Download volcano eruption styles

Styles of Eruptions
and
Volcanic Hazards
Styles of volcanic eruptions
Some volcanoes may erupt only once
- monogenetic (Diamond Head)
 Other volcanoes erupt many times polygenetic (Kilauea)
 Some erupt very gently (Kilauea)
 Others are very violent and explosive
(Mt. St. Helens, Mt. Pinatubo)

 How
come?
Explosive volcanoes found
associated with subduction zones
Explosiveness is a function of magma
viscosity (resistance to flow)
 Magmas that generate the explosive
volcanoes are much more viscous
than the non-explosive magmas

 More
silica, cooler magma, more gas
Hawaiian magmas
Not very explosive
 Not very viscous

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Low silica, hot magma, moderate gas content
Eruptive styles are
Classified by level of eruption
explosiveness
I. Flood eruptions
Least explosive eruptions
 Very fluid basalt erupted in very large
quantities VERY FAST
 Lavas erupted over large areas
 Thought to develop as hot spots burn
thru crust

Columbia
Plateau
More than
420,000
cubic km
of lava
Flood basalts
II. Hawaiian-type eruptions
Hawaiian-type eruptions
The next least explosive kind of
eruption
 Fluid magmas with small amounts of
gas
 Eruptions relatively gentle
 Periodically have a violent eruption but
very rare - Drive in volcanoes

Hawaiian-type eruptions
Build shield volcanoes
Fragmentation (grain size)
Surtseyan
phreatoplinian
Plinian
Peléan
Vulcanian
Strombolian
Intensity (dispersal)
Modified from Julia Sable
Styles of explosive volcanism
III. Strombolian eruptions

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Named for volcanic island off coast of Italy
Characterized by less fluid lavas
Moderate explosive activity
Tephra common
Lots of ash blankets country side
Basalt and andesite common
Large steep-sided composite volcanoes built by
repeated Strombolian eruptions
More explosive eruptions
Build composite cones
Mt. Shasta,
California
‘A’a flows
IV. Vulcanian eruptions
Characterized by more viscous lavas
 “Stubbly” flows are common
 Lots of ash
 Andesite most common

Arenal Volcano, Costa Rica
V. Peléan eruptions

Named for 1902 eruptions of Mount
Pelée on Martinique in the
Caribbean
Mt. Pelé
eruption
Almost
30,000
people
were killed
instantly
Peléan eruptions
Lavas highly viscous, very explosive
 Explosive eruption of highly gas-charged
lava leads to nuée ardente (glowing
avalanche) or pyroclastic flow which
move at 60+ kph and are 300deg C inside
 Don’t outrun these guys!!!

Pyroclastic flows
formed during 1968
eruption of Mt. Mayon
Ash cloud is 30,000 ft
high
Flows caused by ash
cloud collapse or
lava dome collapse
VI. Plinian Eruption
most powerful eruption
Named for Roman naturalist killed in
explosion of Mt. Vesuvius in 79 A.D
 Very destructive
 Accompanied by major collapse

Plinian Eruption
Mt. St. Helens is good example
before
during
Plinian = most powerful eruption
Crater Lake in Oregon formed by similar
explosive eruption
 Ash from this volcano (Mt. Mazama)
found all over the Pacific Northwest &
as far east as the Mississippi River!

Plinian = most powerful
eruption
Greatest Plinian eruptions of modern
times:
 1813 explosion of Tambora volcano
(eastern Indonesia)
 1883 explosion of Krakatau (Sunda
Strait between Java and Sumatra)

 Explosion
km away
heard in northern Australian, 2400
Other Recent Eruptions
Pinatubo = Vulcanian-type eruption
 Mt. Unzen (Japan,1991) -- generated a
number of lava domes that collapsed,
sending pyroclastic flows down the side
of the volcano, so it can be classified as a
Peléan eruption

Volcanoes & Plate Tectonics
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OK. So, where do you find all these
volcanic eruptive styles?
Flood eruptions - atop hot spots
Hawaiian - at hot spots & along MOR
All the rest are associated with subduction!
Fragmentation (grain size)
Surtseyan
phreatoplinian
Plinian
Peléan
Vulcanian
Strombolian
Intensity (dispersal)
Styles of explosive volcanism
What are the hazards?
Volcanic
Hazards
1. Lava
Flows
Volcanic Hazards
2. Falling Tephra
Like one sees at the
beginning of the
movie Dante’s Peak.
Falling tephra in Yakima, Washington
during Mt. St. Helens eruption
More Volcanic Hazards
Pyroclastic flows
 Mudflows - Lahars
 Toxic volcanic gases

Hazards in Hawaii
Lava flows
Note:
The next few slides are courtesy of
G&G graduate student Chris Gregg
Lava Flow Hazard
Zone Map of Hawaii
Historic Eruptions
Mauna Loa:
33 flows since 1843
5 reached ocean in Kona
Hualalai:
3 flows since ~1800
2 reached ocean in Kona
High effusion rates:
3-12 x 106 m3 day -1
Steep slopes > 6 %:
Hualalai: >50 %
Mauna Loa: 35 %
Kilauea:
<5 %
Fast transit times:
< 24
hours
1877
Lava Flows
From Hualalai and
Mauna Loa That
Have Affected
Kailua-Kona
Resorts
Airport
Subdivision
Hualalai’s last eruptions (c. 1800-1801)
MAUNA LOA’s
Radial Vents (33)
and Rift Zones
Historic radial vent
eruptions: 1843,
1859, 1877, 1935
Typical Mauna Loa
Eruptions:
Summit followed by
fissure eruptions
What Controls the Flow Paths
of Lava Flows? Topography
What Controls the Speed of
Lava Flows? Slope angle,
surface roughness, eruption
rate, lava type (viscosity)
1950 Eruption:
Flow velocities
16-48 km/hr
Note that all of these hazards are associated with the big island! How come?
Worst volcanic hazards often
occur after major eruptions
Ash covers sides of volcano
 Ash becomes unstable during heavy
rain
 Ash mud flow - LAHARS
 10 years+ after Pinatubo eruption,
mudflows were still killing people

LAHAR - ASH MUD FLOW
Volcanic gases
Very dangerous
 CO2, CO, SO2, H2S, HCl and HF

Hawaiian volcanoes
Do not usually emit enough gas to
harm people
 Except for Vog which forms as
volcano erupts and as lava enters the
ocean (Even reaches O`ahu with
Kona wind)

Attempts to control flows

In the past, people have tried to control,
direct lava flows by:
Diverting the flow with barriers built with
bulldozers
 Diverting by bombing one or all of the
following locations - the vent, edge of a flow,
tube entrance
 Water the flow front - not very successful!

Avoiding volcanic hazards
Predict them
 Volcanologists getting good at predicting
eruptions of dangerous volcanoes
 Mt. St. Helens, Unzen and Pinatubo
 But, missed 1993 Mayon eruption

Predictions eruptions
 Mostly
made based on monitoring:
 Seismic
activity increases
 Ground tilting
 Increased heat flow
 Increase in %sulfur in volcanic gas
 Because
magma is moving into
shallow levels under volcano!
Cyclic nature of Kilauea eruptions
Wai`anae
Volcano
Ko`olau
Volcano
Thurston Lava Tube
Meteorites have struck
the Earth in the past.
Many meteorites are made
of iron and nickel.
We think this represents
material of planets similar
to Earth.
Earth’s interior (core) is
probably also composed of
iron and nickel.
The end!