GEOS 470R/570R Volcanology
L20, 3 April 2015

Handing out
 PowerPoint slides for today

Note
 No lecture Fri 10 Apr 15 (GeoDaze)
“Look deep, deep into nature, and then you will
understand everything better.”
--Albert Einstein
Readings from textbook

For L20 from Lockwood and Hazlett
(2010) Volcanoes—Global Perspectives
Chapters 5, 6, and 9

For L21 from Lockwood and Hazlett
(2010) Volcanoes—Global Perspectives
Chapter 12
Assigned reading

For today L20
None

For L24, 20 April 2015
Voight, B., 1990, The 1985 Nevado del Ruiz
volcano catastrophe: Anatomy and
retrospection: Journal of Volcanology and
Geothermal Research, v. 44, p. 349-386.
Last time : Basaltic volcanoes and
settings of mafic magmatism

Types of basaltic subaerial volcanoes
Cinder (scoria) cones
Mafic shield volcanoes
Composite cones (stratovolcanoes)

Contrasting settings of mafic magmatism
Arcs
Basaltic shield volcanism
Basaltic flood (plateau) volcanism
Basaltic plains volcanism
Oceanic islands
Mid-ocean ridges
Lava and cinders at Sunset Crater
P. Kresan
Puu ka Pele cinder cone

Location
Between
Mauna Kea
and Mauna
Loa shield
volcanoes,
Hawaii

Height
95 m

Lockwood and Hazlett, 2010, Fig. 9.18
Summit
crater
400 m in
diameter
Shield volcanoes

Broad, gently sloping (<15°)
 Similar to a warrior’s shield


Schmincke, 2004, Fig. 6.2
Dominantly mafic (basaltic)
Constitute ~15% of subaerial volcanoes on Earth
 Hot spots and extensional settings
Mauna Loa
Cinder cones
capping
Mauna Kea
Simkin and Siebert, 2000, Fig. 1
Mt. Damavand, Iran
Sizes of shield volcanoes

Recall that largest
stratovolcanoes
(intermediate
composite cones)
have a total volume
of ~1000 km3
 Mt. Adams, WA ~200
km3
 Mt. Damavand, Iran
>400 km3

Basaltic shield
volcanoes are much
larger than largest
stratovolcanoes
Mt. Adams, WA
Hildreth, 2007, Fig. 24
Davidson and
De Silva, 2000, Fig. 3c
Mauna Loa, Hawaii
 Some shield
volcanoes have 300 X
the volume of the
largest composite
cones
 Mauna Loa 80,000
km3
Simkin and Siebert, 2000, Fig. 1
Icelandic shield volcanoes

Twenty built since post-glacial time
 Tiny compared to Hawaiian examples
 Prototypical shield volcano: Skjalbreidur, near Reykjavik
 Fed almost entirely by effusive eruptions from central summit
vents
 Exceptionally thin flows (30-100 cm thick), almost all pahoehoe
with many small lava tubes

Summit craters
 Approximately circular
 Most <1 km in diameter
 Raised rims built of
spatter from lava fountains
and repeated overflow from
lava lakes

Fissures are uncommon
 Few radial or lines of peripheral vents on flanks
 Concentric fissures around summit vents also rare
P. Kresan
Dimensions of Icelandic shields

Height
 50 to 1000 m; mean 350 m

Slope angles
 Generally 1° to 5° but as steep as 10°

Prototypical Skjalbreidhur shield volcano
 Almost uniform slopes of 7° to 8°
 Measures 10 km across at base
 Rises to height of 600 m
 Volume of 15 km3
Schmincke, 2004, Fig. 6.2
Mauna Kea shield volcano

Silhouette of classic shield volcano
 Elevation 4214m; 60 km across
Schmincke, 2004, Fig. 6.1
Shield volcanoes



Broad, gently sloping
Dominantly mafic (basaltic) in composition
Hot spots and extensional settings
Mauna Loa
Cinder cones
capping
Mauna Kea
Simkin and Siebert, 2000, Fig. 1
Hawaiian shield volcanoes

Schematic cross section of a typical Hawaiian shield volcano
 In the main stage of development
 Note slumps and slides
Lockwood and Hazlett, 2010, Fig. 9.3
Hawaiian shield volcanoes
Largest volcanoes
on Earth
 Height

