Index
Dikes
on Pavonis Mons
Submarine
domes and terraces on Kilauea
Project summaries
Dikes
on Pavonis Mons
I started working on this project as my DEA thesis in the university
of Paris XI (Orsay, France) under the direction of J. Bébien and
B. Bonin. There is still a lot to see on the Viking images of Mars! I mapped
Pavonis Mons, a giant shield volcano on Mars, and found evidence for a
concentric dike swarm, a pretty amazing beast with important indications
on the structure and state of state of the volcano. Then I crossed the
atlantic and forgot most about it, until I met Richard Ernst, who
presuaded me to go back to that project and write it up! I took the occasion
to add a numerical modeling effort of the state of stress of the edifice,
and quite a few comments on the implication for plumes in the region of
Tharsis.
Montési, L. G. J. , Concentric dike swarms on the flanks of Pavonis Mons: Implications for the evolution of Martian shield volcanoes and mantle plumes. Locating Pre-Mesozoic Mantle Plumes, Geol. Soc. Spec. Pap., eds. R. E. Ernst and K. L. Buchan, accepted, 2000
AbstractConference Abstract: EUG 1997; LPSC 1999
Full text (PDF version)
Submarine
domes and terraces on Kilauea
This is mostly the work of Wenlu Zhu and Debbie smith, but I do help a little, especially in the modelling aspects of this projects. Wenlu and Debbie went on a research cruise in Hawaii, to take a close look at the Puna ridge, a submarine extension of Kilauea volcano. Unlike its subaerial counterpart, the East rift zone, Puna ridge has quite few domical feature and its flanks are covered with "terraces". We try to find how these domes are formed, by using simple numerical model of flow enplacement. This is a preliminary study, where we focus mainly on slope effects on a lava flow: Why are there domes on the ummit of the ridge and terraces on the flanks? We hope to complete the study by including the effect of colling and freezing of the lava. the largest dome is called Maka Nui, "big eye" in hawaiian. Someday, this study might involve pancake domes on Venus, or dike propagation in the Puna ridge,
Zhu, W., Smith, D. K., and Montési, L. G. J. , Effects of regional slope on viscous flows: A preliminary study of lava terrace emplacement at submarine rift zones. Journal of Volcanology and Geothermal research, submitted, 2001
Abstract
Full text (PDF version)
Conference
Abstract: Fall AGU 1999
Conference
Abstracts
Zhu,
W., Smith, D. K., and Montési, L. G. J., Effects of regional
slope on viscous flows: A preliminary study of submarine terrace emplacement,
EOS
Trans. Am. Geophys. Un., 80, Fall Meet. Suppl., F1100, 1999
The Puna Ridge is the submarine extension of Kilauea Volcano's East Rift Zone (ERZ). It extends ~75 km from the shoreline to its distal end, plunging from sea level to a depth of 5400 m. The volcanic morphology of the submarine Puna ridge is strikingly different from the subaerial ERZ morphology at a scale of 1 to 2 km despite similar modes of construction, i.e. piling up of lava erupted from fissures along a rift zone. Low-relief lava flows drape the smooth and gentle slopes of the ERZ. Large edifices are not commonly observed. By contrast, the lateral slopes of the Puna Ridge are both steeper (~200 m/km compared to ~50 m/km on the ERZ) and more irregular at the 1-2 km scale. Semi-circular flat-topped features (terraces) that have diameters ranging up to 1 km or more and sides up to several hundreds of meters high cover the Puna Ridge axis and flanks over its entire length.
To understand how the submarine lava terraces at the Puna Ridge formed and why they are not observed on the subaerial ERZ, we adapted the existing isoviscous gravity flow models on an inclined surface to simulate the evolution and emplacement of lava flows under both subaerial and submarine conditions. Using this preliminary model, we are able to understand how lava viscosity, pre-existing slope, effusion rate, and lava volume affect meso-scale lava morphology. For example, our numerical results show that the spreading of a gravity flow is relatively slower in submarine environments than that in subaerial environments because of the buoyancy of the seawater. Ultimately, we aim to develop and implement a more comprehensive and realistic model in which temperature variations and cooling effects will be taken into account and gain a better understanding of the controls on submarine lava terrace formation.
Montési, L. G. J., Concentric dike swarm and internal structure of Pavonis Mons (Mars), Lunar Planet. Sci. XXX, abstr. 1251 , 1999.PDF version
Bébien, J., Montési, L., and Bonin, B., Flank morphology and internal structure of the Tharsis shield volcanoes (Mars), Terra Nova, 9, abst. Suppl. 01, p. 192, 1997
Paper
Abstracts
Montési,
L. G. J. , Concentric dike swarms on the flanks of Pavonis Mons: Implications
for the evolution of Martian shield volcanoes and mantle plumes. Locating
Pre-Mesozoic Mantle Plumes, Geol. Soc. Spec. Pap., eds. R. E. Ernst
and K. L. Buchan, accepted, 2000
The volcanoes of the Tharsis province are the most recent surface manifestation
of mantle plumes on Mars. Therefore, studying their structure and evolution
helps to constrain the nature of planetary heat loss. A generic evolution
of shields in the Tharsis province has been proposed in the literature,
in which Arsia Mons is the most evolved edifice and Olympus Mons the least
evolved. This study analyzes concentric depressions on the flanks of the
volcanoes, using mostly Viking Orbiter images of Pavonis Mons, Mars. We
document a morphological evolution from simple grabens to continuous troughs
and pit chains that can be explained as the result of interaction between
shallow dikes and the Martian permafrost. The concentric motif of the dike
swarm implies that the least compressive stress was radial. Several mechanisms
generating radial tension are reviewed, among which we favor either magmatic
underplating or burial of the lower flanks of the edifice. This may constitute
an analogue to the concentric dike swarms recently proposed as indicative
of terrestrial plumes. The Tharsis Montes may also possess off-center magma
reservoirs. Although Arsia Mons is the most evolved of the Tharsis Montes
in some aspects, other evidence suggests evolution from an Arsia-like to
an Olympus-like volcano. Thus, Martian shields can follow two divergent
branches of evolution. We also discuss a 2-scale plume model to explain
the volcanism of the Tharsis province.
Zhu, W., Smith, D. K., and Montési, L. G. J. , Effects of regional slope on viscous flows: A preliminary study of lava terrace emplacement at submarine rift zones. Journal of Volcanology and Geothermal research, submitted, 2001
To understand how large submarine lava terraces form and why they are not commonly observed on land, we developed an isoviscous gravity flow model on an inclined surface that simulates the evolution and emplacement of lava flows under submarine conditions. Using this preliminary model, we are able to quantify how laa viscosity, pre-existing topographic slope, effusion rate, and lava volume affect meso-scale lava morphology. Our simulation results show that in general high lava viscosity, gentle regional slope, and low effusion rate favor the formation of large teeaces, buut environmental conditions also play an important role. A gravity flow spreads more slowly underwater than subaerially. We also conclude that for low viscosity basaltic lava, the cooling of the lava body is one of the most critical factors that affect its shape. This study shoes that the isoviscous model, though oversimplified, provides a quantitative tool to relate lava morphology to eruption characteristics. To gain a better understanding of the controls on submarine lava terrace formation, future models must take into account the temporal and spatial variation of lava viscosity, especially the effects of a brittle outer shell.
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