Volcanos and earthquakes
Volcanos
Forms of volcanos
Volcanic landforms are classified into:
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Explosive landforms, such as explosive vets and ash
Effusive landforms, such as shield volcanos and lava 1lateau
Mixed landforms, such as strato volcanoes
The two main types are therefore: lava cones (shield volcanos) and composite cones (strato
volcanoes
Volcano Type
Shield volcano
Characteristics
Example
(Schildvulkan)
Liquid lava emitted
from e central vent;
large widespread;
sometimes has a
collapsed caldera
Hawaiian Volcanos.
Iceland
Composite cone or
More viscous
(zähflüssig) lava, a lot
of explosive
(pyroclastic) debris;
large, emitted from a
central vent;
They have different
layers (strato->schicht)
A sunken crater at the
center of a volcano,
formed as a result of
subsidence. As the
magma founders so
the center of the
volcano collapses.
Very large composite
volcanoes collapsed
after the explosive
period.
Mount St. Helens,
Krakatoa,
Mt. Vesuvius,
Pintaubo,
Kilimandscharo,
Mt. Etna,
Mt. Stromboli,
Popocarepetl
Stratovolcano
(Schichtvulkan)
Caldera
Yellowstone,
Ngorngoro,
Crater lake
Illustration
Hotspot
Hotspots are volcanic regions that are fed by the underlying mantle that is extremely hot compared
to the rest of the mantle. They can be on, near to, or far from plate boundaries. Hopt spots don’t
move with the plates, but stay where they are. Hotspots are huge magma chambers that lye under
the earth’s surface. If they get hot, a volcano forms. Because the hotspot lies under the earth’s
surface, it doesn’t move with the plate, it stays where it is. A new volcano forms, because the old
volcano moves away. Hotspot volcanos are located above a point of localized heat under a tectonic
plate.
There are two hypotheses to explain them. The first one says, that they exist, because of hot mantle
plumes that rise as thermal dispairs from the core-mantle boundary. The other hypothesis suggests,
that it is not high temperature that causes the volcanism, but lithospheric extension that permits the
passive rising of melt from shallow depths.
Geothermal activity
Gases dissolved into magma are the driving force for volcanic eruptions. During volcanic activity and
its dormant periods volcanic gases reach the surface. These gas emissions mainly consist of H2O, So2,
H2S, CO, N2, HCI, H2. Geothermal activity is caused by the transfer f heat from depth to the erath’s
surface.
Surface manifestations of geothermal activity:
Warm ground
Fuzhou (South China)
Ngawha (New Zealand)
Steam vents, Kilauea (Hawaii)
Hot steaming ground
Olkaria system (Kenya)
Hot pools
Waiotapu (New Zealand)
Tongonan (Philippines)
Hot springs
Inferno crater (Waimangu, New
Zealand)
Fumaroles
Valley of ten thousand smokes (Alaska)
Yellowstone national park (USA)
Rincon de la Vieja (Costa Rica)
Solfatara
Solfatara, Pozzuoli (Naples, I)
Geysers
Old faithful, Yellowstone (USA)
Low level of geothermal activity,
warmth does not come to the surface
Result of underground thermal conduction
Hot vapours rise near the surface, but are not actually
discharged.
Not released to atmosphere
Steam, water heated up to 100°C
Hot water or steam heating a pool of ground water
Temperature is always different
Can’t know the temperature
Most common type
Water from geothermal system reaches surface
Pilsate and release water in cycles (Iceland)
No active volcanoes but many hot spring areas
(Australia)
Steam discharge from ahydrothermal or volcanic
system (that can burn)
Steam is most common type of emission
Steam comes from groundwater and magma
Chloride is added to seawater
Noisy fumaroles-discharge rates >20 m/s
Quiet fumaroles-discharge rates <20 m/s
A fumarole that emits sulphorous gases.
“Land of sulphur” is caused when groundwater
interacts with magma
A vent from which hot water and steam are violently
emitted.
Rajabasa (Indonesia)
Hydrothermal eruptions
Waiotapu (New Zealand)
Rotarua (New Zealand)
Kawah Komojang field (Java, Indonesia)
Yangbajing (Tibet)
Exhalations
(Mt. Etna, Italy)
Very rare
Requirements for formation include: fractured rocks
and boiling water at shallow depth
They don’t erupt
They can get hot, but not as hot as Hydrothermal
eruptions
Caused by catastrophic discharges of water close to the
boiling point. It is a phreatic eruption. No ash,
incandesence (Glut) or calsts are erupted.
Caused by a reduction in the overlying pressure
Emission of gas or ash from a vent in relatively short
burts
Geothermal gradient
The geothermal gradient is the natural increase in the temperature of the earth as depth increases.
How warm does it get if I dig a hole in the earth. The smaller the geothermal gradient is, the less
volcanic activity.
Average value 3°/100 m
South Africa 1°/130m-135m
Zurzach 1°/14m
Etna 1°/5m
Term
Stratovolcano
Definition
Steep, conical shape. Consists of
different layers
Pahoehoe lava
Basaltic lava that has a smooth,
hummocky, or ropy surface. A
pahoehoe flow typically advances
as a series of small lobes and toes
that continually break out from a
cooled crust.
Picture
Bomb
lava fragments that were ejected
while viscous. and larger than 64
mm
Lapilli
Small pieces of material ejected by
a volcano ranging in size from
about 2 and 64 mm across
Ash
Consists of rock, mineral, and
volcanic glass fragments smaller
than 2 mm. It is hard, does not
dissolve in water, ash particles less
than 0.025 mm in diameter are
common. Ash is created during
explosive eruptions by the
shattering of solid rocks and
violent separation of magma into
tiny pieces.