Summits typically
Simkin and Siebert, 2000, Fig. 1
>2 km above sea level
Mauna Kea and Mauna Loa both >4 km
above sea level
Measured from true base, comparable to Mt.
Everest ~ 10km

But dwarfed by Olympus Mons on Mars
Growth of
Hawaiian shield
volcanoes


Magmatism migrates
Eruptive stages
 Corresponds with
changes in composition
of eruptive products
 Failure of flanks of
volcano

Why are the crust and
mantle shown with this
topology?
Lipman et al., 2002, Plate 2
Slump blocks and debris
avalanches on Hawaii

Submarine slumps
At least 68 have been mapped
Lengths up to 200 km
Volumes up to X000 km

Debris flows and turbidites
Can extend for >1000 km
Largest ones triggered by earthquakes
Can led to tsunamis
Continental and oceanic flood basalt
provinces
Hooper, 2000, Table 1
Columnar jointing

Devil's Postpile National
Monument, CA
 Large Quaternary basaltic lava flow
west of Long Valley
 Tops of columns exposed by glacial
erosion

Impounded in Middle Fork of
San Joaquin River
 Cooled very slowly

NOAA Volcanic
Rocks and
Features
Columns
 Average about 46 cm across

Joints form perpendicular to
cooling surfaces
 Tend to form in three directions ~60°
to each other (i.e., 6-sides columns)
 But 4-, 5-, and 7-sided columns also
present
 Cut off by joints formed parallel to
flow surface

Similar features
 Also form during cooling of ash-flow
tuffs, sills, other intrusions
What would columns look like if a lava
flow filled a steep canyon?
Lockwood and Hazlett, 2010, Fig. 6.42
Columnar jointing in lava flows
from flood basalts

Wider and more regular columns at
top and bottom compared to middle
 Colonnade vs. entablature

Upper colonnade
 Thinner but less regular columns at top
 More rapid cooling by convective and
radiative heat transfer through the air than
at base

Entablature
 Thin, less regularly oriented columns in
middle
 Rapid transition from plasticity into brittle
deformation

Lower colonnade
 Thicker and more regular columns at base
 Slow conductive heat loss to underlying
ground
Lockwood and Hazlett,
2010, Fig. 6.43
Columbia River Basalts
Press and Siever, 2001, Fig. 5.2
Lockwood and Hazlett,
2010, Fig. 6.43
Basaltic plains volcanism

Lava flows emplaced primarily in one of three forms
 Low shield volcanoes—central vent features having flank slopes of less than 1°
 Fissure flows
 Tube-fed flows emplaced through major systems of lava tubes

Interplay of these three forms results in a relatively flat basaltic plain
 Example: Eastern Snake River Plain
 Upcoming lab with map of Craters of the Moon, ID

Style of basaltic volcanism that is intermediate between
 Basaltic flood (or plateau) volcanism: fissures, rift zones, and a flat surface, and
 Hawaiian (shield) volcanism: central vents, lava tube flows
Greeley, 1982b,
Fig. 6
Hawaiian mantle plume

Basaltic melt
production rate as a
function of age
 Calculated from
volumes of individual
seamounts and
shield volcanoes
above mean seafloor
level and
underplated material

Volume has
increased steadily in
last 35 Ma
 Value today of 0.18
km3/y
Sigurdsson, 2000, Fig. 4; after White, 1993
Reunion mantle plume

Basaltic melt production
rate
 Along trail of Reunion
mantle plume in Indian
Ocean

Rate peaked at 66 Ma
 During extrusion of Deccan
Traps in India

Production has steadily
declined since then
 Value today on Reunion
Island of 0.04 km3/y
Sigurdsson, 2000, Fig. 5; after White, 1993
Patchy,
irregular
seamounts
Schmidt and Schmincke,
2000, Fig. 1B
Small
seamounts
along ridges
Schmidt and Schmincke,
2000, Fig. 2
Growth stages of seamounts
Schmidt and Schmincke, 2000, Fig. 3
Seamounts and guyots
Schmidt and Schmincke, 2000, Fig. 4
Evolution of volcanic island to
guyot stage
Schmincke, 2004, Fig. 6.7, based on Schmidt and Schmincke, 2000, Fig. 5
Mid-ocean ridge bathymetric profiles
Perfit and Davidson, 2000, Fig. 6
Summary: Basaltic volcanoes and
settings of mafic magmatism

