GEOS 470R/570R Volcanology
L21, 8 April 2015

Handing out
 PowerPoint slides for today

Note
 No lecture Fri 10 Apr 15
“One does not discover new continents without consenting
to lose sight of the shore for a very long time.”
--Andre Gide
Readings from textbook

For L21 from Lockwood and Hazlett
(2010) Volcanoes—Global Perspectives
Chapter 12

For L22 from Lockwood and Hazlett
(2010) Volcanoes—Global Perspectives
Chapter 3
Assigned reading

For today L21
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: Styles of mafic eruptions
and subaerial mafic flow
morphologies
Styles of mafic eruptions
Strombolian
Hawaiian
Subaerial mafic flow morphologies
 Remnant volcanic and subvolcanic
features

Strombolian style eruptions


Usually monogenetic cone-building stage of basaltic
andesite, e.g., Parícutin
Products
 Cinders that are solid when deposited near vent
 With less viscous magmas—get 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
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
Products of Hawaiian style
eruptions


Spatter bombs
Scoria
 Quenched frothy pyroclasts with large
vesicles

Pele’s tears
 Droplets of shiny black glass (spherical,
dumbbell, 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
Vergniolle and Mangan, 2000, Fig. 4B, 5A,B
Subaerial basaltic aa and
pahoehoe lava flows
Lava flows from the
AD 1969-1974
eruption of Mauna
Ulu, Chain of
Craters Road,
Kilauea volcano, HI
McPhie et al., 1993, Plate 19 #7
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
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
Formation
of lava
tubes and
craters
P. Kresan
P. Kresan
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

Height
 500 m

Composition
of dikes
 Minette
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
Sills

Dolerite sill, Salisbury Crags near Edinburgh,
Scotland
NOAA Volcanic
Rocks and
Features
Summary: Styles of mafic eruptions
and subaerial mafic flow morphologies

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 produces sustained lava
fountain
Begin with propagation of earthquakes, ground fissures; vents form along
fissures, creating wall of lava; “curtain of fire” collapses into single fountain
above 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 display many features observed in
volcanic rocks, such as columnar jointing
 Volcanic necks, laccoliths, dikes, and sills
Lecture 21: Interactions of mafic
magma with water

Mafic magma erupted subaerially flowing into
standing water
 Littoral cones

Mafic magma interacting with groundwater in a
subaerial setting
 Maar-diatreme complexes, tuff rings, tuff cones

Mafic magma erupted beneath shallow bodies
of water
 Surtseyan (tuff cone—high rim) and Taalian (tuff
ring—low rim) eruptions

Deep subaqueous mafic eruptions
 Subaqueous sheet and pillow flows

Submarine hydrothermal vents
Lava flows going into water
If there is a smooth magma surface
(pahoehoe) with a thin insulating crust,
water does not rapidly flash to steam
 Water flashes to steam if insulating
surface blanket is absent

Aa and blocky flows
If magma falls off a cliff into sea
Lava meets sea, Hawaii
P. Kresan
Littoral cone
Formed by phreatic
(steam) explosions
 Littoral cones

Lockwood and Hazlett, 2010, Fig. 9.24
Cones that look like volcanoes, but they
have no subjacent vent

Compare with phreatomagmatic
eruptions that form
Maars
Tuff rings (low rim)
Tuff cones (high rim)
Puu Hou, Island
of Hawaii, HI


Puu Hou: “New Hill”
One of three historic
littoral cones on Island of
Hawaii
 Sand Hills (1840)
 Puu Hou (1868)
 Alika Cone (1912)

Puu Hou formed in 1868
when the Kahuku fissure
eruption from the south
side of Mauna Loa
flowed into the sea
Fisher et al., 1997, Fig. 4-7A
Littoral cone of Puu Hou

Where lava flow
enters the sea
 Five days of
continuous
explosions in
1868 built
mounds of blocks
and ash

Littoral cone
 Volcanic landform
but has no
underlying vent
Fisher et al., 1997, Fig. 4-7B; photo by R. V. Fisher
Hydrovolcanic systems: Access
to water in and near the conduit

Hydrovolcanic systems
 We talked briefly about hydrovolcanic systems and maars
in L09 in the context of surge deposits

A key distinction between cinder cone and maar
 Access to water at shallow depths

