GEOS 470R/570R Volcanology
L27, 1 May 2015

Handing out
 PowerPoint slides for today

Lecture final
 Wednesday, 13 May 2015, 10:30-12:30pm, G-S 203
 Also an early offering?
 Time of lecture review session?

Course evaluation
“For every complex problem there is an answer that is
clear, simple, and wrong.”
--H. L. Mencken
Science: Balancing learning and skepticism
Readings from textbook

For L27 from Lockwood and Hazlett
(2010) Volcanoes—Global Perspectives
Chapter 12

For L28 from Lockwood and Hazlett
(2010) Volcanoes—Global Perspectives
Chapters 15 and 13
Last time: Volcanism and mineral
deposits, II., and Extraterrestrial
volcanism, I.
Volcanism and mineral deposits, II.
 Volcanogenic submarine massive sulfide
deposits
Extraterrestrial volcanism, I.
 Comparative planetology
 The Moon
 Mercury
Seafloor massive sulfide deposits
Press and Siever, 2001, Fig. 22.25
Evolution of black
smoker chimney
stacks

Stage 1
 Black “smoke” is hot water charged
with fine sulfide particles
 Hot fluids emerge from fracture
seafloor to begin accretion of calcium
sulfate (anhydrite) walls
 Anhydrite crystallizes from seawater
heated around the margins of jet of
hot fluid
 Anhydrite partially replaced by Fe and
Zn sulfides

Stage 2
 Anhydrite walls protect hot fluids from
mixing with seawater
 Cu and Fe sulfides can then crystallize
on inner walls of chimney

Fluids and chimneys
 Temperatures may attain 350°C
 Chimneys usually <10 m high and 1 –
30 cm in diameter
Fisher et al., 1997, Fig. 4-11; adapted
from Hayman and Macdonald, 1985
Hydrothermal activity and
mineralization on modern ocean floor

Most common types
Polymetallic sulfides (Fe, Cu, Zn, Pb)
Shallow submarine hot springs
Low-temperature Fe + Mn oxide deposits

But much more varied than previously
recognized
Hannington and Herzig, 2000
Hydrothermal activity and
mineralization on modern ocean floor

Less common types
 Polymetallic vein mineralization
 Submarine solfataras
 Acid-sulfate type hot springs
 Epithermal-style As-Sb-Hg mineralization
 Au-Ag-barite deposits
 Carbonate-rich hot springs
 Silica sinters
 Pyritiferous muds
 Sediment-hosted subseafloor replacement deposits
 Ultramafic-hosted Cu + Co stockworks
Hannington and Herzig, 2000
Comparative planetology
Press and Siever, 2001, Fig. 1.3
Controls on planetary volcanism

Presence and type of global volcanism
 Sensitive to dominant mode in which internal heat is
transferred to the surface

Plate tectonics (Earth)
 Broad convection, upwelling of mantle at spreading
ridges, sinking of cold plates at subduction zones
liberates much of the heat from the interior

Hot spot tectonics (other planets)
 Style of volcanism characteristic of intraplate hot
spots on Earth
 Heat is released via isolated volcanoes distributed
over the surface and by normal conduction through
the lithosphere
Crumpler and Aubele, 2000
The Moon: A world of flood basalts

Light, rough highlands (terrae)
 Heavily cratered—older
 ~4.5 Ga
 Similar to Earth’s anorthosites
(mostly Ca-rich plag)

Earth-facing surface of the Moon
Dark, smooth lowlands (maria) of
flood basalts
 4.3- 3.1 Ga
 Suggests episodic partial melting,
possibly associated with meteorite
impacts

Origin of maria
 Some workers invoke analogies with
flood basalts
 Whereas others make analogies to
Earth’s MORBs

Youngest dated rocks
 0.8 Ga
 Planet is now too cold to generate
volcanic activity
Lockwood and Hazlett, 2010, Fig. 12.16
Lunar maria

Extensive mare flooding on near side
 Rare on far side

Maria comprise 16% of surface area of lunar
surface
 But <1% of the volume of the crust
Near side
Far side
Spudis, 2000, Fig. 2
Lunar lava flows


Flow fronts visible in
close up views
Basalts are low in Al,
and alkalis and high
in Fe
Flow fronts in Mare Imbrium (FOV
~150 km)
Flows here are 800 km long, 20-40
km wide, 20-60 m thick
Mons La Hire massif at upper right
 Implies magmas with
very low viscosities
 Consistent with thin
flows, long run-out
distances, low-relief
volcanic landforms
Spudis, 2000, Fig. 4
Central vent volcanoes
Marius Hills (FOV ~ 150 km)
Numerous domes, cones, rilles
Domes are typically 8-12 km in
diameter, locally 20 km
Isolated cone in Mare Serenitis
(FOV ~ 20 km)
Spudis, 2000, Fig. 5B
Spudis, 2000, Fig. 5A
Pyroclastic rocks