Types of basaltic subaerial volcanoes
Composite cones (stratovolcanoes)
Cinder (scoria) cones
Mafic shield volcanoes

Contrasting settings of mafic magmatism
Arcs
Basaltic shield volcanism
Basaltic flood (plateau) volcanism
Basaltic plains volcanism
Oceanic islands
Mid-ocean ridges
Lecture 20: Styles of mafic
eruptions and subaerial mafic flow
morphologies
Volcanic plumes and mafic volcanism
 Styles of mafic eruptions

Strombolian
Hawaiian
Subaerial mafic flow morphologies
 Remnant volcanic and subvolcanic
features

Volcanic plumes

Fed by
 Thermal energy from fine grained basaltic ash
 Gases exsolved from the magma
 Air heated by cooling of magma in fire fountains

Volcanic plume generated over a basaltic fissure eruptions
 Only if fragmentation produces source of sufficient small particles
and gas
Carey and Bursik, 2000, Fig. 12
Mafic eruptive products not dispersed
widely

Solid circles
 Strombolian deposits (Etna 1971, Algar do Carvao I, Galiarte) and Hawaiian
deposits (Kilauea Iki 1959)

Solid triangles
 Subplinian

Open squares
Thickness vs. square root of area
 Plinian and
phreatoplinian
Houghton, Wilson, and Pyle, 2000, Fig. 3A
Why square root of area (km)?

Interested in thickness (mm) decrease with distance
(km) from vent
 Different settling laws involving fragments of different sizes

Distances from vent are asymmetrically distributed
because of axis of wind dispersal
 Use square root of area to normalize the distance
Dispersal of
pyroclasts from 18
May 1980 eruption
of Mount St. Helens
Cas and Wright,
1987, Fig. 5.8; after
Sarna-Wojcicki et
al., 1981
Strombolian and Hawaiian eruptions

Subdued
Intensity
Magnitude
Dispersive power

Result of low viscosity of magma erupted
Typically basalt or basaltic andesite

Low viscosity
Allows gas to segregate and escape with
relative ease
Strombolian style eruptions

Origin
 Stromboli, Lipari Islands, Italy

Gas is released in discrete, mildly explosive,
often rhythmic, bursts
 Large gas bubbles (10 m diameter) near top of
magma conduit burst
 Stromboli: Typically 3 - 5 explosions/hr; rare periods
with 100s of explosions/hr

Each burst disrupts the top of the magma
column
 Hurls a shower of incandescent pyroclasts (scoria,
lapilli, and bombs) above the crater rim
 Small eruptive clouds (few hundred meters high)
Strombolian style eruptions


Usually monogenetic cone-building stage of basaltic
andesite
Products
 Cinders that are solid when deposited near vent
 With less viscous magmas—produce fusiform bombs,
spatter/agglutinate
 Lava flow may form during Strombolian eruption—block or aa

Strombolian eruptions can last for months or years
 Versus hours for Plinian
 May follow a Plinian eruption, as at Crater Lake

May be punctuated by more violent, ash-forming
Vulcanian eruptions
 Cannon-like blasts, dense ash cloud
Examples of Strombolian eruptions
Stromboli, Italy
 Mt. Etna, Sicily, Italy
 Parícutin, México, 1943 – 1952
 Mount Veniaminof, Alaska, 1993-1995
 Pacaya, Guatemala, 1995-1996
 Rabaul, Papua New Guinea, 1996
 Villarrica, Chile, 1996-1998

Parícutin, México
Cinder cone, Parícutin, México

Nine-year
lifespan
 1943-1952

Built 610-m high
cone
 Lava fields
around base

In first two years
 Ash, cinders,
and lava
covered 2 km2

Night photo of
cinder cone
NOAA Volcanoes in Eruption 1; by Ray E. Wilcox, USGS
Parícutin, México

Ash fall
Press and Siever, 2001, Fig. 5.2
Parícutin, México

Toe of aa flow at Parícutin, México
P. Kresan
Parícutin,
México

Cinder cone soon
after birth in 1943
in a corn field
NOAA Volcanoes in Eruption 2; photo by
K. Segerstrom, 1943
Cinder cone