Interaction with groundwater
 Maar-diatreme complexes
 Surficial landform: maar
 Underlying root: diatreme

Many settings with standing bodies of water, e.g.
 Seas and lakes
 Shallow and deep water depths
Hydrovolcanic eruption

An explosion
or eruption
caused by
sudden
expansion of
water when
mixed with
magma
Heiken et al., 1996, Fig. W11
Hydromagmatic explosion system


Explosion focused at
site where ascending
magma contacts
external water
Produces pyroclastic
surge and fall
deposits
 Including ballistic
clasts

Builds a low tuff ring
around a deepening
maar crater
Best and Christiansen, 2001, Fig. 10.23
Fields of pyroclastic deposition
Surge vs. flow
Particle
concentration
is a key
variable
vertical
fall
Angle of trajectory

surge
flow
horizontal
high
low
Particle concentration
After Wilson and Houghton, 2000, Fig. 4
Traction transport in surges
McPhie et al., 1993, Table 4
Wilson and Houghton,
2000, Fig. 3
Diamond Head, Island of Oahu, HI
NOAA Volcanic
Rocks and Features




Large palagonite tuff cone composed of glassy basaltic ash
Ejecta thrown out at shallow angle, accumulate far from vent
2.5 km across at base
Crater 1 km across at rim, averaging 120 m deep
Maars and cinder cones on Oahu


Inland from Diamond
Head but also located
close to the sea is the
Punchbowl maar
Farther inland from the
Punchbowl maar, and
at higher elevations,
are three cinder cones
 Tantalus
 Sugar Loaf
 Round Top

All similarly basaltic in
composition
Fisher et al., 1997, Fig. 4-6
Honolulu Group, Oahu, HI
Hay and Iijima, 1968, Fig. 1
Distinguishing between cinder cones,
tuff cones, tuff rings, and maars
Zimanowski, 1998, Fig. 1
Wohletz and Heiken, 1992, Table 2.3, after Heiken, 1971
Hydrovolcanic
landforms

Diagrammatic sections
 Maar
 Tuff ring (Taalian eruption)
 Tuff cone (Surtseyan
eruption)

Type of volcanic activity
and resulting landform
are controlled mostly by
 Depth, amount, and nature
of the waters meeting the
rising magma
Scarth, 1994, Fig. 12.1
Maar


A small, low-standing type
of volcano with a very wide,
bowl-shaped crater
Maar at Pinacate, Sonora, México
Crater floor commonly lies
below the level of the
surrounding topography


Underlain by a diatreme pipe
Origin
 Formed in presence of water
 Steam explosions excavate a
large crater (the maar)
 Explosions occur when rising
magma comes in contacts
with and mixes with
groundwater or surface
water, forming a diatreme
 When magma mixes with
water, it is blasted into finegrained particles
E. Seedorff, Dec 1998
Maar volcano





A: Groundwater aquifer
C: Upward-flaring, funnel-shaped conduit or pipe formed by
explosive interaction of magma with groundwater—diatreme;
narrows downward and merges into feeder dikes
L: Crater filling, consisting of fallback tephra, reworked tephra
from rim beds, and lake sediments
I: Inward-dipping rim bed
O: Outward-dipping rim bed
Vespermann and Schmincke, 2000, Fig. 6; from Fisher and Schmincke, 1984
Eroded maar volcano: Volcanic
neck with radiating feeder dikes

Ship Rock, NM

 Eroded 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
Zones of a diatreme

Upper diatreme
 Bedded lapilli tuffs and tuff
breccias that sometimes have
inward dips that steepen with
depth

Lower diatreme
 Relatively massive tuff breccia
with crosscutting, subvertical
contacts separating tuff breccias
of varying clast compositions
 May contain isolated slabs or
fragmental domains of country
rock or ejecta rim derived from
higher levels

Root zone
 Contains irregularly shaped
intrusive bodies, commonly
surrounded by in situ country
rock breccia
 Merge downward into coherent
feeder dikes
White and Ross, 2011, Fig. 14
Diatreme
Tuffaceous breccia
(right) of a
diatreme
 Intruded into
limestone (left)

Swabia,
Southwestern
Germany
Lockwood and Hazlett, 2010, Fig. 4.8
Lunar Crater maar, Nevada