Dark mantling
deposits near Rima
Bode (FOV ~ 180 km)
Comprised of basaltic
glass (FOV ~ 2 mm)
 Various colors
 Pyroclastic origin
 Inferred to have
formed during
Hawaiian-style lava
fountaining
Spudis, 2000, Fig. 6A, B
Rilles

Sinuous rilles around
the ancient flooded
crater Prinz (D ~ 50
km)
 Prominent deep
crater is Aristarchus
crater
 Flooded crater in
distance is Herodotus

Rilles are lava
channels
 Layers of basalt
exposed in walls
 In some cases roofed
over to form lava
tubes
NASA Archive AS 15-93-12601HR, Wikipedia site,
Geology of the Moon; see also Spudis, 2000, Fig. 7
Evolution of the Moon


Accretion 4.55 Ga
Early differentiation of planet
 Melting event, perhaps of the entire moon
 Formation of a “magma ocean”
 Lunar crust formed by floating plagioclase; olivine and
pyroxene sink
 Crystallize anorthosite within first 100 m.y.

Collisions with remaining planetesimals and large
meteorites
 Gigantic impacts created large, multi-ring basins, 4.5 –
4.1Ga
 Early volcanism, formation of KREEP ~4.1 Ga
 Basaltic lavas fill floors of impact basins with maria, 3.93.1 Ga, but perhaps for much longer period of time
 Smaller impacts and regolith formation since 3.3 Ga
Harrison Hagan “Jack” Schmitt

Born, July 3, 1935 in Santa Rita, NM
(age 79)
 Son of the famous porphyry copper
exploration geologist Harrison A.
Schmitt :
 Schmitt, H. A., 1966, The porphyry
copper deposits in their regional
setting, in Titley, S. R., and Hicks, C.
L., eds., Geology of the porphyry
copper deposits, southwestern North
America: Tucson, University of
Arizona Press, p. 17-33.
 Jack grew up in Silver City, NM

B.S., Geology, California Institute of
Technology, 1957
 Then studied for a year at University
of Oslo, Norway

Ph.D., Geology, Harvard University,
1964
 Thesis area was in Norway
NASA photo, 1971, Wikipedia Harrison
Schmitt site
Harrison Hagan “Jack” Schmitt

Before joining NASA
 Worked in USGS Astrogeology
Center at Flagstaff, AZ,
developing field techniques to be
used by astronauts

Apollo 17 mission 7-19
December 1972
 Schmitt claims to have taken the
photo known as The Blue Marble
(officially credited by NASA to
the entire crew), one of the most
widely distributed photographic
images
 Is the only geologist to have
walked on the Moon
 Is the only person to have
walked on the Moon who was
never a member of US Armed
Forces
NASA photo taken by Cernan of Schmitt
on the Moon, 12 Dec 1972, Wikipedia
site, Apollo 17
The Blue Marble
NASA photo, 7 Dec 1972, Wikipedia Apollo 17 site
Mercury



Numerous impact
craters
Bright lines of
ejecta deposits or
rays radiating
outward from
young craters
Lobate scarps in
lower left
Photomosaic of Michelangelo
Quadrangle H-12
Turcotte and Schubert, 2002, Fig. 1-64
Mercury

Has an intrinsic global magnetic
field
Internal structure of Mercury
 Magnetic equator shifted 20% of
planet’s radius to the north-largest ratio of any planet
 Possibly dynamo action in a liquid
part of core surrounding solid
center

Unusual structure
 Large core; thin crust and mantle

Evolution
 Separation of iron and silicates
and crustal differentiation
 Heavy bombardment
 Filling of basins that are relatively
free of craters
 Unclear evidence for much
volcanism
 Lobate scarps (rupes) formed
Turcotte and Schubert, 2002;
Wikipedia Geology of Mercury
http://www.wired.com/wiredscience/201
2/03/dynamic-mercurygeology/?pid=3478&viewall=true
Lecture 27: Extraterrestrial
volcanism, II.
Mars





Venus
Mars
Io
Cryovolcanism
Comparative
planetology revisited
Press and Siever, 2001, Fig. 1.10
Venus: A mantle plume world

Size and density similar to Earth
 Diameter only 330 km less than Earth

Covered with dense atmosphere rich in carbon
dioxide
 Capped with clouds with sulfuric acid droplets
 Clouds circulate planet once every four days
 High winds aloft, but mostly calm at surface

Explored by
 Pioneer Venus radar
 Earth-based radar
 Soviet Venera 15-16 orbital imaging radar
 Soviet Venera and Vegas landers
 Magellan radar, altimetry, and gravity (1990-1994)
Lunar and Planetary Institute, 1997, Venus Slide Set, #2
Optical images from landers

Moderately flat terrain
 Dry desert landscape

Characterized by local
soil patches
Wide-angle, panoramic surface
image from Venera 13, 1 Mar 82
(foot of lander at bottom)
 Between flat outcrops of
dark, more consolidated
material

Chemical compositions
 Most sites tholeiitic basalt
 Possibility of more
evolved, alkali-rich
(trachytic)
 One similar to alkali basalt
(Venera 13)
 One more mafic, gabbroic
Crumpler and Aubele, 2000
Lunar and Planetary Institute, 1997,
Venus Slide Set, #3
Characteristics of Venus


Only major planet that lacks a satellite
Rotation is retrograde (opposite direction as
Earth)
 Single day is 243 Earth-days long

Similar size and mass as Earth
 Implies a metallic core

Planetary magnetic field, however, is
nonexistent or weak
 Consequence of slow rotation on circulation
necessary to excite a magnetic dynamo in the core?
 Fundamental difference in core composition or size
compared to Earth?