Cinder cone
and lava
flow at
SP Crater,
AZ
Press and Siever, 1994, Fig. 5.4
Hawaiian Islands
Hawaiian style eruptions

Origin
Hawaiian Islands, USA
Gas is also released in discrete rhythmic
bursts
 Each burst in gas flux gives rise to a
sustained lava fountain

Progress of Hawaiian eruptions



Eruptions begin with propagation of
earthquakes, ground fissures
Vents form along fissures as they lengthen,
creating wall of lava (“curtain of fire”)
Curtain collapses into a single fountain above a
central vent
 Sustained gas jet with molten clots
 Usually 100 – 500 m high; rarely >1500 m
 Vent may have many fountaining episodes

Ends with low-level, quiescent, persistent
effusion of lava
Fissure eruption, Hawaii
Press and Siever, 1994, Fig. 5.2
Lava fountain, Hawaii
Press and Siever, 1994, Fig. 5.1
Hawaiian volcano
P. Kresan
Lava meets sea, Hawaii
P. Kresan
Volcanic ejecta

Shapes and sizes
of different kinds
of ejecta
As a function of
eruptive conditions
(eruption type)
Which are a
function of
viscosity and
temperature of
magma
Which, in turn,
relate to bulk
composition
Lockwood and Hazlett, 2010, Fig. 6.2
Products of Hawaiian style
eruptions


Spatter bombs
Scoria
 Quenched frothy pyroclasts with large vesicles

Pele’s tears
 Droplets of shiny black glass; spherical, dumbbell,
and tadpole shapes

Pele’s hair
 Long golden threads of glass; quenched filaments

Reticulite (extremely vesicular scoria)
 Delicate golden-brown honeycombs of glass, with
bubbles deformed into polygons

Lava
Bombs from Hawaiian eruptions

Cow-pie or cowdung bomb
Formed as fluid
spatter
impacted
ground at 1969
eruption of
Kilauea
Why is it so flat
compared with
bombs from
intermediate
and silicic
eruptions?
Lockwood and Hazlett, 2010, Fig. 7.4a
Scoria and spatter bomb from Kilauea

Quenched frothy pyroclasts with large vesicles
Vergniolle and Mangan, 2000, Fig. 4A
Pele’s tears


Droplets of shiny black
glass
Shapes
 Spherical
 Dumbbell
 Tadpole
Vergniolle and Mangan,
2000, Fig. 5A
Pele’s hair

Long golden threads
of glass; quenched
filaments
Vergniolle and Mangan,
2000, Fig. 5B
Reticulite from Kilauea


Extremely vesicular
scoria
Delicate goldenbrown honeycombs
of glass, with bubbles
deformed into
polygons
Vergniolle and Mangan,
2000, Fig. 4B
Examples of Hawaiian-style
eruptions
Kilauea, HI, 1959, 1969, 1983-1986
 Mauna Loa, HI, 1950, 1975, 1984
 Piton de la Fournaise, Réunion, 1992,
1998

Continuum between Strombolian and
Hawaiian eruptive styles

One type of activity may give way to
another
Askja, Iceland, 1961
Heimaey, Iceland, 1973
Tolbachik, Kamchatka, 1975
Izu-Oshima, Japan, 1987
Mount Etna, Sicily, Italy, 1996
Pavlof, Aleutian Islands, 1996-1997
Okmok, Aleutian Islands, 1996-1997
Factors that control development of
lava flows
Discharge rate of lava
 Physical properties of the lava
 Local environment

Whether eruption occurs on land, below
water, or below ice
Ground slope
Topography
Definitions of mafic lava types

Pahoehoe
 Lava with billowy,
undulating surface
 Smooth, continuous skin
 Thin congealed skin
remains plastic over the
hot fluid interior and
insulates underlying
magma
 Polynesian for “On which
one can walk”

Alternating pahoehoe and aa lava
flows on southern flank of Kilauea
Aa
 Lava with a rough, jagged
surface known as clinker,
which resembles slag of a
furnace, formed by
autobrecciation of lava
Schmincke, 2004, Fig. 4.13
Aa vs. pahoehoe

