluidity because ___.
it reduces formation of long silicate chains by breaking silicon-oxygen (silicate) bonds.
the loss of gases renders magma ___.
more viscous
there are two types of eruption patterns, namely:
1.
2.
- explosive eruption
- effusive eruption
caused by large amounts of gas and high viscosity magma, this is the most violent eruption of all due to the gases and magma trapped in the volcano.
explosive eruption
this eruption pattern is characterized by outpourings of lava onto the ground.
described as quiet and gentle, the eruptions contain small amounts of gas and/or low viscosity magma.
the lava is very runny and can move fast.
effusive eruption
most of the gas released during eruptions is ___, which condenses as steam.
water vapor
collectively regarded as extrusive igneous rock or surface rock resulting from volcanic activity.
tephra
when magma solidified quickly as it was blasted explosively by gases into the air, it produces rock fragments known as ___.
pyroclasts
types of volcanic hazards:
1.
2.
3.
4.
- pyroclastic fall
- pyroclastic flow
- volcanic mudflows
- volcanic lightning
the fallout of rock, debris and ash from an explosive eruption column
pyroclastic fall
most of the deaths due to pyroclastic fall are caused by ___ or ___.
- collapse of ash-covered roof
- being hit by falling rock fragments
a mixture of hot gas and pyroclastic debris that rapidly flows down a volcano’s flanks
pyroclastic flow
characteristics of pyroclastic flows
1.
2.
3.
- they can reach over 100 km distances from a volcano
- they can travel 100 km/h
- temperature is > 400C
pyroclastic flows can happen ___ or ___ the eruption
before or after
a flowing mixture of soil, fine pyroclastic debris, and water from heavy rains
volcanic mudflows or lahars
this volcanic hazard is generated by tiny particles of rocks thrown out by the volcano. the ash causes friction that generates an electrical charge.
volcanic lightning