“Volcanologic paradise and tectonic nightmare”
Crumpler and Aubele, 2000
Best telescopic image of Venus

Taken by Hubble
Space Telescope in
1995 in ultraviolet
wavelengths (false
color)
 Reveals cloud
patterns
 No surface features
visible

At optical
wavelengths, not
even cloud patterns
are visible
Lunar and Planetary Institute, 1997,
Venus Slide Set, #1
Magellan


Magellan exiting the
space shuttle Atlantis,
May 1989
Large radar dish
collected synthetic
aperture radar (SAR)
data
 Illuminates a surface with
radar energy in directions
at right angles to the
antenna (spacecraft)
motion

Smaller altimeter horn to
its left was used to collect
the altimetry data and
related products
Lunar and Planetary Institute, 1997,
Venus Slide Set, #4
Synthetic aperture radar (SAR) images


Not optical images; illuminate surface with radar energy
Surface properties that affect a radar image are shown:
Lunar and
Planetary
Institute,
1997, Venus
Slide Set, #6
Magellan’s SAR technology



Magellan data acquired late 1990 to late 1992
Surface of Venus is more completely and
uniformly mapped—and at higher resolution—
than seafloor of Earth
Mountains are inherently more reflective at
elevations >4 km above mean planetary radius
 Differences in chemical weathering at high and low
elevations?
Crumpler and Aubele, 2000
Infernal surface environment

Atmospheric surface pressure (9.2 MPa, or 92
atm) is almost 100 X that of Earth
 Equivalent to pressures at ~1-km depth in the sea
 What are the potential geologic and volcanologic
implications?

Perpetual clouds make the surface extremely
hot (surface T ~ 735K = 460 C)
 Glowing, yellowish white sky, “like being inside a
giant fluorescent light bulb”
 Runaway greenhouse effect
 Surface temperatures are hot enough to melt Pb
 What are the potential geologic and volcanologic
implications?
Crumpler and Aubele, 2000
Volcanologic implications of
atmospheric pressure and heat

High atmospheric surface pressure
 Everything else being equal, will inhibit vesiculation of magma,
leading to less explosive eruption (some ash suspected; no ashflow tuffs documented)
 Makes wind velocities very low (few dunes observed on Venus)

High ambient surface temperature
 Slow the rate of solidification of lavas
 Prevent water from existing on or below surface
 Everything else being equal, would diminish potential to form
maars, tuff rings, etc.
 Potentially could increase long term rates of geological strain in
areas of high, mountainous relief
Tesserae

Complexly fractured, and frequently elevated,
terrain
 Characterized by a mosaic-like pattern of pervasive
orthogonal fractures, ridges, and troughs

Oldest preserved surfaces on Venus
 Include most of the large, continent-like elevated
areas that constitute ~15% of the surface

Frequently embayed or covered by later
volcanic plains and individual volcanic centers
Turcotte and Schubert, 2002
Distribution of tesserae
Lunar and Planetary Institute, 1997, Venus Slide Set, #37
Impact craters

840 impact craters have been identified on Venus
 Diameters range from 2 to 280 km
 Essentially randomly distributed

Has few small impact craters
 Relative to Moon, Mercury, or Mars
 Attributed to dense atmosphere of Venus, which burns up
small meteors

Surface of Venus appears to be of a near-uniform
age
 Unlike Moon and Mars, where older and younger terrains
are identified
 Correlation of impact flux with craters on Moon, the Earth,
and Mars indicate a mean surface age of 0.5 ± 0.3 Ga
 Hypothesized that a large fraction (80-90%) of Venus was
covered by fresh volcanic flows during a period of 10-50
Myr
Turcotte and Schubert, 2002
Distribution of impact craters
Lunar and Planetary Institute, 1997, Venus Slide Set, #34
Impact craters
Small-medium impact craters
Lunar and Planetary Institute, 1997,
Venus Slide Set, #31
Large impact craters
Lunar and Planetary Institute,
1997, Venus Slide Set, #32
Terrae

Most of highlands concentrated into two main continentsized areas
 Ishtar Terra and Aphrodite Terra

Ishtar Terra
 Located in Venus’ northern hemisphere
 Size of Australia
 Contains only elevated plateau, Lakshmi Planum, which is
ringed by mountain belts

