Volcanoes and volcanism

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Volcanoes and volcanism

• Volcanoes represent venting of the Earths
  interior
• Molten magma rises within the Earth and is
  erupted either quietly (lavas) or violently
  (pyroclastics)

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Quiet vs. violent activity

• Quiet eruptions tend to produce lava flows, which
  are not so dangerous
• Explosive eruptions produce fragmental, or
  pyroclastic, material these are dangerous

• Two controls on explosivity are (1) the silica
  content and (2) the gas content of the magma
• Basalt 50 SiO2, gas-poor
• Andesite 60 SiO2, gas-rich
• Rhyolite 70 SiO2, gas-rich
• Magmas with higher silica contents are more
  viscous

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Global distribution of volcanoes
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Magma generation at mid-ocean ridges

• In these zones, the mantle rises and melts,
  producing magma of silicate composition
• the magma continues to rise, and erupts mainly as
  basaltic lava flows

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Magma generation at hot spots

• Magmas at hot spots are derived from deep within
  the mantle
• the magmas are fed by deep mantle plumes which
  are stationary relative to the drifting tectonic
  plates

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Magma generation at subduction zones

• During subduction, the subducted oceanic plate is
  heated as it plunges into the mantle
• At a depth of 80-120 km, melting begins, and
  volcanoes are produced which parallel the
  subduction zone

Andesitic magmas are typical of these volcanoes
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Plate tectonics and volcanism
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Volcanic hazards of North America
Active volcanoes have erupted at least once in
the past 10,000 years The most active volcanoes
(in red) are those associated with subduction
zones
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Volcanic hazards of Canada
Canada has active volcanoes (black triangles)
which pose a potential threat in B.C. Another
major hazard is ashfall from explosive eruptions
of Cascade volcanoes in Washington state
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Volcano types
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Volcano types cinder cones

• Cinder cones are volcanoes which erupt only
  during one episode
• They are explosive, but small in size
• The cone is a pile of pyroclastic debris which
  piles up at the angle of repose

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Volcano types cinder cones

• The cinders are generally of basaltic composition
• The eruptive activity typically lasts a few
  months or years

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Cinder cones Parícutin

• Parícutin volcano in Mexico is a classic cinder
  cone
• The region contains many cinder cones
• It consists of both pyroclastics and lava

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Parícutin - lava flows
These images shows the development of lavas in
1943 and in 1951-52 Red areas show new lava flows
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Parícutin - five views taken from Luhr and Simkin
(1993)

• The eruption was preceded by about 1½ months of
  felt seismicity
• The eruption began in a farmers field on 20
  February 1943
• It erupted for a comparatively long (?) time
  (1943-1951)

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Parícutin

• Here is a photo of the volcano showing the
  classic form of cinder cones
• In the foreground is the obviously distressed
  farmer, Dionisio Pulido

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Parícutin

• This is a view of the volcano in March 1944
• In the foreground, note the flat-lying lava flows
  from the volcano

lava
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Parícutin

• The partly unfinished towers of San Juan
  Parangaricutico surrounded by 1944 lava flows
  from the volcano
• Note how the lava fills, but does not destroy,
  the church

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Parícutin

• Note how the percentage of pyroclastic material
  declines steadily with time
• while the opposite is observed for lava
• The daily mass eruption rate also declines
  steadily

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Volcano types shield volcanoes

• Shield volcanoes are broad, gently sloping
  volcanoes
• They are composed mainly of basaltic lava flows
• This is a view of Mauna Loa, Hawaii, from the
  cinder cones of Mauna Kea

Mauna Loa is the tallest volcano on Earth, as
measured from the sea floor
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Shield volcanoes on Mars

• Other planets also have shield volcanoes
• This is the largest shield volcano in the solar
  system, Olympus Mons on Mars
• Check out the scale !

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Shield volcanoes Earth vs. Mars

• Red Hawaiian chain, which is superimposed on
  Olympus Mons
• this says it pretty well, I think !