In Lunar Crater volcanic field
Valentine et al., 2011, Fig.7
 At Citadel Mountain
 Reveille and southern Pancake Ranges, Nye County,
Nevada

Age
 Probably ~0.6-2 Ma
Valentine et al., 2011
MacDougal Crater, Pinacate
volcanic field, Sonora, México

Tuff ring
 ~1.6 km in diameter, 130 m deep
Best and Christiansen,
2001, Fig. 10.34; photo
by John S. Shelton
MacDougal
Gutmann, 2002, Fig. 1
Crater Elegante, Pinacate volcanic
field, Sonora, México

Tuff ring
 ~1.6 km in diameter, 244 m deep
Older cinder cone in
wall of maar
Older cinder cone
outside maar
Elegante
Gutmann, 2002, Fig. 1
Pinacate volcanic field, Sonora

Early shield volcano (Volcán Sta Clara)
 Basanite, trachyandesite, trachyte

Craters and cinder cones
 Alkali basalts and tholeiitic basalts
 >400 cinder cones and maars

Isotopic results (Lynch et al., 1993)
Maars of the Pinacate volcanic
field (numbered features except
1, 3, and 9 are maars)
 Consistent with asthenospheric mantle
sources (like many basalts in W N Amer)

Most maar-forming, phreatomagmatic
eruptions were immediately preceded by
effusive and Strombolian activity
 Rather than occurring when magma first
approached the surface
 Strombolian activity may have facilitated
access of groundwater to the conduits in
this arid region

Ancient, more westerly course of
Sonoyta River
 May have controlled spatial distribution
of maars and lithology of tuffaceous
ejecta (Gutmann, 2002)
Gutmann, 2002, Fig. 1
High explosivity of magma-water
interactions: An MFCI

Molten fuel-coolant interaction (MFCI)
 Strong explosions caused by interaction of hot fluids and a cold fluid
 Can arise during meltdown of a nuclear reactor

Hot fluids (molten fuel)
 Molten metals, magma

Cold fluid
 Water

Efficient heat exchange
 Requires large surface area
 Hot magma must be fragmented completely in milliseconds to generate
a steam explosion

Fragmentation of magma
 Caused by collapse of vapor bubbles, grown at the fuel-coolant
contact, and their injection into the magma

Importance
 Kinetic energy of explosions from magma-water interaction are much
higher than in dry magmatic eruptions (other conditions being equal)
Boundary conditions

First important control on amount of
kinetic energy released
 Depth at which magma encounters
water

Change in volume ratio of
steam to liquid water with
decreasing water depth
Density difference between water
vapor and liquid
 Is great at atmospheric pressures
(~1700X) but decreases rapidly as
pressure increases, i.e., with depth

Explosive interactions can occur at any
level where water pressure is below
critical pressure of water
 If aquifer is unconfined, <2 km
 More effective at depths < 1 km
 Especially at depths <100 m

Rock strength increases with depth
 So deeper explosions damage larger
volume of wall rock
Schmincke, 2004, Fig. 12.13
Boundary conditions
Dependence of form and structure of monogenetic
volcanoes on water/magma ratio
Schmincke, 2004,
Fig. 12.14

Second important control on amount of kinetic energy released
 Ratio of magma interacting with external water

Largest amount of energy
 When ratio is ~0.1-0.3
 Generates maars and tuff rings
Preexisting conceptual model for
maar-diatreme complexes

Maar
 Lunar Crater, NV

Diatreme
 Standing Rocks West, AZ

Lorenz model
 Not specific to magma composition
 Caused by MFCI: Molten fuelcoolant interactions
 Lorenz, 1986
Valentine and White, 2012, Fig. 1
Revised
conceptual
model for maardiatreme
complexes

 Created by explosions that erupt
and excavate small crater
 Explosions most effective at
shallow depths

Developing diatreme
 New magma fed into diatreme,
causing explosions
 Occur at any depth where
Phydrostatic < Pcritical but widen upper
part more rapidly, producing
upward flaring
 Diatreme crater walls fail and
collapse into crater
 Irregular dikes with bulbous tops
extend into diatreme fill, rising to
various levels and causing
phreatomagmatic explosions
 Only shallow explosions or
especially powerful explosions
now erupt

