Olympus Mons Mars: Inferred Changes in Late Stage Effusive Activity Based on Mars Express High Resolution Stereo Camera Data

Details Olympus Mons Mars: Inferred Changes in Late Stage Effusive Activity Based on Mars Express High Resolution Stereo Camera Data Olympus Mons Mars: Inferred Changes in Late Stage Effusive Activity Based on Mars Express High Resolution Stereo Camera Data

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufm.v33c1472b&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #V33C-1472

Other

8429 Lava Rheology And Morphology, 8450 Planetary Volcanism (5480), 5464 Remote Sensing, 5480 Volcanism (8450), 6225 Mars

Scientific paper

Maps of the south flank of Olympus Mons (OM) show the percentage of surface lava flows that were emplaced through lava tubes or channels. Lava tubes are thermally insulated, roofed conduits that transport lava to flow fronts, reflecting long-lived eruptions at low to moderate, fairly steady effusion rates of low viscosity lavas. Lava channels generally result from shorter-lived eruptions and higher, fluctuating effusion rates of higher viscosity lavas. Thus, because channels and tubes tend to result from different eruptive conditions their abundance can be used to characterize the effusive stages of eruptions. We mapped four zones (each 60 by 30 km) extending from the summit of OM (zone 1) to the basal scarp (zone 4). No tube-fed flows (TFF) are present in zone 1. Zone 2 contains up to 40% TFF, while zones 3 and 4 contain 15 to 20% TFF. Fan shaped deposits appear to represent local eruptive centers from which small lava channels radiate. However, these deposits are often associated with TFF upflow; it appears that TFF are disrupted at breaks in slope, forming lava fans, and that this disruption is a controlling factor in the decrease in TFF abundance with distance from the summit. Thus, the fans seem to be the only point sources on the southern flank of OM and their relationship to TFF suggests that in the latest stages of effusive activity the summit was the only eruptive center. Although TFF abundances are not uniform down the flank, at most contacts channels embay TFF. This relationship suggests that the south flank of OM underwent a late-stage change from longer-lived, steady, less viscous, tube-forming eruptions to shorter-lived, fluctuating, more viscous, channel-forming eruptions. Hawaiian shields undergo a similar change in morphology through time; this change could involve (in part) plate tectonics disrupting and increasing the length of the conduit, and/or fractionation of the magma source. In both cases transport of magma to the surface might be more difficult, leading to a change from tube- to channel-forming eruptions. Because Mars probably lacks plate tectonics, we suggest that the change in effusive style on OM is consistent with a cooling planet in which fractionating magmas become more viscous and eruptions become shorter and unsteady. Future research will compare OM with other Tharsis shields to determine if this was a province-wide phenomenon.

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