Chapter 5
Volcanoes & The Environment
Define - A fissure in the ground through which lava erupts (flows)
& the events that accompany the eruption.
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Process is VOLCANISM
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A volcano is the CONICAL feature formed by the erupted lava.
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Volcanoes & volcanism are often associated with danger, e.g.,
Volcanic Eruption of Mt. Versuvius in Aug. 24, 79 AD - in Italy
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Buried two cities: Pompeii & Herculaneum
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The Burial of Pompeii killed 3,000 people under 6m of pyroclastic
material (fire-broken)
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Unlike Pompeii, Herculaneum, mudflow covered town up to 20 m
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Mudflow resulted from water vapor from volcano mixed with loose ash
Less 30 people died up to date.
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Volcanoes are unpredictable
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Corrosive gases from volcanoes are dangerous to humans & plants
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Fatality from volcanoes vary according to the strength of volcano
Example
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April 10, 1815 - Tambora, Indonesia - > 92,000
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August 27, 1883 - Krakatau, Indonesia, 36,417 people died
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May 18, 1980 - Mt. St. Helens, Washington, 63 killed
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November 13, 1986 - Nevada del Ruiz, Columbia -> Mudflow killed 23,000
people
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February 1993 - Maum (??), Philippines, at least 70 people died
Good Aspects of Volcanoes
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Volcanoes are not all bad.
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Volcanoes are beautiful - used for skiing, hiking, etc. in various
parts of the world.
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Soils around volvanoes are very productive for plants
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Attempt to exhume bodies or other buried ruins in Pompeii in 1738
led to new science of archaeology.
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Form building materials -> blocks, concrete, stone etc.
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Cooling of magmas around volcanoes at depth heats water, & had
been converted to steam to produce electricity -> Italy, Iceland, California,
Nevada & Mexico
Location of Volcanoes
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Found around & along plate boundary
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Places where most of earth’s most dangerous events occur (earthquakes,
etc.)
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Observation, most explosive volcanoes are found around convergent
boundaries (subduction), e.g., the Pacific Rim (around the Pacific Ocean)
->New Zealand, Japan, Alaska, Mexico, Central America
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At divergent boundaries, volcanoes are milder & some productive
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More volcanoes in northern hemisphere relative to southern hemisphere
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Dangerous volcanoes & volcanic centers are found in the US (Washington,
Oregon & California)
VEI GDnbsp;
CCH(km)
QuD
CL
0 Non-explosive
<0 - 1
Gentle
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1 Small
0.1 - 1
Effusive Strombolian
Hawaiian
2 Moderate
1 - 5
Explosive
3 Moderate, Large
3 - 15
Explosive Volcanian
4 Large
10 - 25
Explosive Volcanian
5 Very large
25
Cataclysmic Plinian
6
Pyroclastic Plinian
7
Colossal
Plinian
8
Ultra
Plinian
Measurement of Volcanoes
Scales based on criteria for description of eruption’s explosivity.
The Volcanic Explosivity Index (VEI) ranges from 0 - 8
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materials ejected
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height to which materials rose
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duration of th e explosion
General Description (GD)
Cloud Column Height (CCH)
Qualitative Description (QuD)
Classification (CL)
Types of Volcanoes
Quiet Eruptions
Shield Cones: Convex upward shield - like bodies of lava
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Produced from gentle outpouring
(Figure here) Fissure Eruption
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Eruption of lava from long cracks.
Explosive Eruptions
Composite Cone: Concave upward body of lava
(Figure here)
Lava Dome: Bulb-like masses of high -silica, glassy lava
(Figure here)
Cinder Cones
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Small & numerous cones (Figure here)
Prediction & Mitigation of Volcanoes
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Currently being predicted to a large degree
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Using studies of seismic activity
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Mitigation (by diversion) has been done successfully in places, e.g., Hawaii,
Iceland
(Read)
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