Aphrodite Terra




Located near the equator
Size of Africa
Length of 1500 km
Reminiscent of major continental collision zones on Earth, like
mountain belt extending from Alps to Himalayas
Turcotte and Schubert, 2002
Ishtar Terra and Lakshmi Planum
Lunar and Planetary Institute, 1997, Venus Slide Set, #14
Tectonic features similar to
continental rifts on Earth

Beta Regio
 Domal structure with diameter of 2000 km
 Swell amplitude of ~2 km
 Well-defined central rift valley with a depth of 1 – 2
km
 Some evidence of a three-armed form (aulacogen)

Beta Regio is dominated by two basaltic shield
volcanic features
 Theia Mons and Rhea Mons, each 4 km high
A smooth planet
Major highland and lowland areas

64% of surface is a plains
province
 Elevation differences of <2 km

5% of surface is highland areas
 As much as 10 km above the
plains

31% of surface is lowlands
 2 to 3 km below the plains

Lunar and Planetary Institute, 1997,
Venus Slide Set, #7
Local elevation extremes
roughly comparable to Earth
 But global topographic
variations are much smaller on
Venus
Turcotte and Schubert, 2002
Composite radar images of two
hemispheres of Venus
0° E
180° E
Maxwell Montes
Heng-o Corona
Alpha Regio
Aphrodite Terra
Artemis Corona
Turcotte and Schubert, 2002, Fig. 1-73
Volcanic and magmatic centers on
Venus
Crumpler and Aubele, 2000, Fig. 1
Types of magmatic features on
Venus

Volcanoes
 Large volcanoes
 Intermediate
volcanoes
 Small volcanoes and
fields of small shield
volcanoes (colles)
 Calderas (often,
patera, irregular
depressions)

Lava flows and
channels
 Plains lavas
 Lava flow fields (fluctii)
 Unusual lava flows
 Lava channels (canali)

Magmatic structures
 Coronae
 Arachnoids
 Radial (stellate)
fracture centers
Classification of volcanoes by size

Large volcanoes
Diameters >100 km

Intermediate volcanoes
Diameters 20 - 100 km

Small volcanoes and fields of small shield
volcanoes (colles)
Diameters <20 km
Morphologic types of volcanoes


Large volcano
Intermediate volcano
 Radially patterned domes
 Steep-sided domes
 Pancake domes
 Scalloped domes
 Modified or fluted domes


Small volcanoes and fields of small shield
volcanoes (colles)
Calderas (often, patera, irregular depressions)
Large volcanoes

Chloris Mons
 Shield volcano
 300 km in diameter


Numerous light and
dark lava flows and
radiating fractures
Distal ends of flows are
radar bright
 Relatively rough and
blockier?

Several small
volcanoes with steepsided dome morphology
near the summit
Crumpler and Aubele, 2000, Fig. 2
Large volcanoes


Diameter >100 km
Relatively low relief
 Averaging 1.5 km high

Overall morphology similar to many terrestrial
shield volcanoes such as Mauna Kea or Etna
 Subsidiary cones with steep-sided morphology and
central pits are scattered about the summit

Total identified on Venus: 168
 Occur preferentially in intermediate to higher
elevations

Volcanoes of equivalent diameter occur on Mars
 But volumes of large volcanoes on Venus are much
less because of lower relief
Sapas Mons, Venus



3-D perspective view with 10X vert. exag.
Large, broad shield volcano
Maat Mons, another volcano in the distance, is only 1.5 km high
Crumpler and Aubele, 2000, Title Banner; JPL image
Maat Mons, Venus

Simulated view of Maat
Mons
 Large, broad shield
volcano at 1°N, 195°E


False-colored SAR
imagery overlaid on
topography rendered as
a 3-D surface, with
simulated clouds
Perspective view with
20X vert. exag.
 Field of view ~1000 km
Lunar and Planetary Institute, 1997,
Venus Slide Set, #21
Distribution of large volcanoes and
calderas
Lunar and Planetary Institute, 1997, Venus Slide Set, #35
Intermediate volcanoes
Diameter 20 - 100 km
 Morphologic types

Radially patterned domes
Steep-sided domes
Pancake domes (farra)
Scalloped domes
Modified or fluted domes
Tholi
Volcano of intermediate size

A simple intermediate
volcano
 20 km in diameter


Radial bright and
dark lava flows
Summit caldera
Crumpler and Aubele, 2000, Fig. 3
Volcano of intermediate size

Intermediate
volcano located
at 13.5°S,
315.5°E
Lunar and Planetary
Institute, 1997, Venus
Slide Set, #23
Steep-sided dome

Steep-sided dome
 Convex profile
 ~40 km in diameter

Located on set of
annular fractures
defining the margins
of a corona
Crumpler and Aubele, 2000, Fig. 4
Pancake domes (farra)

Steep sided domes that
are
 Broad and flat
 Very circular
 Steep along their
perimeter

Apparent emplacement
 In a single episode of
volcanism

Seem to require
 Highly viscous, perhaps
silicic magma

Located just southeast of
Alpha Regio
 At 30°S, 12°E
Lunar and Planetary Institute,
1997, Venus Slide Set, #24
Fluted dome