Mauna Loa is about here
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Volcano types stratovolcanoes

• Stratovolcanoes consist of alternating layers of
  lava and pyroclastics
• They are dominantly andesitic in composition
• These volcanoes are typical of subduction zones

Mt. St. Helens (pre-1980)
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Shield volcanoes vs. strato-volcanoes

• Note the morphological differences between the
  two types
• This is mainly the result of (1) the proportion
  of pyroclastics, and (2) the magma composition
  (viscosity)

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Volcano types calderas
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Crater Lake caldera

• Crater lake is a medium-sized caldera, about 10
  km in diameter
• The upper parts of a big stratovolcano (Mt.
  Mazama) once rested on top
• Mt. Mazama is now at the bottom of Crater Lake !

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Yellowstone caldera

• Yellowstone is a good example of a big
  continental caldera
• It is rhyolitic in composition and formed about
  600,000 years ago
• It actually sits within an older, much larger
  caldera extending west into Idaho

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Martian calderas

• Here are two Martian calderas. Again, you should
  appreciate the difference in scale between these
  structures and those on Earth

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Volcanic activity

• In the following slides, I will give you some
  examples of volcanic activity
• lava flows, including flood basalts
• lava domes
• pyroclastic falls and pyroclastic flows
• lahars and debris avalanches
• volcanic gases

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Volcanic activity lava flows

• This is a basalt lava flow in a channel
• Due to its low silica content and high
  temperature, it is quite fluid (but stickier than
  maple syrup)
• Yet lava usually flows fairly slowly

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Pahoehoe lava
Do you want to walk on pahoehoe ?
This is a Hawaiian term for smooth, ropy lava It
generally exhibits fluid-like textures
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Aa lava

• This type of lava is quite blocky on the surface,
  and comparatively cool
• Yet below the surface, the lava is fairly massive
  and much hotter
• Do you want to walk on aa ?

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Fire fountaining

• Sometimes, basaltic lava can contain lots of gas
• Then, small explosive eruptions form fire
  fountains
• As partially liquid drops fall back to the
  ground, they may coalesce to form a lava flow

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Flood basalts

• The previous examples represent small-scale
  activity
• But basaltic eruptions can be huge, forming lava
  plateaus
• These huge outpourings may occur quickly (1-3 Ma)
  and may contribute to mass extinctions

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Global distribution of large igneous provinces
(LIPS)
Mainly flood basalts
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Lava domes
Mt. Unzen, Japan
Unzen began growing a lava dome in mid-1991. The
dome complex continued to grow until 1995
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Lava domes at Unzen

• This dome was the first to be erupted, in May
  1991
• The lava is silica-rich and thus highly viscous
  (sticky) and cannot easily flow
• Thus it tends to form steep-sided domal structures

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Volcanic activity lava domes

• By early 1995, the dome complex had grown
  substantially and was highly oversteepened
• As pieces of the dome broke off, they would
  fragment, creating pyroclastic flows

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Volcanic activity pyroclastic falls

• During explosive volcanic eruptions, ash falls
  downwind of the volcano
• In the case of very large eruptions, the ash may
  be deposited over a vast area

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Volcanic activity pyroclastic flows

• Pyroclastic flows are suspensions of hot
  pyroclastic material, air, and gas which descend
  under the influence of gravity
• Their velocity is generally very high (50-500
  km/hr)
• This example is a flow from Mt. St. Helens

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Volcanic activity pyroclastic flows

• This is another example, descending the slopes of
  Unzen volcano after part of the dome has
  collapsed
• The flow has a dense core which is hidden by the
  billows of ash which are rising

Unzen, 24 June 1993
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Volcanic activity lahars

• Lahar is an Indonesian word for volcanic debris
  flow
• Lahars are flows of water and loose volcanic
  debris
• They are especially prevalent at snow-clad and
  ice-clad volcanoes

