Transcript urban_volcanoes

Introduction to Volcanoes
Origin of magma
• Magma originates when essentially solid
rock, located in the crust and upper mantle,
melts
Origin of magma
• Factors:
– Role of heat
• Earth’s natural temperature increases with depth
(geothermal gradient) is not sufficient to melt rock
at the lower crust and upper mantle
• Additional heat is generated by
– Friction in subduction zones
– Crustal rocks heated during subduction
– Rising, hot mantle rocks
Origin of magma
• Factors:
– Role of heat
– Role of pressure
• Increase in confining pressure causes an increase in
melting temperature
• Drop in confining pressure can cause decompression
melting
– Lowers the melting temperature
– Occurs when rock ascends
Origin of magma
• Factors:
– Role of heat
– Role of pressure
– Role of volatiles
• Primarily water
• Cause rock to melt at a lower temperature
• Play an important role in subducting ocean plates
Origin of magma
• Factors:
–
–
–
–
Role of heat
Role of pressure
Role of volatiles
Partial melting
• Igneous rocks are mixtures of minerals
• Melting occurs over a range of temperatures
• Produces a magma with a higher silica content than
the original rock
Plate Tectonics and Magma Generation
How Magma Rises
Where do volcanoes form?
• Volcanoes form at:
– Hot Spots (10% of all volcanic activity)
Where do volcanoes form?
• Volcanoes form at:
– Hot Spots (10%)
– Spreading Centers (80% of all volcanic activity)
Where do volcanoes form?
• Volcanoes form at:
– Hot Spots (10%)
– Spreading Centers (80%)
– Convergent Plate
Boundaries
(10% of all volcanic
activity)
• Ocean–Continental
• Ocean – Ocean
Tectonic Settings and Volcanic Activity
Lithospheric Plates
Volcanoes of the World
Volcanic Eruptions
• Factors that determine the violence of an
eruption
– Temperature of the magma
– Composition of the magma
– Dissolved gases in the magma
• The above three factors actually control the
viscosity of a given magma which in turn
controls the nature of an eruption
Volcanic Eruptions
• Factors affecting viscosity
– Temperature
• hotter magmas are less viscous
Volcanic Eruptions
• Factors affecting viscosity
– Temperature
– Composition (silica content)
• High silica – high viscosity (e.g., rhyolitic lava)
• Low silica – more fluid (e.g., basaltic lava
Volcanic Eruptions
• Factors affecting viscosity
– Temperature
– Composition
– Dissolved gases (volatiles)
•
•
•
•
Mainly water vapor and carbon dioxide
Gases expand near the surface
Provide the force to extrude lava
Violence of an eruption = how easily gases escape
Viscosity, Temperature and Water
Content of Magmas
Rock Type
SiO2 content
Basalt
Andesite
Rhyolite
45-55%
55-65%
65-75%
800 – 1,000 ºC
600-900 ºC
Magma
1,000 – 1,250ºC
temperature
Viscosity
Low
increasing
High
Gas escape from
magma
Easy
increasing
Difficult
Eruptive style
Peaceful
increasing
Explosive
Plate-Tectonic Setting of
Volcanoes Revisited
• Why more volcanic
activity at spreading
centers?
– Low SiO2 content
– High temperature
– Low pressure as plates pull
apart
• Fluid basaltic lavas
generally produce quiet
eruptions
• Why less volcanic
activity at subduction
zones?