Fluted dome on right
 Convex profile
 ~25 km in diameter


Deep central crater
with inverted conical
profile
Pancake-like steepsided dome at left
 ~35 km in diameter
Crumpler and Aubele, 2000, Fig. 5
Tholi


Intermediate volcano in
which the flanks appear
steep relative to most
volcanoes on Venus
Mahuea Tholus
 Located at 37.3°S, 165.1°E
 The bright, ridged flows
stand about 600 m above
the surrounding plains
 Inner tier sits >1000 m high
 Thickness suggests that
they were unusually
viscous at time of
emplacement
Lunar and Planetary Institute, 1997,
Venus Slide Set, #25
Small volcanic field

“Shield field”
 Diameter 150 km
 Mixture of steep-sided domes and shields
Crumpler and Aubele, 2000, Fig. 6
Small volcanic field

“Shield field”
 Centered at
78.4°S, 43.0°E
 Located in the
volcanic plains
Lunar and Planetary Institute,
1997, Venus Slide Set, #26
Caldera


Circular caldera with
ring fractures
Radar altimetry
profile
 Demonstrating depth
of caldera of 1 km
Crumpler and Aubele, 2000, Fig. 7A, B
Lava flows and channels
Plains lavas
 Lava flow fields (fluctii)
 Unusual lava flows
 Lava channels (canali)

Large lava field


Large lava field (FOV
400 km)
Many small
volcanoes located
near source area
Crumpler and Aubele, 2000, Fig. 8
Lava channels
Crumpler and Aubele, 2000, Fig. 9A, B
Magmatic structures

Features characterized by surface deformation
associated with subsurface magmatism on a
large scale
 Magmatism may be deep-seated reservoirs
 Volcanic edifices may be relatively minor or
subsidiary to the structures indicative of deformation

Process of formation may be more akin to
dynamic topography on Earth
 Associated from regional uplift from upwelling mantle
plumes
Types of magmatic structures

Coronae
Almost unique to Venus
But also observed on Miranda, a moon of
Uranus
Arachnoids
 Radial (stellate) fracture centers

Coronae

Dominantly circular to elliptical
structures
 May be associated with mantle
plumes or hot spots

Characteristics
 Annulus of concentric ridges or
fractures
 Interior that may be high or low
 Peripheral moat or trough
 Large and small volcanoes
frequently present within the
corona or on its margins
 But exhibit a variety of
topographic forms

Interpreted origin
 Rising plumes push the crust
upward into a dome
 Dome collapses in center
 Molten lava leaks out around
sides
Crumpler and Aubele, 2000, Fig. 10
Small to medium coronae
Lunar and Planetary Institute,
1997, Venus Slide Set, #28
Large coronae
Lunar and Planetary Institute,
1997, Venus Slide Set, #29
Stages of corona evolution

Surface domes and
cracks in a radial fashion
(A-A’)
 As a response to rise of
hot magma body a few
hundred km across in the
mantle

Three features centered at 29.8°S,
274.3°E in an area 945 x 945 km along a
rift zone that illustrate evolutionary
sequence of corona structures
Concentric faults and a
surrounding trough begin
to form (B-B’)
 As the domed structure
begins to collapse

Central plateau with a
raised annulus
surrounded by a circular
trough (C-C’)
 When collapse is
complete
Lunar and Planetary Institute, 1997, Venus
Slide Set, #30
Arachnoids


Similar to coronae, but with strongly developed
radial patterns
Annular structural patterns consisting of
 Concentric or circular pattern of fractures or ridges,
With
 Radial arrays of fractures or ridges extending
outward for several radii
 Interior flows and small shield volcanoes

Radial fractures frequently merge outward with
the linear patterns of the fracture belts on which
arachnoids are arranged
 Hence the name: spiders along webs of linear
fracture belts
Arachnoids
Crumpler and Aubele, 2000, Fig. 12A, B
Simple radial fracture center
Crumpler and Aubele, 2000, Fig. 13
Distribution of coronae
Lunar and Planetary Institute, 1997, Venus Slide Set, #36
What did Venus teach us about
volcanology of Earth?

Or, what did it reveal about
 “What we don’t know we don’t know” about
volcanism on Earth?