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Volcanic activity lahars

• To better understand lahar formation,
  experimental flumes are used to create
  small-scale lahar flows

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Volcanic activity lahars

• This is the product of an experimental lahar
• The different dark layers represent progressive
  accumulation of sediment from a series of flow
  waves

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Volcanic activity debris avalanches

• Sometimes a volcanic edifice is weakened
• Wholesale collapse of part of the volcano may
  ensue
• During collapse, a debris avalanche occurs, and a
  scalloped scar remains

Unzen volcano, with the 1792 scar in the
foreground
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Volcanic activity gases

• Volcanic gases are typically highly acid
• Major constituents include H2O, CO2, HCl, SO2,
  and HF
• This photo shows gas emission from Masaya volcano
  in Nicaragua

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Volcanic activity gases

• This is also Masaya volcano
• but this photo was taken from the space shuttle
• it shows the gas plume being blown out over the
  Pacific Ocean

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Volcanic activity gases

• About 15 km downwind from Masaya, the coffee crop
  is adversely affected by the acid gases

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Sizes of volcanic eruptions

• The Volcano Explosivity Index (VEI) is similar to
  the Richter scale for quakes
• It is logarithmic
• It emphasizes the degree of explosivity of
  eruptions

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VEI
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Volcanic activity through time

• Are volcanoes more active today than in the past?
• -in terms of the historic record
• -in terms of the geologic record

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Case history Mount St. Helens, Washington state,
USA
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Tectonic setting of Mt. St. Helens
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Previous eruptions of Mt. St. Helens

• The volcano is the most active of all the
  Cascades volcanoes
• Based on previous activity, there was a fairly
  high probability that the volcano would again
  erupt before the millenium

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Stages at Mt. St. Helens

• Stage 1 precursory activity, 20 March - 18 May
  1980
• Stage 2 the climactic eruption of 18 May 1980
• Stage 3 post-climactic activity, 1980-present

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Stage 1 Precursory activity eruptions

• The first phreatic eruption occurred on 27 March
  1980
• then explosions continuedthe volcano was
  preparing itself
• The eruptions of 13, 18 April consisted of steam
  and ash

27 March 1980 eruption
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Precursory activity seismicity

• A magnitude 4.1 earthquake was recorded on 20
  March 1980 under the volcano
• By 1 April, harmonic tremor was observed
  (continuous seismic signal of similar wavelength)
• this is a pretty good indication that magma is
  involved

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A seismogram from seismic station RAN on 2 April
showing the occurrence of harmonic tremor
Harmonic tremor
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Precursory activity deformation

• A bulge was first detected on the NNE flank of
  the volcano on 19 April 1980
• Deformation was as high as 5 feet/day !
• This was an indication that magma had moved into
  the volcano itself
• At the same time, eruptive activity decreased
  during 14-23 April

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Development of the bulge
bulge
28 September 1979
17 May 1980
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Precursory activity gas emissions

• Although some sulfur dioxide was detected, not
  very much was actually being emitted
• This suggests that the volcano had somehow sealed
  itself, and that pressure was building
• This interpretation is consistent with (a) the
  bulge and (b) decreased eruptive activity

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Stage 2 The climactic eruption, 18 May 1980

• At 0832 local time, a M 5.1 earthquake struck the
  volcano
• A large portion of the volcano slid away
• This simultaneously developed a debris avalanche
  and a lateral blast

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Sliding...
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Sliding and depressurizing...
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and blasting
And blasting
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The blast
Note trees still standing

• The lateral blast was comparatively cool at
  100-300 C
• But its speed approached 500 km/hr
• It was therefore devastating to a very large area
  (180, up to 20 km distance)

Tree blowdown by the blast
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Sector collapse and the debris avalanche

• The sector collapse reduced the height of the
  volcano substantially
• A horseshoe-shaped amphitheatre was formed
• The avalanche deposit was emplaced in the Toutle
  River valley

