Class Notes: Geo 1330: Dr Dupre΄
VOLCANOES:
Surface expression of igneous activity.
Why Study Volcanoes?
Major landforms
Volcanic soils feed much
of the world
Major geologic hazards
How Bad Can It Be?
|
1815 |
Indonesia |
92,000 died* |
|
1822 |
Indonesia |
5,500 killed |
|
1826 |
Indonesia |
3,000 killed |
|
1883 |
Indonesia |
36,417 killed |
|
1902 |
Martinique |
29,000 killed |
|
1902 |
Guatemala |
6,000 killed |
|
1919 |
Indonesia |
5,110 killed |
|
1951 |
New Guinea |
2,942 killed |
|
1982 |
Mexico |
1,700 killed |
|
1985 |
Columbia |
23,000 killed |
Major Volcanoes of the
World
Tectonic Setting Controls
Composition! What About Morphology?
Material ejected from
volcanoes includes:
______________: magma that has flowed
on the surface of the Earth.
______________: fragments that were
ejected and solidified in the air during eruption (tephra).
______________: erupted as gases
Types of Lava:
A. _______________
(mafic)
1)
flood basalts
2)
pahoehoe
3)
aa
4)
pillow basalts
B.
________________(intermediate)
C.
________________(felsic)
Columbia Plateau Flood
Basalts
Rivers of Hawaiian basalt
Paheohoe flow
Paheohoe and aa flows
Lava tubes
Pillow lava on the
seafloor
Ancient pillow basalt exposed
on land
Images of andesitic lava
flows in Guatemala
Rhyolite Domes in California
How do pahoehoe, aa, andesitic,
and rhyolitic flows differ, (other than in composition)?
________________ is
defined as a:
Factors controlling the
viscosity of magmas include:
1) ______________:
a) higher _________ results in
___________ viscosity
b) higher _________ results in
___________ viscosity
2) ______________:
higher____________ results in ____________
viscosity
Q. Why does the
%silica affect the viscosity of lava?
A.
Pyroclastic eruption: Costa
Rica
PYROCLASTIC: material ejected
during an eruption
Includes: airfall, pyroclastic
flows, and lahars
Air fall: from dust to boulder-sized fragments
Ash plume form eruption
of Mt St Helens
Ash mantling village in
Mexico
Volcanic tuff (indurated
ash), Alaska
Volcanic bombs
Volcanic breccia
_____________________ (nuee ardente): mixture
of hot gases and pyroclastic material to form a super-heated, potentially
lethal density current capable of moving 150 km/hr! Form ash-flow deposits.
Pyroclastic flow during
an eruption of Mt St Helens
Ash-flow sheets draping
topography
__________________ (volcanic mudflow): a
mixture of water and pyroclastic material to form a concrete-like slurry
capable of moving up to 100km/hr!
Volcanic mudflow formed
during an eruption of Mt St Helens.
Typical Gas Content of
a Hawaiian Basalt
70% - H2O
15 % - CO2
5 % - N
5 % - SO2
Trace - Others: e.g. Cl,
He, Ar, F
Effect of Composition on
Magma Properties and Landforms (table 5.1)
|
Magma composition |
Silica content |
Gas content |
viscosity |
pyroclastics |
Landforms |
|
Mafic |
|
|
|
|
|
|
Intermediate |
|
|
|
|
|
|
Felsic |
|
|
|
|
|
Some volcanic features
formed from central vent eruptions:
Shield volcanoes
Cinder cones
Composite volcanoes
Lava Domes
Calderas
Shield Volcanoes (e.g. Hawaii)
- Formed
mainly of ________________ lavas
- gentle sides: ~___________ degrees
- Can be huge: up to ___________ wide!
- long duration of activity:_______________
-Eruptions
usually ________________
Cinder Cones
(e.g. Sunset Crater)
Formed mainly of _____________________ material
- Steep sides: ~_______ degrees
- Relatively small: ~ __________ wide
- Short -lived: typically ________________
Composite Volcanoes (e.g. Mt Fuji, Mt Ranier)
Formed
mainly by alternating _________________ and _________________
Slopes________________________
in steepness
Relatively
large: ~ ______________wide
Intermittent
eruptions over longtime span: _________________
Eruptions
often highly explosive
Relative sizes of typical
volcanoes
Lava Domes (e.g. in Mt St Helens)
- Formed
by_________________
- Steep-sided and small:
~ ________________
- Associated
with__________________
____________________a constructional depression formed at the mouth of a volcano
Crater of a Composite Volcano
(e.g. Popo)
________________- a large depression (typically
____________ wide, formed by the collapse of a volcano into a partially drained
magma chamber. May have younger domes and cinder cones in it.
Crater Lake Caldera: after
5,700 B.C.
Mount Mazama and the formation
of Crater Lake
_________________:
resistant vents left standing after erosion has removed the volcanic cone
Shiprock: an exposed volcanic
neck
______________________ A volcanic eruption originating
along an elongate fissure rather than a central vent
1971 Fissure eruption,
Kilauea, Hawaii
1783 Laki fissure eruption,
Iceland the largest lava flow in human history)
Types of Volcanic
Hazards
____________: e.g. Hawaii, 1998
_________: e.g. Lake Nyos (Cameroon),1984 - 1700 people
killed
___________: e.g. Mt Pinatubo, 1991,
ClarkAir Force base
_________________:e.g. Mt Pelee, 1902 - 28,000
killed
_______________________:
e.g. Montserrat
___________________ (volcanic mudflows): e.g.
Nevadodel Ruiz, 1985 - 23,000 killed
Mt St Helens,
1980:Case Study
_______________: e.g.
________________,
1883: Case Study - 36,417 killed
- Before and After
1883 A.D.
Effects of the 1883 Eruption:
2/3 of island missing
Ash: thrown
50miles into the air. Blanketed 300,000 square miles. W. Sumatra in the dark
for2 1/2 days
Noise: "loudest
noise in the world" - heard 3,000 miles away
Tsunami: A wave
up to 130 feet high swept up to 10 miles inland - Approx. 36,000 drown
Vesuvius 79 AD:
Pompeii and Herculaneum
Santorina (figure
5.18)
What is the effect of
volcanic eruptions on climate?