Gravitational spreading, structure, and evolution of Martian & terrestrial volcanoes

 

Principal Investigator:

Juli Morgan (Rice University)

Collaborators:

Pat McGovern (Lunar & Planet. Institute)

John Smith (University of Hawaii)

Mark Bulmer (University of Maryland)

Undergraduate Students:

Ulyana Horodyskij

Funding Sources:

NASA (MDAP)

 

Figure 1

 

Many large volcanoes undergo gravitational spreading as they grow.  Such spreading is accommodated by a range of processes, including surficial avalanching and slumping, as well as deep-seated landsliding, and in rare cases, full-blown volcanic spreading, in which the volcanic flanks are translated outwards as the summit regions subside.  Hawaiian volcanoes are known to exhibit this behavior today, and Olympus Mons on Mars is thought to have done so in the past (Figure 1).  As a test of this hypothesis, we have examined the morphology and surficial structure of Olympus Mons using data and images from the Mars Orbital Camera (MOC) and MOLA altimetry.  We have compared our observations to similar terrestrial volcanoes, such as Kilauea and several Canarian volcanoes.  The evidence strongly supports the concept that Olympus Mons has undergone repeated cycles of flank collapse followed by outward spreading and frontal overthrusting [McGovern et al., 2004].

 

2D particle dynamics simulations of granular piles provide further insights into the mechanical conditions responsible for different modes of volcanic spreading [Morgan & McGovern, 2005a, 2005b].  Under uniform basal and internal strength conditions, granular piles grow self-similarly, developing distinctive stratigraphies, morphologies, and structures (Figure 2).  Piles constructed upon cohesive substrates exhibit particle avalanching, forming outward dipping strata and angle of repose slopes.  Systematic decreases in basal strength lead to progressively deeper and steeper internal detachment faults and slip along a basal d残ollement; landslide forms grade from shallow slumps, to deep-seated landslide, and finally, axial subsidence and outward flank displacements, or volcanic spreading.  Surface slopes decrease, and develop concave up morphologies with decreasing d残ollement strength; depositional layers tilt progressively inward. The gentle slopes of Hawaiian volcanoes and Olympus Mons on Mars suggest weak basal d残ollements that enable volcanic spreading.  High-angle normal faults, favored above weak d残ollements, are interpreted in both settings, and explain catastrophic sector collapse in Hawaii, and broad aureole deposits surrounding Olympus Mons.  In contrast, steeper slopes and shallow detachment faults predominate in the Canary Islands, thought to lack a weak d残ollement, favoring smaller, more frequent slope failures than predicted for Hawaii.

 

Figure 2

 

Volcanoes that grow upon pre-existing edifices, such as Kilauea upon Mauna Loa volcano, produced asymmetric spreading scenarios in which the volcanoes buttress each other [Morgan, 2006].  The degree of buttressing depends on the relative positions of the two edifices: if the secondary edifice grows high upon the flanks of the primary edifice, outward spreading of the underlying flank is enhanced; if the secondary edifice is built low upon the primary flanks, spreading of the underlying flank is effectively prevented, or possibly reversed.  Furthermore, as the second edifice grows, it subsides into the underlying flank, partitioning it into a mobile downslope region entrained by spreading of the second edifice, and a comparatively stable upper flank region.  These results suggest that much of the mass of volcano may lie deeply buried within the underlying flank of Mauna Loa, while older Mauna Loa rocks may lie far from their source beneath the mobile flank of the younger volcano.

 

Figure 3

 

Papers:

McGovern, P.J., Morgan, J.K., and Higbie, M.A., in prep., Volcanic Spreading and the Quadrant Structure of Olympus Mons, Mars, to be submitted to Geology.

Morgan, J.K., 2006, Volcanotectonic interactions between Mauna Loa and Kilauea volcanoes, Insights from 2-D discrete element simulations, J. Volc. Geotherm. Res., 151, 109-131.

Morgan, J.K., and McGovern, P.J., 2005, Discrete element simulations of gravitational volcanic deformation: 1. Deformation structures and geometries, J. Geophys. Res., 110, B05402, doi: 10.1029/2004JB003252.

Morgan, J.K., and McGovern, P.J., 2005, Discrete element simulations of gravitational volcanic deformation: 2. Mechanical analysis, J. Geophys. Res., 110, B05403, doi: 10.1029/2004JB003253.

McGovern, P.J., Smith, J.R., Morgan, J.K., Bulmer, M., 2004, Olympus Mons aureole deposits: New evidence for a flank-failure origin, J. Geophys. Res., 109, E8, E08008, doi: 10.1029/2004JE002258.

 

Abstracts:

McGovern, P.J., Morgan, J.K., and Higbie, M.A., Structure and evolution of the Olympus Mons volcanic edifice and basal escarpment, Mars, 37th Lunar Planet. Sci. Conf., Abstract 2329.

McGovern, P.J., and Morgan, J.K., 2005, Spreading of the Olympus Mons edifice, Mars, 36th Lunar Planet. Sci. Conf., Abstract 2258.

McGovern, P.J., Smith, J.R., Morgan, J.K, and Bulmer, M.H., 2004, Repeated cycles of flank growth and collapse on Olympus Mons, Mars:  Comparisons to Hawaiian volcanoes , EOS Trans. AGU, 85, Fall Meet. Suppl., OS23B-1318.

McGovern, P. J., Smith, J.R., Morgan, J.K., and Bulmer, M., 2004, The Olympus Mons aureole deposits: New evidence for a flank failure origin, 35th Lunar Planet. Sci. Conf., Abstract 1980.

Morgan, J.K., and McGovern, P.J., 2003, Discrete element simulations of volcanic spreading: Implications for the structure of Olympus Mons, 34th Lunar Planet. Sci. Conf., Abstract 2088.

McGovern, P.J., Smith, J.R., Morgan, J.K., Bulmer, M., 2003, Olympus Mons aureole deposits and basal scarp: Structural characteristics and implications for flank failure scenarios, 34th Lunar Planet. Sci. Conf., Abstract 2080.

 

Page last modified: 29-Dec-2006