Example: Radial fractures and concentric
fractures are typical of almost all magmatic and
volcanic centers on Venus
 And they extend for 100s and 1000s of km

Does similar deformation occur on Earth, but it
is poorly preserved or erased during lifetime of
volcanic activity?
 On Earth, most recognized radial dike swarms are
deeply eroded; connection with surface deformation
no longer available for study
Volcanologic comparisons

Absolute numbers of volcanoes
Venus is second only to Earth
Is a reflection of similarity of planetary size

Number of well-preserved and pristine
volcanic landforms
Venus exceeds Earth and Mars combined
Dry, CO2–rich atmosphere on Venus
preserves volcanic landforms
Comparison to Earth

Planetary size and density control
magnitude and longevity of geologic
activity and volcanism
Barring unusual circumstances such as
extraordinary tidal forces (e.g., Io)

Size and density of Venus similar to Earth
Diameter only 330 km less than Earth
Volcanism, thus, likely to be most Earth-like
of all planets
Evidence for lack of an
asthenosphere
High correlation between gravity and
topography on Venus compared to Earth
 Used to infer that Venus lacks a lowviscosity layer (asthenosphere)

Asthenosphere acts as a lubricating layer for
terrestrial plate tectonics

Thus volcanism on Venus probably is
dominated by plume-like origins
Mars

Explored by
 Flybys of Mariner 4
(1965), Mariners 6 and 7
(1969), and Mariner 9
(1971)
 Viking 1 and 2 orbiters
and landers (1976)
 Mars Pathfinder and
Sojourner Rover (19971998)
 Mars Global Surveyor
(1999-present)
 Mars Odyssey (2002present)
 Mars Express (2003present)
 Mars Exploration Rovers
Spirit and Opportunity
(2004)
 Phoenix Lander (2008)
 Curiosity Rover (2012)
Press and Siever, 2001, Fig. 1.10
Comparison of properties

Equatorial radius (km)
 Earth 6378
 Mars 3394
Therefore, about half the radius of Earth

Mass (1024 kg)
 Earth 5.97
 Mars 0.64
Therefore, about one-ninth the mass of Earth

Density (kg m-3)
 Earth 5515
 Mars 3933
Combined with a small moment of inertia, is evidence that Mars has a
metallic core
Model values of core radius range from 0.4 to 0.6 of Martian radius

Mean surface temperature (K)
 Earth 288
 Mars 218
Turcotte and Schubert, 2002
Mars

Phobos
There is no global Martian
magnetic field
 In spite of having a metallic
core

Crust of Mars has strong
concentrations of remanent
magnetism
 Implying that Mars had a
global magnetic field in the
past, probably prior to 4 Ga

Has two very small (10-20
km across), irregularly
shaped satellites
 Phobos (inner, larger)
 Deimos
Deimos
Phobos
Turcotte and Schubert, 2002, Fig. 1-72
Early history

Initially hot and differentiated Mars
 Acceptance of Mars as a parent body of SNC group of
meteorites
 Would require core formation at about 4.6 Ma

SNC group of meteorites
 Meteorites found on Earth that apparently escaped Martian
gravity field after one or more large impacts
 SNC: S-Shergotty, N-Nakhla, C-Chassigny
 Have a relatively young age, 4.6 Ga
 Trapped gases similar to atmosphere of Mars


Old age (>4 Ga) of southern highlands suggests early
crustal differentiation (a “hot” early Mars)
Inference of old, water-carved features consistent with
early outgassing and an early atmosphere
Turcotte and Schubert, 2002
Present surface
Sand dune field

Being actively
modified by
atmospheric erosion
and deposition
 Eolian dune fields
 Yardangs
 Dust devils and dust
storms
Turcotte and Schubert, 2002, Fig. 1-71
Chemical compositions of Martian
materials and Shergotty meteorite
Zimbelman, 2000, Table 1
Mars: Land of large volcanoes,
though few in number


Central volcanoes and volcanic fields (white)
Cratered highlands (black)
Zimbelman, 2000, Fig. 1
Volcanic features on Mars

Mons
Large isolated mountain

Tholus (pl. tholi)
Isolated domical small mountain or hill, with
slopes much steeper than that of a patera

Patera (pl. paterae)
Irregular or complex crater with scalloped
edges, surrounded by shallow flank slopes
Named volcanic centers on Mars
Zimbelman, 2000, Fig. 1
Zimbelman, 2000, Table 1
Mons

Typical basaltic shield
volcanoes
Olympus Mons
 But on a grander scale than on
Earth

Maximum slopes
 Flanks typically ~5° (steeper
for Elysium Mons)
 Shallower on summit and at
base

Escarpment around base
 Irregular, up to 8 km high

Nested summit craters
 Collapse of magma reservoirs

Large size of Olympus Mons
 Equivalent to integrated
volume of Hawaiian-Emperor
chain
 Stationary mantle source,
stationary lithosphere
Zimbelman, 2000, Fig. 2
Olympus Mons

A shield volcano on Mars the size of Arizona
 Diameter ~600 km
 Relief: 21 km above datum (akin to sea level)
Mons

The three Tharsis Montes
and smaller volcanoes to
the north
 Form a straight line

Possible interpretations
 Were formed while a
crustal plate moved over
a hot spot
 Constitute extinct island
arc volcanoes during a
period of subduction

Olympus Mons
 May have formed after the
plate motion stopped
Zimbelman, 2000, Fig. 1
Aligned Tharsis Montes
Lockwood and Hazlett, 2010, Fig. 12.20
Lockwood and Hazlett, 2010, Fig. 12.19
Tholi