Valentine and White,
2012, Fig. 1
Protodiatreme
Post-eruptive maar-diatreme
 Tephra ring surrounding diatreme
Contrasts in models
Lorentz, 1986
 Usage of water by MFCI
 Results in water table drawdown
 Therefore deepening of explosion
locus with time

 Occur at any level at any time

Fragments erupted that originated
at depth
 Mainly a result of deep explosions
Level of water table
 Probably stays fairly constant
 Because permeability probably prevents
draining; diatreme probably captures
water and remains saturated
Diatreme
 Growth by subsidence
 Death by depletion of water
source or magma flux

Valentine and White, 2012
 Explosions

Vertical mixing of clasts
 Churning by upward-directed debris jets
and downward subsidence

Fragments erupted that originated at
depth
 Followed complex path during churning
Distinguishing between cinder cones,
tuff cones, tuff rings, and maars
Zimanowski, 1998, Fig. 1
Wohletz and Heiken, 1992, Table 2.3, after Heiken, 1971
Growth of a tuff ring
Interaction of magma rising
in a dike with an aquifer
Cross section through wall of tuff ring off
Madeira near Porto Moniz; unconformity at inner
crater wall indicates transport from right to left
Schmincke, 2004, Fig. 12.16
Schmincke, 2004, Fig. 12.19
Tuff ring

Tuff ring near Açigöl, central Turkey
Scarth, 1994, Fig. 12.3
Christmas Lake Valley, Oregon
Scarth, 1994, Fig. 12.4
Fort Rock, Christmas Lake Valley,
Oregon: An eroded tuff ring



Built ~15,000 yr ago
Tuff ring 60m high and 1 km across
Waves of Christmas Lake eroded its outer slopes and
breached the southern wall
Scarth, 1994, Fig. 12.5
Maar near Reykjavík, Iceland
Scarth, 1994, Fig. 12.2
Kilbourne Hole
maar, New
Mexico
 Potrillo
volcanic field,
Doña Ana
County, New
Mexico
Hoffer et al., 1998, Fig. 1
Surge facies in a blast surge deposit
Ballistic fragments
Sandwave
Massive
Planar
Lockwood and Hazlett, 2010, Fig. 7.36
Kilbourne Hole
maar, New
Mexico
 Late
Pleistocene
(<0.1 Ma) maar
volcano
 Dimensions
2.7 km northsouth X 1.6 km
east-west
Padovani and Reid, 1989, Fig. 1
Kilbourne Hole
Hunts Hole
Kilbourne Hole maar, New Mexico

View across the maar
E. Seedorff, Jan 2003
Kilbourne Hole maar, New Mexico

Surge beds on lip of the maar, resting on
sedimentary rocks of the Santa Fe Group
E. Seedorff, Jan 2003
Kilbourne Hole maar, New Mexico

Wave forms
E. Seedorff, Jan 2003
Kilbourne Hole maar, New Mexico

Nice dunes
E. Seedorff, Jan 2003
Kilbourne Hole maar, New Mexico

Moe waveforms
E. Seedorff, Jan 2003
Kilbourne Hole maar, New Mexico

Massive and planar bed forms, accretionary
lapilli?
E. Seedorff, Jan 2003
Kilbourne Hole maar, New Mexico

Dunes and massive bed forms
E. Seedorff, Jan 2003
Kilbourne Hole maar, New Mexico

Dunes
E. Seedorff, Jan 2003
Kilbourne Hole maar, New Mexico

Ballistic fragment with “bomb-sag” structure
at rim of maar
E. Seedorff, Jan 2003
Taal volcano, Philippines, 1965

Numerous historic eruptions from Volcano
Island
 1000 people killed in 1911 eruption

Volcano Island
 Lies within Taal caldera
 Surrounded by Lake Taal

In 1965, rising mafic magma interacted with lake
water
 Started with strombolian activity 1 km inland from
lake on Volcano Island
 One hour later, explosive phase began as fissure
eruption propagated to lake

Eruptive products dominated by nonjuvenile
material
Geologic map of Taal volcano


Elongate
eruption crater
intersecting the
lake
Transport
directions of
pyroclastic
density currents
(surges) by
blown down and
abraded trees
and by surge
dunes
White and Houghton, 2000, Fig. 5; after Moore et al., 1966
Taal eruption, 1965