Stability fields of pahoehoe and aa
Flow only begins
 When shear stress is larger
than the yield strength

Aa favored over pahoehoe
 By combination of higher
shear rate and higher viscosity
(which increases during
cooling, crystallization, and
bubble formation)

Pahoehoe can change into
aa during flow
Aa and
pahoehoe
together in
Hawaii
Press and Siever, 1994, Fig. 5.6
Schmincke, 2004, Fig. 4.16
Aa vs. pahoehoe

Rheological paths for
aa-pahoehoe
transition
Lockwood and Hazlett, 2010, Fig. 6.13
Subaerial basaltic aa and
pahoehoe lava flows
Lava flows of
aa overlying
pahoehoe,
from the AD
1969-1974
eruption of
Mauna Ulu,
Chain of
Craters Road,
Kilauea
volcano, HI
McPhie et al., 1993, Plate 19 #7
Major flow structures

In aa and blocky lava
flows, open channels
feed lava to simple
flow fronts
 In long-lived eruptions,
may evolve into tubes

In pahoehoe flows,
flow structures are
complex intermingling
tongues and toes
 Fed by a tube system
Kilburn, 2000, Fig. 1; after Lipman
and Banks, 1987
Glassy basaltic lava

Glassy pahoehoe lava flow near Mauna Ulu
NOAA Volcanic
Rocks and
Features
Pahoehoe

Pahoehoe lava flow from
Hawaii

Billowy, undulating
surface
Smooth, continuous skin
Thin congealed skin
remains plastic over the
hot fluid interior
Crust is an insulator



 Interior may remain hot
and fluid for months
 Surface may be sturdy
enough to walk on
NOAA Volcanic Rocks and Features
Pahoehoe
Pahoehoe lava tongue
Flowing pahoehoe lava, Pu’u O’o
scoria cone near Kilauea (note tubes)
Press and Siever, 1994, Fig. 5.7
Schmincke, 2004, Fig. 4.12
Subaerial pahoehoe lava flow in
cross section



Upper unit (A) in stack of spongy pahoehoe lava flow units shows an inward
increase in vesicle size, and has a medial gas blister (G) lined by disrupted
vesicles
Unit B also has a medial gas blister but it has been filled by a younger lava
tongue (C)
Lava in floor and roof of flow unit D displays concentric layers of differing
vesicle size and abundance
Mauna Iki pit crater,
Holocene; Kilauea
volcano, HI
McPhie et al., 1993,
Plate 19 #6
Length of pahoehoe flow fields

Historical
 Several tens of kilometers (e.g., Big Island of Hawaii,
HI)

Prehistoric
 Tube system >100 km long (e.g., Queensland,
Australia)

Ancient flood basalts (e.g., Columbia River
Basalts)
 Previously thought to be extreme aa fields
 Recent proposal that they are enormous pahoehoe
lavas
 Drained tubes are tens of meters across, 10 – 20 m
high
 Drained tube system for more than several
kilometers
Clinker
Slag from furnace of a steel mill
 A rough, jagged pyroclastic or
autobrecciated fragment, such as aa, that
resembles slag of a furnace

Aa lava
Aa from Puna rift,
Island of Hawaii,
partially burying a
home and car

Rough, jagged,
clinkery surface
 Caused by disruption
of viscous crust by
movement of flow beneath

NOAA Volcanic Rocks and Features
Congeals on the front and sides
 Forms steep flow fronts that are overridden by molten lava within
the flows

Difference from pahoehoe caused by rate of cooling and
gas separation
 Transition from pahoehoe to aa may occur in single lava flow,
such as where it plunges over a steep slope
Aa lava
Front of aa flow from eastern flank of Kilauea
Schmincke, 2004, Fig. 4.11
Rough surface

Top of lava flow
is extremely
rough
Can include
spines
Example from
1999 Mt.
Cameroon lava
flow, Cameroon
Lockwood and Hazlett, 2010, Fig. 6.45
Cross section of
an aa lava flow

Cross section
through lava flow,
Kilauea volcano,
HI
Coherent core
Breccias at top and
base
Flow ~40 cm thick
Schmincke, 2004, Fig. 4.14
Internal flow of fluid lava propels
tractor tread advance of lava flow

