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Volcanic Features and Processes
Spring 2003
Why Study Volcanism?
Key part of geologic history of all terrestrial planets. Provides chemical and sometimes mineralogical information about the interior. Dating of volcanic surfaces, and composition estimates, permit modelling of planetary thermal history and evolution.
Comparative Physical Volcanology
Ascent of magma:
Driving force, Crack formation, Flow of magma, Cooling
Eruption dynamics/pyroclastic deposits:
Volatile exsolution, Plume height, 
Pyroclastic
deposits.
Lava flows
- Rheology;
composition, 
Bingham plastic model. - Lengths of lava flows;
viscosity 1, effusion rate, cooling rate - Shape of volcanic constructs; Si/Fe ratio, volatile abundances, vent geometry and effusion rate
composition
Bingham plastic model
viscositySilicic Volcanism
- Terrestrial (< 60% SiO2)
- Other Terrestrial Planets; No stratovolcanoes or plate tectonics recognized yet, but....
Explosive, volatile rich Stratavolcanoes - 
Etna, Fuji, Ranier
Ash flows, ignimbrites, Katmai
Plate Tectonic 
setting
Andesite reported on Mars in Pathfinder, MGS interpretations
Basaltic Volcanism on the Terrestrial Planets
(back to top)
Major Types of
Basaltic Volcanism
Major Types of
Basaltic VolcanismMid-Ocean Ridges. Only terrestrial.
- Flood basalts = Plateau basalts =
Maria - Earth,
Mars 
closeup,
Moon 
global and 
closeup 1 and probably 
Mercury 1, 
Mercury 2.
Sheets of basalt covering < 105 km 2 to a depth
of km’s. No vents visible, but terrestrial examples have fissure sources.
Mare ridges 1, 
ridges 2. Rare tubes
and 
flow fronts 1,
flow fronts 2. On
all the terrestrial planets. High effusion rates??? Massive Climate
change??? - Plains basalts A region ~104 km2 dotted
with small cones and lava flows. Flows fed by
fissures, cones, and 
tubes
. Need high resolution images but
hints on all except Mercury. - Patera = coronas = low shields Very shallow slopes.
Apollinaris Patera the
only huge example on Mars (1600 km diameter).
Tyrrhena Patera. 100 km scale Coronas
common on Venus. Terrestrial low shields only a few km in size. Made of
long, skinny flows. - Shield volcanos 2°-12°; ~5° slopes, often have
calderas. Both point
and fissure sources. 
Tubes common on the 
Earth, 
Mars, Venus. 
Few km to 
few 
100s of 
km in scale. Low extrusion rates, frequent, 
vent control. - Spatter ramparts: channels
4.19, 
4.20. - Lava lakes/ponds: inflation features
- Smaller Basaltic Landforms
Maria
closeup
global
Mercury 1,
Mercury 2
ridges 2
flow fronts 1,
fissures
tubes
.
Apollinaris Patera
calderas
Tubes
Earth
Mars
Few km
few
100s
km
vent control
4.19
4.20
| Vent area and shape: | Lava flows: |
|---|---|
| Calderas F4.29, 4.32, 4.35 | ‘a’a vs pahoehoe |
| Cinder cones P5 |  Flow lobes |
| Fissures F4.36, 4.21, 4.22, 4.33 | tubes 4.2 |
References
(back to top)Pyroclastic deposits:
Cas and Wright, 1987, Volcanic Successions, 528 pp.
Basaltic eruptions:
Wilson and Head, 1983. "A comparison of volcanic eruption processes on Earth, Moon, Mars, Io, and Venus". Nature, 302, pp. 663-669.
Bingham Plastic Model:
Moore et al., 1978. "Yield strengths of flows on the Earth, Mars, and Moon". Proceedings of the 9th Lunar and Planetary Science Conference, pp. 3351-3378.
Moon:
Wilhelms, 1987. "The Geologic History of the Moon". USGS Prof. Paper 1348, 320pp
Mars:
Mouginis-Mark, Wilson, and Zuber, 1992. "The Physical volcanology of Mars". Ch 13 in Kieffer et al., Mars, Univ. Arizona Press.
Venus:
Head et al., 1991. "Venus volcanism: initial analysis from Magellan data". Science, 252, pp. 276-288.
Mercury:
- Bruce Murray (Incorporates some notes from Laszlo Keszthelyi, 1993) -
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