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Dispersal of ash over the NW USA and western
Canada
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Lahars

• The mixing of melted snow and ice with loose
  pyroclastic material created the perfect
  conditions for lahars
• Also, the debris avalanche deposit was
  water-saturated, producing lahars

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Debris carried by lahars
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Note the high-water mud marks on the trees
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Final costs from the 18 May devastation

• 35 people dead (it was a Sunday)
• 22 people never found
• 2.7 billion US in damage
• contrast this with the 10-20 billion in losses
  from the 1989 Loma Prieta and 1994 Northridge
  earthquakes

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Would you call this event a disaster?
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Stage 3 Post-climactic activity

• Subsequent activity consisted of generally
  diminishing explosive eruptions
• By mid-late 1980, lava domes began to grow in the
  amphitheatre
• these were repeatedly destroyed by small
  explosive eruptions

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Explosive eruptions
Explosive activity diminished gradually over the
next several years
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Pyroclastic flows
Spectacular pyroclastic flows were observed
forming from the crater These are some of the
best examples you will ever see
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Pyroclastic flows - note big rounded pumices
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Dome growth-destruction cycles
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Dome growth-destruction cycles
Early lava dome
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Dome growth-destruction cycles
Late lava dome
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Case history Nevado del Ruiz volcano, Colombia

• Nevado de Ruiz is 5389 m, ice-clad volcano in the
  Colombian Andes
• Eruptions occurred in 1595, 1845, and 13
  November 1985
• It is a subduction-related stratovolcano

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View of Ruiz on 26 November 1985
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View of summit and Arenas crater, late November
1985. Note fresh ash
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Tectonic setting of Nevado del Ruiz
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Precursory activity, 1984-1985

• Increased fumarolic activity in the crater was
  observed in late 1984
• Anomalous seismicity also was recorded
• This figure shows banded tremor (a continuous
  seismic signal) on 7 September 1985
• Small eruption on 11 September 1985

Nereidas Station, 7 September 1985, duration of
bands 15-20 minutes. From Martinelli (1990)
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Hazards maps

• Two different versions of the Ruiz hazard map
  were published
• The first was presented on 7 October 1985, about
  1 month after the 11 September eruption
• The second version was completed on 12 November
  1985, one day before the big eruption

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Both versions clearly show the lahar danger to
Armero
The lahar danger is serious because the volcano
has a ready source of water - glacier ice on it
summit
Maps from Parra and Cepeda (1990)
7 Oct. 1985
12 Nov. 1985
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Ruiz - 13 November 1985

• The main eruption occurred at 908 PM local time,
  preceded by a smaller event at 305 PM
• The eruption was significantly smaller than that
  of Mt. St. Helens in 1980
• The eruption produced ashfall to the northeast of
  the volcano
• The worst results were devastating lahars from
  melting of the summit ice by the heat of the
  eruption

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Ashfall and lahars
From Naranjo et al. (1986)
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Lahars

• The lahars moved at speeds up to 60 km/hr
• The lahars were valley-confined in the mountains
  the lahars grew in volume as they incorporated
  debris by erosion (bulking)
• The lahars spread as they emerged at the mountain
  fronts

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Lahar deposits in the Gualí River valley. Bulking
occurred here
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Villages above the river valleys were protected
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Principal lahar channels (from Pierson et al.,
1990)
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Lahars in Armero

• Although several towns were affected, by far the
  worst was Armero
• At Armero, the lahars arrived in a series of
  pulses
• The first pulse arrived 2-2½ hours after the
  eruption onset
• The pulses continued for about 1½ hours

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Spreading and slowing of lahars as they emerged
from the mountains
Armero afterwards
High ground
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Armero

• Some of the few remaining structures in Armero
• The lahar flow was 2-5 m in depth, yet 25,000
  people died

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The human cost at Armero

• A victim just after rescue from the lahar
• She is completely coated in the mud of the lahar
• In general, survivors had great difficulty
  extricating themselves

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Rescue efforts

• Civil defense workers in the process of rescuing
  a woman from the lahar deposit
• They must walk on wood planks to avoid sinking
  into the quicksand-like lahar material

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A view of the lahar deposit

• Gravesites on the lahar deposit
• Many people were simply interred within the lahar

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Post-eruptive activity

• Very high levels of gas emissions and seismicity
  during 1985-1995
• Small ash emissions, but no large eruptions
• A restless, non-erupting, open system?