Damped-down
eruption column
and hurricane-like
base surge
Expanding surge
with 4-km diameter
at time photograph
was taken
Fisher et al., 1997, Fig. 4-3
Taal volcano, Philippines
E. Seedorff, 1995
White and Houghton, 2000, Fig. 5
Volcano Island, Taal
E. Seedorff, 1995
Maar crater
E. Seedorff, 1995
Lava flow
E. Seedorff, 1995
Lava flows and fishing nets
E. Seedorff, 1995
Taal

Thickness of
total ejecta (cm)
 Surge plus fall
deposits

Range of
accretionary
lapilli
Cas and Wright, 1987, Fig. 5.19A; after Moore, 1967
Taal

Thickness of base
surge deposits
(cm)
 Much less than fall
component

Outer limit
determined by
faint sandblasting
of objects
Cas and Wright, 1987, Fig. 5.19B; after Moore, 1967
Taal

Maximum clast
size in base
surge deposits
(cm)
Cas and Wright, 1987, Fig. 5.19C; after Moore, 1967
Taal


Distribution of
dune bedforms
in base surge
deposits
Flow directions
of major base
surge
movement
 Measured by
sand blasting
and by tilting
and coating of
trees and
houses
Cas and Wright, 1987, Fig. 5.19D; after Moore, 1967
Dunes at Taal

Dunes 600 m from blast, formed by base surge
Fisher et al., 1997, Fig. 4-3; photo by R. V. Fisher
Distinguishing between cinder cones,
tuff cones, tuff rings, and maars
Zimanowski, 1998, Fig. 1
Wohletz and Heiken, 1992, Table 2.3, after Heiken, 1971
Eruption into standing body of
shallow water

Magma will vesiculate
 Water <400 m deep

Form Surtseyan
eruptions
 Cypressoid (named
after Cypress trees) or
Cock’s tail jets

Hydrovolcanic eruption
 Near island of Hunga
Ha’apai, Tonga
 Island is subaerial rim
of a large submarine
caldera along Tonga
arc
 Cloud with cypressoid
jets is 500 m high
Lockwood and Hazlett, 2010, Fig. 7.22
Recall: Hyaloclastite and peperite



Hyaloclastite = clastic aggregates formed by
non-explosive quenching, fracturing and
mechanical disintegration of hot magma upon
contact with water
Peperite = genetic term for in situ
disintegration of magma intruding and
mingling with unconsolidated or poorly
consolidated, typically wet, sediment
Both peperite and hyaloclastite commonly
form
In eruptions into shallow water, ice, or waterbearing sediments
In diatremes
Hyaloclastite

Hyaloclastite = clastic
aggregates formed by
non-explosive
quenching, fracturing
and mechanical
disintegration of hot
magma
 Upon contact with
water

Late Pleistocene
basaltic hyaloclastite
formed beneath glacial
ice
 40 km E of Thingvullir,
Iceland
Lockwood and Hazlett, 2010, Fig. 12.15
Peperite


Peperite = rock
generated by mixing
of coherent lava or
magma with
unconsolidated wet
sediment
Characterized by
clastic texture
Ordovician Bedded Pyroclastic
Formation, Llanberis Pass, Snowdonia,
northern Wales, UK
 In which either
component may form
the matrix
McPhie et al., 1993, Plate 14#1
Surtsey,
Iceland


Map of Surtsey
volcano
New island
formed during
eruption of 19631967
Wohletz and Heiken, 1992, Fig.
6.19; adapted from Jakobsson and
Moore, 1982
Birth of Surtsey

Cypressoid tephra jets
from slightly submerged
Surtla vent
 Represents earliest
observed phase of
volcano-building episode

Dark base to pale tips of
jets
 Due to steam
condensation, spreading
form

White and Houghton, 2000, Fig. 1
Base-surge of steam
spreads outward above
agitated, whitened water
 Due to intersection of spall
dome with water surface
Inferred temporal
development of a
Surtseyan volcano

A) Early, fully subaqueous jetting


B) Tephra pile shallowing



Explosions and collapsing jets form
turbulent, dilute gravity flows
Local water-exclusion zones at vent
margin in which clasts are
transported in part by steam,
forming armored lapilli
Most ejecta carried as gravity flows
C) Volcano grown into shallow
water