– High SiO2 content
– Lower temperatures
– Higher pressures
• Highly viscous lavas
produce more explosive
eruptions
Volcanic Explosivity Index
Plume
Height
VEI
Description
Volume
Classification
How often
Example
0
non-explosive
< 100 m
1000s m3
Hawaiian
daily
Kilauea
1
gentle
100-1000 m
10,000s m3
Haw/Strombolian
daily
Stromboli
2
explosive
1-5 km
1,000,000s m3
Strom/Vulcanian
weekly
Galeras, 1992
3
severe
3-15 km
10,000,000s m3
Vulcanian
yearly
Ruiz, 1985
4
cataclysmic
10-25 km
100,000,000s m3
Vulc/Plinian
10's of years
Galunggung, 1982
5
paroxysmal
>25 km
1 km3
Plinian
100's of years
St. Helens, 1981
6
colossal
>25 km
10s km3
Plin/Ultra-Plinian
100's of years
Krakatau, 1883
7
super-colossal
>25 km
100s km3
Ultra-Plinian
1000's of years
Tambora, 1815
8
mega-colossal
>25 km
1,000s km3
Ultra-Plinian
10,000's of years
Yellowstone, 2 Ma
Source: http://volcano.und.edu/vwdocs/eruption_scale.html
Volcanoes
• General features
– Conduit, caries gas-rich magma to the surface
– Vent, the surface opening (connected to the
magma chamber via a pipe)
– Crater, steep-walled depression at the summit
• Caldera (a summit depression greater than 1 km
diameter)
– Parasitic cones
– Fumaroles
Volcano Types
Types of volcanoes
• Shield volcano
–
–
–
–
Low Viscosity, Low Volatiles, Large Volume
Broad, slightly domed, very large
Primarily made of basaltic (fluid) lava
Hawaiian Islands
Types of volcanoes
• Cinder cone
–
–
–
–
–
Low Viscosity, Medium Volatiles, Small Volume
Built from ejected lava fragments
Steep slope angle
Rather small size
Frequently occur
in groups
Types of volcanoes
• Composite cone (or stratovolcano)
–
–
–
–
High Viscosity, High Volatiles, Large Volume
Most are adjacent to the Pacific Ocean
Large in size
Interbedded lavas and pyroclastics
Types of Volcanoes
• Composite cone (or stratovolcano)
– Often produce nuée ardente
– May produce a lahar - volcanic mudflow
A size comparison of the three
types of volcanoes
Other volcanic landforms
• Calderas
– High Viscosity, High Volatiles, Very Large Volume
– Steep walled depression at the summit formed by
collapse
– Size exceeds one kilometer in diameter
How Calderas Form
Other volcanic landforms
• Fissure eruptions and lava
plateaus
– Low Viscosity, Low Volatiles,
Very Large Volume
– Basaltic lava extruded from
crustal fractures
– Incredibly large volumes of lava
pour out of fissures over 2-3
million years
– Can affect global climate
Other volcanic landforms
• Lava Domes
– Bulbous mass of congealed lava
– Most are associated with explosive eruptions of
gas-rich magma
– One is currently developing in Mt. St. Helens
Volcanism In Urban Areas
California Volcanoes
Volcano Name
Volcano Type
Location
Shasta
Stratovolcano
US - California
Medicine Lake
Shield volcano
US - California
Brushy Butte
Shield volcano
US - California
Big Cave
Shield volcano
US - California
Twin Buttes
Cinder cones
US - California
Tumble Buttes
Cinder cones
US - California
Lassen Volc Center
Stratovolcano
US - California
Eagle Lake Field
Fissure vents
US - California
Clear Lake
Volcanic field
US - California
Mono Lake Volc Field
Cinder cones
US - California
Mono Craters
Lava domes
US - California
Inyo Craters
Lava domes
US - California
Long Valley
Caldera
US - California
Red Cones
Cinder cones
US - California
Ubehebe Craters
Maars
US - California
Golden Trout Creek
Volcanic field
US - California
Coso Volc Field
Lava domes
US - California
Lavic Lake
Volcanic field
US - California
Amboy
Cinder cone
US - California
Source: http://www.volcano.si.edu/world
Evaluation Of Volcanic Risk In
California
• Population changes since 1915
– Last violent eruption was Mt Lassen in 1915
• California population was 2,800,000
• 1999 population was >34,000,000
– Some of this population has extended into
volcanically hazardous areas
Evaluation Of Volcanic Risk In
California
• The 3 Most Dangerous Areas in California
– Mt Shasta especially around Weed on west side
– ashflows
– Mt Lassen - mudflows and rock avalanches
– Long Valley - Mammoth Mountain area
How Volcanoes Cause Damage
•
•
•
•
•
•
Lava Flow Eruption
Explosions and Ashflows
Ashfall
Mudflows/Lahars
Gas
Caldera Collapse
Lava Flow Eruption
• Kapoho, Hawaii
– The January 1960
flank eruption followed
the December 1959
summit eruption
– Seismic swarms
indicated the eruption
was coming
Lava Flow Eruption
• Kapoho, Hawaii
– January 13, 1960
• Increased seismic
activity
• Cracks throughout town
of Kapoho along
Kapoho fault
• Residents evacuate
• 7:35 PM eruption began
(fissure)
Lava Flow Eruption
• Kapoho, Hawaii
– January 15, 1960
• A’a flows 6 m thick
builds out 100 m past
original shoreline
• Fissure eruptions
produce fountains 200 –
275 m in height &
creates a cinder cone
• A’a flow reaches
Higashi Pond
• Town of Kapoho
threatened
Lava Flow Eruption
• Kapoho, Hawaii
– January 18-19, 1960
• Higashi Pond fills with
lava
• Fountains of lava 365425 m
• Cinder cone partially
collapses, sends lava
towards village
• Kuki`i-Kapoho Lava
Barrier built
Lava Flow Eruption
• Kapoho, Hawaii
– January 20, 1960
• A’a lava flow destroys
barrier
• Second barrier built –
lasted 7 days
• Cinder Cone now 72 m
high
Lava Flow Eruption
• Kapoho, Hawaii
– January 25, 1960
• Third barrier
constructed (most
massive)
• Cinder Cone now 92 m
high
• Increased ash and
pumice fall
Lava Flow Eruption
• Kapoho, Hawaii
– January 27, 1960
• All barriers failed
• Town destroyed
Lava Flow Eruption
• Kapoho, Hawaii
– January 30-31, 1960
• Eruption slows and finally
ceases by February 13th.