Caldera
Large, usually circular depression
at the summit of a volcano, formed
when magma is withdrawn/erupted
from an underground magma
reservoir. Loss of a lot of magma
can lead to loss of structural
support for the overlying rock, ->
collapse of the ground and
formation of a large depression.
Shield volcano
Huge volcano. Looks like a shield.
Only lava flows out. Effusive.
1.
Volcanic gas
Volcanic gas is released from
magma as it rises toward the
surface and during eruptions.
Mixture of steam CO2 and NO2;
volcanic gas forms acid when it
dissolves in ground water, tends to
attack most rocks, breaking them
down into weak clay materials. The
interiors of volcanoes often become
seriously weakened because of this,
-> sudden landslides. Volcanic gas
is one of the clues used to detect
rising magma and a potential
eruption. Volcanic gas also escapes
through cracks or vents called
fumaroles.
Fumaroles
Vents from which volcanic gas
escapes into the atmosphere.
Fumaroles occur along tiny cracks
or long fissures, in chaotic clusters
or fields, and on the surfaces of
lava flows and thick deposits of
pyroclastic flows. Can live very long
Cinder cone
Steep, conical hill of volcanic
fragments that accumulate around
and downwind from a vent. The
rock fragments, often called
cinders or scoria, are glassy and
contain numerous gas bubbles
'frozen' into place as magma
exploded into the air and then
cooled quickly. Cinder cones range
in size from tens to hundreds of
meters in height. Cinder cones are
commonly found on the flanks of
shield volcanoes, stratovolcanoes,
and calderas
Eruption cloud
cloud of tephra and gases that
forms downwind of an erupting
volcano is called an eruption cloud.
The vertical pillar of tephra and
gases rising directly above a vent is
an eruption column
1.
Dyke
Dikes are tabular or sheet-like
bodies of lava that cut through and
across the layering of adjacent
rocks. They form when magma
rises into an existing fracture, or
creates a new crack by forcing its
way through existing rock, and
then solidifies
Strombolian
eruption
Intermittent explosion or
fountaining of basaltic lava from a
single vent or crater. caused by the
release of volcanic gases, and they
typically occur every few minutes or
so, sometimes rhythmically and
sometimes irregularly
Plinian eruption
Large explosive events that form
enormous dark columns of tephra
and gas high into the stratosphere.
It is more dangerous. Eruptive
Tephra
any material that is ejected by a
volcano into the atmosphere.
includes blocks and bombs, and
lighter materials such as lapilli and
ash. The further away from the
volcano, the finer the tephra
Aa-lava
Quicker. It’s brittle. Hardens
quickly.
Lava fountain
Lava sprayed into the air by rapid
formation and expansion of gas
bubbles in the molten rock. 10 to
100 m in height, but occasionally
reach more than 500 m.
Lava flow
Mass of molten rock that pours
onto the Earth's surface during an
effusive eruption. Both moving lava
and the resulting solidified deposit
are referred to as lava flows.
Reasons to live next to a volcano
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Volcanos are just there. Sometimes there are too many people to leave that area
uninhabited.
Der is high fertility on volcanos
They are tourist attractions ¨
But unexpected volcanic eruptions cause a lot of death.
1600-1899 186’000 people died average: 620 a year
1900-1886 76’000 people died average: 880 a year
But the reasons why people died changed dramatically.
Aftermaths of a volcano:
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Ash: Ash causes crop failure, because the ash destroys the fields. Flights had to be canceled
because pilots couldn’t see. Annual degrees dropped. Caused diseases.
 Famines
Tsunamis: They wash everything away -> people die
Pyroclastic flows and lava: like an avalanche. Extremely hot. Can also destroy fields,
Lahars: ash mixes with water and form mudflows
Why they aren’t so bad anymore/grew worse:
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Famines: Got better. Transportation system is better. Other nations can help out and
transport food.
Tsunamis: Got better. They are more predictable. People can be evacuated.
Lahars: Got worse. Cities are located closer to volcanos.
How can you predict volcanic eruptions?
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Plate tectonics sometimes give a hint
There can be steam coming out of a volcano
The sides sometimes blow up
The volcano gets bigger
Animals react. -> they get away from a volcano when an explosion is near
Earthquakes
Earthquakes are a series of vibrations and shock waves which are initiated by volcanic eruptions,
humans (explosions, Blowing up…) meteorites, or movements along the plate boundaries of oceanic
and continental plates and can occur along plate margins. These movements can be concentrated in
a single shock (more intense) or in a series of shocks. Aftershocks occur later as stresses are
redistributed.
Rock under stress
Rock deforms
Breaking point is reached
Stored energy is released
Focus and epicenter
The focus is the point underground where the rock springs apart. From the focus shock waves travel
through the rock in all directions.
The point directly above is called the epicenter, this is the place on the earth’s surface where most
damage will be caused. By the time shock waves have reached the earth’s surface further away, they
have lost their energy and less damage is caused.
Shock waves
There are two main types of waves, body waves and surface waves. Body waves are transmitted to
the surface from the center of the earthquake (focus) (they are inside the earth). Shock waves inside
the earth include the following:
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Primary waves (P) or pressure waves are the fastes and can move through solids and liquids.
They shake the earth back- and forwards.
Secondary waves (S) or shear waves move with a side ways motion and can only move
through solids. They move the ground horizontally and cause a lot of damage.
When P-waves and S-waves reach the surface some of them are transformed into surface waves,
causing much damage.
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Love waves cause the ground to move sideways
Rayleigh waves cause the ground to move up and down