Jets intermittently emergent
Gravity flows interact with currents,
ambient surface waves, and
concentric waves induced by
eruption
White and Houghton, 2000, Fig. 2;
after White, 1996
Sea surface
Sea floor
Multiple vents

Differing eruptive
activities from
adjacent vents
 At left, plume
maintained by
continuous uprush
activity
 At right, Cypressoid or
Cock’s tail tephra jets,
with condensing vapor
forming white margins
and ends of jets

White background
 Formed by billowing
convective steam
clouds
White and Houghton, 2000, Fig. 3; after
Thorarinsson, 1967
Model for processes in surtseyan
vent

Shear-instability
entrainment
and mixing of a
slurry
 Contains
recycled tephra
and water with
rising magma

Drives uprush
activity
 Discrete or
continuous
White and Houghton, 2000, Fig. 10; after Kokelaar, 1983
Hydrovolcanic explosions, summit
crater lake, Ruapehu, New Zealand

Initial blast from
lake surface
 About 3 seconds
after initiation

“Rooster tail”
ejecta trails radial
to explosion
source
 Rises to height of
300 m
Lockwood and Hazlett, 2010, Fig. 7.23a
Hydrovolcanic explosions, summit
crater lake, Ruapehu, New Zealand

New, larger blast
blast from lake
surface
 About 14 seconds
later

Ripped through first
explosion column
 Later sent steam
column to height of
8 km

Nearly killed
observers on
southern rim of
crater
Lockwood and Hazlett, 2010, Fig. 7.23b
White Island, NZ
Discrete explosive eruption on 7 Sept 87

1976-1982 eruptive
episode
 Seven phases of
alternating
Strombolian and
phreatomagmatic
activity
 3-km high
convective plume

Basaltic andesite
volcano
 With hightemperature
magmatichydrothermal
geothermal system
White and Houghton, 2000, Fig. 6B; photo by R. Mead
White Island,
NZ

Near-continuous
eruptions resulted from
streaming of magmatic
volatiles and phreatic
steam through open
conduit systems
 Frittering of juvenile
particles from the
quenched margins of the
magma
 Eroding of loose particles
from unconsolidated,
altered walls of conduits
White and Houghton, 2000, Fig. 6A; after
Houghton and Nairn, 1991
Surtseyan vent
White and Houghton, 2000, Fig. 10; after Kokelaar, 1983
Controls on eruption style



Water to magma mass ratios (W/M) are an important control on
eruption style and mode of transport and deposition of ejecta
Scoria cones: Virtually dry
Increasing W/M, increasing hydrovolcanic fragmentation
 Tuff rings: “Taalian”: Water from aquifer or shallow lake; explosions
cease when water supply is cut off
 Tuff cones: “Surtseyan”: Water from deep aquifer, deep lake, or ocean;
vast water supply, so explosions cease when magma stops rising
Vespermann and Schmincke, 2000, Fig. 1, from Wohletz and Sheridan, 1983
Deep submarine eruptions

Eruption in deep water (abyssal plain)
 Magma does not vesiculate due to weight of
overlying column of water

Instead get hyaloclastites (broken glass)
 Glass quenched by water
 Rind shatters
 Broken glass fills pillow basalt interstices

Eruptions
 Begin with surface-fed sheet flows
 End with channelized pillow flows
Mid-ocean
ridge
Perfit and Davidson,
2000, Fig. 9
Rift settings in deep water
Perfit and
Davidson, 2000,
Fig. 8
Galapagos 86°W
Ballard et al., 1982, Fig. 1B
Collapsed submarine lava lake

Axial summit collapse trough of the East Pacific Rise
(9°50’N) where a 1991 eruption occurred. After
drainback of lava, lava pillar, 0.75 m high, remains to
support collapsed lobate flows.
D. Fornari and M. Perfit, Woods Hole Oceanographic
Institution; plate in EoV
Pillow basalts
P. Kresan
Characteristic surface structures of
a pillow lobe
Arrows indicate spreading or flow directions

Based on
detailed
study of
outcrops of
Cretaceous
and Neogene
pillows
 Hokkaido,
Japan
 North
Island, New
Zealand
Yamagishi, 1985, Fig. 1
Symmetrical
longitudinal
spreading
crack on
pillow lobe