• lava flows covered more
than 10 km2
– 2 km2 of new land
• 122 million m3 lava
erupted
• 7.5 million m3 pyroclastic
material erupted
• 3rd largest Kilauea
eruption in 20th century
Explosions and Ashflows
• Ashflows are mixtures of hot gas and ash
that move very quickly along the ground
• Examples:
– Mt. Vesuvius
– Mt. Shasta
– Mt. St. Helens
Explosions and Ashflows
• Mt. Vesuvius
– 79 AD eruption
• 20 mile (32 km) column of
ash (estimated)
• 1 cubic mile (4 cubic
kilometers) of ash was
erupted in about 19 hours
Explosions and Ashflows
• Mt. Vesuvius
• 10 feet (3 m) of
tephra fell on
Pompeii, burying
the town
• Herculaneum buried
under 75 feet (23 m)
of ash deposited by
a pyroclastic flow
• ~3,360 deaths
Explosions and Ashflows
• Mt. Vesuvius
– 1631
• Mudflows and lava flows kill 3,500 people
– 1875-1906
– 1913-1944
• March 1944 eruption
destroyed the villages of
San Sebastiano al Vesuvio,
Massa di Somma and part
of San Giorgio a Cremano
Postcard: “Vesuvio - Eruzione 9
Aprile 1906”
http://volcano.und.edu/vwdocs/volc_images/europe_wes
t_asia/ves_early.html
Explosions and Ashflows
• Mount Shasta, California
– Second tallest in the
Cascade Range
– Erupted 11 times over last
3,400 years
• 3 times last 750
• Last eruption - 1786
Explosions and Ashflows
• Mount Shasta, California
– Slopes covered with
pyroclastic flows such as
lahars
– Event 300,000 years ago
deposited 8x amount of
debris as did the Mt. St.
Helens 1980 event
Mt. Shasta – November 1998
Explosions and Ashflows
• Mt St. Helens
– May 18, 1980 Eruption began in late March and
climaxed
• 5.1 magnitude earthquake on nearby fault
• A landslide followed and caused a huge explosion
– 0.5 cubic miles of rock fell into Spirit Lake causing
mudflows
– Ashflow traveling 150 miles/hr traveled 18 miles
devastating 215 sq miles (Temperature = 300°C)
Mt. St. Helens
New Dome
Vent
1980-1986
Dome
Rock
Glacier
http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=16721
Mt. St. Helens, October 1, 2004
http://www.nasa.gov/vision/earth/lookingatearth/mshelenslidar.html
Ashfall
• Huge areas may be covered by volcanic ash
– Crater Lake ash covers the entire Northwest
• Damage to urban areas can be enormous
–
–
–
–
Crops are destroyed threatening the food supply
Public water contaminated
Buildings collapse under weight of ash
Air travel disrupted
Mudflows
• Ways that volcanoes make mudflows
–
–
–
–
Burn vegetation
Erupt ash
Produce rain
Melt glaciers or displace lakes
Mudflows
• Lassen Volcanic Center
– Comprised of:
•
•
•
•
Lassen Peak
Brokeoff stratovolcano (andesitic)
dacitic lava dome field
and peripheral small andesitic shield volcanoes and
large lava flows
Mudflows
• Lassen Volcanic Center
– History
• 600,000 y.– formation of Brokeoff volcano
• 400,000 y.- dozen dacitic lava domes including
Bumpass Mountain, Mount Helen, Ski Heil Peak,
and Reading Peak formed off north flank of
Brokeoff
• 28,000 y.– Lassen Peak formed
• 1,100 – 1,000 y.– Chaos Crags formed
• ~1600? – Cinder Cone formed
Source: http://www.volcano.si.edu/world
Mudflows
• Lassen Volcanic Center
– Lassen Peak
• Volcano Type:
Stratovolcano
• Last Known
Eruption: 1917
• Summit Elevation:
3187 m (10,456 feet)
Source: http://www.volcano.si.edu/world
Mudflows
• Lassen Volcanic Center
– Lassen Peak
• Began erupting May 1914
– July 18, 1914 – Huge ash cloud ejected 3,350 m into
atmosphere
– May 16 – 18, 1915 – Lava oozed out of crater
» Red glow from the hot lava visible at night 34
kilometers away.