Isolated, domical
mountains or hills
Slopes much
steeper than that of
most paterae
Smaller than 200
km in diameter
Ceraunius Tholus
 Lava dome
 Elongate crater at top
created by oblique
impact at northern base
 Dimensions 150 X 100
km
 Lava channel flowed
into crater
Zimbelman, 2000, Fig. 3
Paterae

Irregular or complex craters
Scalloped edges
Surrounded by shallow flank slopes

Possibly have an important pyroclastic
component
Flows or falls?
Suggestive of increased volatile content of
magmas?
Paterae
Tyrrhena Patera (FOV ~ 120 km)

Highland Paterae
 Irregular or complex
crater with scalloped
edges that are
surrounded by shallow
flank slopes

Intensely eroded
appearance
 Removal of friable
material?
Zimbelman, 2000, Fig. 4
Volcanic fields (white)
Volcanic plains
Lava flow margins (FOV ~ 54 km)
Zimbelman, 2000, Fig. 1
http://mars.nasa.gov/
Zimbelman, 2000, Fig. 6
Volcanoes and
ice on Mars

HiRISE image of possible rootless cones east
of Elysium region. Chains of rings interpreted
to be caused by steam explosions when lava
moved over ground that was rich in water ice.
Large amounts of water
ice
 Believed to be present in
Martian subsurface

Interaction of ice with
molten rock
 Produces distinct
landforms

Features identified
recently include
"Rootless Cones" on Mars – due to lava flows
interacting with water (MRO, January 4, 2013)
 Rootless cones created by
phreatic explosions (e.g.,
Hamilton et al., 2010)
 Lahars or debris flows
Images from Wikipedia Site, Volcanology of Mars
Young
Volcanic history of Mars

Amazonian epoch (<500 Ma?)
 Voluminous eruptions on plains and large central
volcanoes

Hesperian epoch
Old
 Massive eruptions of lava that formed volcanic
plains (basalts, basaltic andesites?)

Noachian epoch (>3.7 Ga?)
 Densely cratered highlands
Io

Galilean satellites
(four largest
satellites of Jupiter)





Io
Europa
Ganymede
Callisto
Io
 Innermost satellite of
Jupiter

Intense magmatism
on Io
 Driven not by
internal heat
 But by
gravitational
attractions of
Jupiter and
Europa
Properties of Io

Size and bulk density
 Similar to those of Earth’s Moon
 Suggests predominantly silicate composition

Absence of impact craters
 Surface was young
 Craters obliterated
 Reflected light dominated by SO2

Enhanced thermal emissions
 400 K “hot spots” related to volcanism
 Compared to typical surface temperatures of 85 K
(night) and 140 K (day)
 Many volcanic plumes, but uncommon near poles
Exploration

Explored by
 Voyager 1 in
1979
 Voyager 2
 Hubble Space
telescope
 International
Ultraviolet
Explorer
satellite
 Galileo
spacecraft
since 1996
Lopes-Gautier, 2000, Fig. 2
Volcanism on Io first seen on this Voyager I
image taken on 8 Mar 1979: Two eruptions:
Pele plume on edge of disk rising 260 km
above the surface, and Loki plume as bright
spot on nightside terminator, catching rays of
rising sun
Io


Most volcanically
active object in the
solar system
Heat flow much higher
than Earth’s
 Several volcanoes
erupt lavas that are
hotter than any erupted
on the Earth today
Lopes-Gautier, 2000, Fig. 1
Surface features



Mountains
Smooth plains
Volcanic constructs
 Absence of large volcanic
edifices


Shield volcanoes are low
Magmas of low viscosity?
 Calderas



Steep walls and flat
floors
20 – 200 km in
diameter
As deep as 2 km
Lockwood and Hazlett, 2010, Fig. 12.21
Scalloped (possibly sapped) volcanic
tableland and compound caldera of
Tvashtar patera on Io; ongoing effusive
eruption on left)
Eruptive products

Red materials
 Ephemeral (lasting a few years?)
 Pyroclastic deposits—fall deposits from plumes?
 Associated with hot spots and plumes

Very dark deposits
 Also associated with hot spots

Different colors may reflect different allotropes
(crystal structures) of sulfur
 Cooled rapidly from different temperatures
Io

Io imaged by Galileo’s Solid State Imaging
System on 7 Sept 1996
Colorful surface result of
constant volcanic
activity
 Silicate materials and
sulfur compounds

Most recent deposits
 Red and black

Volcano Prometheus is
right of center
 Dark lava flow winding
to toward the right
 Annulus of bright
deposits from plume

Volcano Pele is just
below equator at left
edge
 Dark, surrounded by
large red deposits
Lopes-Gautier, 2000, Fig. 1
Changes in bright red deposits
around Pele plume

Changes in
shape of annular
deposits
 Between Voyager
1 in March of
1979 and
Voyager 2 in of
July 1979

Changing shape
of vent from
which plume
emerged
Lopes-Gautier, 2000, Fig. 3
Distribution of volcanic centers on Io