Small graben and
a crack within the
graben
Cretaceous alkalic
basalt, Nemuro
Peninsula,
Hokkaido, Japan
Yamagishi, 1985, Fig. 4a, b
Two pillow lobes diverging from
single pillow by formation of
longitudinal spreading crack
Cretaceous
alkalic basalt,
Nemuro
Peninsula,
Hokkaido,
Japan
Yamagishi, 1985, Fig. 4c
New pillow lobe emerging from toe
of old lobe by formation of
transverse spreading crack and
constriction
Cretaceous
alkalic
basalt,
Nemuro
Peninsula,
Hokkaido,
Japan
Yamagishi, 1985, Fig. 4d
Constrictions,
brecciated
crusts, and
pillow bud
Sakaehama Beach,
Hokkaido, Japan

Yamagishi, 1985, Fig. 6b
For comparison, schematic views of pillow lobe in plan
view (b) and vertical cross section (d)
Yamagishi, 1985, Fig. 5b, d
Multiple crusts
overlying inner
lobe displaying
ropy wrinkles
on surfaces
Sakaehama Beach,
Hokkaido, Japan
Yamagishi, 1985, Fig. 6d

Schematic view of
pillow lobe in vertical
cross section
Yamagishi, 1985, Fig. 5c
Corrugations on pillow lobes
Sakaehama Beach, Hokkaido, Japan
Yamagishi, 1985, Fig. 7a,b

For comparison,
schematic drawing of
corrugations on a
pillow lobe
Yamagishi, 1985, Fig. 1
Model of growth of pillow lobe

A) Lobe filled with liquid lava,
enveloped by solidified crust
 Due to quenching by water

B and C) Interior liquid lava
breaks a toe, and new pillow
emerges through crusts
 Simultaneously, water
penetrates into shear joints
between crust and interior
 Symmetrical longitudinal
spreading crack opens on top
surfaces of lobe during growth

D) Multiple crusts form at end
of toe by repeated surge of
liquid lava
 Two lobes diverge from old
single pillow lobe by formation
of symmetrical longitudinal
spreading crack
 Each lobe advances by
transverse spreading crack
Yamagishi, 1985, Fig. 8
Hydrothermal fluid circulation at midocean ridges

Hot springs at
submarine vents
 Form volcanogenic
massive sulfide
deposits (generally
Cu, Zn, Pb, and/or
Ag)

Black smokers
 Hot, precipitating
sulfides

White smokers
 Cooler,
precipitating barite
Schmincke, 2004, Fig. 15-7
White smokers

White, barite-rich fluid exiting hydrothermal vent at >300°C
 Vent in the Lau Basin
Schmincke, 2004,
Fig. 15-8; photo
courtesy of Yves
Fouquet
Submarine hydrothermal vents

Hydrothermal hot
springs at spreading
centers
 Produce volcanogenic
massive sulfide
deposits
 Give sustenance to
blood worms, giant
clams, giant crabs

Fisher et al., 1997, Fig. 4-10; photo by
Rachel Hayman
Anaerobic
communities, no
photosynthesis
 Bacteria at base of
food chain derive
energy by oxidation of
H2S
Summary

Mafic magma erupted subaerially flowing into standing water
 Littoral cones (site of explosive fragmentation but no subjacent vent)

Mafic magma interacting with groundwater in a subaerial setting
 Little or no water: Cinder cone
 Maar-diatreme complexes, tuff rings (low rim), tuff cones (high rim)
 Controls: Water depth and ratio of magma interacting with external water

Mafic magma erupted beneath shallow bodies of water
 Surtseyan (tuff cone—high rim) and Taalian (tuff ring—low rim) eruptions

Deep subaqueous mafic eruptions
 Subaqueous sheet and pillow flows

Pillow basalts
 Single lobes of pillow basalt grow by formation of transverse spreading cracks
 Pillow basalt lobes diverge by formation of longitudinal surface spreading cracks

Submarine hydrothermal vents
 Deposition of metal sulfides on and immediately beneath sea floor
 Sustain distinctive faunal communities
Next time: Alkalic mafic rocks, carbonatites, kimberlites, komatiites,
sulfur flows