– May 19, 1915 – avalanche of hot rocks combined with
snow and triggered a lahar that extended more than 50 km
– Eruptions continued through 1917, then ceased
The northeast flank of Lassen Peak photographed on 22 May 1915 by B.F. Loomis from the position
marked on Fig. 5, several hours prior to the 22 May eruptions. Peaks labeled A and B can be used as
registration points when comparing Fig. 2a and Fig. 3. The label "hot rock" was written on the original
glass plate by Loomis over the image of a piece of 19 May dacite lava and alludes to the fact that the
rock was still too hot to touch ~48 hr after it was erupted. From: http://barsoom.msss.com/earth/lassen/
Mudflows
• St. Helens, Washington
– Mudflow was caused by the displaced Spirit
Lake
– Mudflow went 60 miles to the Columbia River
– 45 million cubic yards sediment entered
Columbia River
Surface details of the debris (mud) flow on
the North Fork of the Toutle River near
Coldwater Creek (see map). There is
approximately 50 feet of relief between the
pond and the mudflow surface.
http://www.iris.edu/gifs/slides/sthelens/slideshow/pages/16.htm
Devastation occurring at the log camp on
the South Fork Toutle River - overturned
trucks and caterpillers.
http://vulcan.wr.usgs.gov/Volcanoes/MSH/Images/may18_devasta
tion.html
Mudflows
• Nevada del Ruiz,
Columbia
– 2 eruptions on Nov 13,
1985
• Summit glaciers melted
• Mudflows travelled in all
directions from the
summit
• Mud traveling 30 mph
and 50 feet deep buries
Amero 30 miles away
• 25,000 killed
Mudflows
• Mt. Rainier
– Mudflows threaten
the towns and
villages blow this
dangerous volcano
– Evacuation plans
and drills are the
key to survival
Gas
• Cameroon – Lake Nyos
– Type of volcanism:
Maar
• A volcanic crater that is
produced by an explosion
in an area of low relief, is
generally more or less
circular, and often
contains a lake, pond, or
marsh.
(http://volcano.und.nodak.edu/vwdocs/
glossary.html)
Landsat image of Lake Nyos
processed by Sarah Sherman, April
2000.
Gas
• Cameroon – Lake Nyos
– Maars in Oku volcanic
field formed during an
explosive eruption of
carbon dioxide gas
– Lake Nyos formed
about 400 years ago
Gas
• Cameroon – Lake Nyos
– August of 1986
• 1 km of CO2 released
• ~1700 people killed up
to 26 km away
– August of 1984
• smaller gas burst from
Lake Monoun
• 37 people killed
Photo by Jack Lockwood, U.S. Geological Survey
Gas
• Cameroon – Lake Nyos
– Only three lakes in the world are known to
contain high concentrations of dissolved gas in
their bottom waters:
• Lakes Nyos and Monoun in Cameroon
• and Lake Kivu in East Africa.
– Only Lakes Nyos and Monoun are known to
have recently released gas resulting in the loss
of human life.
Using Science to Solve Problems: The Killer Lakes of Cameroon By Dr. George Kling
Caldera Collapse
• Believed to be caused by magma evacuating
its chamber
• Caldera eruptions in New Zealand could
damage cities like Auckland
• Famous (or infamous) collapsed calderas:
–
–
–
–
Crater Lake, Oregon
Yellowstone, Wyoming
Long Valley Caldera, California
Krakatoa & Toba, Indonesia
Caldera Collapse
• Crater Lake
– About 6,850 years
ago Mount Mazama
erupted
– Produced Crater
Lake
– Eruption released
~12 cubic miles (50
cubic km) of
magma to the
surface..
Caldera Collapse
• Yellowstone, Wyoming
– A Hot Spot Volcano
– Three very large eruptions
in the last 2 million years
– 2.0, 1.3, and 0.6 million
years ago
– Still active today
The Snake River Plain and the
Yellowstone Hot Spot
http://volcano.und.edu/vwdocs/volc_image
s/north_america/yellowstone.html
Caldera Collapse
• Long Valley Caldera, California
– One of the largest Quaternary
rhyolitic volcanic centers in
North America
– Caldera is 10 by 20 miles
(15 by 30 km)
Caldera Collapse
• Long Valley Caldera, California
– Volcanic activity began
in the area ~3.6 million
years ago
– Catastrophic eruption
~730,000 years ago
• Bishop Tuff
Caldera Collapse
• Long Valley Caldera, California
– Mammoth Mountain formed along the
southwest rim of
Long Valley caldera
from 200,000 to
50,000 years ago
Caldera Collapse
• Long Valley Caldera, California
– Current issues
• Carbon Dioxide and Helium Discharge from
Mammoth Mountain
Horseshoe Lake and Mammoth
Mountain
Caldera Collapse
• Long Valley Caldera, California
– Current issues
• 1980 EQs resulted from
magma rising toward
the surface
• Currently being
monitored.
