Mathematics – Logic
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p61d..03m&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #P61D-03
Mathematics
Logic
5480 Volcanism (8450), 8414 Eruption Mechanisms
Scientific paper
Like their terrestrial counterparts, Martian calderas are believed to be the surface products of the partial evacuation of a magma chamber at a few kilometers depth. Mars Orbiter Laser Altimeter (MOLA) data show that sagging of the caldera center may exceed 1.6 km at Biblis Patera, 1.3 km at Olympus Mons, and 300 m at Alba Patera, suggesting post-eruption deflation of the magma chamber. In order to understand the physical structure of Martian volcanoes, we are conducting a detailed morphologic and topographic comparison of Olympus Mons caldera, Mars, and the Nindiri pit crater of Masaya volcano, Nicaragua. Masaya volcano, Nicaragua, is a persistently active basaltic volcano that comprises four main pit craters, which are named (from east to west) Masaya, Santiago, Nindiri, and San Pedro. Nindiri crater is partially filled by frozen lava lakes that formed between 1570 and 1670. The lava surface in the crater subsequently sagged downward plastically before failure in a brittle fashion along circular bounding faults, producing fractures that are morphologically similar to the circumferential fractures seen around the perimeter of the floor of Olympus Mons caldera. The walls of San Pedro and Santiago pit craters that formed following lava lake emplacement now cut these Nindiri features. Exposure of the lava lake pile in the pit crater wall allows a vertical section in excess of 300 m to be studied. Lava flows preserved in the eastern wall of Nindiri have sagged about 50 meters. A more recent lava lake was also erupted onto the sagged crater floor in 1852 where it ponded within the sag-structure. Our on-going study of Nindiri as a terrestrial analog to Martian calderas is focused on analysis of the structural features and on the timing of the eruptions and deformation events. Numerous features are common to both calderas, including extensional fractures around the perimeter of their floors, compressional ridges near the center of collapse, and ponded lava flows that have now been dissected by more recent collapse events. If we can show that one collapse event deformed plastically (as at Nindiri), then this suggests that the subsidence took place within a few years of lava lake emplacement so that the lava was still at a high enough temperature to allow plastic deformation. Brittle deformation is more likely to imply a longer time period between lava lake emplacement and collapse. In either case, extrapolation of these ideas to Mars has significance for inferring magma supply rates at the summit of Olympus Mons and other Martian volcanoes.
Harris Jessica A.
Mouginis-Mark Peter J.
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