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A model of Ruiz according to Giggenbach et al.
(1990)
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Some lessons learned

• Need only a small eruption to melt ice and
  generate large lahars
• The lahars may travels tens to hundreds of
  kilometers from the volcano
• We need effective communication among scientists,
  politicians, officials, and the public

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Effects volcanic ash and aviation safety

• DATE 06/24/1982
• TIME 2044
• LOCATION Mount Galunggung, Indonesia
• AIRLINE British Airways
• FLIGHT 009
• ROUTE
• AC TYPE Boeing B-747
• REG G-BDXH
• MSN/LN 21365/365
• ABOARD 257
• FATAL 0
• GROUND 0
• DETAILS The aircraft flew into a plume from a
  volcanic eruption at 37,000
• feet during the night. All engines failed
  and the windshield lost
• transparency because of pitting. The first
  engine was restarted at 12,000
• feet, followed by the other three and the
  plane landed safely at Jakarta.
• The aircraft was named City of Edinburgh.

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Volcanic ash and aviation safety

• Many of the worlds civil air routes cross active
  volcanoes
• Ash erupted by a volcano frequently reaches
  aircraft altitudes (9-12 km)
• Aircraft encounters with ash are potentially
  fatal
• Ash can clog engines, causing them to fail

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Global air routes
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North Pacific air routes
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Mt. Pinatubo, Philippines, 1991

• Mt. Pinatubo erupted climactically on 15 June
  1991
• This figure shows the leading edge of the
  eruption cloud at 3-hour intervals

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Pinatubo, 1991

• 16 aircraft-ash encounters
• 12 encounters at 720-1740 km distance from the
  volcano (very far away)
• 10 engines damaged and replaced
• 7 airports closed from ashfall

Aircraft-ash encounters
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Pinatubo, 1991

• The combination of ash and water makes a very
  heavy load
• This photo shows a DC-10 damaged by ash at the
  Subic Bay military base near Pinatubo

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Redoubt, Alaska, 1989

• This is a sketch map showing the route of a KLM
  747 aircraft as it flew through the ash plume
  from the eruption of Redoubt volcano

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Mt. Spurr, Alaska, 1992

• Dispersion of ash from large explosive eruptions
  occurs on a continental, or even global, scale
• This figure shows ash dispersion from the 1992
  Mt. Spurr eruption

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Volcanic ash and aviation safety

• All this shows that good communication among
  volcanologists, meteorologists, and aviation
  people (especially pilots!) is essential

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Volcanoes - web

• Four good starting points for volcanoes
• http//gsc.nrcan.gc.ca/volcanoes/index_e.php
• http//vulcan.wr.usgs.gov/home.html
• http//www.geo.mtu.edu/volcanoes/
• http//volcano.und.nodak.edu

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Volcanoes - reading

• Francis, P., 1993. Volcanoes a planetary
  perspective. Oxford, Clarendon Press.
• Sigurdsson, H., B.F. Houghton, S.R. McNutt, H.
  Rymer, and J. Stix, eds., 2000. Encyclopedia of
  volcanoes. San Diego, Academic Press.
• Smith, W.S., 1983. High-altitude conk out.
  Natural History, v. 92, no. 11, November 1983,
  pp. 26-34.
• Tilling, R.I., 1998. Volcanoes.
  http//pubs.usgs.gov/gip/volc/text.html