Caldera Collapse
• Krakatoa
– Inactive for 200 years before 1883
– Eruption began in May and climaxed on August
26 & 27
•
•
•
•
VEI = 6
Lava, ash, and gas erupted
Ash covered neighboring islands
Pumice choked the Sunda Strait
Caldera Collapse
• Krakatoa
– Suddenly 10 sq miles
collapsed
– A strong Earthquake
occurred
– Sound could be heard
3000 miles away
– Tsunami over 100 feet
high killed 36,000
people in Java and
Sumatra
Caldera Collapse
• Toba, Sumatra
– Last erupted 74,000 years
ago
• The resultant caldera formed
Lake Toba, 100 km long, 60
km wide
• 3,000 km3 of ejected material
• large quantities of SO2
Caldera Collapse
• Toba, Sumatra
– Ash and SO2 ejected
into the stratosphere
reflects solar radiation
back into space
– Est. global cooling of
5ºC
– 15 ºC in temperate &
high latitudes
– Genetic research on
mitochondrial DNA
Caldera Collapse
• The Eruption Of Thera - An Entire
Civilization Destroyed
– Located in the eastern Mediterranean
• Southern most of Cycladic Islands
The Eruption Of Thera - An
Entire Civilization Destroyed
• The Minoan Civilization
– Minoans developed an advanced, maritimebased civilization in the eastern Mediterranean
between 2000 and 1450 B.C.
The Eruption Of Thera - An
Entire Civilization Destroyed
– Civilization was most developed on Crete
•
•
•
•
Palaces built at Knossos, Phaestos, and Zakros
Aqueducts and sewage systems
Good ports
Advanced art in painting and ceramics
The Eruption Of Thera - An
Entire Civilization Destroyed
– Thera or the Minoans are probably Plato's lost
Atlantis
• From Plato's Timaeus - "But afterwards there
occurred violent earthquakes and floods and in a
single day and night of misfortune the island of
Atlantis disappeared in the depth of the sea. For
which reason the sea in those parts is impassable
because there is a shoal of mud in the way."
The Eruption Of Thera - An
Entire Civilization Destroyed
• The Eruptions
– The first historic eruption occurred in 1500
B.C.
• Thera was evacuated permanently
The Eruption Of Thera - An
Entire Civilization Destroyed
• The Eruptions
– Caldera collapse occurred on 1450 C.
• 32 sq miles collapsed into the Mediterranean
• A tsunami spread through the Mediterranean hitting
Crete perhaps 300 feet high
• Earthquakes preceded and followed the eruption
• Ash over 1 foot deep destroyed crops on Crete starvation followed
• All Minoan population centers were destroyed
simultaneously
Exposure of about 150 feet (50 m) of Minoan
tephra. The tephra consists of pumice,
pyroclastic surge, and pyroclastic flow
deposits. Photography copyrighted by Robert
Decker.
http://volcano.und.nodak.edu/vwdocs/volc_images/europe_w
est_asia/santorini.html
Akroteri, a Minoan city on the south part of
Thera, is being excavated. About 3-6 feet (1-2
m) of ash fell on the city which had a
population of about 30,000. The residents
appear to have been successfully evacuated
prior to the eruption. No bodies have been
found in the ash like those at Vesuvius.
Archeologists also reported that movable
objects had been taken from the city.
Photography copyrighted by Robert Decker.
http://volcano.und.nodak.edu/vwdocs/volc_images/europe_w
est_asia/santorini.html
The Eruption Of Thera - An
Entire Civilization Destroyed
• The Mycenaeans rose to rule the
Mediterranean
– Trade collapsed as piracy took over
– Agamemnon led a prolonged war against Troy
around 1250 B.C.
• Mycennaean resources were greatly depleted.
• Agememnon was murdered by his wife upon return
to Mycenae
The Eruption Of Thera - An
Entire Civilization Destroyed
• Dorian Barbarians conquered the
Mycenaeans around 1100 B.C.
– Greece retreated to Stone Age conditions
similar to the year 3000 B.C.
• The Archean period began
~ End ~