Aa lava flow
 Buries its own
surface rubble as it
advances

Note changing
position of reference
blocks
 Black, circled in red

Blocks start as
carapace breccia
 Later move to toe of
lava flow
 Final position is in
basal breccia
Lockwood and Hazlett, 2010, Fig. 6.46
Lava tubes and craters
Craters of the
Moon, ID
Lava tube,
East Rift, HI
NOAA Volcanic Rocks and Features
Press and Siever, 1994, Fig. 5.5
Formation
of lava
tubes and
craters
P. Kresan
P. Kresan
Mafic lava flows
Wohletz and Heiken, 1992, Fig. A7
Spatter cone


Spatter cone, Little Beggar cone in Kilauea
caldera, HI
Spatter: Molten
material that
soldifies after
landing
 Forming
agglutinate

Lava at a small
vent was thrown
into the air and
solidified
NOAA Volcanic Rocks and Features
Spatter cones and cinder cone

Small spatter
cones and
larger cinder
cone, Craters
of the Moon,
ID
NOAA Volcanic Rocks and Features
Agglutinate

Bombs that fall on a cone, sinter to substrate while hot
 If they are thrown too far from the cone, they will cool too much to
sinter
E. Seedorff, 1995
E. Seedorff, 1995
Spatter cone, Fort Rock, OR
E. Seedorff, 1995
Remnant volcanic and subvolcanic
features
Volcanic necks
 Laccoliths
 Dikes
 Sills

Shapes of igneous intrusions
(a) Dike
(b) Cone-sheet
(c) Cup-shaped
(d) Saucer-shaped
(e) Sill
(f) Lopolith
(g) Pluton
(h) Laccolith
(i) Ring dike
Mathieu et al., 2008, Fig. 1

Analogue experiments suggest

Magma can propagate along a self-induced hear
fault rather than a hydraulic tension-fracture
(Mathieu et al., 2008)
Eroded Tertiary trachyte
volcanic neck

Mt. Tibrogargan,
Glasshouse
Mountains
 Near Brisbane,
Queensland,
Australia
NOAA Volcanic Rocks and Features
Volcanic neck (or laccolith?)

Devils Tower,
WY
 Note columnar
jointing

Height
 254 m

Composition
 Phonolite
NOAA Volcanic Rocks and Features
Volcanic neck with radiating feeder
dikes

Shiprock, NM

 Neck with a
diatreme pipe
with welded tuff
breccia
Age
 ~25-30 Ma

Height
 500 m

Dikes
 Minette

Wall rocks
 Sedimentary rocks
that are less
resistant than dikes
and diatreme
NOAA Volcanic Rocks and Features
Dike with columnar jointing

From dike
swarm north of
Hofn, Iceland
 Feeder dikes
for basaltic
lavas
NOAA Volcanic Rocks and Features
Dikes

Great Wall dike
 North of Spanish Peaks, CO
NOAA Volcanic Rocks and Features
Sills

Dolerite sill, Salisbury Crags
 Nnear Edinburgh, Scotland
NOAA Volcanic
Rocks and
Features
Summary

Large volcanic plumes rarely generated over basaltic vents

Strombolian eruptions



Hawaiian eruptions





Pele’s tears (shiny black glass)
Pele’s hair (quenched filaments of golden glass)
Reticulite (vesicular scoria with delicate golden honeycombs of glass)
Subaerial mafic flow morphologies



Gas also released in rhythmic bursts; each burst gives rise to sustained lava
fountain
Begin with propagation of earthquakes, ground fissures; vents form along
fissures, creating wall of lava; “curtain of fire” collapses into a single fountain
above a central vent; end with effusion of lava
Distinctive products of Hawaiian style eruptions


Gas is released in discrete, mildly explosive, often rhythmic, bursts; large
gas bubbles near top of magma conduit burst
Hurls shower of incandescent pyroclasts above crater rim; effusion of lava
Transition from pahoehoe to aa lavas governed by rheological paths
Expressed on plots of Temperature (or 1/viscosity) vs. Shear rate
Remnant subvolcanic features
 Volcanic necks, laccoliths, dikes, and sills
 Display many features observed in volcanic rocks, such as columnar jointing
Next time: Interactions of mafic magma and water