Named features are active plumes
Lopes-Gautier, 2000, Fig. 7; after McEwen et al., 1999
Cryovolcanism

Definition
 Eruption of liquid or vapor phases (with or without
entrained solids) of water or other volatiles that would
be frozen solid at the normal temperature of an icy
satellite’s surface

Known to occur
 Geyser-like plumes of nitrogen were discovered on
Triton, a moon of Neptune, by Voyager 2

Indirect evidence that it has taken place
elsewhere
 Might be active today
Physical properties of larger natural
satellites of the outer solar system
Geissler, 2000, Table 1
Density issue

Buoyant rise of silicate magmas is driven by
liquid-solid density contrast
 In contrast, water undergoes a volume reduction
(density increase) upon melting
 Would not buoyantly rise to surface

Melting of water-rich magmas probably requires
presence of salts or ammonia
 Variety of possible ices, liquids, clathrates (cage-like
structures that trap absorbed gases such as CH4,
CO2, N2)
Major ices of
outer solar
system
Geissler, 2000, Table 2
Densities of
candidate
cryomagmas
Geissler, 2000, Fig. 1
Mobilities of
cryomagmas

Comparison of
mobilities
 Crystal-free
cryomagmas at their
liquidus temperatures
 Silicate lavas
Geissler, 2000, Fig. 2
South pole of Triton, Neptune’s
only planet-sized moon

Bright polar
cap
 Made up of
relatively
mobile N2
ice,
subliming
in the
summer
sunshine

Dark
streaks are
active or
recent
plumes
Geissler, 2000, Fig. 3
Nitrogen geyser
on Triton

Mahilani plume
extending downwind
 Plume rises 8 km from
surface
 Extends 150 km
downwind
Geissler, 2000, Fig. 4
Cryovolcanic flows on Triton

Evidence of
extensive melting
 Perhaps when
moon was
gravitationally
captured into orbit
about Neptune

Two large calderalike lake features
near the equator
 Rimless pits to the
right of the impact
crater may be the
source of the
smooth materials
Geissler, 2000, Fig. 5
Ductile material on Ariel

Ariel
 A moon of Uranus

Central channels
resemble collapsed
lava tubes
 Arrow indicates 30km-diameter crater
now buried by viscous
flows
Geissler, 2000, Fig. 6
Miranda

Miranda
 An icy moon of Uranus

Exhibits
 Three polygonal-shaped
regions of intense
deformation known as
coronae: Elsinore,
Inverness, and Arden

Coronae
 Have concentric orientation
of ridges and troughs

Numerical models
 Coronae can be created by
sluggish-lid convection of ice
powered by tidal heating
 Convection develops if core
radius is less than half the
satellite radius
Hammond and Barr, 2014, Fig. 1
Enceladus

Enceladus
 A moon of Saturn

Evidence for
extensive resurfacing
 Large areas are
smooth and
uncratered
 Narrow fractures cut
the crust—note strikeslip fault in lower left

High albedo--snowwhite surface
 Surface composition
of nearly pure H2O
frost
Geissler, 2000, Fig. 8
Puzzle of Enceladus

Energy sources for the activity are unclear
 Satellite is too small for gravitational or radiogenic
heating
 Tidal heating insufficient to be effective

Enceladus may be the source of the particles
that make up the outermost of Saturn’s rings
 Faint E ring
 Orbit of Enceladus is embedded in densest part of
the ring
Dione

Dione
 A moon of Saturn

Wispy albedo,
perhaps due to
frost deposited
during a
cryovolcanic
eruption
Geissler, 2000, Fig. 9
Ganymede

Ganymede
 A moon of
Jupiter

Evidence for
tectonism
rather than
cryovolcanism
Geissler, 2000, Fig. 10
Ganymede

Ganymede
 A moon of
Jupiter

Largest moon in
the solar
system
 Larger than the
planet Mercury
(though less
dense and less
massive)

Groove lanes
thought to be
volcanic in origin
 Uruk Sulcus
region
Geissler, 2000, Fig. 11
Comparative planetology, revisited
Press and Siever, 2001, Fig. 1.3
Comparison of Mons
Lunar and Planetary Institute, 1997, Venus Slide Set, #38
Comparison of craters
Lunar and Planetary Institute,
1997, Venus Slide Set, #39
Comparison of
rifts
Lunar and Planetary Institute,
1997, Venus Slide Set, #40
Summary

Venus
 Volcanoes: Large volcanoes, intermediate volcanoes (various
domes), small volcanoes and fields of small shield volcanoes,
calderas, lava flows and channels
 Magmatic structures characterized by surface deformation
associated with large-scale subsurface magmatism: Coronae,
arachnoids, radial fracture centers

Mars
 Volcanically inactive planet with huge volcanoes

Io
 Vigorous volcanism driven by tidal forces; sulfur is an important
product

Cryovolcanism
 May be common on outer planets and their satellites

Comparative planetology, revisited
 Many features are similar on various planetary bodies
Next time: Societal applications: Geothermal resources,
soils, and climate