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Title: Volcanoes and volcanism


1
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)

2
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

3
Global distribution of volcanoes
4
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

5
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

6
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
7
Plate tectonics and volcanism
8
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
9
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
10
Volcano types
11
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

12
Volcano types cinder cones
  • The cinders are generally of basaltic composition
  • The eruptive activity typically lasts a few
    months or years

13
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

14
Parícutin - lava flows
These images shows the development of lavas in
1943 and in 1951-52 Red areas show new lava flows
15
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)

16
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

17
Parícutin
  • This is a view of the volcano in March 1944
  • In the foreground, note the flat-lying lava flows
    from the volcano

lava
18
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

19
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

20
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
21
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 !

22
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
23
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)
24
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)

25
Volcano types calderas
26
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 !

27
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

28
Martian calderas
  • Here are two Martian calderas. Again, you should
    appreciate the difference in scale between these
    structures and those on Earth

29
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

30
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

31
Pahoehoe lava
Do you want to walk on pahoehoe ?
This is a Hawaiian term for smooth, ropy lava It
generally exhibits fluid-like textures
32
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 ?

33
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

34
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

35
Global distribution of large igneous provinces
(LIPS)
Mainly flood basalts
36
Lava domes
Mt. Unzen, Japan
Unzen began growing a lava dome in mid-1991. The
dome complex continued to grow until 1995
37
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

38
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

39
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

40
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

41
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
42
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

43
Volcanic activity lahars
  • To better understand lahar formation,
    experimental flumes are used to create
    small-scale lahar flows

44
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

45
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
46
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

47
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

48
Volcanic activity gases
  • About 15 km downwind from Masaya, the coffee crop
    is adversely affected by the acid gases

49
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

50
VEI
51
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

52
Case history Mount St. Helens, Washington state,
USA
53
Tectonic setting of Mt. St. Helens
54
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

55
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

56
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
57
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

58
A seismogram from seismic station RAN on 2 April
showing the occurrence of harmonic tremor
Harmonic tremor
59
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

60
Development of the bulge
bulge
28 September 1979
17 May 1980
61
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

62
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

63
Sliding...
64
Sliding and depressurizing...
65
and blasting
And blasting
66
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
67
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68
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

69
Dispersal of ash over the NW USA and western
Canada
70
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

71
Debris carried by lahars
72
Note the high-water mud marks on the trees
73
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

74
Would you call this event a disaster?
75
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

76
Explosive eruptions
Explosive activity diminished gradually over the
next several years
77
Pyroclastic flows
Spectacular pyroclastic flows were observed
forming from the crater These are some of the
best examples you will ever see
78
Pyroclastic flows - note big rounded pumices
79
Dome growth-destruction cycles
80
Dome growth-destruction cycles
Early lava dome
81
Dome growth-destruction cycles
Late lava dome
82
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

83
View of Ruiz on 26 November 1985
84
View of summit and Arenas crater, late November
1985. Note fresh ash
85
Tectonic setting of Nevado del Ruiz
86
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)
87
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88
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

89
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
90
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91
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

92
Ashfall and lahars
From Naranjo et al. (1986)
93
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

94
Lahar deposits in the Gualí River valley. Bulking
occurred here
95
Villages above the river valleys were protected
96
Principal lahar channels (from Pierson et al.,
1990)
97
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

98
Spreading and slowing of lahars as they emerged
from the mountains
Armero afterwards
High ground
99
Armero
  • Some of the few remaining structures in Armero
  • The lahar flow was 2-5 m in depth, yet 25,000
    people died

100
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

101
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

102
A view of the lahar deposit
  • Gravesites on the lahar deposit
  • Many people were simply interred within the lahar

103
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?

104
A model of Ruiz according to Giggenbach et al.
(1990)
105
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

106
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.

107
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

108
Global air routes
109
North Pacific air routes
110
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

111
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
112
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

113
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

114
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

115
Volcanic ash and aviation safety
  • All this shows that good communication among
    volcanologists, meteorologists, and aviation
    people (especially pilots!) is essential

116
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

117
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
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